两个棉花Rac蛋白基因的克隆与表达分析

Cloning and Expression Analysis of Two Rac Genes from Cotton (Gossypium hirsutum L.)

为研究棉花纤维起始和伸长的分子机理 ,在棉花纤维EST序列分析的基础上 ,从棉花纤维中扩增并克隆了 2个棉花Rac蛋白的cDNA基因 ,分别命名为GhRacA和GhRacB。GhRacAcDNA长 95 9bp ,推测的编码蛋白包含2 11个氨基酸。GhRacBcDNA长 92 0bp ,编码 195个氨基酸的蛋白。GhRacA和GhRacB蛋白均含有GTP/GDP结合和激活区域、Effector区和碱性氨基酸区。GhRacB的C末端有保守的异戊烯基化位点CSIL ,而GhRacA没有明显的异戊烯基化位点。序列比较分析表明 ,GhRacA和GhRacB是 2个新的棉花Rac蛋白。RT PCR分析表明 ,GhRacA和GhRacB在根、下胚轴、茎、叶和纤维中都有表达 ,但均在棉花纤维起始和伸长时期有优势表达 ,推测

Plant Rac proteins belong to an important group of signal switches anchoring on membranes,involved in various physiological processes including cell polar growth,synthesis of secondary wall,resistance response and hormone signaling.In the attempt to elucidate the molecular mechanism of initiation and elongation of cotton fiber,two cotton Rac protein genes,designated as GhRacA and GhRacB,were amplified from elongating fibers and cloned.It was demonstrated that,the cDNA of GhRacA contained 959 bp and encoded a putative polypepetide of 211 aa,while GhRacB was 920 bp in length,encoding a predicted protein of 195 aa.These two cotton Rac proteins,GhRacA and GhRacB,contained conserved regions involved in GTP/GDP binding and activation,an effector region and a polybasic region.A conserved prenylation site CSIL was found in GhRacB,while no apparent prenylation site was discovered in GhRacA.Sequence comparisons showed that GhRacA and GhRacB were two novel Rac proteins from cotton.The expression patterns of GhRacA and GhRacB was analyzed by RT-PCR.It was demonstrated that these two Rac protein genes were both expressed in root,hypocotyls,stem,leaf and fibers,and the highest level of transcripts was to accumulate in the fibers at the stage of initiation and elongation,suggesting that the two Rac genes,GhRacA and GhRacB,might play an important role in the early stage of fiber development.