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Plant and Cell Physiology Advance Access first published online on April 5, 2007
This version published online on April 10, 2007
Plant and Cell Physiology, doi:10.1093/pcp/pcm042
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© The Author 2007. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Identification of the Gravitropism-Related Rice Gene LAZY1 and Elucidation of LAZY1-Dependent and -Independent Gravity Signaling Pathways

Takeshi Yoshihara and Moritoshi Iino*

Botanical Gardens, Graduate School of Science, Osaka City University, Kisaichi, Katano-shi, Osaka 576-0004, Japan

* Corresponding author: Moritoshi Iino. Botanical Gardens, Graduate School of Science, Osaka City University, Kisaichi, Katano-shi, Osaka 576-0004, Japan. Telephone: +81-(0)72-891-2681; Fax: +81-(0)72-891-7199; Email: iino{at}sci.osaka-cu.ac.jp


  Abstract

We identified the gene responsible for three allelic lazy1 mutations of Japonica rice (Oryza sativa L.) by map-based cloning, complementation, and RNA interference. Sequence analysis and database searches indicated that the wild-type gene (LAZY1) encodes a novel and unique protein (LAZY1) and that rice has no homologous gene. Two lazy1 mutants were LAZY1 null. Confirming and advancing the previously reported results on lazy1 mutants, we found the followings. (1) Gravitropism is impaired, but only partially, in lazy1 coleoptiles. (2) Circumnutation, observed in dark-grown coleoptiles, is totally absent from lazy1 coleoptiles. (3) Primary roots of lazy1 mutants show normal gravitropism and circumnutation. (4) LAZY1 is expressed in a tissue-specific manner in gravity-sensitive shoot tissues (i.e., coleoptiles, leaf sheath pulvini, and lamina joints) and is little expressed in roots. (5) The gravitropic response of lazy1 coleoptiles is kinetically separable from that absent from lazy1 coleoptiles. (6) Gravity-induced lateral translocation of auxin, found in wild-type coleoptiles, does not occur in lazy1 coleoptiles. Based on the genetic and physiological evidence obtained, it is concluded that LAZY1 is specifically involved in shoot gravitropism and that LAZY1-dependent and -independent signaling pathways occur in coleoptiles. It is further concluded that, in coleoptiles, only the LAZY1-dependent gravity signaling involves asymmetric distribution of auxin between the two lateral halves and is required for circumnutation.

Keywords: auxin - circumnutation - gravitropism - lazy mutants - LAZY1 - Oryza sativa


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