Detection and characterization of eravacycline heteroresistance in clinical bacterial isolates.

Eravacycline (ERV) has emerged as a therapeutic option for the treatment of carbapenem-resistant pathogens. However, the advent of heteroresistance (HR) to ERV poses a challenge to these therapeutic strategies. This study aimed to investigate ERV HR prevalence among common clinical isolates and further characterize ERV HR in carbapenem-resistant Klebsiella pneumoniae (CRKP). A total of 280 clinical pathogens from two centers were selected for HR and analyzed using population analysis profiling (PAP) and modified E-tests. The PAP assay revealed an overall ERV HR prevalence of 0.7% (2/280), with intermediate heterogeneity observed in 24.3% (68/280) of strains. The proportion of heteroresistant strains was 18.3% according to modified E-test results. A time-killing assay demonstrated that CRKP CFU increased significantly after 10 h of ERV treatment, contributing to the reduced bactericidal effect of ERV in vitro. Interestingly, dual treatment with ERV and polymyxin B effectively inhibited the total CFU, simultaneously reducing the required polymyxin B concentration. Furthermore, fitness cost measurements revealed a growth trade-off in CRKP upon acquiring drug resistance, highlighting fitness costs as crucial factors in the emergence of ERV HR in CRKP. Overall, the findings of the current study suggest that ERV HR in clinical strains presents a potential obstacle in its clinical application.

Fine Mapping of the Affecting Tillering and Plant Height Gene CHA-1 in Rice.

The plant architecture of rice is an important factor affecting yield. Strigolactones (SLs) are newly discovered carotenoid-derived plant hormones that play an important role in rice plant architecture. In this study, a high-tillering dwarf mutant, CHA-1, was identified by spatial mutagenesis. CHA-1 was located in the region of 31.52-31.55 MB on chromosome 1 by map-based cloning. Compared with the wild-type THZ, the CHA-1 mutant showed that ACCAC replaced TGGT in the coding region of the candidate gene LOC_Os01g54810, leading to premature termination of expression. Genetic complementation experiments proved that LOC_Os01g54810 was CHA-1, which encodes a putative member of Class III lipase. Expression analysis showed that CHA-1 was constitutively expressed in various organs of rice. Compared with those in THZ, the expression levels of the D17 and D10 genes were significantly downregulated in the CHA-1 mutant. In addition, the concentrations of ent-2'-epi-5-deoxystrigol (epi-5DS) in the root exudates of the CHA-1 mutant was significantly reduced compared with that of THZ, and exogenous application of GR24 inhibited the tillering of the CHA-1 mutant. These results suggest that CHA-1 influences rice architecture by affecting SL biosynthesis.

The DnaJ domain-containing heat-shock protein NAL11 determines plant architecture by mediating gibberellin homeostasis in rice (Oryza sativa).

Ideal Plant Architecture 1 (IPA1) is a key regulator of plant architecture. However, knowledge of downstream genes applicable for improving rice plant architecture is very limited. We identified the plant architecture regulatory gene NARROW LEAF 11 (NAL11), which encodes a heat-shock protein (HSP) containing a DnaJ domain. A promising rare allele of NAL11 (NAL11-923del-1552 ) positively selected in Aus cultivars was identified; this allele exhibited increased expression and generated relatively few tillers, thick stems, and large panicles, components of the ideal plant architecture (IPA). NAL11 is involved in regulating the cell cycle and cell proliferation. NAL11 loss-of-function mutants present impaired chloroplast development and gibberellin (GA) defects. Biochemical analyses show that IPA1 directly binds to elements in the missing fragment of the NAL11-923del-1552 promoter and negatively regulates NAL11 expression. Genetic analyses support the hypothesis that NAL11 acts downstream of IPA1 to regulate IPA by modulating GA homeostasis, and NAL11 may be an essential complement for IPA1. Our work revealed that avoidance of the inhibition of NAL11-923del-1552 caused by IPA1 represents a positive strategy for rescuing GA defects accompanied by the upregulation of IPA1 in breeding high-yield rice.

