Light Activates Brassinosteroid Biosynthesis to Promote Hook Opening and Petiole Development in Arabidopsis thaliana

Author:

Hamasaki Hidefumi1,Ayano Madoka2,Nakamura Ayako1,Fujioka Shozo23,Asami Tadao4,Takatsuto Suguru5,Yoshida Shigeo23,Oka Yoshito2,Matsui Minami26,Shimada Yukihisa12

Affiliation:

1. Kihara Institute for Biological Research, Yokohama City University Kihara Institute for Biological Research, Maiokacho 641-12, Totsuka, Yokohama, Kanagawa, 244-0813 Japan

2. RIKEN Plant Science Center, Suehirocho 1-7-22, Tsurumi, Yokohama, 230-0045 Japan

3. RIKEN Advanced Science Institute, Wako, Saitama, 351-0198 Japan

4. Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo, 113-8657 Japan

5. Department of Chemistry, Joetsu University of Education, Joetsu, Niigata, 943-8512 Japan

6. RIKEN Center for Sustainable Resource Science, Suehirocho 1-7-22, Tsurumi, Yokohama, 230-0045 Japan

Abstract

Abstract Although brassinosteroids (BRs) have been proposed to be negative regulators of photomorphogenesis, their physiological role therein has remained elusive. We studied light-induced photomorphogenic development in the presence of the BR biosynthesis inhibitor, brassinazole (Brz). Hook opening was inhibited in the presence of Brz; this inhibition was reversed in the presence of brassinolide (BL). Hook opening was accompanied by cell expansion on the inner (concave) side of the hook. This cell expansion was inhibited in the presence of Brz but was restored upon the addition of BL. We then evaluated light-induced organ-specific expression of three BR biosynthesis genes, DWF4, BR6ox1 and BR6ox2, and a BR-responsive gene, SAUR-AC1, during the photomorphogenesis of Arabidopsis. Expression of these genes was induced, particularly in the hook region, in response to illumination. The induction peaked after 3 h of light exposure and preceded hook opening. Phytochrome-deficient mutants, hy1, hy2 and phyAphyB, and a light-signaling mutant, hy5, were defective in light-induced expression of BR6ox1, BR6ox2 and SAUR-AC1. Light induced both expression of BR6ox genes and petiole development. Petiole development was inhibited in the presence of Brz. Our results largely contradict the early view that BRs are negative regulators of photomorphogenesis. Our data collectively suggest that light activates the expression of BR biosynthesis genes in the hook region via a phytochrome-signaling pathway and HY5 and that BR biosynthesis is essential for hook opening and petiole development during photomorphogenesis.

Funder

JSPS

Publisher

Oxford University Press (OUP)

Subject

Cell Biology,Plant Science,Physiology,General Medicine

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