Effect Of Shade On Lignin Biosynthesis In Soybean Stem

Lignin plays an important role in maintaining mechanical strength of stem and resisting bad environment.In recent years,in the southwest of China,maize-soybean relay strip intercropping system has developed rapidly,and its cultivation system has already been matured,which had some great contribution to the local agriculture production and farmers’ income,by now,the maize-soybean relay-cropping system has been a key technology in agriculture.But in maize-soybean relay strip intercropping system,the soybean stem was elongated and lignin content was reduced because of the shade of the canopy of maizes,which easily made the soybean lodging,and seriously limited the high yield and high quality of soybean.Therefore,an experiment was conducted using two different shade susceptive soybean(Glycine max L.)varieties Nandou 12 and Nan 032-4 to investigate the transcriptome changes in response to shade stress by RNA-seq technology,and studying the molecular mechanisms for shade stress responses of soybean grown in the intercropping system,then screened some key genes involved in lignin synthesis,and combined with metabolic intermediate in pathway of lignin biosynthesis,to investigate the effect of shade stress on lignin biosynthesis in soybean stem.The results were as follows:1.In shade condition,287 differentially expressed genes in Nandou 12 and 110 genes in Nan 032-4 were significantly affected by shade,and the expression of the genes was mainly up-regulated.Gene functional annotation showed that 60 differentially expressed genes were shared by Nandou 12 and Nan 032-4,and 42 genes had functional annotation,18 genes had no functional annotation.In addition,the genes of two annotation of Nandou 12 accounted for separately as 75.3%and 24.7%,that of Nan 032-4 accounted for separately as 44.0%and 56.0%.2.In shade condition,the number of significant enrichment of entries of Nandou 12 and Nan 032-4 were 263 and 189,respectively,and 98 significant enrichment of entries were owned by the two materials.In special significant enrichment of entries,the biological process,celluar compontent,molecular function of Nan 032-4 had 55,2 and 34 differentially expressed genes,and that of Nandou 12 had 107,6 and 52 differentially expressed genes,respectively.Furthermore,for the common significant enrichment of entries,the biological process,celluar compontent,molecular function accounted for separately as 58.2%,11.2%and 30.6%.There were 111 and 129 highly significant enrichment of entries in Nan 032-4 and Nandou 12,respectively.Moreover,52 highly significant enrichment of entries owned by both materials,which refered to secondary cell wall biogenesis,polysaccharides synthesis,calmodulin binding,hydrolase activity,lignin biosynthesis and so on.Nan 032-4 had 59 special highly significant enrichment of entries,that mainly refered to jasmonic acid,gibberellin and ethylene metabolism processes,Nandou 12 had 77 special highly significant enrichment of entries,that mainly refered to polysaccharides,lignin and auxin biosynthetic processes.All genes in this entries were up-regulated other than responding to gibberellin metabolic process.However,Nandou 12 had more differentially expressed genes than Nan 032-4.3.There were 2 significant KEGG enrichments in Nan 032-4 under shade condition,including flavone and flavonol biosynthesis and gtalactose metabolism,and the number of significant KEGG enrichments in Nandou 12 was 24,which mainly involved phenylpropanoid biosynthesis,flavono lid biosynthesis,flavone and flavonol biosynthesis,PI3K-Akt signaling pathway,glycine,serine and threonine metabolism,biosynthesis of secondary metabolites,carbon metabolism,metabolic pathways and so on.4.Compared with normal light condition,both Nandou 12 and Nan 032-4 showed more plant height and internode length with lesser stem diameter under shade treatment.In shade condition,Nandou 12 showed lower plant height and internode length than that of Nan 032-4,whereas the stem diameter was thicker.The lignin content of Nandou 12 and Nan 032-4 were decreased significantly by 13.8%and 9.75%by shade,respectively.Both normal light condition and shade condition,the lignin content of Nandou 12 were increased by 11.20%、9.61%compared with Nan 032-4,respectively.In addition,there were significant interaction of light environment and variety on lignin content of soybean stem.5.Compared with normal light condition,these genes(C3H,CCR,CCoAOMT,POD,PAL,4CL,C4H,CAD,COMT,LAC)of Nandou 12 were up-regulated in shade condition,but for Nan 032-4,there were only 4 up-regulated genes(C3H,CCR,CCoAOMT,POD).As the treatment time went on,Nan 032-4 expressed bigger differential expression level later than Nandou 12 under shade.Anyway,as the treatment time was prolonged to 8.5 h,the all of genes expression levels of Nandou 12 and Nan 032-4 did significantly change under shade condition.In addition,for interaction of light environment and variety,the expression levels of eight genes(PAL,C4H,C3H,4CL,COMT,CCR,CAD,LAC)were extremely significant.Therefore,four genes(C3H,CCR,CCoAOMT,POD)were the key genes in lignin biosynthesis process.6.Compared with normal light condition,shade stress significantly increased the cinnamic acid and p-coumaric acid,for Nandou 12,significantly increased by 7.7%and 96.4%,respectively,for Nan 032-4,significantly increased by 24.0%and 21.2%,respectively.Meanwhile,shade stress significantly reduced the caffeic acid,sinapic acid and ferulic acid,Nandou 12 significantly reduced by 30.04%,20.11%,20.24%,respectively,and Nan 032-4 significantly reduced by 10.7%,24.1%,24.0%,respectively.In shade condition,the caffeic acid,sinapic acid and ferulic acid of Nandou 12 were higher than Nan 032-4.