Abstract

A G-protein α (Gα) subunit encoding gene (pngpa1) was isolated from an oomycete plant pathogen Phytophthora nicotianae, the causal agent of severe diseases in a wide variety of crops. Comparison on the genomic DNA and cDNA sequence of pngpa1 reveals that it contains an intron and encodes a polypeptide of 355 amino acid residues. The deduced amino acid sequence of PnGPA1 shares a high degree of identity with Gα subunits from oomycetes of the genus Phytophthora. Reverse transcription PCR analysis of pngpa1revealed that, unlike psgpa1 and pigpa1 which were expressed in only sporangia and zoospores but not in mycelia, pngpa1 was expressed not only in sporangia and zoospores but also in mycelia. A modified Agrobacterium-mediated transformation method was used to silence pngpa1 gene expression in P. nicotianae and phenotypic effects were analyzed. Our results suggested that pngpa1 influenced multiple physiological processes in P. nicotianae including hyphal growth, zoospore release, osmo-sensitivity and tolerance to the fungicide metalaxyl.

Key words: Phytophthora nicotianae, G-protein α subunit, gene disruption, osmotic stress, tolerance to metalaxyl