Ethylene promotes submergence-induced expression of OsABA8ox1, a gene that encodes ABA 8'-hydroxylase in rice.
A rapid decrease of the plant hormone ABA under submergence is thought to be a prerequisite for the enhanced elongation of submerged shoots of rice (Oryza sativa L.). Here, we report that the level of phaseic acid (PA), an oxidized form of ABA, increased with decreasing ABA level during submergence. The oxidation of ABA to PA is catalyzed by ABA 8'-hydroxylase, which is possibly encoded by three genes (OsABA8ox1, -2 and -3) in rice. The ABA 8'-hydroxylase activity was confirmed in microsomes from yeast expressing OsABA8ox1. OsABA8ox1-green fluorescent protein (GFP) fusion protein in onion cells was localized to the endoplasmic reticulum. The mRNA level of OsABA8ox1, but not the mRNA levels of other OsABA8ox genes, increased dramatically within 1 h after submergence. On the other hand, the mRNA levels of genes involved in ABA biosynthesis (OsZEP and OsNCEDs) decreased after 1-2 h of submergence. Treatment of aerobic seedlings with ethylene and its precursor, 1-aminocyclopropane-1-carboxylate (ACC), rapidly induced the expression of OsABA8ox1, but the ethylene treatment did not strongly affect the expression of ABA biosynthetic genes. Moreover, pre-treatment with 1-methylcyclopropene (1-MCP), a potent inhibitor of ethylene action, partially suppressed induction of OsABA8ox1 expression under submergence. The ABA level was found to be negatively correlated with OsABA8ox1 expression under ACC or 1-MCP treatment. Together, these results indicate that the rapid decrease in ABA levels in submerged rice shoots is controlled partly by ethylene-induced expression of OsABA8ox1 and partly by ethylene-independent suppression of genes involved in the biosynthesis of ABA.
Saika
Hiroaki
H
Laboratory of Plant Molecular Genetics, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, Japan.
Okamoto
Masanori
M
Miyoshi
Kentaro
K
Kushiro
Tetsuo
T
Shinoda
Shoko
S
Jikumaru
Yusuke
Y
Fujimoto
Masaru
M
Arikawa
Taku
T
Takahashi
Hirokazu
H
Ando
Miho
M
Arimura
Shin-Ichi
S
Miyao
Akio
A
Hirochika
Hirohiko
H
Kamiya
Yuji
Y
Tsutsumi
Nobuhiro
N
Nambara
Eiji
E
Nakazono
Mikio
M
D001483:Base Sequence; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D017931:DNA Primers; D005030:Ethylenes / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D017343:Genes, Plant; D006899:Mixed Function Oxygenases / Q000235:genetics*; D012275:Oryza / Q000235:genetics*; D010940:Plant Proteins; D012333:RNA, Messenger / Q000235:genetics
D017931:DNA Primers; D005030:Ethylenes; D010940:Plant Proteins; D012333:RNA, Messenger; D003577:Cytochrome P-450 Enzyme System; C036216:ethylene; D006899:Mixed Function Oxygenases; C107203:abscisic acid 8'-hydroxylase