No.42 - è¾²æ¥­ç”Ÿç‰©è³‡æºç ”ç©¶æ‰€

MECHANISM OF BRASSINOSTEROID SIGNALING
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gibberellin biosynthesis inhibitor paclobutrazol, and the gene was found to encode a homolog of N-
acetylglucosamine transferase (Jacobsen et al., 1996). Research in the brassinosteroid signaling
field is now proceeding to the second strategy for Arabidopsis mutant screening, using
brassinosteroid-deficient mutants.
In order to analyze in detail the mechanisms of brassinosteroid biosynthesis and signal
transduction, we performed a screen for mutants with altered responses to Brz220 treatment in
darkness in the germination stage (Fig. 4). A screen of 140,000 Arabidopsis seeds that had been
subjected to EMS and fast neutron mutagenesis revealed several mutants that had significantly
longer hypocotyls than the wild type when grown in the dark and treated with Brz220. These
plants were designated bil mutants (Brz-insensitive-long hypocotyl).
bil1, Brz-insensitive-long hypocotyl1
Initially, we identified a dominant mutant, bil1-1D, from the EMS-treated lines. When grown
in medium containing 3 µM Brz, wild-type plants had quite short hypocotyls, but bil1 mutants had
hypocotyls as long as those of wild-type plants grown on unsupplemented medium (Fig. 5). In
parallel, bzr1-1D and bes1-1D were identified as Brz-resistant and bri1-suppressor mutants,
respectively (Fig. 5). Gene sequencing revealed that the bzr1-1D gene is the same gene as bil1-1D,
even containing the same mutation (Wang et al., 2002). These genes are 88% identical to BES1,
Fig. 4 Strategy for new brassinosteroid signaling mutants by using of Brz.
Hopeful bil (Brz-insensitive-long hypocotyl) mutant can overcome the dwarf
and shorten hypocotyl that are caused by brassinosteroid deficiency with Brz.