SN-38 Sensitizes BRCA-Proficient Ovarian Cancers to PARP Inhibitors through Inhibiting Homologous Recombination Repair.

As a multifunctional protein posttranslational modification enzyme in eukaryotic cells, Poly-ADP-ribose polymerase (PARP) acts as a DNA damage sensor, which helps to repair DNA damage through recruiting repair proteins to the DNA break sites. PARP inhibitors offer a significant clinical benefit for ovarian cancer with BRCA1/2 mutations. However, the majority of ovarian cancer patients harbor wild-type (WT) BRCA1/2 status, which narrows its clinical application. Here, we identified a small compound, SN-38, a CPT analog, which sensitizes BRCA-proficient ovarian cancer cells to PARP inhibitor treatment by inhibiting homologous recombination (HR) repair. SN-38 treatment greatly enhanced PARP inhibitor olaparib induced DNA double-strand breaks (DSBs) and DNA replication stress. Meanwhile, the combination of SN-38 and olaparib synergistically induced apoptosis in ovarian cancer. Furthermore, combination administration of SN-38 and olaparib induced synergistic antitumor efficacy in an ovarian cancer xenograft model in vivo. Therefore, our study provides a novel therapeutic strategy to optimize PARP inhibitor therapy for patients with BRCA-proficient ovarian cancer.

USP5 facilitates non-small cell lung cancer progression through stabilization of PD-L1.

PD-L1(CD274) is a well-known immunosuppressive molecule, which confers immunoescape features to cancer cells and has become one of the major targets in cancer immunotherapies. Understanding the regulatory mechanisms that control PD-L1 protein expression is important for guiding immune checkpoint blockade therapy. Here, we showed that ubiquitin specific peptidase 5 (USP5) was a novel PD-L1 deubiquitinase in non-small cell lung cancer (NSCLC) cells. USP5 directly interacted with PD-L1 and deubiquitinated PD-L1, therefore enhances PD-L1 protein stability. Meanwhile, USP5 protein levels were highly elevated and positively correlated to PD-L1 levels in NSCLC tissues, and were closely correlated with poor prognosis of these patients. In addition, knockdown of USP5 retarded tumor growth in the Lewis lung carcinoma mouse model. Thus, we identified that USP5 was a new regulator of PD-L1 and targeting USP5 is a promising strategy for cancer therapy.

Palladium-Catalyzed Reductive Aminocarbonylation of Benzylammonium Triflates with o-Nitrobenzaldehydes for the Synthesis of 3-Arylquinolin-2(1H)-ones.

A palladium-catalyzed straightforward procedure for the synthesis of 3-arylquinolin-2(1H)-ones has been developed. The synthesis proceeds through a palladium-catalyzed reductive aminocarbonylation reaction of benzylic ammonium triflates with o-nitrobenzaldehydes, and a wide range of 3-arylquinolin-2(1H)-ones was obtained in moderate to good yields with very good functional group compatibility.

Dynamic transcriptome and metabolome analyses of two types of rice during the seed germination and young seedling growth stages.

BACKGROUND: Seed germination and young seedling growth are important agricultural traits for developing populations of both irrigated and directly seeded rice. Previous studies have focused on the identification of QTLs. However, there are few studies on the metabolome or transcriptome of germination and young seedling growth in rice. RESULTS: Here, an indica rice and a japonica rice were used as materials, and the transcripts and metabolites were detected during the germination and young seedling growth periods on a large scale by using RNA sequencing and a widely targeted metabolomics method, respectively. Fourteen shared transcripts and 15 shared metabolites that were continuously differentially expressed in the two materials were identified and may be essential for seed germination and young seedling growth. Enrichment analysis of differentially expressed genes in transcriptome expression profiles at different stages indicated that cell wall metabolism, lipid metabolism, nucleotide degradation, amino acid, etc., were enriched at 0-2 days, and most of the results are consistent with those of previous reports. Specifically, phenylpropanoid biosynthesis and glutathione metabolism were continuously enriched during the seed germination and young seedling growth stages. Next, KO enrichment analysis was conducted by using the differentially expressed genes of the two materials at 2, 3 and 4 days. Fourteen pathways were enriched. Additionally, 44 differentially expressed metabolites at 2, 3 and 4 days were identified. These metabolites may be responsible for the differences in germination and young seedling growth between the two materials. Further attention was focused on the ascorbate-glutathione pathway, and it was found that differences in ROS-scavenging abilities mediated by some APX, GPX and GST genes may be directly involved in mediating differences in the germination and young seedling growth speed of the two materials. CONCLUSIONS: In summary, these results may enhance the understanding of the overall mechanism of seed germination and young seedling growth, and the outcome of this study is expected to facilitate rice breeding for direct seeding.

