Insight Into The Relationship Between S-Lignin And Fiber Quality Based On Multiple Research Methods

Cotton is one of the important economic crops in the world,providing high-quality natural raw materials for the textile industry.Lignin is one of the important components of cotton fiber,and its content is second only to cellulose.During the thickening of the secondary wall,lignin fills the cellulose skeleton as a main substance.Lignin has three different lignin structural units,H-,G-and S-type,which play a key role in the formation of cotton fiber.However,the formation mechanism of lignin in cotton fiber and its relationship with cotton fiber quality are still unclear.In this study,based on the analysis of transcriptome data of high-intensity parent,low-intensity parent,positive superparent and negative superparent of upland cotton recombinant inbred lines,candidate genes involved in lignin biosynthesis were screened.The expression levels of candidate genes in various stages of fiber development were identified by qRT-PCR,and the results were basically consistent with transcriptome data.A total of 62 genes from 9 gene families related to lignin synthesis were identified from the upland cotton genome,involving 9 gene families,including 9 PALs,4 C4Hs,1 C3H,7 COMTs,2 F5Hs,6 CCoAOMTs,14 4CLs,7 CCRs,12 CADs.The rate-limiting enzyme cinnamyl alcohol dehydrogenase(CAD)in the lignin synthesis pathway is 20,17,13 and 12 in the genomes of G.hirsutum,G.barbadense,G.arboreum and G.raimondii,respectively.The FPKM values of the paragenes of the same gene family vary greatly,indicating that their expression levels are significantly different.The transcriptome data analysis results indicate that the paragenes of the same gene family exhibit specific expression patterns during the fiber development stage.In order to elucidate the molecular mechanism of lignin synthesis,this study analyzed the phylogenetic evolution and gene structure of cinnamyl alcohol dehydrogenase.Based on the above results,it is speculated that GhCAD7 plays an important role in regulating the biosynthesis of lignin,and the ratio of S-type lignin to G-type lignin has an important influence on the formation of cotton fiber quality.Finally,the statistical analysis of the content of small molecule metabolites in the lignin pathway shows that Sinapyl alcohol,Sinapic acid and Sinapinaldehyde,which are located in the S-type lignin synthesis branch,are labeled compounds.It is speculated that the S-type lignin synthesis branch of these three compounds may play an important role in the formation of fiber quality.This study provides a new method for distinguishing cotton fiber materials of different quality,and also lays a foundation for further study on the synthesis of lignin and the relationship between lignin and fiber quality.