A method for screening salt stress tolerance in Indian mustard (Brassica juncea) (L.) Czern & Coss at seedling stage.

Fifty-nine diverse Brassica juncea (Indian mustard) genotypes were used to find an effective screening method to identify salt tolerance at the germination and seedling stages. Salinity stress limits crop productivity and is difficult to simulate on farms, hindering parental selection for hybridization programmes and the development of tolerant cultivars. To estimate an optimum salt concentration for screening, seeds of 15 genotypes were selected randomly and grown in vitro at 0 mM/L, 75 mM/L, 150 mM/L, 225 mM/L, and 300 mM/L concentrations of NaCl in 2 replications in a complete randomized design. Various morphological parameters, viz., length of seedling, root and shoot length, fresh weight, and dry weight, were observed to determine a single concentration using the Salt Injury Index. Then, this optimum concentration (225 mM/L) was used to assess the salt tolerance of all the 59 genotypes in 4 replications while observing the same morphological parameters. With the help of Mean Membership Function Value evaluation criteria, the genotypes were categorized into 5 grades: 4 highly salt-tolerant (HST), 6 salt-tolerant (ST), 19 moderately salt-tolerant (MST), 21 salt-sensitive (SS), and 9 highly salt-sensitive (HSS). Seedling fresh weight (SFW) at 225 mM/L was found to be an ideal trait, which demonstrates the extent to which B. juncea genotypes respond to saline conditions. This is the first report that establishes a highly efficient and reliable method for evaluating the salinity tolerance of Indian mustard at the seedling stage and will facilitate breeders in the development of salt-tolerant cultivars.

Sensor based precise nitrogen application augmented productivity and profitability of mustard (Brassica juncea L.).

Unremitting decline in crop productivity and nutrient recovery are resulted due to dearth of need based fertilizer recommendation over blanket application apart from nitrogen pollution in several means. An advance nutrient management tactic, GreenSeeker (GS) has developed and used in many field crops following the principle of four "R" (right source, right amount at right time, and place) nutrients stewardship technologies. But no studies have been conducted for evaluation of GS in mustard for improving productivity, profitability and nutrient use efficiency (NUE) while minimizing environmental risks. With this objective, a study was planned to conduct an experiment in rabi season of 2021-22 and 2022-23 to assess optical sensor based nitrogen management in mustard over blanket recommendation. The experiment was comprised of ten N treatments including control in randomized block design in triplicates. Research findings indicated that application of GreenSeeker based N significantly improved all growth traits and yield parameters in Brassica juncea L. Per cent enhancement in seed yield, net monetary returns and benefit-cost ratio was higher as 19.3 and 64.5%, 125.1 & 36.2% and 58.8 & 24.4%, respectively under GS based multi split N application over RDF and control. Further, real time N management with GS acquired higher crop production efficiency (CPE) (19.9 kg/day) with lesser cost/kg production (Rs 15.7/kg). Split application of N using GS increased oil yield by 79.9 and 26% over control and recommended dose of fertilizer (RDF) with maximum oil content (42.3%), and increases soil organic carbon (SOC) content by 16.1% from its initial value. Moreover, GS crop sensor could be the probable solution to minimize the crop nitrogen requirement by 15-20% with a yield enhancement of about 18.7% over RDF.

Enhancement of the germination and growth of Panicum miliaceum and Brassica juncea in Cd- and Zn-contaminated soil inoculated with heavy-metal-tolerant Leifsonia sp. ZP3.