Identification of QTLs involved in cold tolerance during the germination and bud stages of rice (Oryza sativa L.) via a high-density genetic map.

Low-temperature tolerance during the germination and bud stages is an important characteristic of direct-seeded rice (DSR). Recombinant inbred lines (RILs) derived from indica rice H335, which is highly tolerant to low temperature, and indica rice CHA-1, which is sensitive to low temperature, were used to identify quantitative trait loci (QTLs) associated with low-temperature tolerance during the germination and bud stages. a total of 11 QTLs were detected based on a high-density genetic map; among these, six QTLs explained 5.13-9.42% of the total phenotypic variation explained (PVE) during the germination stage, and five QTLs explained 4.17-6.42% of the total PVE during the bud stage. All QTLs were distributed on chromosome 9, and all favourable alleles originated from H335. The physical position of each QTL was determined, and 11 QTLs were combined into five genetic loci; three of these loci are involved during the germination stage (loci 1, 2, and 3), and three are involved during the bud stage (loci 3, 4, and 5). Loci 2, 4 and 5 were repeatedly detected in the wet season (WS) and dry season (DS). Notably, loci 3 was detected during both the germination and bud stages. These loci are good candidates for future studies of gene function and could serve as highly valuable genetic factors for improving cold tolerance during the germination and bud stages of rice.

Improvement of rice blast resistance by developing monogenic lines, two-gene pyramids and three-gene pyramid through MAS.

BACKGROUND: Rice blast caused by Magnaporthe oryzae (M. oryzae) is one of the most destructive diseases in rice production. Development of resistant varieties through pyramiding of resistant (R) genes is considered as an effective strategy to cope with the disease. However, is it really essential to pyramid more R genes in a specific ecological regions? To answer this question, a set of rice improved lines were developed in this study. Afterwards, the blast disease resistance and agronomic traits of the recurrent parent (RP), donor parents (DPs) and improved lines were investigated. RESULTS: We developed seven improved lines, comprising three monogenic lines, three two-gene pyramids and one three-gene pyramid, by introgression of R gene(s) into a common genetic background using marker-assisted backcross breeding (MABB). Based on 302 SSR markers, the recurrent genome of the seven improved lines reached a range of 89.1 to 95.5%, with the average genome recovery of 92.9%. The pathogenicity assays inoculated with 32 different blast isolates under artificial conditions showed that the resistance spectrum of all the improved lines was significantly broadened. The assays further showed that the two-gene pyramids and the three-gene pyramid exhibited wider resistance spectrum than the monogenic lines. At natural nurseries, the three monogenic lines still showed high ratios of infected panicles, whereas the two-gene pyramids and the three-gene pyramid showed high level of panicle blast resistance. However, the two-gene pyramid R504 reached the similar resistance effect of the three-gene pyramid R507 considering resistance spectrum under artificial conditions and panicle blast resistance under field conditions. Generally, the improved lines showed comparable agronomic traits compared with the recurrent parent (RP), but the three-gene pyramid showed reduced grain yield per plant. CONCLUSIONS: All the improved lines conferred wider resistance spectrum compared with the RP. Yet, the three monogenic lines did not work under field conditions of the two nurseries. Given the similar performances on the main agronomic traits as the RP, the two-gene pyramids have achieved the breeding goals of broad resistance spectrum and effective panicle blast resistance. Whereas, the three-gene pyramid harboring Pi2, Pi46 and Pita seems superfluous considering its reduced yield, although it also showed displayed high level of blast resistance. Thus, rational use of R genes rather than stacking more R genes is recommended to control the disease.

