P5: withdrawn

The soil fungus Hypocrea jecorina (anamorph Trichoderma reesei) is capable of responding to environmental cues to compete for nutrients in its natural habitat despite its genome encodes fewer degradative enzymes. Efficient signaling pathways for perception and interpretation of environmental signals are in dispensable in this process. The role of signal proteins TrRas1 and TrRas2, homologues to Saccharomyces cerevisiae Ras1 and Ras2, during fungal development and cellulase production was investigated. T. reesei strains defective for TrRas1 show a small and dense colony with short and swollen hyphae cells, suggesting that TrRas1 signaling controls the events involved in filamentous growth. In addition, deletion of TrRas2 causes a reduced colony on solid media with less aerial hyphae and irregular borders, while expression of dominant activated TrRas2^G16V promotes filamentous growth greatly. Strikingly, while TrRas1 deletion causes a 42% decrease in cellular cAMP, deletion of TrRas2 shows a wild-type level. Together, TrRas1and TrRas2 plays varied and overlapping roles in filamentation and development. Moreover, TrRas2 signaling pathway modulates the cellulase gene expression through regulating the transcription of Xyr1. These findings elucidate new functions for Ras in cellular morphogenesis and cellulase production which is believed to be the first direct genetic study on the roles of Ras signaling in a Trichoderma sp.