The addition of plant-growth-promoting bacteria (PGPB) to heavy-metal-contaminated soils can significantly improve plant growth and productivity. This study isolated heavy-metal-tolerant bacteria with growth-promoting traits and investigated their inoculation effects on the germination rates and growth of millet (Panicum miliaceum) and mustard (Brassica juncea) in Cd- and Zn-contaminated soil. Leifsonia sp. ZP3, which is resistant to Cd (0.5 mM) and Zn (1 mM), was isolated from forest soil. The ZP3 strain exhibited plant-growth-promoting activity, including indole-3-acetic acid production, phosphate solubilization, catalase activity, and 2,2-diphenyl-1-picrylhydrazyl radical scavenging. In soil contaminated with low concentrations of Cd (0.232 ± 0.006 mM) and Zn (6.376 ± 0.256 mM), ZP3 inoculation significantly increased the germination rates of millet and mustard 8.35- and 31.60-fold, respectively, compared to the non-inoculated control group, while the shoot and root lengths of millet increased 1.77- and 4.44-fold (p < 0.05). The chlorophyll content and seedling vigor index were also 4.40 and 18.78 times higher in the ZP3-treated group than in the control group (p < 0.05). The shoot length of mustard increased 1.89-fold, and the seedling vigor index improved 53.11-fold with the addition of ZP3 to the contaminated soil (p < 0.05). In soil contaminated with high concentrations of Cd and Zn (0.327 ± 0.016 and 8.448 ± 0.250 mM, respectively), ZP3 inoculation led to a 1.98-fold increase in the shoot length and a 2.07-fold improvement in the seedling vigor index compared to the control (p < 0.05). The heavy-metal-tolerant bacterium ZP3 isolated in this study thus represents a promising microbial resource for improving the efficiency of phytoremediation in Cd- and Zn-contaminated soil.

[Brassica juncea BjuWRKY71-1 accelerates flowering by regulating the expression of SOC1].

Brassica juncea (mustard) is a vegetable crop of Brassica, which is widely planted in China. The yield and quality of stem mustard are greatly influenced by the transition from vegetative growth to reproductive growth, i.e., flowering. The WRKY transcription factor family is ubiquitous in higher plants, and its members are involved in the regulation of many growth and development processes, including biological/abiotic stress responses and flowering regulation. WRKY71 is an important member of the WRKY family. However, its function and mechanism in mustard have not been reported. In this study, the BjuWRKY71-1 gene was cloned from B. juncea. Bioinformatics analysis and phylogenetic tree analysis showed that the protein encoded by BjuWRKY71-1 has a conserved WRKY domain, belonging to class Ⅱ WRKY protein, which is closely related to BraWRKY71-1 in Brassica rapa. The expression abundance of BjuWRKY71-1 in leaves and flowers was significantly higher than that in roots and stems, and the expression level increased gradually along with plant development. The result of subcellular localization showed that BjuWRKY71-1 protein was located in nucleus. The flowering time of overexpressing BjuWRKY71-1 Arabidopsis plants was significantly earlier than that of the wild type. Yeast two-hybrid assay and dual-luciferase reporter assay showed that BjuWRKY71-1 interacted with the promoter of the flowering integrator BjuSOC1 and promoted the expression of its downstream genes. In conclusion, BjuWRKY71-1 protein can directly target BjuSOC1 to promote plant flowering. This discovery may facilitate further clarifying the molecular mechanism of BjuWRKY71-1 in flowering time control, and creating new germplasm with bolting and flowering tolerance in mustard.

Effect of Far-Red Light on Biomass Accumulation, Plant Morphology, and Phytonutrient Composition of Ruby Streaks Mustard at Microgreen, Baby Leaf, and Flowering Stages.

Far-red (FR) light influences plant development significantly through shade avoidance response and photosynthetic modulation, but there is limited knowledge on how FR treatments influence the growth and nutrition of vegetables at different maturity stages in controlled environment agriculture (CEA). Here, we comprehensively investigated the impacts of FR on the yield, morphology, and phytonutrients of ruby streaks mustard (RS) at microgreen, baby leaf, and flowering stages. Treatments including white control, white with supplementary FR, white followed by singularly applied FR, and enhanced white (WE) matching the extended daily light integral (eDLI) of FR were designed for separating the effects of light intensity and quality. Results showed that singular and supplemental FR affected plant development and nutrition similarly throughout the growth cycle, with light intensity and quality playing varying roles at different stages. Specifically, FR did not affect the fresh and dry weight of microgreens but increased those values for baby leaves, although not as effectively as WE. Meanwhile, FR caused significant morphological change and accelerated the development of leaves, flowers, and seedpods more dramatically than WE. With regard to phytonutrients, light treatments affected the metabolomic profiles for baby leaves more dramatically than microgreens and flowers. FR decreased the glucosinolate and anthocyanin contents in microgreens and baby leaves, while WE increased the contents of those compounds in baby leaves. This study illustrates the complex impacts of FR on RS and provides valuable information for selecting optimal lighting conditions in CEA.

