Characterization Of CesAs Involved In Cellulose Biosynthesis Of Primary Cell Walls In Plants

Cellulose is a major wall polymers and it largely affects plant cell wall property for biomass enzymatic saccharification.Cellulose is synthesized by cellulose synthase(CESA)complexes,and the Ces As have been classified into distinct primary and secondary cell wall family.Despite of many reports about secondary wall Ces As,much remains unknown about primary wall Ces As functions in cell wall formation and related plant growth.In this study,we selected transgenic rice lines that respectively over-expressed Os Ces As and At Ces As genes of primary cell walls,and identified the related Os Ces A mutant.Then,we observed plant growth and examined cell wall composition and cellulose features in both transgenic rice plants and mutants.Finally,we determined biomass enzymatic saccahrification of mature rice straws.The main results are as follows:1.The identified T-DNA insertion mutant(OsCesA5)was observed with significantly reduced plant height and internode lengths,but the transgenic rice lines overexpressed OsCesA5 showed much increased plant heights.2.Based on Q-PCR analysis of gene expression,the mutant showed significantly reduced transcript levels of three Os Ces A3,5,6 involved in cellulose biosynthesis of primary cell walls,compared to the wild type,whereas the transgenic rice plants exhibited much increased expression levels.3.Compared to the wild type,the mutant was observed with thinner primary cell walls under transmission electron microscopy,but the transgenic rice plants showed the thicker primary walls with relatively thinner secondary cell walls.4.The mature mutant had significantly reduced cellulose features(Cr I,DP),but the transgenic rice plants showed much raised ones in the stem tissues.5.The mature mutant showed much reduced wall polymers levels(cellulose, hemicellulose and lignin),whereas the transgenic rice plants had significantly raised ones in the stem tissues.6.The transcript levels of IRX14 for hemicellulose synthesis and 4CL1,4CL3,4CL4 involved in lignin synthesis were significantly decreased in the mutant,but were significantly increased in the transgenic lines.7.Under mild 1% NaOH pretreatment,the mutant showed much higher biomass enzymatic saccharification with bioethanol yield at 21%(% dry matter),compared to the wild type.8.The transgenic rice lines that over-expressed At Ces A3,6,7,9 genes showed significantly reduced plant height,compared to the control cultivar.