Metabolic profile analysis and identification of key metabolites during rice seed germination under low-temperature stress.

The metabolic profile of rice (Oryza sativa) during germination under low temperature (LT) has not been reported. In this study, the rice varieties 02428 (japonica) and YZX (indica) were subjected to experiments consisting of treatments including LT, normal temperature (NT) and a transition from LT to NT, and tissues were sampled at different time points during germination. A total of 730 metabolites were detected by a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based widely targeted metabolomics method. On the basis of the screening criteria of increased contents under LT and decreased contents under NT, we identified 35 different metabolites that responded to LT stress among the 730 metabolites. Furthermore, the content differences of the 35 metabolites were compared when the samples were transferred from LT to NT. According to a fold change <0.5 or a variable importance in projection (VIP) score>1 at the transition point, 7 out of the 35 metabolites responded significantly to LT stress and were defined as key metabolites. A partial least squares (PLS) regression model of seven key metabolites with seedling length (SL), seedling area (SSA), and seedling volume (SV) was constructed, and the fitting effect was good. These seven key metabolites participate in the biosynthesis of amino acids and phenylpropanoids and in the metabolism of glutathione and inositol phosphate. This study laid a foundation for an improved understanding of the LT-germination mechanism of rice seeds.

Identification of stable QTLs and candidate genes involved in anaerobic germination tolerance in rice via high-density genetic mapping and RNA-Seq.

BACKGROUND: Anaerobic germination tolerance is an important trait for direct-seeded rice varieties. Understanding the genetic basis of anaerobic germination is a key for breeding direct-seeded rice varieties. RESULTS: In this study, a recombinant inbred line (RIL) population derived from a cross between YZX and 02428 exhibited obvious coleoptile phenotypic differences. Mapping analysis using a high-density bin map indicated that a total of 25 loci were detected across two cropping seasons, including 10 previously detected loci and a total of 13 stable loci. Analysis of the 13 stable loci demonstrated that the more elite alleles that were pyramided in an individual, the higher the values of these traits were in the two cropping seasons. Furthermore, some anaerobic germination-tolerant recombinant inbred lines, namely G9, G10, G16, and G151, were identified. A total of 84 differentially expressed genes were obtained from the 13 stable loci via genome-wide expression analysis of the two parents at three key periods. Among them, Os06g0110200, Os07g0638300, Os07g0638400, Os09g0532900, Os09g0531701 and Os12g0539751 constitute the best candidates associated with anaerobic germination. CONCLUSIONS: Both the anaerobic germination-tolerant recombinant inbred lines and the loci identified in this study will provide new genetic resources for improving the anaerobic germination tolerance of rice using molecular breeding strategies, as well as will broaden our understanding of the genetic control of germination tolerance under anaerobic conditions.

Development of a core SNP arrays based on the KASP method for molecular breeding of rice.

