title: G protein signaling mediates developmental processes and pathogenesis of Alternaria alternata.
abstract: A G protein alpha subunit gene (AGA1) has been cloned and characterized from a toxigenic and necrotrophic Alternaria alternata pathogen. Targeted disruption of AGA1 in the apple pathotype of A. alternata gave rise to mutants that differed in colony and conidial morphology as well as sporulation. The conidia of wild type and deltaAGA1 mutants showed equal germination on cellulose membranes. However, wild-type germ tubes formed readily from different points around the conidia, grew randomly, and were often branched, whereas those of the mutants formed only at one or both ends of the conidia and tended to grow in straight paths. Targeted disruption of AGA1 also resulted in reduction of pathogenicity on apple leaves, although the mutant produced host-specific AM-toxin, a fungal secondary metabolite associated with pathogenicity of the pathogen, at levels similar to the wild-type strain. Measurement of the intracellular cAMP levels of the mutant revealed that it was consistently higher than that of the wild type, indicating that AGA1 negatively regulates cAMP levels similar to mammalian Galphai systems. These results indicate that the signal transduction pathway represented by AGA1 appears to be involved in developmental pathways leading to sporulation and pathogenesis of A. alternata.
authors.affiliation: Laboratory of Plant Pathology, Faculty of Agriculture, Tottori University, 4-101 Koyama-Minami, Tottori 680-8553, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Yamagishi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Otani
authors.forename: Motoichiro
authors.initials: M
authors.lastname: Kodama
mesh_terms: D000528:Alternaria / Q000378:metabolism* / Q000472:pathogenicity / Q000502:physiology; D003001:Cloning, Molecular; D000242:Cyclic AMP / Q000378:metabolism; D044385:GTP-Binding Protein alpha Subunits / Q000235:genetics / Q000378:metabolism*; D018390:Gene Targeting; D005816:Genetic Complementation Test; D027845:Malus / Q000382:microbiology; D008969:Molecular Sequence Data; D009183:Mycotoxins / Q000096:biosynthesis; D010641:Phenotype; D015398:Signal Transduction; D013172:Spores, Fungal / Q000235:genetics; D014774:Virulence / Q000235:genetics
chemical_list: D044385:GTP-Binding Protein alpha Subunits; D009183:Mycotoxins; D000242:Cyclic AMP