Journal Article

Ethylene Promotes Submergence-Induced Expression of <i>OsABA8ox1</i>, a Gene that Encodes ABA 8′-Hydroxylase in Rice<sup>†</sup>

Hiroaki Saika, Masanori Okamoto, Kentaro Miyoshi, Tetsuo Kushiro, Shoko Shinoda, Yusuke Jikumaru, Masaru Fujimoto, Taku Arikawa, Hirokazu Takahashi, Miho Ando, Shin-ichi Arimura, Akio Miyao, Hirohiko Hirochika, Yuji Kamiya, Nobuhiro Tsutsumi, Eiji Nambara and Mikio Nakazono

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 48, issue 2, pages 287-298
Published in print February 2007 | ISSN: 0032-0781
Published online February 2007 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcm003
Ethylene Promotes Submergence-Induced Expression of OsABA8ox1, a Gene that Encodes ABA 8′-Hydroxylase in Rice†

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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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.

Keywords: ABA 8′-hydroxylase; Ethylene; Rice; Submergence

Journal Article.  6840 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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