pH effect on strain-specific transcriptomes of the take-all fungus.

The soilborne fungus Gaeumannomyces graminis var. tritici (Ggt) causes take-all, a wheat root disease. The ambient pH is critical all along the Ggt life steps for survival in bulk soil, saprophytic growth, and pathogenicity on plants. In an original strain-specific way, previous studies indicated that (i) inside the Ggt species, some strains grew preferentially at acidic pH and others at neutral/alkaline pH; (ii) the expression of genes involved in pH-signal transduction pathway and pathogenesis was regulated by the ambient pH and the strain. To go further in studying pH-related mechanisms involved in the life steps of Ggt, transcriptome sequencing was achieved on two strains (PG6 and PG38) which displayed opposite growth profiles in two pH conditions (acidic and neutral). This study showed that ambient pH modulated expression of genes involved in different metabolic pathways depending on the strain. PG6, growing better at acidic pH, overexpressed in this condition genes related to energy production and protein deubiquitination. PG38, which grew better at neutral pH, overexpressed in this condition genes involved in fatty acids metabolism. This strain also implemented stress resistance mechanisms at both pH, allowing growth whatever the ambient pH. These differences in metabolic pathway expression in function of the pH and the strain could have consequences on survivability and growth of Ggt strains, and so on frequencies of each genetically group during wheat monocultures.