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Cotton produces natural fiber for the textile industry. The genetic effects of genomic structural variations underlying agronomic traits remain unclear. Here, we generate two high-quality genomes of Gossypium hirsutum cv. NDM8 and Gossypium barbadense acc. Pima90, and identify large-scale structural variations in the two species and 1,081 G. hirsutum accessions. The density of structural variations is higher in the D-subgenome than in the A-subgenome, indicating that the D-subgenome undergoes stronger selection during species formation and variety development. Many structural variations in genes and/or regulatory regions potentially influencing agronomic traits were discovered. Of 446 significantly associated structural variations, those for fiber quality and Verticillium wilt resistance are located mainly in the D-subgenome and those for yield mainly in the A-subgenome. Our research provides insight into the role of structural variations in genotype-to-phenotype relationships and their potential utility in crop improvement., High-quality genomes of two cultivated tetraploid cottons Gossypium hirsutum cv. NDM8 and Gossypium barbadense acc. Pima90 and resequencing of 1,081 G. hirsutum accessions provide insights into the role of structural variations.

Cotton (Gossypium hirsutum) is constantly attacked by pathogens and insects. The most efficient control strategy is to develop resistant varieties using broad-spectrum gene resources. Several resistance loci harboured by superior varieties have been identified through genome-wide association studies. However, the key genes and/or loci have not been functionally identified. In this study, we identified a locus significantly associated with Verticillium wilt (VW) resistance, and within a 145.5-kb linkage disequilibrium, two non-specific lipid transfer protein genes (named GhnsLTPsA10) were highly expressed under Verticillium pathogen stress. The expression of GhnsLTPsA10 significantly increased in roots upon Verticillium dahliae stress but significantly decreased in leaves under insect attack. Furthermore, GhnsLTPsA10 played antagonistic roles in positively regulating VW and Fusarium wilt resistance and negatively mediating aphid and bollworm resistance in transgenic Arabidopsis and silenced cotton. By combining transcriptomic, histological and physiological analyses, we determined that GhnsLTPsA10-mediated phenylpropanoid metabolism further affected the balance of the downstream metabolic flux of flavonoid and lignin biosynthesis. The divergent expression of GhnsLTPsA10 in roots and leaves coordinated resistance of cotton against fungal pathogens and insects via the redirection of metabolic flux. In addition, GhnsLTPsA10 contributed to reactive oxygen species accumulation. Therefore, in this study, we elucidated the novel function of GhnsLTP and the molecular association between disease resistance and insect resistance, balanced by GhnsLTPsA10. This broadens our knowledge of the biological function of GhnsLTPsA10 in crops and provides a useful locus for genetic improvement of cotton.

Lipids are major and essential constituents of plant cells and provide energy for various metabolic processes. However, the function of the lipid signal in defence against Verticillium dahliae, a hemibiotrophic pathogen, remains unknown. Here, we characterized 19 conserved stearoyl‐ACP desaturase family proteins from upland cotton (Gossypium hirsutum). We further confirmed that GhSSI2 isoforms, including GhSSI2‐A, GhSSI2‐B, and GhSSI2‐C located on chromosomes A10, D10, and A12, respectively, played a dominant role to the cotton 18:1 (oleic acid) pool. Suppressing the expression of GhSSI2s reduced the 18:1 level, which autoactivated the hypersensitive response (HR) and enhanced cotton Verticillium wilt and Fusarium wilt resistance. We found that low 18:1 levels induced phenylalanine ammonia‐lyase‐mediated salicylic acid (SA) accumulation and activated a SA‐independent defence response in GhSSI2s‐silenced cotton, whereas suppressing expression of GhSSI2s affected PDF1.2‐dependent jasmonic acid (JA) perception but not the biosynthesis and signalling cascade of JA. Further investigation showed that structurally divergent resistance‐related genes and nitric oxide (NO) signal were activated in GhSSI2s‐silenced cotton. Taken together, these results indicate that SA‐independent defence response, multiple resistance‐related proteins, and elevated NO level play an important role in GhSSI2s‐regulated Verticillium wilt resistance. These findings broaden our knowledge regarding the lipid signal in disease resistance and provide novel insights into the molecular mechanism of cotton fungal disease resistance., GhSACPD gene family isoforms GhSSI2‐A, GhSSI2‐B, and GhSSI2‐C displayed an important role in regulating 18:1 fatty acid level and negatively regulated cotton disease resistance to Verticillium wilt.