An enhanced productivity of pink oyster mushroom with improved nutritional profile, characterization and attempt for commercial exploitation.

BACKGROUND: An attempt has been made to explore the nutritional profile of pink oyster mushrooms that have been grown in various agricultural residues, including sugarcane bagasse, rice straw, coconut coir and sawdust, along with other nutrient supplements such as defatted mustard and chickpea powder, for appropriate growth and fruiting body formation in a short span of time. The spawn production was experimented with five different grain varieties. The study became interesting when the observations differed slightly from the traditional practices, with the addition of defatted mustard supplements resulting in a positive correlation with respect to reducing the fruiting time, as well as improving yield and the nutritional profile of Pleurotus djamor. RESULTS: An elevated yield of 651.93 g kg-1 was recorded in the medium where the RS and DM were used in the ratio of 1:0.01 (rice straw +1% w/w defatted mustard) bag, whereas, in terms of protein content, a maximum yield of 32.57 ± 0.79 mg g-1 was observed when SB:DM was in the same ratio (sugarcane bagasse +1% w/w defatted mustard) bag. CONCLUSION: To confer the best outcomes from the screened substrates, a series of experiments were performed by varying the concentration of RS and SB, with 1% w/w DM. It is worth noting that the highest protein content of 32.76 ± 0.38 mg g-1 was obtained along with the total yield of 702.56 ± 2.9 g kg-1 of mushroom when the ratio of RS:SB was 0.7:0.3. © 2024 Society of Chemical Industry.

The expression and interaction proteins analysis of BjuFKF1/LKP2 in B. juncea.

Brassica juncea is one of a unique vegetable in China, its tumorous stem can be processed into pickle or as fresh vegetable. For a long time, early-bolting as a main factor affects yield and quality of B. juncea, which happens about 15% all year round. As plant specific blue light receptors, FKF1/LKP2 involved in photoperiod flowering. To analyze the expression levels of BjuFKF1/BjuLKP2 and screen their interaction proteins in B. juncea, qRT-PCR and yeast two hybrid assays were recruited. qRT-PCR assays found that the expression levels of BjuFKF1 and BjuLKP2 were up-regulated expressed under both white and blue light. When under different light, BjuFKF1 was significantly increased at vegetative growth stage, but decreased in flowers under blue light. For BjuLKP2, its expression levels did not show significant changes under different light treatment. To investigate interaction proteins, BjuFKF1 and BjuLKP2 were used as bait proteins, and nine potential proteins were screened from yeast library. Yeast two hybrid assays was recruited to further verify their interaction, the results showed that both BjuFKF1 and BjuLKP2 interacted with BjuCOL, BjuCOL3, BjuCOL5, BjuAP2, BjuAP2-1 and BjuSKP1f, only BjuLKP2 interacted with BjuSVP-1 and BjuCDF1 in vivo. In this study, BjuFKF1 and BjuLKP2 were up-regulated expressed under both white and blue light. Yeast two hybrid results verified that BjuFKF1 and BjuLKP2 interacted with six and eight of those nine proteins in vivo, respectively. All of those results will provided reference genes to study BjuFKF1/BjuLKP2 regulated flowering pathway in B. juncea.

Leaf nodule endosymbiotic Burkholderia confer targeted allelopathy to their Psychotria hosts.

