Volume 272, Number 40,
Issue of October 3, 1997
pp. 24747-24750
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
COMMUNICATION:
CHRC, Encoding a Chromoplast-specific
Carotenoid-associated Protein, Is an Early Gibberellic Acid-responsive
Gene
(Received for publication, July 10, 1997)
Michael
Vishnevetsky
,
Marianna
Ovadis
,
Hanan
Itzhaki
and
Alexander
Vainstein
From the Kennedy Leigh Centre for Horticultural Research and The
Otto Warburg Center for Biotechnology in Agriculture, Faculty of
Agriculture, The Hebrew University of Jerusalem,
Rehovot 76100, Israel
CHRC, a corolla-specific carotenoid-associated
protein, is a major component of carotenoid-lipoprotein complexes in
Cucumis sativus chromoplasts. Using an in vitro
flower bud culture system that mimics in vivo flower
development, CHRC mRNA levels in corollas were shown to
be specifically up-regulated by gibberellic acid. The response to
gibberellic acid was very rapid (within 20 min) and insensitive to
protein synthesis inhibition by cycloheximide. Abscisic acid, known to
antagonize gibberellin in many developmental systems, strongly
down-regulated CHRC mRNA levels. The gibberellin synthesis inhibitor paclobutrazol exhibited a similar negative effect
on CHRC expression. Inclusion of exogenous gibberellic acid
into the in vitro bud culture system with the paclobutrazol not only prevented the CHRC mRNA down-regulation, it
up-regulated transcript accumulation to the level of gibberellic
acid-treated corollas. CHRC mRNA accumulation in
response to gibberellic acid displayed a dose-dependent
increase up to 10
4 M gibberellic acid. The
up-regulation could be detected with as little as 10
7
M gibberellic acid. Based on these data, we suggest that
CHRC is the first structural gene identified to date whose
expression is regulated by gibberellic acid in a primary fashion. The
critical role of the rapid response of CHRC to gibberellic
acid in aiding carotenoid sequestration while preserving chromoplast
structural organization is discussed.