The regulation of different metabolic pathways through the Pal/Rim pathway in Ustilago maydis.

One of the most important physicochemical factors that affect cell growth and development is pH, and living organisms have developed specific mechanisms to adapt to media with variable pH values. Most fungi posses a specific mechanism for such adaptation: the Pal/Rim pathway. To analyze the different metabolic processes regulated by this pathway, and its possible relationships with other physiological regulatory mechanisms, we analyzed the phenotype of a mutant in the PALB/RIM13 gene of the phytopathogenic fungus Ustilago maydis. The mutant displayed important alterations in the synthesis and organization of the cell wall and was affected in its response to stress, revealing its relationship with the MAPKC pathway involved in maintaining the integrity of the cell wall, and the stress response pathway, but not with the HOG pathway. An important observation was that the mutant, in contrast to the wild-type strain, was unable to maintain a constant intracellular pH, suggesting that probably the main function of the Pal/Rim pathway, in collaboration with other regulatory mechanisms, is to maintain a constant intracellular pH, despite the changes occurring in the environment.