A high-density linkage map of an intraspecific RIL population was constructed using 6187 bins to identify QTLs for fibre quality- and yield-related traits in upland cotton by whole-genome resequencing. Good fibre quality and high yield are important production goals in cotton (Gossypium hirsutum L.), which is a leading natural fibre crop worldwide. However, a greater understanding of the genetic variants underlying fibre quality- and yield-related traits is still required. In this study, a large-scale population including 588 F7 recombinant inbred lines, derived from an intraspecific cross between the upland cotton cv. Nongdamian13, which exhibits high quality, and Nongda601, which exhibits a high yield, was genotyped by using 232,946 polymorphic single-nucleotide polymorphisms obtained via a whole-genome resequencing strategy with 4.3-fold genome coverage. We constructed a high-density bin linkage map containing 6187 bin markers spanning 4478.98 cM with an average distance of 0.72 cM. We identified 58 individual quantitative trait loci (QTLs) and 25 QTL clusters harbouring 94 QTLs, and 119 previously undescribed QTLs controlling 13 fibre quality and yield traits across eight environments. Importantly, the QTL counts for fibre quality in the Dt subgenome were more than two times that in the At subgenome, and chromosome D02 harboured the greatest number of QTLs and clusters. Furthermore, we discovered 24 stable QTLs for fibre quality and 12 stable QTLs for yield traits. Four novel major stable QTLs related to fibre length, fibre strength and lint percentage, and seven previously unreported candidate genes with significantly differential expression between the two parents were identified and validated by RNA-seq. Our research provides valuable information for improving the fibre quality and yield in cotton breeding.

BackgroundIdentifying the loci and dissecting the genetic architecture underlying wheat yield- and quality-related traits are essential for wheat breeding. A genome-wide association study was conducted using a high-density 90 K SNP array to analyze the yield- and quality-related traits of 543 bread wheat varieties.ResultsA total of 11,140 polymorphic SNPs were distributed on 21 chromosomes, including 270 significant SNPs associated with 25 yield- and quality-related traits. Additionally, 638 putative candidate genes were detected near the significant SNPs based on BLUP data, including three (TraesCS7A01G482000,TraesCS4B01G343700, andTraesCS6B01G295400) related to spikelet number per spike, diameter of the first internode, and grain volume. The three candidate genes were further analyzed using stage- and tissue- specific gene expression data derived from an RNA-seq analysis. These genes are promising candidates for enhancing yield- and quality-related traits in wheat.ConclusionsThe results of this study provide a new insight to understand the genetic basis of wheat yield and quality. Furthermore, the markers detected in this study may be applicable for marker-assisted selection in wheat breeding programs.

Additional file 9. The original, unprocessed images

Additional file 1: Fig. S1 Manhattan plots of GWAS results (BLUP values) excluding SNS, FD and GV traits. The horizontal line represents the significance threshold (−log10P = 4.05).

