Recent advances in virulence of a broad host range plant pathogen Sclerotinia sclerotiorum: a mini-review.

Sclerotinia sclerotiorum is a typical necrotrophic plant pathogenic fungus, which has a wide host range and can cause a variety of diseases, leading to serious loss of agricultural production around the world. It is difficult to control and completely eliminate the characteristics, chemical control methods is not ideal. Therefore, it is very important to know the pathogenic mechanism of S. sclerotiorum for improving host living environment, relieving agricultural pressure and promoting economic development. In this paper, the life cycle of S. sclerotiorum is introduced to understand the whole process of S. sclerotiorum infection. Through the analysis of the pathogenic mechanism, this paper summarized the reported content, mainly focused on the oxalic acid, cell wall degrading enzyme and effector protein in the process of infection and its mechanism. Besides, recent studies reported virulence-related genes in S. sclerotiorum have been summarized in the paper. According to analysis, those genes were related to the growth and development of the hypha and appressorium, the signaling and regulatory factors of S. sclerotiorum and so on, to further influence the ability to infect the host critically. The application of host-induced gene silencing (HIGS)is considered as a potential effective tool to control various fungi in crops, which provides an important reference for the study of pathogenesis and green control of S. sclerotiorum.

RAS signalling genes can be used as host-induced gene silencing targets to control fungal diseases caused by Sclerotinia sclerotiorum and Botrytis cinerea.

Sclerotinia sclerotiorum causes white mold (also called stem rot, Sclerotinia blight, etc.) in many economically important plants. It is a notorious soilborne fungal pathogen due to its wide host range and ability to survive in soil for long periods of time as sclerotia. Although host-induced gene silencing (HIGS) was recently demonstrated to be an effective method for controlling white mold, limited gene targets are available. Here, using a forward genetics approach, we identified a RAS-GTPase activating protein, SsGAP1, which plays essential roles in sclerotia formation, compound appressoria production and virulence. In parallel, as revealed by our knockout analysis, the SsGAP1 ortholog in Botrytis cinerea, BcGAP1, plays similar roles in fungal development and virulence. By knocking down SsRAS1 and SsRAS2, we also revealed that both SsRAS1 and SsRAS2 are required for vegetative growth, sclerotia development, compound appressoria production and virulence in S. sclerotiorum. Due to the major roles these RAS signalling components play in Sclerotiniaceae biology, they can be used as HIGS targets to control diseases caused by both S. sclerotiorum and B. cinerea. Indeed, when we introduced HIGS constructs targeting SsGAP1, SsRAS1 and SsRAS2 in Nicotiana benthamiana and Arabidopsis thaliana, we observed reduced virulence. Taken together, our forward genetics gene discovery pipeline in S. sclerotiorum is highly effective in identifying novel HIGS targets to control S. sclerotiorum and B. cinerea.

Genome-Wide Identification of GYF-Domain Encoding Genes in Three Brassica Species and Their Expression Responding to Sclerotinia sclerotiorum in Brassica napus.

GYF (glycine-tyrosine-phenylalanine)-domain-containing proteins, which were reported to participate in many aspects of biological processes in yeast and animals, are highly conserved adaptor proteins existing in almost all eukaryotes. Our previous study revealed that GYF protein MUSE11/EXA1 is involved in nucleotide-binding leucine-rich repeat (NLR) receptor-mediated defense in Arabidopsis thaliana. However, the GYF-domain encoding homologous genes are still not clear in other plants. Here, we performed genome-wide identification of GYF-domain encoding genes (GYFs) from Brassica napus and its parental species, Brassica rapa and Brassica oleracea. As a result, 26 GYFs of B. napus (BnaGYFs), 11 GYFs of B. rapa (BraGYFs), and 14 GYFs of B. oleracea (BolGYFs) together with 10 A. thaliana (AtGYFs) were identified, respectively. We, then, conducted gene structure, motif, cis-acting elements, duplication, chromosome localization, and phylogenetic analysis of these genes. Gene structure analysis indicated the diversity of the exon numbers of these genes. We found that the defense and stress responsiveness element existed in 23 genes and also identified 10 motifs in these GYF proteins. Chromosome localization exhibited a similar distribution of BnaGYFs with BraGYFs or BolGYFs in their respective genomes. The phylogenetic and gene collinearity analysis showed the evolutionary conservation of GYFs among B. napus and its parental species as well as Arabidopsis. These 61 identified GYF domain proteins can be classified into seven groups according to their sequence similarity. Expression of BnaGYFs induced by Sclerotinia sclerotiorum provided five highly upregulated genes and five highly downregulated genes, which might be candidates for further research of plant-fungal interaction in B. napus.