BACKGROUND: The development and utilization of genetic markers play a pivotal role in marker-assisted breeding of rice cultivars during pyramiding of valuable genes. Among molecular markers, SNPs have become the most promising due to their wide distribution within genomes and suitability for high -throughput automated genotyping. Although metadata of SNPs have been identified via next generation sequencing in rice, a large gap between the development of SNP markers and the application in breeding still exists. To promote the application of SNP markers based on the KASP (Kompetitive Allele-Specific PCR) method in rice breeding, a set of core SNP arrays was built via the screening of SNP databases and literature resources based on the KASP method. RESULTS: Five hundred and ninety six SNPs classified into eight subsets including quality control, indica-indica variation, highly polymorphic, functional genes, key genes targeting sites, gene cloned region, important trait associated and gap filling sites were chosen to design KASP primers and 565 out of them were successfully designed, and the assay design success rate was 94.8%. Finally, 467 out of the 565 successfully-designed SNPs can display diversity at the loci were used to develop a set of core SNP arrays. To evaluate the application value of the core SNP markers in rice breeding, 481 rice germplasms were genotyped with three functional KASP markers designed from the sequences of GBSSI, SSIIa, and Badh2 from the core SNP arrays for estimation of their grain quality performance. Eighteen rice lines, including Xiangwanxian 13, Basmati 370, Ruanhua A, and PR 33319-9-1-1-5-3-5-4-1, harbor all three favorable alleles. The core KASP arrays were also used for rice germplasm assessment, genetic diversity and population evaluation. Four hundred and eighty-one rice germplasms were divided into 3 groups: POP1, POP2 and POP3. POP1 and POP2 were indica rice subgroups consisting of 263 and 186 rice germplasms, respectively. POP3 was a japonica rice subgroup consisting of 32 rice germplasms. The average FST value for the three subgroups was 0.3501; the FST value of POP1 and POP3 was the largest (0.5482), while that of POP1 and POP2 was the smallest (0.0721). The results showed that the genetic distance between the japonica and indica rice subspecies was large, indicating that the core SNP markers were effective at discriminating the population structure of the germplasms. Finally, the core KASP arrays were used for association analysis with milled grain traits. A total of 31 KASP markers were significantly associated (P < 0.01) with ML and the LWR. Among the 31 markers, 13 were developed based on cloned genes or on identified loci related to yield traits. Notably, several KASP markers associated with grain quality were also found to be associated with brown planthopper resistance or green leafhopper resistance simultaneously. CONCLUSIONS: The core KASP arrays developed in our study were efficient and versatile for rice germplasm assessment, genetic diversity and population evaluation and are valuable for promoting SNP molecular breeding in rice. Our study demonstrated that useful assays combined with molecular breeding can be exploited for important economic trait improvement in rice breeding.

Quantitative Trait Locus Analysis of Seed Germination and Early Seedling Growth in Rice.

Seed germination and early seedling growth are important agricultural traits for developing populations of both irrigated and directly seeded rice (DSR). To investigate the genetic mechanisms underlying seed germination and early seedling growth in rice, 275 recombinant inbred lines (RILs) were genotyped in this study via the genotyping-by-sequencing (GBS) approach to construct a high-density linkage bin map based on the parent-independent genotyping method. Quantitative trait loci (QTLs) for 12 traits related to seed germination and early seedling growth were analyzed. Totally, 22 additive loci were detected, after analysis of the interaction between additive QTLs and environments, five stable additive loci were obtained. Among them, loci 4, 5, 12 and 14 exhibited clear pleiotropic effects that were associated with multiple traits. Analysis of the effects of the five additive stable loci showed that a single locus increased the corresponding phenotypic value. Ten of the 275 RILs pyramided the excellent alleles of the five stable genetic loci. Most phenotypic values of the ten RILs were greater than the average values. Four RILs (G260, G342, G371, and G401) with more excellent phenotypic values were subsequently selected; these RILs could serve as donor parents of favorable alleles in the breeding process. Due to the existence of pleiotropy, the use of these genetic loci for pyramid breeding can further increase the efficiency to reach breeding goals. In addition, these five stable loci have an average physical interval of only 170 kb, we also further identified five promising candidate genes by qRT-PCR, which provides us with a basis for future cloning of these genes. Overall, this work will help broaden our understanding of the genetic control of seed germination and early seedling growth, and this study provides both a good theoretical basis and a new genetic resource for the breeding of direct-seeded rice.

NBS-LRR Protein Pik-H4 Interacts with OsBIHD1 to Balance Rice Blast Resistance and Growth by Coordinating Ethylene-Brassinosteroid Pathway.