Background Dirigent (DIR) proteins mediate regioselectivity and stereoselectivity during lignan biosynthesis and are also involved in lignin, gossypol and pterocarpan biosynthesis. This gene family plays a vital role in enhancing stress resistance and in secondary cell-wall development, but systematical understanding is lacking in cotton. Results In this study, 107 GbDIRs and 107 GhDIRs were identified in Gossypium barbadense and Gossypium hirsutum, respectively. Most of these genes have a classical gene structure without intron and encode proteins containing a signal peptide. Phylogenetic analysis showed that cotton DIR genes were classified into four distinct subfamilies (a, b/d, e, and f). Of these groups, DIR-a and DIR-e were evolutionarily conserved, and segmental and tandem duplications contributed equally to their formation. In contrast, DIR-b/d mainly expanded by recent tandem duplications, accompanying with a number of gene clusters. With the rapid evolution, DIR-b/d-III was a Gossypium-specific clade involved in atropselective synthesis of gossypol. RNA-seq data highlighted GhDIRs in response to Verticillium dahliae infection and suggested that DIR gene family could confer Verticillium wilt resistance. We also identified candidate DIR genes related to fiber development in G. barbadense and G. hirsutum and revealed their differential expression. To further determine the involvement of DIR genes in fiber development, we overexpressed a fiber length-related gene GbDIR78 in Arabidopsis and validated its function in trichomes and hypocotyls. Conclusions These findings contribute novel insights towards the evolution of DIR gene family and provide valuable information for further understanding the roles of DIR genes in cotton fiber development as well as in stress responses.

Non-specific lipid transfer proteins (nsLTPs) had been previously isolated from cotton fiber but their functions were unclear so far. Bioinformatic analysis of the tetraploid cotton genome database identified 138 nsLTP genes, falling into the 11 groups as reported previously. Different from Arabidopsis, cacao, and other crops, cotton type XI genes were considerably expanded and diverged earlier on chromosome At11, Dt11, and Dt08. Corresponding to the type XI genes, the type XI proteins (GhLtpXIs) all contained an extra N-terminal cap resulting in larger molecular weight. The research revealed that the expression of type XI genes was dramatically increased in fibers of tetraploid cotton compared with the two diploid progenitors. High-level of GhLtpXIs expression was observed in long-fibered cotton cultivars during fiber elongation. Ectopic expression of GhLtpXIs in Arabidopsis significantly enhanced trichome length, suggesting that GhLtpXIs promoted fiber elongation. Overall, the findings of this research provide insights into phenotypic evolution of Gossypium species and regulatory mechanism of nsLTPs during fiber development. HIGHLIGHT A specific group, type XI nsLTPs, was identified with predominant expression in elongating fibers of Gossypium hirsutum based on evolutionary, transcriptional, and functional analyses.

Nitrate is one form of available nitrogen nutrient, and its uptake and transport in plants was mediated by nitrate transporters. It is important to elucidate the transcription mechanism of nitrate genes at the molecular level. In this study, the promoter of OsNrt2.1, a rice nitrate transporter gene previously cloned in our group, has been characterized. Based on PLACE online analysis, some important cis-regulatory elements were identified. Under the control of the full length fragment of OsNrt2.1 promoter (P-2047), the expression of the reporter gene Gus was up-regulated when exposed to low nitrogen. Promoter deletion analysis indicated that the low nitrate responding elements located at position − 524 to − 1 and − 980 to − 525. Several cis-regulatory elements such as CIACADIANLELHC and − 10 promoter element, located at positions of − 524 to − 1, − 980 to − 525, − 1487 to − 981, and − 2047 to − 1488 in P-2047, were possibly involved in the circadian regulation of the OsNrt2.1 gene. Sugar signaling and sugar-responsive motif WBOXHVISO1 and TATCCAOSAMY were also identified in P-2047, suggesting that the exogenous sugar variations resulted from the photosynthesis changes were related to the up-regulated expression of Gus during the day time. It is guessed that the expression pattern of Gus with lownitrate inducible and diurnal rhythm was partly, at least, via the mediation of Ca2+ signal transduction pathway. Owing to its regulation pattern with low nitrate inducible and typical circadian pattern, the OsNrt2.1 promoter maybe has a potential role in the generation of transgenic crop varieties with high-N use efficiency in the future.