After a century of investigations, the function of the obligate betaproteobacterial endosymbionts accommodated in leaf nodules of tropical Rubiaceae remained enigmatic. We report that the α-D-glucose analogue (+)-streptol, systemically supplied by mature Ca. Burkholderia kirkii nodules to their Psychotria hosts, exhibits potent and selective root growth inhibiting activity. We provide compelling evidence that (+)-streptol specifically affects meristematic root cells transitioning to anisotropic elongation by disrupting cell wall organization in a mechanism of action that is distinct from canonical cellulose biosynthesis inhibitors. We observed no inhibitory or cytotoxic effects on organisms other than seed plants, further suggesting (+)-streptol as a bona fide allelochemical. We propose that the suppression of growth of plant competitors is a major driver of the formation and maintenance of the Psychotria-Burkholderia association. In addition to potential agricultural applications as a herbicidal agent, (+)-streptol might also prove useful to dissect plant cell and organ growth processes.

Effect of potassium fertilizer on the growth, physiological parameters, and water status of Brassica juncea cultivars under different irrigation regimes.

Abiotic stress, especially a lack of water, can significantly reduce crop yields. In this study, we evaluated the physiological and biochemical effects of potassium sulfate (K2SO4) fertilizer and varied irrigation regimes on the economically significant oilseed crop, Brassica juncea L, under open field conditions. Two cultivars (RH-725 and RH-749) of B. juncea were used in a randomized complete block design experiment with three replicates. Irrigation regimes consisted of a control (double irrigation: once at the 50% flowering and another at 50% fruiting stages), early irrigation (at 50% flowering only), late irrigation (at 50% fruiting only) and stress (no irrigation). The K2SO4 applications were: control (K0, no fertilization); K1, 10 kg ha-1; and K2, 20 kg ha-1. We measured growth via fresh and dry plant weight, plant height, root length, and leaf area. All the growth parameters were higher in RH-749. The physiological attributes, including the membrane stability index and relative water content, were higher at the 50% flowering stage in RH-749. The amount of antioxidant enzymes (catalase (CAT), guaiacol peroxidase (POX), ascorbate peroxidase (APX), and superoxide dismutase (SOD)) was enhanced when both plants were fertilized during water stress. All of these enzymes had higher activity in RH-749. The total chlorophyll content and photosynthesis rate were considerably higher in RH-749, which leaked fewer electrolytes and maintained a less destructive osmotic potential under limited water conditions. The results indicated that it is water-stress tolerant when given a high concentration of K2SO4, which alleviated the adverse effects of water stress on growth and physiology.

Development of B. carinata with super-high erucic acid content through interspecific hybridization.

KEY MESSAGE: Disomic alien chromosome addition Brassica carinata lines with super-high erucic acid content were developed through interspecific hybridization with B. juncea and characterized using molecular, cytological and biochemical techniques. Brassica carinata [A.] Braun (BBCC, 2n = 34) is a climate-resilient oilseed. Its seed oil is high in erucic acid (> 40%), rendering it well suited for the production of biofuel and other bio-based applications. To enhance the competitiveness of B. carinata with high erucic B. napus (HEAR), lines with super-high erucic acid content were developed through interspecific hybridization. To this end, a fad2B null allele from Brassica juncea (AABB, 2n = 36) was introgressed into B. carinata, resulting in a B. carinata fad2B mutant with erucic acid levels of over 50%. Subsequently, the FAE allele from B. rapa spp. yellow sarson (AA, 2n = 20) was transferred to the fad2B B. carinata line, yielding lines with erucic acid contents of up to 57.9%. Molecular analysis using the Brassica 90 K Illumina Infinium™ SNP genotyping array identified these lines as disomic alien chromosome addition lines, with two extra A08 chromosomes containing the BrFAE gene. The alien chromosomes from B. rapa were clearly distinguished by molecular cytogenetics in one of the addition lines. Analysis of microspore-derived offspring and hybrids from crosses with a CMS B. carinata line showed that the transfer rate of the A08 chromosome into male gametes was over 98%, resulting in almost completely stable transmission of an A08 chromosome copy into the progeny. The increase in erucic acid levels was accompanied by changes in the proportions of other fatty acids depending on the genetic changes that were introduced in the interspecific hybrids, providing valuable insights into erucic acid metabolism in Brassica.

Protocol for the Production of Doubled Haploid Plants of Brassica carinata.

