GENE-EXPRESSION ANALYSIS DURING CONIDIAL GERM TUBE AND APPRESSORIUM DEVELOPMENT IN COLLETOTRICHUM-TRIFOLII

Preinfection development in Colletotrichum spp. exhibits three morphol ogies (conidia, germ tubes, and appressoria) and is directed by a comp lex interplay of environmental signals. Germ tube morphogenesis for Co lletotrichum trifolii and the related fungus Colletotrichum gloeospori oides f. sp. aeschynomene was shown to be partially dependent on a bal ance between self-germination inhibitors and environmental nutrients o r cutin. The degree of responsiveness to these environmental signals w as strikingly different between the two fungal species. A solid contac t surface stimulated germ tube morphogenesis and was the only apparent requirement for appressorium morphogenesis in both fungi. A populatio n of C. trifolii conidia was incubated on a solid surface in the prese nce of cutin to stimulate nearly synchronous preinfection morphogenesi s for gene expression analysis. RNA analysis of signal-transducing gen es from C. trifolii, including genes for a serine-threonine kinase (TB 3), calmodulin, and protein kinase C, showed that maximum transcriptio n of all three genes occurred in conidia prior to or during germ tube morphogenesis. Transcription of melanin biosynthetic genes THR1 and SC D1 (Y. Kubo, Y. Takano, and I. Furusawa, Colletotrichum Newsl. II:5-10 , 1996; N. S. Perpetua, Y. Kubo, N. Yasuda, Y. Takano, and I. Furusawa , Mol. Plant-Microbe Interact. 9:323-329, 1996) was highest prior to a nd during appressorium morphogenesis.