Genome-wide survey of Calcium-Dependent Protein Kinases (CPKs) in five Brassica species and identification of CPKs induced by Plasmodiophora brassicae in B. rapa, B. oleracea, and B. napus.

Calcium-dependent protein kinase (CPK) is a class of Ser/Thr protein kinase that exists in plants and some protozoa, possessing Ca2+ sensing functions and kinase activity. To better reveal the roles that Brassica CPKs played during plant response to stresses, five Brassica species, namely Brassica rapa (B. rapa), Brassica nigra (B. nigra), Brassica oleracea (B. oleracea), Brassica juncea (B. juncea), and Brassica napus (B. napus) were selected and analyzed. In total, 51 BraCPK, 56 BniCPK, 56 BolCPK, 88 BjuCPK, and 107 BnaCPK genes were identified genome wide and phylogenetics, chromosomal mapping, collinearity, promoter analysis, and biological stress analysis were conducted. The results showed that a typical CPK gene was constituted by a long exon and tandem short exons. They were unevenly distributed on most chromosomes except chromosome A08 in B. napus and B. rapa, and almost all CPK genes were located on regions of high gene density as non-tandem form. The promoter regions of BraCPKs, BolCPKs, and BnaCPKs possessed at least three types of cis-elements, among which the abscisic acid responsive-related accounted for the largest proportion. In the phylogenetic tree, CPKs were clustered into four primary groups, among which group I contained the most CPK genes while group IV contained the fewest. Some clades, like AT5G23580.1(CPK12) and AT2G31500.1 (CPK24) contained much more gene members than others, indicating a possibility that gene expansion occurred during evolution. Furthermore, 4 BraCPKs, 14 BolCPKs, and 31 BnaCPKs involved in the Plasmodiophora brassicae (P. brassicae) defense response in resistant (R) or susceptible (S) materials were derived from online databases, leading to the discovery that some R-specific induced CPKs, such as BnaC02g08720D, BnaA03g03800D, and BolC04g018270.2J.m1 might be ideal candidate genes for P. brassicae resistant research. Overall, these results provide valuable information for research on the function and evolution of CDK genes.

Genome-wide characterization of PEBP gene family in Perilla frutescens and PfFT1 promotes flowering time in Arabidopsis thaliana.

Phosphatidylethanolamine-binding proteins (PEBP) family plays important roles in regulating plant flowering time and morphogenesis. However, geneme-wide identification and functional analysis of PEBP genes in the rigorous short-day plant Perilla frutescens (PfPEBP) have not been studied. In this study, 10 PfPEBP were identified and divided into three subfamilies based on their phylogenetic relationships: FT-like, TFL1-like and MFT-like. Gene structure analysis showed that all PfPEBP genes contain 4 exons and 3 introns. Motifs DPDxP and GIHR essential for anion-binding activity are highly conserved in PfPEBP. A large number of light-responsive elements were detected in promoter regions of PfPEBP. Gene expression of PfFT1 exhibited a diurnal rhythm. It was highly expressed in leaves under the short-day photoperiod, but higher in flowers and seeds under the long-day photoperiod. Overexpression of PfFT1 in Arabidopsis thaliana not only promoted early flowering of Col-0 or Ler, but also rescued the late flowering phenotype of ft-1 mutant. We concluded that PfFT1 promotes early flowering by regulating the expression of flowering-related genes AtAP1, AtLFY, AtFUL and AtSOC1. In conclusion, our results provided valuable information for elucidating the functions of PfPEBP in P. frutescens and shed light on the promoting effect of PfFT1 on flowering.

An Amidase Contributes to Full Virulence of Sclerotinia sclerotiorum.

