Molecular evolution of Aphanomyces cochlioides flavone receptor protein which functions in host recognition of the oomycetes zoospores.

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Aphanomyces cohlioides is a phytopathogen that attacks beet and spinach, using their characteristic secondary metabolite5-hydroxy-6,7-methylenedioxyflavone (cochliophilin A) as host recognition signal compound. We searched receptor protein to cause strong attractant activity of the B-ring non-substituted simple flavone. By using affinity column chromatography of solubilized membrane-binding proteins obtained from A. chochlioides zoospores, we successfully purified one candidate of the flavonoid receptor protein. Using a degenerate primer designed from the amino-acid sequence at the N-terminal of this protein, EST region of the target protein was successfully characterized to be aβ-barrel-type transmembrane protein of a 32 kDa, and named Aphanomyces cochliophilin A receptor protein 1 (ACCR1). From the mRNA library, full length of its cDNA was obtained. Amino acid sequence of ACCR1 had a high homology with voltage-dependent anion channel protein (VDAC), but ACCR1 ismissing 70AA from the C-terminus of VDAC. Our immunofluorescence assay for ACCR1 revealed that ACCR1 locates only cytoplasmic membrane but not on mitochondrion. All together, we proposed a hypothesis on molecular evolution of ACCR1 in Aphanomyces cochlioides.