PLANT PHYSIOLOGY , Vol 101, Issue 2 421-428, Copyright © 1993 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
Expression of an Endopeptidase (EP-C1) in Phaseolus vulgaris Plants
T. Tanaka, T. Minamikawa, D. Yamauchi and Y. Ogushi
Department of Biology, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-03, Japan
Endopeptidase activity increases continually in pods of maturing fruits of
French bean (Phaseolus vulgaris L. cv Goldstar) plants and is thought to
participate in the protein mobilization in pods during the development of
seeds (M. Endo, T. Minamikawa, D. Yamauchi, W. Mitsuhashi [1987] J Exp Bot
38: 1988-1995). In the present studies, one of the major endopeptidase
forms, designated EP-C1, was purified as a 34-kD polypeptide from pods of
maturing French bean fruits. EP-C1 was found to be immunologically
distinguished from other forms in extracts from pods, but homologous to
SH-EP, the major cysteine endopeptidase expressed in cotyledons of
germinating Vigna mungo seeds (W. Mitsuhashi, T. Minamikawa [1989] Plant
Physiol 89: 274-279). The level of endopeptidase that reacted with the
antiserum to EP-C1 increased in pods as the fruit maturation proceeded.
EP-C1 was also immunologically detected in stems of French bean plants
bearing fruits of later maturation stages. Protein immunoblotting showed
that a 34-kD polypeptide corresponding to EP-C1 in molecular mass occurred
in extracts from 7- to 9-d cotyledons of germinating French bean seeds. In
addition, two other polypeptides with slightly higher molecular masses were
observed in extracts from 3- to 5-d cotyledons. We suggest that these two
polypeptides are intermediates involved in posttranslational processing of
EP-C1. RNA blot hybridization with EP-C1 cDNA as a probe showed that EP-C1
mRNA occurred in pods of fruits at later maturing stages and also in
cotyledons of 3- to 7-d germinating seeds.