Sclerotinia sclerotiorum is one of the most notorious and ubiquitous soilborne plant pathogens, causing serious economic losses to a large number of hosts worldwide. Although virulence factors have been identified in this filamentous fungus, including various cell-wall-degrading enzymes, toxins, oxalic acids and effectors, our understanding of its virulence strategies is far from complete. To explore novel factors contributing to disease, a new pipeline combining forward genetic screening and next-generation sequencing was utilized in this study. Analysis of a hypovirulent mutant revealed that a mutation in an amidase-encoding gene, Sscle_10g079050, resulted in reduced virulence. This is a first report on the contribution of an amidase to fungal virulence, likely through affecting oxalic acid homeostasis.

Identification of receptor-like proteins induced by Sclerotinia sclerotiorum in Brassica napus.

Heightening the resistance of plants to microbial infection is a widely concerned issue, especially for economical crops. Receptor-like proteins (RLPs), typically with tandem leucine-rich repeats (LRRs) domain, play a crucial role in mediating immune activation, being an indispensable constituent in the first layer of defense. Based on an analysis of orthologs among Brassica rapa, Brassica oleracea, and Brassica napus using Arabidopsis thaliana RLPs as a reference framework, we found that compared to A. thaliana, there were some obvious evolutionary diversities of RLPs among the three Brassicaceae species. BnRLP encoding genes were unevenly distributed on chromosomes, mainly on chrA01, chrA04, chrC03, chrC04, and chrC06. The orthologs of five AtRLPs (AtRLP3, AtRLP10, AtRLP17, AtRLP44, and AtRLP51) were highly conserved, but retrenchment and functional centralization occurred in Brassicaceae RLPs during evolution. The RLP proteins were clustered into 13 subgroups. Ten BnRLPs presented expression specificity between R and S when elicited by Sclerotinia sclerotiorum, which might be fabulous candidates for S. sclerotiorum resistance research.

Genome-wide analysis of DGAT gene family in Perilla frutescens and functional characterization of PfDGAT2-2 and PfDGAT3-1 in Arabidopsis.

Diacylglycerol acyltransferase (DGAT) is the rate-limiting enzyme that catalyzes the final step in triacylglycerol biosynthesis, however, members of DGAT gene family of Perilla frutescens has not yet been identified and characterized. In this study, a total of 20 PfDGAT genes were identified from the genome of Perilla frutescens and were divided into four groups (PfDGAT1, PfDGAT2, PfDGAT3, PfWS/DGAT) according to their phylogenetic relationships. These were unevenly distributed across the 12 chromosomes. Sequence analysis revealed that PfDGAT members of the same subfamily have highly conserved gene structures, protein motifs and cis-acting elements in their promoters. Gene duplication analysis showed that random duplication and segmental duplication contributed to the expansion of the DGAT family in P. frutescens. RNA-seq and qRT-PCR analysis suggested that they may play a role in the growth and development of Perilla, especially in the accumulation of seed oil. Compared with the wild-type, seed length, width, and 1000-seed weight of transgenic PfDGAT2-2 and PfDGAT3-1 Arabidopsis were significantly increased, as well as the seed oil content increased by 7.36-15.83 %. Over-expression of PfDGAT2-2 could significantly increase the content of C18:3 and C20:1 in Arabidopsis, while over-expression of PfDGAT3-1 could significantly enhance the content of C18:2 and C18:3. In conclusion, in this study the characteristics and potential functions of the PfDGAT family members were elucidated. Our findings provided basic information for further functional studies and helped to increase the yield and quality of Perilla oil.

HSP90 Contributes to chs3-2D-Mediated Autoimmunity.

Plants employ multi-layered immune system to fight against pathogen infections. Different receptors are able to detect the invasion activities of pathogens, transduce signals to downstream components, and activate defense responses. Among those receptors, nucleotide-binding domain leucine-rich repeat containing proteins (NLRs) are the major intracellular ones. CHILLING SENSITIVE 3 (CHS3) is an Arabidopsis NLR with an additional Lin-11, Isl-1 and Mec-3 (LIM) domain at its C terminus. The gain-of-function mutant, chs3-2D, exhibiting severe dwarfism and constitutively activated defense responses, was selected as a genetic background in this study for a forward genetic screen. A mutant allele of hsp90.2 was isolated as a partial suppressor of chs3-2D, suggesting that HSP90 is required for CHS3-mediated defense signaling. In addition, HSP90 is also required for the autoimmunity of the Dominant Negative (DN)-SNIPER1 and gain-of-function ADR1-L2 D484V transgenic lines, suggesting a broad role for HSP90 in NLR-mediated defense. Overall, our work indicates a larger contribution of HSP90 not only at the sensor, but also the helper NLR levels.

