一对大豆淀粉分支酶基因SBE2的表达模式和功能分析

Expression and functional analysis of a pair of soybean SBE2 genes

淀粉分支酶(starch branching enzyme,SBE)是淀粉合成中的关键酶,催化α-1,6糖苷键分支点形成支链淀粉,其功能在大豆(Glycine max)中尚未见报导。大豆种子中淀粉的积累、转化是关系其产量、品质的重要性状,因而对SBE功能的研究在大豆品种改良中具有重要意义。对大豆SBE基因的生物信息学分析表明,大豆基因组中有6个SBE基因,其中一对编号为GmSBE2a和GmSBE2b的基因表达量较高,分别编码868和870个氨基酸的蛋白质,蛋白相似度在90%以上,与多种豆科SBE位于同一进化分支。组织表达模式分析表明大豆SBE基因主要在茎和叶中表达,其蛋白定位于叶绿体中。运用CRISPR/Cas9基因编辑技术创制了GmSBE2s的双突变体,其初荚时间显著晚于野生型,且在营养生长早期突变体的叶绿体发育缓慢。研究结果为大豆淀粉分支酶基因GmSBE2s的功能研究提供了一定的理论基础。

Starch branching enzymes(SBEs)are key enzymes in starch synthesis to catalyzesα-1,6 glycosidic bonding for branching to form amylopectin.The expression and function of SBEs in soybean(Glycine max)are yet explored.The accumulation and conversion of starch in soybean seeds are important for its yield and quality.Therefore,the study of SBE function is of great significance in soybean improvement.Bioinformatic analysis of soybean SBE genes showed that there were 6 SBE genes in soybean genome.A pair of GmSBE2 genes,designating as GmSBE2a and GmSBE2b,expresses at high level.GmSBE2a and GmSBE2b encode proteins of 868 and 870 amino acids,respectively,with protein similarity of more than 90%.GmSBE2a and GmSBE2b are located in the same evolutionary branch with many other legume SBEs.Tissue expression pattern analysis of GmSBE2a and GmSBE2b showed that they are mainly expressed in stems and leaves,and the corresponding proteins are localized in chloroplasts.To investigate the function of GmSBE2,the knock out mutants of GmSBE2 were generated by CRISPR/Cas9 gene editing.Phenotypic observation revealed that the initial ponding time of the mutants was significantly delayed compared to wild type,and the chloroplast development of the mutant was slow at the early vegetative growth stage.The results provide a theoretical basis for the functional study of the soybean starch branching enzyme gene GmSBE2s.