Brassica carinata, also known as Ethiopian or Abyssinian mustard, is a drought- and heat-tolerant oilseed with great potential as a dedicated industrial feedstock crop for use in biofuel and other bio-based applications. Doubled haploid technology, a system that allows for the rapid development of doubled haploid, completely homozygous plants through microspore embryogenesis, has been applied routinely in both B. carinata breeding and basic research. Here, we present a comprehensive isolated microspore culture protocol detailing the various steps involved in doubled haploid plant production for this species, from growing donor plants over harvesting flower buds and isolating, culturing and inducing microspores to regenerating doubled haploid embryos and plantlets.

Metabolite Profiling and Transcriptome Analysis Provide Insight into Seed Coat Color in Brassica juncea.

The allotetraploid species Brassica juncea (mustard) is grown worldwide as oilseed and vegetable crops; the yellow seed-color trait is particularly important for oilseed crops. Here, to examine the factors affecting seed coat color, we performed a metabolic and transcriptomic analysis of yellow- and dark-seeded B. juncea seeds. In this study, we identified 236 compounds, including 31 phenolic acids, 47 flavonoids, 17 glucosinolates, 38 lipids, 69 other hydroxycinnamic acid compounds, and 34 novel unknown compounds. Of these, 36 compounds (especially epicatechin and its derivatives) accumulated significantly different levels during the development of yellow- and dark-seeded B. juncea. In addition, the transcript levels of BjuDFR, BjuANS,BjuBAN, BjuTT8, and BjuTT19 were closely associated with changes to epicatechin and its derivatives during seed development, implicating this pathway in the seed coat color determinant in B. juncea. Furthermore, we found numerous variations of sequences in the TT8A genes that may be associated with the stability of seed coat color in B. rapa, B. napus, and B. juncea, which might have undergone functional differentiation during polyploidization in the Brassica species. The results provide valuable information for understanding the accumulation of metabolites in the seed coat color of B. juncea and lay a foundation for exploring the underlying mechanism.

Amelioration of Chlorpyrifos-Induced Toxicity in Brassica juncea L. by Combination of 24-Epibrassinolide and Plant-Growth-Promoting Rhizobacteria.

Pervasive use of chlorpyrifos (CP), an organophosphorus pesticide, has been proven to be fatal for plant growth, especially at higher concentrations. CP poisoning leads to growth inhibition, chlorosis, browning of roots and lipid and protein degradation, along with membrane dysfunction and nuclear damage. Plants form a linking bridge between the underground and above-ground communities to escape from the unfavourable conditions. Association with beneficial rhizobacteria promotes the growth and development of the plants. Plant hormones are crucial regulators of basically every aspect of plant development. The growing significance of plant hormones in mediating plant-microbe interactions in stress recovery in plants has been extensively highlighted. Hence, the goal of the current study was to investigate the effect of 24-epibrassinolide (EBL) and PGPRs (Pseudomonas aeruginosa (Ma), Burkholderia gladioli (Mb)) on growth and the antioxidative defence system of CP-stressed Brassica juncea L. seedlings. CP toxicity reduced the germination potential, hypocotyl and radicle development and vigour index, which was maximally recuperated after priming with EBL and Mb. CP-exposed seedlings showed higher levels of superoxide anion (O2-), hydrogen peroxide (H2O2), lipid peroxidation and electrolyte leakage (EL) and a lower level of nitric oxide (NO). In-vivo visualisation of CP-stressed seedlings using a light and fluorescent microscope also revealed the increase in O2-, H2O2 and lipid peroxidation, and decreased NO levels. The combination of EBL and PGPRs reduced the reactive oxygen species (ROS) and malondialdehyde (MDA) contents and improved the NO level. In CP-stressed seedlings, increased gene expression of defence enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APOX), glutathione peroxidase (GPOX), dehydroascorbate reductase (DHAR) and glutathione reductase (GPOX) was seen, with the exception of catalase (CAT) on supplementation with EBL and PGPRs. The activity of nitrate reductase (NR) was likewise shown to increase after treatment with EBL and PGPRs. The results obtained from the present study substantiate sufficient evidence regarding the positive association of EBL and PGPRs in amelioration of CP-induced oxidative stress in Brassica juncea seedlings by strengthening the antioxidative defence machinery.