Transcriptomic analysis reveals the mechanism of thermosensitive genic male sterility (TGMS) of Brassica napus under the high temperature inducement.

BACKGROUND: The thermo-sensitive genic male sterility (TGMS) of Brassica napus facilitates reproductive researches and hybrid seed production. Considering the complexity and little information about the molecular mechanism involved in B. napus TGMS, comparative transcriptomic analyses were peroformed for the sterile (160S-MS) and fertile (160S-MF) flowers to identify potential crucial genes and pathways associated with TGMS. RESULTS: In total, RNA-seq analysis showed that 2202 genes (561 up-regulated and 1641 down-regulated) were significantly differentially expressed in the fertile flowers of 160S-MF at 25 °C when compared the sterile flower of 160S-MS at 15 °C. Detailed analysis revealed that expression changes in genes encoding heat shock proteins, antioxidant, skeleton protein, GTPase and calmodulin might be involved in TGMS of B. napus. Moreover, gene expression of some key members in plant hormone signaling pathways, such as auxin, gibberellins, jasmonic acid, abscisic acid, brassinosteroid signalings, were significantly surppressed in the flowers of 160S, suggesting that these genes might be involved in the regulation in B. napus TGMS. Here, we also found that transcription factor MADS, NFY, HSF, MYB/C and WRKY might play a crucial role in male fertility under the high temperature condition. CONCLUSION: High temperature can significant affect gene expression in the flowers. The findings in the current study improve our understanding of B. napus TGMS at the molecular level and also provide an effective foundation for male fertility researches in other important economic crops.

Transcriptomic analysis of Perilla frutescens seed to insight into the biosynthesis and metabolic of unsaturated fatty acids.

BACKGROUND: Perilla frutescens is well known for its high α-linolenic acid (ALA) accumulation in seeds and medicinal values as well as a source of edible and general-purpose oils. However, the regulatory mechanisms of the biosynthesis of fatty acid in its seeds remain poorly understood due to the lacking of sequenced genome. For better understanding the regulation of lipid metabolism and further increase its oil content or modify oil composition, time-course transcriptome and lipid composition analyses were performed. RESULTS: Analysis of fatty acid content and composition showed that the α-linolenic acid and oleic acid accumulated rapidly from 5 DAF to 15 DAF and then kept relatively stable. However, the amount of palmitic acid and linoleic acid decreased quickly from 5 DAF to 15DAF. No significant variation of stearic acid content was observed from 5 DAF to 25DAF. Our transcriptome data analyses revealed that 110,176 unigenes were generated from six seed libraries at 5, 10, 20 DAF. Of these, 53 (31 up, 22 down) and 653 (259 up, 394 down) genes showed temporal and differentially expression during the seed development in 5 DAF vs 10 DAF, 20 vs 10 DAF, respectively. The differentially expressed genes were annotated and found to be involved in distinct functional categories and metabolic pathways. Deep mining of transcriptome data led to the identification of key genes involved in fatty acid and triacylglycerol biosynthesis and metabolism. Thirty seven members of transcription factor family AP2, B3 and NFYB putatively involved in oil synthesis and deposition were differentially expressed during seed development. The results of qRT-PCR for selected genes showed a strong positive correlation with the expression abundance measured in RNA-seq analysis. CONCLUSIONS: The present study provides valuable genomic resources for characterizing Perilla seed gene expression at the transcriptional level and will extend our understanding of the complex molecular and cellular events of oil biosynthesis and accumulation in oilseed crops.

Cloning and Phylogenetic Analysis of Brassica napus L. Caffeic Acid O-Methyltransferase 1 Gene Family and Its Expression Pattern under Drought Stress.

