Tissue-specific Transcriptome Analysis Reveals Lignocellulose Synthesis Regulation In Elephant Grass(pennisetum Purpureum Schum.)

Elephant grass（Pennisetum purpureum Schum.）is a perennial gramineous C4plant（2n=4x=28）,originated in tropical Africa,and then widely distributed in tropical and subtropical climate regions in Asia,Africa and America.It is one of the herbaceous plants with the highest biomass in the world,with a plant height of 3～5 m and an annual biomass of 4500 kg·hm^-2.The main biological characteristics of elephant grass are high photosynthesis,high yield,resistance to biological and abiotic stress.Elephant grass stalks have high cellulose content and low lignin content,which are high-quality fiber raw materials and mainly used in feed processing,alcohol production,biochar manufacturing and paper industry.Although the elephant grass genome has not yet been deciphered,researchers have revealed the biosynthetic pathway of anthocyanins through transcriptome analysis,and the molecular mechanism of early response to cadmium in roots and leaves.On the other hand,some progress has been made in using traditional breeding methods based on phenotypic selection to improve the agronomic traits of elephant grass.Although the fiber synthesis regulatory network of plants has been reported in other species such as Arabidopsis,corn（Zea mays L.）,poplar（Populus L.）,and switchgrass（Panicum virgatum L.）,there are few studies on the molecular biology and regulatory network of elephant grass fiber synthesis.Therefore,in order to understand the transcriptional regulation of lignocellulose synthesis network and explore the important genes of lignocellulose synthesis network in different developmental stages of elephant grass stalks,we conducted transcriptome sequencing analysis,lignocellulose composition analysis and cell wall morphology observation of 12 elephant grass stalks at different developmental stages.The results showed that during the development of elephant grass,the content of cellulose and hemicellulose increased first and then decreased,the content of lignin increased gradually with the development of elephant grass,and the ratio of primary cell wall and secondary cell wall decreased gradually.A total of 3,852 differentially expressed genes（DEGs）were identified in T1,T2,and T3 stages of elephant grass development.KEGG enrichment analysis was performed on the common differential genes,and it was found that the two metabolic pathways with the most significant enrichment were Phenylpropanoid metabolic pathway.Propane metabolism,starch and sucrose metabolism were closely related to cell wall development,lignin and cellulose synthesis.Through the weighted gene co-expression network analysis（WGCNA）of all DEGs,the“blue”module,which is highly correlated with cellulose content,was found,with a total of 20 genes.The“turquoise”module which was highly related to lignin content has 23 genes.The 43 candidate genes have high expression in all samples,which suggested that these genes may be involved in the regulation of cellulose and lignin synthesis in elephant grass.In addition,fiber synthesis gene Ces A,lignin synthesis related genes such as PAL,C4H,C3H,4CL,COMT,CCo AMT,F5H,CAD and CCR have all been identified at different numbers of members to participate in fiber synthesis at various stages and metabolism.This study not only provides new insights into the molecular mechanisms of cellulose and lignin synthesis pathways in elephant grass,but also provides a new and extensive list of candidate genes for more specialized functional studies in the future.The research results will promote the development of high-quality elephant grass varieties with high cellulose content and low lignin content,and have important theoretical significance for the development of papermaking,biochar,energy conversion and other industries.