A complex interplay of Gß and Gγ proteins regulates plant growth and defence traits in the allotetraploid Brassica juncea.

KEY MESSAGE: Gene expression analysis coupled with in-planta studies showed that specific Gßγ combination regulates plant growth and defence traits in the allotetraploid Brassica juncea. Plant heterotrimeric G-proteins regulate a wide range of responses despite their limited repertoire of core components. The roles and functional interactions between different G-protein subunits are quite perplexing, which get further complicated with polyploidy. Here, we show that the allotetraploid Brassica juncea comprises multiple homologs of G-protein genes, encoding six BjuGß and ten highly divergent BjuGγ subunit proteins, later being classified into type-A1, type-A2 and type-C Gγ proteins. The encoded BjuGß and BjuGγ proteins shared close evolutionary relationship and have retained distinct spatio-temporal expression patterns during plant developmental stages and in response to the necrotrophic pathogen, Sclerotinia sclerotiorum. RNAi based suppression of BjuGß and BjuGγ genes suggested functional overlap and selectivity of BjuGßs with three distinct BjuGγ type subunits, to regulate plant height (BjuGßγA2 and BjuGßγC), seed weight (BjuGßGγA1 and BjuGßGγC), silique size (BjuGßGγC) and pathogen response (BjuGßGγA1 and BjuGßGγC). Further, the triplicated BjuGß genes, formed due to Brassica specific whole-genome-triplication event, showed differential involvement during pathogen response, wherein overexpression of BjuGß2 displayed higher resistance to Sclerotinia infection. Taken together, our study demonstrates that multiple BjuGß and BjuGγ proteins have retained distinct spatio-temporal expression and functional selectivity to regulate specific plant growth and defence traits in the oilseed B. juncea.

Genetic mapping reveals BjRf as a candidate gene controlling fertility restoration of the oxa CMS in Brassica juncea.

KEY MESSAGE: A candidate gene for male fertility restoration in Brassica juncea, BjRf, was isolated from a 23-kb interval on chromosome A05 using map-based cloning and BSA methods. The cytoplasmic male sterility/fertility restoration (CMS/Rf) system has been extensively used for heterosis in plants. It also provides valuable resources for studying mitochondrial-nuclear coevolution and interaction. The oxa CMS, which is a new CMS type reported in Brassica juncea (B. juncea), has been broadly used in the exploitation and application of heterosis in this species. However, the oxa CMS fertility restorer gene BjRf has not been reported. In this study, a stable restorer line was successfully constructed via continuous testcross and artificial selection. Besides, a new Rf gene was mapped in a 23-kb region on chromosome A05 in B. juncea with a genetic distance of 0.5 cM by the method incorporating bulk segregant analysis (BSA) and conventional map-based cloning. Finally, BjuA017917, a non-PPR Rf gene encoding a guanosine nucleotide diphosphate dissociation inhibitor (GDI), is proposed to be the candidate gene for fertility restoration of the oxa CMS line in B. juncea. Moreover, a functional marker, CRY3, was developed for marker-assisted selection for Brassica juncea breeding.

Anchoring alien chromosome segment substitutions bearing gene(s) for resistance to mustard aphid in Brassica juncea-B. fruticulosa introgression lines and their possible disruption through gamma irradiation.

