PMID:16531052

Citation	Jung, YH, Agrawal, GK, Rakwal, R, Kim, JA, Lee, MO, Choi, PG, Kim, YJ, Kim, MJ, Shibato, J, Kim, SH, Iwahashi, H and Jwa, NS (2006) Functional characterization of OsRacB GTPase--a potentially negative regulator of basal disease resistance in rice. Plant Physiol. Biochem. 44:68-77
Abstract	The rice genome contains at least seven expressed Rop small GTPase genes. Of these Rops, OsRac1 is the only characterized gene that has been implicated in disease resistance as a positive regulator. To our interest in finding a negative ROP regulator of disease resistance in rice, we applied a "phylogeny of function" approach to rice Rops, and identified OsRacB based on its close genetic orthologous relationship with the barley HvRacB gene, a known negative regulator of disease resistance. To determine the function of OsRacB, we isolated the OsRacB cDNA and conducted gene expression and transgenic studies. OsRacB, a single copy gene in the genome of rice, shared 98% identity with HvRacB at the amino acid level. Its mRNA was strongly expressed in leaf sheath (LS) and in panicles, but was very weakly expressed in young and mature leaves. The basal mRNA level of OsRacB in LS of two-week-old seedlings was strongly down-regulated upon wounding by cut and treatment with jasmonic acid. A dramatic down-regulation in the OsRacB transcripts was also found in plants inoculated with the blast pathogen, Magnaporthe grisea. Interestingly, transgenic rice plants over-expressing OsRacB showed increased symptom development in response to rice blast pathogens. Additionally, fluorescence microscopy of green fluorescent protein (GFP):OsRacB-transformed onion cells and Arabidopsis protoplasts revealed OsRacB association with plasma membrane (PM), suggesting that PM localization is required for proper function of OsRacB. Based on these results, we suggest that OsRacB functions as a potential regulator for a basal disease resistance pathway in rice.
Links	PubMed Online version:10.1016/j.plaphy.2005.12.001
Keywords	Amino Acid Sequence; Arabidopsis/enzymology; Arabidopsis/genetics; Cell Membrane/metabolism; Cells, Cultured; Magnaporthe; Molecular Sequence Data; Monomeric GTP-Binding Proteins/genetics; Monomeric GTP-Binding Proteins/metabolism; Onions/enzymology; Onions/genetics; Oryza sativa/enzymology; Oryza sativa/immunology; Oryza sativa/microbiology; Phylogeny; Plant Diseases; Plant Leaves/metabolism; Plant Proteins/genetics; Plant Proteins/metabolism; Plants, Genetically Modified; RNA, Messenger/metabolism; Sequence Homology, Amino Acid
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
ORYSJ:RAC6		GO:0005886: plasma membrane	ECO:0000314:		C		Figure 7	complete CACAO 8370
ORYSJ:RAC6	part_of	GO:0005886: plasma membrane	ECO:0000314: direct assay evidence used in manual assertion		C		Seeded From UniProt	complete

References

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