Transcript levels for a mung bean cysteine protease during early seedling growth

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Abstract
CDNAs for the major cysteine endopeptidase (CEpase) of mung bean (Vigna radiata [L.] Wilczek) seedling cotyledons have been cloned using gene-specific primers with the polymerase chain reaction (PCR) in a 3'-RACE system. A cDNA clone for CEpase, pKL042, that is 1221 bp long excluding the poly A tail was isolated. It appears to contain the entire coding sequence for a 362-residue-long polypeptide. The N-terminal sequence for the mature CEpase begins at position 128 of the putative translation product, suggesting removal of an N-terminal hydrophobic signal peptide and additional sequences to produce the mature protease. Northern blot hybridization with CEpase cDNA pKL042 as probe indicates that CEpase transcript is not detectable in the cotyledons or the embryonic axis of dry seeds, but is first detectable in the day 1 cotyledons and in the day 3 axis. The level of CEpase mRNA in both cotyledons and axis increases as growth proceeds. A decline of protease activity, however, is observed after day 3 in the cotyledons, even though the level of protease transcripts continues to increase until day 8. Detachment of the axis from the cotyledons before day 3 results in the prevention of the normal increase in both protease activity and CEpase mRNA.