KEY MESSAGE: Heavy doses of gamma irradiation can reduce linkage drag by disrupting large sized alien translocations and promoting exchanges between crop and wild genomes. Resistance to mustard aphid (Lipaphis erysimi) infestation was significantly improved in Brassica juncea through B. juncea-B. fruticulosa introgression. However, linkage drag caused by introgressed chromatin fragments has so far prevented the deployment of this resistance source in commercial cultivars. We investigated the patterns of donor chromatin segment substitutions in the introgression lines (ILs) through genomic in situ hybridization (GISH) coupled with B. juncea chromosome-specific oligonucleotide probes. These allowed identification of large chromosome translocations from B. fruticulosa in the terminal regions of chromosomes A05, B02, B03 and B04 in three founder ILs (AD-64, 101 and 104). Only AD-101 carried an additional translocation at the sub-terminal to intercalary position in both homologues of chromosome A01. We validated these translocations with a reciprocal blast hit analysis using shotgun sequencing of three ILs and species-specific contigs/scaffolds (kb sized) from a de novo assembly of B. fruticulosa. Alien segment substitution on chromosome A05 could not be validated. Current studies also endeavoured to break linkage drag by exposing seeds to a heavy dose (200kR) of gamma radiation. Reduction in the size of introgressed chromatin fragments was observed in many M3 plants. There was a complete loss of the alien chromosome fragment in one instance. A few M3 plants with novel patterns of chromosome segment substitutions displayed improved agronomic performance coupled with resistance to mustard aphid. SNPs in such genomic spaces should aid the development of markers to track introgressed DNA and allow application in plant breeding.

Role of Bacillus cereus in Improving the Growth and Phytoextractability of Brassica nigra (L.) K. Koch in Chromium Contaminated Soil.

Plant growth-promoting rhizobacteria (PGPR) mediate heavy metal tolerance and improve phytoextraction potential in plants. The present research was conducted to find the potential of bacterial strains in improving the growth and phytoextraction abilities of Brassica nigra (L.) K. Koch. in chromium contaminated soil. In this study, a total of 15 bacterial strains were isolated from heavy metal polluted soil and were screened for their heavy metal tolerance and plant growth promotion potential. The most efficient strain was identified by 16S rRNA gene sequencing and was identified as Bacillus cereus. The isolate also showed the potential to solubilize phosphate and synthesize siderophore, phytohormones (indole acetic acid, cytokinin, and abscisic acid), and osmolyte (proline and sugar) in chromium (Cr+3) supplemented medium. The results of the present study showed that chromium stress has negative effects on seed germination and plant growth in B. nigra while inoculation of B. cereus improved plant growth and reduced chromium toxicity. The increase in seed germination percentage, shoot length, and root length was 28.07%, 35.86%, 19.11% while the fresh and dry biomass of the plant increased by 48.00% and 62.16%, respectively, as compared to the uninoculated/control plants. The photosynthetic pigments were also improved by bacterial inoculation as compared to untreated stress-exposed plants, i.e., increase in chlorophyll a, chlorophyll b, chlorophyll a + b, and carotenoid was d 25.94%, 10.65%, 20.35%, and 44.30%, respectively. Bacterial inoculation also resulted in osmotic adjustment (proline 8.76% and sugar 28.71%) and maintained the membrane stability (51.39%) which was also indicated by reduced malondialdehyde content (59.53% decrease). The antioxidant enzyme activities were also improved to 35.90% (superoxide dismutase), 59.61% (peroxide), and 33.33% (catalase) in inoculated stress-exposed plants as compared to the control plants. B. cereus inoculation also improved the uptake, bioaccumulation, and translocation of Cr in the plant. Data showed that B. cereus also increased Cr content in the root (2.71-fold) and shoot (4.01-fold), its bioaccumulation (2.71-fold in root and 4.03-fold in the shoot) and translocation (40%) was also high in B. nigra. The data revealed that B. cereus is a multifarious PGPR that efficiently tolerates heavy metal ions (Cr+3) and it can be used to enhance the growth and phytoextraction potential of B. nigra in heavy metal contaminated soil.

Root NRT, NiR, AMT, GS, GOGAT and GDH expression levels reveal NO and ABA mediated drought tolerance in Brassica juncea L.