The regulation of innate immunity and plant growth, along with the trade-off between them, affects the defense and recovery mechanisms of the plant after it is attacked by pathogens. Although it is known that hormonal crosstalk plays a major role in regulating interaction of plant growth and PAMP-triggered immunity, the relationship between plant growth and effector-triggered immunity (ETI) remains unclear. In a large-scale yeast two-hybrid screening for Pik-H4-interacting proteins, a homeodomain transcription factor OsBIHD1 was identified, which is previously known to function in biotic and abiotic stress responses. The knockout of OsBIHD1 in rice lines carrying Pik-H4 largely compromised the resistance of the rice lines to Magnaporthe oryzae, the fungus that causes rice blast. While overexpression of OsBIHD1 resulted in enhanced expression of the pathogenesis-related (PR) and ethylene (ET) synthesis genes. Moreover, OsBIHD1 was also found to directly bind to the promoter region of ethylene-synthesis enzyme OsACO3. In addition, OsBIHD1 overexpression or deficiency provoked dwarfism and reduced brassinosteroid (BR) insensitivity through repressing the expression of several critical genes involved in BR biosynthesis and BR signaling. During M. oryzae infection, transcript levels of the crucial BR catabolic genes (CYP734A2, CYP734A4, and CYP734A6) were significantly up-regulated in OsBIHD1-OX plants. Furthermore, OsBIHD1 was found to be capable of binding to the sequence-specific cis-elements on the promoters of CYP734A2 to suppress the plant growth under fungal invasion. Our results collectively suggest a model that OsBIHD1 is required for Pik-H4-mediated blast resistance through modulating the trade-off between resistance and growth by coordinating brassinosteroid-ethylene pathway.

CONSTANS-Like 9 (OsCOL9) Interacts with Receptor for Activated C-Kinase 1(OsRACK1) to Regulate Blast Resistance through Salicylic Acid and Ethylene Signaling Pathways.

In a previous transcriptome analysis of early response genes in rice during Magnaporthe oryzae infection, we identified a CONSTANS-like (COL) gene OsCOL9. In the present study, we investigated the functional roles of OsCOL9 in blast resistance. OsCOL9 belonged to group II of the COL protein family, and it contained a BB-box and a C-terminal CCT (CONSTANS, COL and TOC1) domain. OsCOL9 was found in the nucleus of rice cells, and it exerted transcriptional activation activities through its middle region (MR). Magnaporthe oryzae infection induced OsCOL9 expression, and transgenic OsCOL9 knock-out rice plants showed increased pathogen susceptibility. OsCOL9 was a critical regulator of pathogen-related genes, especially PR1b, which were also activated by exogenous salicylic acid (SA) and 1-aminocyclopropane-1-carboxylicacid (ACC), the precursor of ethylene (ET). Further analysis indicated that OsCOL9 over-expression increased the expressions of phytohormone biosynthetic genes, NPR1, WRKY45, OsACO1 and OsACS1, which were related to SA and ET biosynthesis. Interestingly, we found that OsCOL9 physically interacted with the scaffold protein OsRACK1 through its CCT domain, and the OsRACK1 expression was induced in response to exogenous SA and ACC as well as M. oryzae infection. Taken together, these results indicated that the COL protein OsCOL9 interacted with OsRACK1, and it enhanced the rice blast resistance through SA and ET signaling pathways.

High-resolution QTL mapping for grain appearance traits and co-localization of chalkiness-associated differentially expressed candidate genes in rice.

BACKGROUND: Grain appearance quality is a main determinant of market value in rice and one of the highly important traits requiring improvement in breeding programs. The genetic basis of grain shape and endosperm chalkiness have been given significant attention because of their importance in affecting grain quality. Meanwhile, the introduction of NGS (Next Generation Sequencing) has a significant part to play in the area of genomics, and offers the possibility for high-resolution genetic map construction, population genetics analysis and systematic expression profile study. RESULTS: A RIL population derived from an inter-subspecific cross between indica rice PYZX and japonica rice P02428 was generated, based on the significant variations for the grain morphology and cytological structure between these two parents. Using the Genotyping-By-Sequencing (GBS) approach, 2711 recombination bin markers with an average physical length of 137.68 kb were obtained, and a high-density genetic map was constructed. Global genetic mapping of QTLs affecting grain shape and chalkiness traits was performed across four environments and the newly identified stable loci were obtained. Twelve important QTL clusters were detected, four of which were coincident with the genomic regions of cloned genes or fine mapped QTL reported. Eight novel QTL clusters (including six for grain shape, one for chalkiness, and one for both grain shape and chalkiness) were firstly obtained and highlighted the value and reliability of the QTL analysis. The important QTL cluster on chromosome 5 affects multiple traits including circularity (CS), grain width (GW), area size of grain (AS), percentage of grains with chalkiness (PGWC) and degree of endosperm chalkiness (DEC), indicating some potentially pleiotropic effects. The transcriptome analysis demonstrated an available gene expression profile responsible for the development of chalkiness, and several DEGs (differentially expressed genes) were co-located nearby the three chalkiness-related QTL regions on chromosomes 5, 7, and 8. Candidate genes were extrapolated, which were suitable for functional validation and breeding utilization. CONCLUSION: QTLs affecting grain shape (grain width, grain length, length-width ratio, circularity, area size of grain, and perimeter length of grain) and chalkiness traits (percentage of grains with chalkiness and degree of endosperm chalkiness) were mapped with the high-density GBS-SNP based markers. The important differentially expressed genes (DEGs) were co-located in the QTL cluster regions on chromosomes 5, 7 and 8 affecting PGWC and DEC parameters. Our research provides a crucial insight into the genetic architecture of rice grain shape and chalkiness, and acquired potential candidate loci for molecular cloning and grain quality improvement.