For many plants, regulating lignin content and composition to improve lodging resistance is a crucial issue. Caffeic acid O-methyltransferase (COMT) is a lignin monomer-specific enzyme that controls S subunit synthesis in plant vascular cell walls. Here, we identified 12 BnCOMT1 gene homologues, namely BnCOMT1-1 to BnCOMT1-12. Ten of 12 genes were composed of four highly conserved exons and three weakly conserved introns. The length of intron I, in particular, showed enormous diversification. Intron I of homologous BnCOMT1 genes showed high identity with counterpart genes in Brassica rapa and Brassica oleracea, and intron I from positional close genes in the same chromosome were relatively highly conserved. A phylogenetic analysis suggested that COMT genes experience considerable diversification and conservation in Brassicaceae species, and some COMT1 genes are unique in the Brassica genus. Our expression studies indicated that BnCOMT1 genes were differentially expressed in different tissues, with BnCOMT1-4, BnCOMT1-5, BnCOMT1-8, and BnCOMT1-10 exhibiting stem specificity. These four BnCOMT1 genes were expressed at all developmental periods (the bud, early flowering, late flowering and mature stages) and their expression level peaked in the early flowering stage in the stem. Drought stress augmented and accelerated lignin accumulation in high-lignin plants but delayed it in low-lignin plants. The expression levels of BnCOMT1s were generally reduced in water deficit condition. The desynchrony of the accumulation processes of total lignin and BnCOMT1s transcripts in most growth stages indicated that BnCOMT1s could be responsible for the synthesis of a specific subunit of lignin or that they participate in other pathways such as the melatonin biosynthesis pathway.

Genome-Wide Survey and Expression Profile Analysis of the Mitogen-Activated Protein Kinase (MAPK) Gene Family in Brassica rapa.

Mitogen-activated protein kinase (MAPK) cascades are fundamental signal transduction modules in plants, controlling cell division, development, hormone signaling, and biotic and abiotic stress responses. Although MAPKs have been investigated in several plant species, a comprehensive analysis of the MAPK gene family has hitherto not been performed in Brassica rapa. In this study, we identified 32 MAPKs in the B. rapa genome by conducting BLASTP and syntenic block analyses, and screening for the essential signature motif (TDY or TEY) of plant MAPK proteins. Of the 32 BraMAPK genes retrieved from the Brassica Database, 13 exhibited exon splicing errors, excessive splicing of the 5' sequence, excessive retention of the 5' sequence, and sequencing errors of the 3' end. Phylogenetic trees of the 32 corrected MAPKs from B. rapa and of MAPKs from other plants generated by the neighbor-joining and maximum likelihood methods suggested that BraMAPKs could be divided into four groups (groups A, B, C, and D). Gene number expansion was observed for BraMAPK genes in groups A and D, which may have been caused by the tandem duplication and genome triplication of the ancestral genome of the Brassica progenitor. Except for five members of the BraMAPK10 subfamily, the identified BraMAPKs were expressed in most of the tissues examined, including callus, root, stem, leaf, flower, and silique. Quantitative real-time PCR demonstrated that at least six and five BraMAPKs were induced or repressed by various abiotic stresses and hormone treatments, respectively, suggesting their potential roles in the abiotic stress response and various hormone signal transduction pathways in B. rapa. This study provides valuable insight into the putative physiological and biochemical functions of MAPK genes in B. rapa.

Differential accumulation of phenolic compounds and expression of related genes in black- and yellow-seeded Brassica napus.

Developing yellow-seeded Brassica napus (rapeseed) with improved qualities is a major breeding goal. The intermediate and final metabolites of the phenylpropanoid and flavonoid pathways affect not only oil quality but also seed coat colour of B. napus. Here, the accumulation of phenolic compounds was analysed in the seed coats of black-seeded (ZY821) and yellow-seeded (GH06) B. napus. Using toluidine blue O staining and liquid chromatography-mass spectrometry, histochemical and biochemical differences were identified in the accumulation of phenolic compounds between ZY821 and GH06. Two and 13 unique flavonol derivatives were detected in ZY821 and GH06, respectively. Quantitative real-time PCR analysis revealed significant differences between ZY821 and GH06 in the expression of common phenylpropanoid biosynthetic genes (BnPAL and BnC4H), common flavonoid biosynthetic genes (BnTT4 and BnTT6), anthocyanin- and proanthocyandin-specific genes (BnTT3 and BnTT18), proanthocyandin-specific genes (BnTT12, BnTT10, and BnUGT2) and three transcription factor genes (BnTTG1, BnTTG2, and BnTT8) that function in the flavonoid biosynthetic pathway. These data provide insight into pigment accumulation in B. napus, and serve as a useful resource for researchers analysing the formation of seed coat colour and the underlying regulatory mechanisms in B. napus.