Regulatory mechanism of expression of plant thiol-endopeptidase genes

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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.