Little is known about the interactive effects of exogenous nitric oxide (NO) and abscisic acid (ABA) on nitrogen (N) metabolism and related changes at molecular and biochemical levels under drought stress. The present study highlights the independent and combined effect of NO and ABA (grouped as "nitrate agonists") on expression profiles of representative key genes known to be involved in N-uptake and assimilation, together with proline metabolism, N-NO metabolism enzyme's activity and nutrient content in polyethylene glycol (PEG) treated roots of Indian mustard (B. juncea cv. Varuna). Here we report that PEG mediated drought stress negatively inhibited growth performance, as manifested by reduced biomass (fresh and dry weight) production. Total N content and other nitrogenous compounds (NO3-, NO2-) were decreased; however, NH4+, NH4+/ NO3- ratio and total free amino acids content were increased. These results were positively correlated with the PEG induced changes in expression of genes and enzymes involved in N-uptake and assimilation. Also, PEG supply lowered the content of macro- and micro-nutrients but proline level and the activity of ∆1-pyrroline-5-carboxylate synthetase increased indicating increased oxidative stress. However, all these responses were reversed upon the exogenous application of nitrate agonists (PEG + NO, PEG + NO + ABA, and PEG + ABA) where NO containing nitrate agonist treatment i.e. PEG + NO was significantly more effective than PEG + ABA in alleviating drought stress. Further, increases in activities of L-arginine dependent NOS-like enzyme and S-nitrosoglutathione reductase were observed under nitrate agonist treatments. This indicates that the balanced endogenous change in NO and ABA levels together during synthesis and degradation of NO mitigated the oxidative stress in Indian mustard seedlings. Overall, our results reveal that NO independently or together with ABA may contribute to improved crop growth and productivity under drought stress.

Heterotrimeric Gα subunit regulates plant architecture, organ size and seed weight in the oilseed Brassica juncea.

KEY MESSAGE: Two BjuGα proteins exhibit conserved GTP-binding and GTP-hydrolysis activities, and function in maintaining overall plant architecture and controlling multiple yield-related traits in the oilseed Brassica juncea. Heterotrimeric G-protein (Gα, Gß and Gγ) are key signal transducers, well characterized in model plants Arabidopsis and rice. However, our knowledge about the roles played by G-proteins in regulating various growth and developmental traits in polyploid crops, having a complex G-protein signalling network, is quite sparse. In the present study, two Gα encoding genes (BjuA.Gα1 and BjuB.Gα1) were isolated from the allotetraploid Brassica juncea, a globally cultivated oilseed crop of the Brassicaceae family. BjuGα1 genes share a close evolutionary relationship, and the encoded proteins exhibit highly conserved G-protein activities while showing expression differentiation, wherein BjuA.Gα1 was the highly abundant transcript during plant growth and developmental stages. RNAi based suppression of BjuGα1 displayed compromised effects on most of the tested vegetative and reproductive parameters, particularly plant height (32-58%), flower and siliques dimensions, and seed weight (11-13%). Further, over-expression of a constitutively active Gα, lacking the GTPase activity, produced plants with increased height, organ size and seed weight (7-25%), without altering seed quality traits like fatty acid composition, glucosinolates, oil and protein contents. Our study demonstrates that BjuGα1 proteins control overall plant architecture and multiple yield-related traits in the oilseed B. juncea, suggesting that BjuGα1 could be a promising target for crop improvement.

Genome-Wide Analysis of the Heat Shock Transcription Factor Gene Family in Brassica juncea: Structure, Evolution, and Expression Profiles.

Heat shock transcription factor (HSF) is ubiquitous in the whole biological world and plays an important role in regulating growth and development and responses to environment stress. In this study, a total of 60 HSF transcription factors in Brassica juncea genome were identified and analyzed. Phylogenetic analysis showed that HSF genes were divided into three groups namely: A, B, and C, of which group A was further divided into nine subgroups (A1-A9). The analysis of gene structure and conserved motifs showed that some homologous genes are highly conserved. There was strong conservative microcollinearity among Brassica rapa, B. juncea, and Brassica oleracea, which provides a basis for studying the replication of gene families. Moreover, the results revealed that the promoter regions of BjuHSF genes were rich in cis-elements related to growth and development, hormone signal, and stress response. The prediction of protein interaction results showed that HSFs could interact with multiple transcription factors and proteins in the genome, while functional annotation revealed that BjuHSF genes were involved in many biological processes. The expression patterns of BjuHSF genes were analyzed by qPCR, and the results showed that these genes were closely linked to stress response, hormones, and development process. These results are a foundation for further analysis of the regulation mechanism of HSF gene family.