4-Coumarate-CoA Ligase-Like Gene OsAAE3 Negatively Mediates the Rice Blast Resistance, Floret Development and Lignin Biosynthesis.

Although adenosine monophosphate (AMP) binding domain is widely distributed in multiple plant species, detailed molecular functions of AMP binding proteins (AMPBPs) in plant development and plant-pathogen interaction remain unclear. In the present study, we identified an AMPBP OsAAE3 from a previous analysis of early responsive genes in rice during Magnaporthe oryzae infection. OsAAE3 is a homolog of Arabidopsis AAE3 in rice, which encodes a 4-coumarate-Co-A ligase (4CL) like protein. A phylogenetic analysis showed that OsAAE3 was most likely 4CL-like 10 in an independent group. OsAAE3 was localized to cytoplasm, and it could be expressed in various tissues. Histochemical staining of transgenic plants carrying OsAAE3 promoter-driven GUS (ß-glucuronidase) reporter gene suggested that OsAAE3 was expressed in all tissues of rice. Furthermore, OsAAE3-OX plants showed increased susceptibility to M. Oryzae, and this finding was attributable to decreased expression of pathogen-related 1a (PR1) and low level of peroxidase (POD) activity. Moreover, OsAAE3 over-expression resulted in increased content of H2O2, leading to programmed cell-death induced by reactive oxygen species (ROS). In addition, OsAAE3 over-expression repressed the floret development, exhibiting dramatically twisted glume and decreased fertility rate of anther. Meanwhile, the expressions of lignin biosynthesis genes were significantly decreased in OsAAE3-OX plants, thereby leading to reduced lignin content. Taken together, OsAAE3 functioned as a negative regulator in rice blast resistance, floret development, and lignin biosynthesis. Our findings further expanded the knowledge in functions of AMBPs in plant floret development and the regulation of rice-fungus interaction.

Phenolic compounds from Merremia umbellata subsp. orientalis and their allelopathic effects on Arabidopsis seed germination.

A bioassay-directed phytochemical study was carried out to investigate potential allelochemicals of the invasive plant Merremia umbellata subsp. orientalis (Hall. f.). Eight phenolic compounds, including a salicylic acid (SA)-derived new natural product, SA 2-O-ß-D-(3',6'-dicaffeoyl)-glucopyranoside (1), and seven known ones 2-8 were isolated and identified from two bioactive sub-fractions of the acetone extract of this plant. The structure of new compound 1 was established by spectral and chemical methods. The potential allelopathic effects of these compounds at 0.5 and 1.0 mM concentrations on the germination of Arabidopsis seeds were tested. Results showed that 2 remarkably inhibited seed germination at concentrations as low as 0.5 mM. Compound 3 only moderately inhibited seed germination at 0.5 mM, but displayed strong inhibitory bioactivity at 1.0 mM concentration. Compounds 4 and 5 showed only slight inhibitory bioactivity at 1.0 mM, while the other compounds showed no obvious inhibitory effects.