HogA and PacC regulated alternariol biosynthesis by Alternaria alternata is important for successful substrate colonization
During the colonization process, fungi have to interact with the plant tissues. Several plant pathogenic fungi are able to produce mycotoxins. For several of these mycotoxins, e.g., trichothecenes or patulin, it has been proved that they can act as pathogenicity factors, supporting the colonization of the respective plant tissue by the fungus. This activity was also demonstrated for alternariol biosynthesis in A. alternata. Mutant strains of A. alternata, not able to produce alternariol, had a greatly reduced capacity to colonize tomatoes compared to the wild type. After addition of external alternariol, the colonization capacity of A. alternata was increased in a concentration-dependent manner. Since the alternariol production by the fungus seems to be important for its colonization, the fungus must carefully control the biosynthesis of this secondary metabolite. Usually tomato tissue has a high water activity and a low pH. This means that alternariol biosynthesis must be possible under these conditions. The HOG signalling cascade pathway senses changes in the osmotic conditions, which mean changes in water activity. Whereas changes in pH are mediated to the transcriptional level by the PacC signal transduction system. Both signalling transduction pathways play an important role to ensure that alternariol is produced at optimum substrate conditions.
Geisen, R., Graf, E. and Schmidt-Heydt, M. (2016). HogA and PacC regulated alternariol biosynthesis by Alternaria alternata is important for successful substrate colonization. Acta Hortic. 1144, 141-148
tomato, mycotoxin, signal transduction, osmotic condition, pH, infection