Regulatory mechanism of expression of plant thiol-endopeptidase genes

半胱氨酸内肽酶(SH-EP)参与了豌豆种子萌发种子子叶中贮藏球蛋白的降解。以SH-EP基因为探针，从芒果弧菌基因组文库中分离得到SH-EP基因的两个重叠克隆。对核DNA的Southern杂交分析结果表明，SH-EP只有一个基因。转录起始位置位于起始密码子上游31bp。蛋白质免疫印迹显示，除了萌发种子的子叶中存在该蛋白质外，与SH-EP抗血清反应的蛋白质水平在芒果成熟果实的豆荚中增加，而在幼苗的其他器官中含量很低。萌发种子子叶中SH-EP基因表达水平的变化规律与α-淀粉酶基因的变化规律相似。用蛋白质免疫印迹法和RNA印迹杂交法分别检测了其他三种豆科植物幼苗子叶中这两种酶的水平及其mRNAs的水平。

A cysteine endopeptidase (SH-EP) is involved in the degradation of storage globulin in cotyledons of germinating seeds of Vigna mungo seeds. Using SH-EP cDNA as a probe, we isolated two overlapping genomic clones for SH-EP from a V. mungo genomic library. The results of Southern blot analysis of the nuclear DNA suggested that there is a single gene for SH-EP. The site of initiation of transcription was located 31 bp upstream from the initiation codon. Protein immunoblotting showed that, in addition to the presence of the protein in cotyledons of germinating seeds, levels of a protein that reacted with an antiserum against SH-EP increased in pods of maturing fruits of V. mungo, with very low levels being present in other organs of the seedlings. The change in levels of SH-EP mRNA in cotyledons of germinating seeds followed a time course similar to that of alpha-amylase mRNA. Levels of both enzymes, as well as levels of their mRNAs, were also examined in cotyledons of seedlings of three other legumes by protein immunoblotting and RNA blot hybridization, respectively.