IDENTIFICATION OF A GENE-PRODUCT INDUCED BY HARD-SURFACE CONTACT OF COLLETOTRICHUM-GLOEOSPORIOIDES CONIDIA AS A UBIQUITIN-CONJUGATING ENZYME BY YEAST COMPLEMENTATION

The germinating conidia of many phytopathogenic fungi on hosts must di fferentiate into an infection structure called the appressorium in ord er to penetrate their hosts. Chemical signals, such as the host's surf ace nas or fruit ripening hormone, ethylene, trigger germination and a ppressorium formation of the avocado pathogen Colletotrichum gloeospor ioides only after the conidia are in contact with a hard surface, What role this contact plays is unknown. Here, we describe isolation of ge nes expressed during the early stage of hard-surface treatment by a di fferential-display method and report characterization of one of these cloned genes, chip1 (Colletotrichum hard-surface induced protein 1 gen e), which encodes a ubiquitin-conjugating enzyme. RNA blots clearly sh owed that it is induced by hard-surface contact and that ethylene trea tment enhanced this induction. The predicted open reading frame (ubc1( Cg)) would encode a 16.2-kDa ubiquitin conjugating enzyme, which shows 82% identity to the Saccharomyces cerevisiae UBC4-UBC5 E2 enzyme, com prising a major part of total ubiquitin-conjugating activity in stress ed yeast cells, UBC1(Cg) can complement the proteolysis deficiency of the S, cerevisiae ubc4 ubc5 mutant, indicating that ubiquitin-dependen t protein degradation is involved in conidial germination and appresso rial differentiation.