Mlo, a modulator of plant defense and cell death, is a novel calmodulin-binding protein - Isolation and characterization of a rice Mlo homologue
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- Mlo, a modulator of plant defense and cell death, is a novel calmodulin-binding protein - Isolation and characterization of a rice Mlo homologue
- Kim, MC; Lee, SH; Kim, JK; Chun, HJ; Choi, MS; Chung, WS; Moon, BC; Kang, CH; Park, Chan Young; Yoo, JH; Kang, YH; Koo, SC; Koo, YD; Jung, JC; Kim, ST; Schulze-Lefert, P; Lee, SY; Cho, Moo Je
- Issue Date
- AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
- JOURNAL OF BIOLOGICAL CHEMISTRY, v.277, no.22, pp.19304 - 19314
- Transient influx of Ca2+ constitutes an early event in the signaling cascades that trigger plant defense responses. However, the downstream components of defense-associated Ca2+ signaling are largely unknown. Because Ca2+ signals are mediated by Ca2+-binding proteins, including calmodulin (CaM), identification and characterization of CaM-binding proteins elicited by pathogens should provide insights into the mechanism by which Ca2+ regulates defense responses. In this study, we isolated a gene encoding rice Mlo (Oryza sativa Mlo; OsMlo) using a protein-protein interaction-based screening of a cDNA expression library constructed from pathogen-elicited rice suspension cells. OsMlo has a molecular mass of 62 kDa and shares 65% sequence identity and scaffold topology with barley Mlo, a heptahelical transmembrane protein known to function as a negative regulator of broad spectrum disease resistance and leaf cell death. By using gel overlay assays, we showed that OsMlo produced in Escherichia coli binds to soybean CaM isoform-1 (SCaM-1) in a Ca2+-dependent manner. We located a 20-amino acid CaM-binding domain (CaMBD) in the OsMlo C-terminal cytoplasmic tail that is necessary and sufficient for Ca2+-dependent CaM complex formation. Specific binding of the conserved CaMBD to CaM was corroborated by site-directed mutagenesis, a gel mobility shift assay, and a competition assay with a Ca2+/CaM-dependent enzyme. Expression of OsMlo was strongly induced by a fungal pathogen and by plant defense signaling molecules. We propose that binding of Ca2+-loaded CaM to the C-terminal tail may be a common feature of Mlo proteins.
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