Plant and Cell Physiology Advance Access originally published online on January 11, 2007
Plant and Cell Physiology 2007 48(2):332-344; doi:10.1093/pcp/pcm007
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A Calmodulin-Binding Mitogen-Activated Protein Kinase Phosphatase is Induced by Wounding and Regulates the Activities of Stress-Related Mitogen-Activated Protein Kinases in Rice
1National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, 305-8602 Japan
2Program for Promotion of Basic Research Activities for Innovative Biosciences, Minato-ku, Tokyo, 105-0001 Japan
*Corresponding author: E-mail, yohashi{at}affrc.go.jp; Fax, +81-29-838-7469.
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Abstract |
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The mitogen-activated protein kinase (MAPK) phosphatases (MKPs) are negative regulators of MAPKs. In dicotyledons such as Arabidopsis and tobacco, MKPs have been shown to play pivotal roles in abiotic stress responses, hormone responses and microtubule organization. However, little is known about the role of MKPs in monocotyledons such as rice. Database searches identified five putative MKPs in rice. We investigated their expression in response to wounding, and found that the expression of OsMKP1 is rapidly induced by wounding. In this study, we functionally characterized the involvement of OsMKP1 in wound responses. The deduced amino acid sequence of OsMKP1 shows strong similarity to Arabidopsis AtMKP1 and tobacco NtMKP1. Moreover, OsMKP1 bound calmodulin in a manner similar to NtMKP1. To determine the biological function of OsMKP1, we obtained osmkp1, a loss-of-function mutant, in which retrotransposon Tos17 was inserted in the second exon of OsMKP1. Unlike the Arabidopsis atmkp1 loss-of-function mutant, which shows no abnormal phenotype without stimuli, osmkp1 showed a semi-dwarf phenotype. Exogenous supply of neither gibberellin nor brassinosteroid complemented the semi-dwarf phenotype of osmkp1. Activities of two stress-responsive MAPKs, OsMPK3 and OsMPK6, in osmkp1 were higher than those in the wild type both before and after wounding. Microarray analysis identified 13 up-regulated and eight down-regulated genes in osmkp1. Among the up-regulated genes, the expression of five genes showed clear responses to wounding, indicating that wound responses are constitutively activated in osmkp1. These results suggest that OsMKP1 is involved in the negative regulation of rice wound responses.
Keywords: MAPK - MAPK phosphatase - Oryza sativa - Phosphorylation - Wound
Abbreviations: BL, brassinolide; BR, brassinosteroid; CaM, calmodulin; CHX, cycloheximide; DSP, dual-specificity phosphatase; EST, expressed sequence tag; GST, glutathione S-transferase; IPTG, isopropyl ß-D-thiogalactopyranoside; MAPK, mitogen-activated protein kinase; MBP, myelin basic protein; MKP, MAPK phosphatase
3 Present address: Department of Wood Properties, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, 305-8687 Japan.
4 Present address: Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0101 Japan.
(Received November 21, 2006; Accepted December 30, 2006)
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