Polar growth is affected by environmental factors during sexual and asexual development in filamentous fungi. It has been shown that light, nutrient depletion, and mycelial injury are determinant in morphogenetic changes occurring during asexual development. We recently identified large sets of genes in Trichoderma atroviride, which expression is switched on or off in response to environmental cues such as blue-light and mycelial injury. We propose to study the role of two types of genes (transcription factors and signalling proteins) that are turned on by these stimuli, and may therefore play important roles in determining the switch from polarized to non-polarized growth. Our gene expression data suggest the involvement of oxidative stress and the MAPK homologue of Hog-1 in the morphological transition. Therefore, we will analyze the effect of oxidative stress in the process, as well as that of Hog-1, a putative member of the signalling cascade involved in the response to oxidative stress, a transcription factors.
Microscopic analysis of mycelial injury induced conidiation. Colonies were observed by light microscopy using Nomarski (top panels) or bright field upon staining with cotton blue (bottom panels), and photographed 6h (left panels) or 36h (right panels) after injury. The top two panels show a diagram of the structures formed 6 and 36h after injury. The left panels show a thin hyphae (green arrow) coming out of the cell just behind the damaged one. The right panel shows the formation of mature conidiophores (red arrow).