First published online June 25, 2004; 10.1104/pp.103.036384
Plant Physiology 135:1447-1456 (2004)
© 2004 American Society of Plant Biologists
CELL BIOLOGY AND SIGNAL TRANSDUCTION
Down-Regulation of Metallothionein, a Reactive Oxygen Scavenger, by the Small GTPase OsRac1 in Rice
Hann Ling Wong,
Tsuyoshi Sakamoto,
Tsutomu Kawasaki,
Kenji Umemura and
Ko Shimamoto*
Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology, Takayama 8916–5, Ikoma, Nara 630–0101, Japan (H.L.W., T.S., T.K., K.S.); and Bioscience Laboratories, Meiji Seika Kaisha Ltd., 5–3–1, Chiyoda, Sakado-shi, Saitama 350–0289, Japan (K.U.)
Metallothioneins are small, ubiquitous Cys-rich proteins known to be involved in reactive oxygen species (ROS) scavenging and metal homeostasis. We found that the expression of a metallothionein gene (OsMT2b) was synergically down-regulated by OsRac1 and rice (Oryza sativa) blast-derived elicitors. Transgenic plants overexpressing OsMT2b showed increased susceptibility to bacterial blight and blast fungus. OsMT2b-overexpressing cells showed reduced elicitor-induced hydrogen peroxide production. In contrast, homozygous OsMT2b::Tos17-inserted mutant and OsMT2b-RNAi-silenced transgenic cells showed significantly higher elicitor-induced hydrogen peroxide production than the wild-type cells. In vitro assay showed that recombinant OsMT2b protein possessed superoxide- and hydroxyl radical-scavenging activities. Taken together, these results showed that OsMT2b is an ROS scavenger and its expression is down-regulated by OsRac1, thus potentiating ROS, which function as signals in resistance response. The results suggest that OsRac1 plays a dual role as an inducer of ROS production and a suppressor of ROS scavenging.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.103.036384.
* Corresponding author; e-mail: simamoto{at}bs.naist.jp; fax 81–743–72–5509.
Received November 19, 2003;
returned for revision January 29, 2004;
accepted February 1, 2004.
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