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Proc Natl Acad Sci U S A. 2002 Oct 1;99(20):13307-12. Epub 2002 Sep 17.

The heterotrimeric G protein alpha subunit acts upstream of the small GTPase Rac in disease resistance of rice.

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  • 1Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan.


We used rice dwarf1 (d1) mutants lacking a single-copy Galpha gene and addressed Galpha's role in disease resistance. d1 mutants exhibited a highly reduced hypersensitive response to infection by an avirulent race of rice blast. Activation of PR gene expression in the leaves of the mutants infected with rice blast was delayed for 24 h relative to the wild type. H(2)O(2) production and PR gene expression induced by sphingolipid elicitors (SE) were strongly suppressed in d1 cell cultures. Expression of the constitutively active OsRac1, a small GTPase Rac of rice, in d1 mutants restored SE-dependent defense signaling and resistance to rice blast. Galpha mRNA was induced by an avirulent race of rice blast and SE application on the leaf. These results indicated the role of Galpha in R gene-mediated disease resistance of rice. We have proposed a model for the defense signaling of rice in which the heterotrimeric G protein functions upstream of the small GTPase OsRac1 in the early steps of signaling.

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