Differential Expression Analysis Of Genes Involved In Sugar Metabolism Between Parenchyma And Sclerenchyma Cells In Sugarcane

Sugarcane(Saccharum spp.)is one of the highest biomass crops currently cultivated in globally.Mature sugarcane stalks can accumulate sucrose at high concentration.Sugar production in sugarcane accounts for about two-thirds of the world's sugar production.How to increase sugar yield per unit area of sugarcane has been a long lasting questions in sugarcane breeding program.In the sugarcane stem,the parenchyma cells store sucrose while the Sclerenchyma cells with thick cell wall and high fiber content consume and transport sucrose.Because of the different functions between the two types of cell,differential expression of genes involved in sugar metabolism could be identified by comparing their transcriptome.In this study,differential expression analysis was performed on the transcriptomes of parenchyma and sclerenchyma cells that were at the stage of sugar accumulation.Their functions were annotated to screen candidate genes contributing to sugar accumulation.The aims of this study are to identify the differentially expressed genes involved in the process of sugar metabolism,and to provide ideas for the follow-up research of sugarcane genetics and breeding.The main results are below:(1)RNA-seq analysis was performed on transcriptomes of the parenchyma and sclerenchyma from stem 13 of LA-Purple at the pre-mature stage.The overall expression level of transcripts was relatively low,fewer genes are highly expressed.Genes accounted for 89.12%within the FPKM 0.3-10 region,9.93%for the FPKM 10-100 region,and only 0.95%genes' FPKM value is above 100.The functions of expressed genes were mainly involved in cellular processes,metabolic processes,response to stimulus,etc.(2)The transcriptome profiles of parenchyma and sclerenchyma are significantly different.Firstly,the genes expressed and the level of gene expression were different.Genes that expressed in both tissues accounted for 69.3%,genes that expressed specifically in parenchyma cells accounted for 13.4%,and genes that only expressed in sclerenchyma accounted for 17.3%.Secondly,the functions of expressed genes in parenchyma and sclerenchyma were quite different.The number of genes involved in the immune system function,transporter activity and molecular transduction activity of parenchyma was significantly higher than that of sclerenchyma.In addition,number of genes in parenchyma cell was much less than that in sclerenchyma.(3)The results of differential expression analysis showed that the number of differentially expressed genes in parenchyma was significantly less than that of sclerenchyma.The number of differentially expressed genes in sclerenchyma is 3.13 times of that in parenchyma.The differential expression of genes in parenchyma is prominent in transporter activity and molecular transduction activity.The functions of differentially expressed genes are mainly involved in metabolic processes,response to stimulus,and catalytic reactions.The expression level of differentially expressed genes in sclerenchyma was more than 2 times higher than that in parenchyma in terms of molecular function regulation and transcription factor activity.(4)The difference of sugar-related metabolites in the stem of LA-Purple at different maturation stages was determined by mass spectrometry analysis.The content of glucose and fructose increased first and then decreased with the maturity of the stem,while the sucrose content increased continuously with the maturity of the stem.(5)Through the annotation analysis of the functions of differentially expressed genes specifically in of parenchyma cell,18 genes related to sugar metabolism were selected.According to the corresponding product of the gene,the 18 genes could be divided into eight categories:a.UDP-glycosyltransferases,UDP-sugar synthesis enzyme;b.WRKY protein;c.cellulose synthase,starch synthase;d.xylosyltransferase,xyloglucan endotransglucosylase,endoxyloglucan transferase A3;e.glycosyl hydrolase superfamily proteins;f.fructokinase 2,fucosyltransferase 1;g.hydroxyproline-rich glycoproteins Family protein;h.nucleotide diphosphate glycosyltransferase superfamily protein.(6)Combining 16 transcriptome profiles of LA-purple at the seedling,pre-maturation,and maturation stages,the 18 genes were analyzed for their expression patterns.Genes involved in glycosyl transfer and hydrolysis include cellulose synthase in c,d,e,f,and g.Their expression patterns are similar:the expression in leaves is generally lower than that in stems.The expression in young stems and leaves is higher than it in mature stems and leaves,that is,with the maturity of the stem,its expression decreases.Among them,the cellulose synthase T012 may only participate in the synthesis of cellulose in the primary wall of parenchyma in the stem.The hydroxyproline-rich glycoprotein family protein gene T523 may act on the parenchyma's cell wall in the younger period of sugarcane.The UDP-glycosyltransferases and UDP-glycosynthase gene members have different receptors and their expression in stems does not have a uniform pattern.Among them,UDP-glycosyltransferase T172 may have high correlation with fructose and glucose.T231 and T711 had high correlation with sucrose.The expression levels of WRKY family genes T318 and T016 decreased first and then increased during the early maturity period,during the mature period they increased first and then decreased.Their function may be related to fructose synthesis.This study systematically analyzed the differences in expression and function of parenchyma and sclerenchyma in sugarcane stems.Sugar-metabolism-related genes that were specifically expressed in parenchyma were identified.The pattern changes in expression levels of these gene during different mature stages of sugarcane and their possible regulation were analyzed.The results laid the foundation for further study on sugar metabolism related gene regulatory mechanisms in sugarcane.