No.42 - è¾²æ¥­ç”Ÿç‰©è³‡æºç ”ç©¶æ‰€

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Takeshi NAKANO, Shigeo YOSHIDA and Tadao ASAMI
mutant can be rescued by less stressful conditions, which may relate to the cross-talk between
brassinosteroids and ABA. The bil5 mutation maps to the lower arm of chromosome I. Isolation
of the bil5 mutant gene, by sequencing and complementation, is in progress.
To screen for more bil mutants, we are starting from an activation-tagged line, in collaboration
with the groups of Dr. Shinozaki and Dr. Matsui. The genes identified by analysis of these mutants
may also be members of the brassinosteroid signaling cascade.
Additional new players for brassinosteroid signaling
brs1 and bak1 were identified as bri1-5 dwarf suppressor mutants by activation tagging.
BRS1 encodes a carboxypeptidase, and its role in BR signalling has not been defined (Li et al.,
2001) (Fig. 7). BAK1, however, encodes a leucine-rich-repeat type receptor-like kinase that could
interact directly with BRI1 (Li et al., 2002, Nam and Li, 2002) (Fig. 7). On the basis of their
phenotypes, bak1-1D and brs1-1D mutants could potentially be Brz-insensitive mutants. Several
Fig. 7 Current key players on brassinosteroid signaling.
BIL1: Brz-insensitive-long hypocotyl, BRI1: brassinosteroid insentive1, BAK1:bri1
associated kinase, BIN: brassinosteorid insenstive, BRS1: bri1 suppressor. Brz:
Brassinosteroid biosynthesis inhibitor.