|Ph.D Student||Trushina Naomi|
|Subject||Gene Expression in Response to pH Signals in Mycoparasitic|
Interactions of Trichoderma virens
|Department||Department of Biology||Supervisor||Professor Benjamin Horwitz|
|Full Thesis text|
pH is an important environmental signal controlling development. Furthermore, the ability to maintain homeostasis is likely required for fitness as a pathogen of plants or animals. Surprisingly, little is known about the role of pH in fungal-fungal interactions. Trichoderma spp. grow as soil saprobes or mycotrophs using other fungi as hosts, and so are studied for their potential in biocontrol of plant diseases. Particularly in alkaline soil, pH may limit use of these biofungicides, whose optimal growth pH is 4-6. Understanding pH adaptability will help broaden the activity spectrum of these economically important fungi. We studied the pH-responsive transcription factor PacC by gene knockout and by introduction of an allele (pacCc) encoding a constitutively active protein. DpacC grew slowly at alkaline pH, while pacCc strains grew poorly at acidic pH. In plate confrontation assays, DpacC mutants showed decreased ability to compete with the plant pathogens Rhizoctonia solani and Sclerotium rolfsii. The pacCc strain overgrew R. solani like the wild type, but was unable to overgrow S. rolfsii. To identify genes whose expression depends on pH and pacC, we compared, by microarray hybridization, the transcriptomes of wild type and mutant cultures exposed to high or low pH. Transcript levels from several functional classes were dependent on pacC, on pH, or on both. As much as 5% of the transcriptome is pH-dependent, and of these genes, some 25% depend on pacC. Secondary metabolite biosynthesis and ion transport are among the relevant gene classes. We suggest that DpacC mutants may have lost their full biocontrol potential due to their inability to adapt to alkaline pH, to perceive ambient pH, or both (1). We constructed knockout mutants for eight genes that were pH and pacC dependent. Two of the eight showed phenotypes under the conditions studied so far. One mutant, ATPase ena1, are hypersensitive to a combination of alkaline pH with Na or Li, as reported for the ortholog in other fungi. Mutants in the second, ATPase Pma1, resemble pacC, with decreased spore production and hypersensitivity to pH values above 5. Loss of PacC resulted in greater sensitivity to alkaline pH than loss of Pma1, in agreement with the role of PacC in regulating a large number of genes. The results raise the novel possibility of genetically manipulating Trichoderma in order to improve adaptability and biocontrol at alkaline pH.
1. Trushina et al. (2013) BMC Genomics