| As plant cell wall decides cell size and shape,it plays a central role in plant cell growth and morphogenesis,and in particular its features basically affect biomass enzymatic saccharification.Over the past years,numerous genes are identified to involve in plant cell wall biosynthesis and their related transcription factors(TFs)have been characterized in Arabidopsis,a model of diocot plants.However,much remains unknown about TFs regulation on secondary cell wall(SCW)synthesis of monocot plants.Rice is an important food crop and also as the model monocot plant.In this study,using public bioinformatics database of rice,we screened out two new OsMYBs highly related to SCW synthesis,characterized their biological functions and biomass enzymatic saccharification in the transgenic rice plants,providing new insights into genetic modification of plant cell wall and bioenergy crop breeding.The main results are described as follows:1.Overexpression of OsMYB63 and OsMYB86 caused distinct leaf rolling phenotypes.Compared with the wild type at the heading stage,the flag leaves of OsMYB63-overexpressed lines showed significantly increased abacial rolling index with much increased bulliform cell areas and numbers.The cell wall thickness of OsMYB63-overexpressed leaves was decreased by 12%-13%,with the cellulose content increased by 17%-20%,hemicelluloses increased by 4%-8%,and lignin decreased by3%-11%.Meanwhile,OsMYB86 was identified by an activation tagging T-DNA insertion leading to much increased expression.Overexpression of OsMYB86 showed a similar adacial leaf rolling phenotype to the OsMYB86 heterozygote(M86He).The cell wall thickness of M86 He was increased by 32% without significant changes of bulliform cell compared to the wild type.2.Overexpression of OsMYB63 and OsMYB86 affected stem mechanical strength.Compared with the wild type,the stem strength of OsMYB63-overexpressed plants was significantly decreased by 22%-30%.Their cell wall composition was altered with cellulose increased by 10%-25%,hemicellulose increased by 4%-14%,and lignin decreased by 3%-11%,consistent with their genes expression alteration involved in SCW synthesis.At the mature stage,the M86 He showed significantly enhanced plant lodging resistance by increasing the stem diameter by 12% and stem mechanical strength by 23%.Overexpression of OsMYB86 increased the expression of cellulose synthetic genes and cellulose content by17% with not significant change of hemicellulose and lignin.3.Based on the co-expression model of OsMYB86 and OsMYB63,this study performed Yeast two-hybrid,Co-Immunoprecipitation and other genetic assays among these two TF proteins,and the preliminary data suggested that OsMYB63 and OsMYB86 proteins may have an interaction for co-regulations of plant architechture in rice.4.Largely enhanced lignocellulose enzymatic saccharificaiton and bioethanol production in the OsMYBs-overexpressed plants and mutants.Compared with the wild type,the OsMYB63-overexpressed plants showed much enhanced biomass enzymatic saccharification by 21% and bioethanol production by 14% under mild alkali pretreatment with the mature straw;The OsMYB86 mutant showed enhanced enzymatic saccharification by 28% and bioethanol yield by 16%;The OsMYB103-RNAi plants and mutant also displayed increased enzymatic saccharification by 18%-26% and bioethanol yield by 10%-20%.The much enhanced biomass enzymatic saccharification might due to reduction of their cell wall composition and wall polymer features including lignin content,cellulose Cr I,hemicellulosic Xyl/Ara and lignin S/G ratio.5.Due to complicated cell wall structures and diverse lignocellulose resources,this study also established a near infrared spectroscopy assay for quickly predicting cell wall compositions and lignocellulose enzymatic saccharification by using 173 distinct sweet sorghum samples,which should be applicable for bioenergy crop breeding and biomass saccharification evaluation in the future. |
PDF Full Text Request