Functional Analysis Of Sucrose Synthase Genes In Rice And Biomass Digestibility Of Genus Saccharum

Sucrose synthase(SUSy)is a glycosyltransferase involving in sucrose metabolism.It plays a central role in carbon partioning in starch synthesis and cellulose synthesis in plants.There are six SUSy isoforms existing in rice encoded by a small gene family.But,the gene family encoding iso forms of rice remains largely unknown,especially in identifying specific function of each gene.Here,this study is aimed to analysis of each OsSUS function by selecting the transgenic plants that overexpressed all six SUSy genes in rice.1.OsSUS regulates starch accumulation in rice grainUsing the transgenic plants that overexpressed OsSUS genes in the background of ZH11(wild type-WT),the 1,000-grain weight of mature grain were measured.Compared with WT,all transgenic lines showed the increased grain weights from 3.7%to 18.3%at P<0.01.Furthermore,both seed and hull weights were respectively increased by 1.00 g and 0.84 g in the transgenic line(S3-pUbi:OsSUS3).Accordingly,the grain length was significantly increased,the grain width is similar to WT,but the grain thickness was decreased slightly.Hence,the results indicated that OsSUS could enhance starch accumulation,leading to a large grain size.2.OsSUS regulates cellulose biosynthesis in rice stemAll transgenic lines showed much increased lodging resistance,and crystalline cellulose level in the stem was ranging from 0.5%to 16.2%,as compared with WT,suggesting that overproduction of sucrose synthase may provide more UDPG as substrate for enhancing cellulose biosynthesis in the transgenic plants.3.The OsSUS isoforms may not have accumulative effectsThis study further selected the transgenic plants that co-expressed two isoform OsSUS genes between pUbi:OsSUS3 and OsSUS1,2,4,5,6,and no more enhancement on cellulose level was determined,compared with the transgenic plant that only overexpressed single OsSUS gene.Saccharum officinarum,Saccharum spontaneum Linn and Saccharum arundinaceum are all species in genus Saccharum.As typical C4 perennial grasses,they have high biomass yields,and are considered as dedicated bioenergy plants.Hence,it is important to determine their lignocellulose structiires/features and biomass enzyme saccharification after various physical and chemical pretreatments in order to select the desired genetic germplasms/accessions for bioenergy crop breeding.In this study,total six samples from three species were used for determining their biomass enzymatic saccharification under pretreatments with NaOH,H2SO4,CaO and LHW at various concentrations.As a result,the optimal condition for each pretreatment is 4% NaOH or 1% H2SO4 or 10% CaO or LHW at 200? for 4 minutes.As a comparison,except for LHW,three species show different rates of biomass saccharification: Saccharum qfficinarum > Saccharum arundinaceum > Saccharum spontaneum Linn.In addition,four pretreatments lead to different enhancements on biomass enzymatic digestibility: alkali pretreatment(NaOH/CaO)> H2SO4 pretreatment >LHW pretreatment.Furthermore,the cell wall features of the three species were detected,and the samples with relatively low cellulose DP and CrI and monolignol S/G ratio exhibited high biomass enzyme saccharification,consistent with the previous reports in Populus,Oryza sativa L and Miscanthus.Hence,the data confirms that those three cell wall features are negative factors on biomass saccharification.