Molecular mechanisms of pathogen adaptation to plant defenses

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Plant diseases represent a constraint for all economic crops in Canada and worldwide. The development and deployment of disease resistant varieties is a constant exercise in both public and private sectors, but the sustainability of such varieties frequently faces challenges. In absence of resistant lines, growers use cultural practices and chemicals to mitigate the negative impact of diseases. However, satisfactory results can only be achieved with integrated and sustainable disease management strategies. More than ever, establishing such approaches requires better understanding of host-pathogen interactions in each considered disease, i.e., pathogens’ ability to infect/colonize plants and plants’ responses to such attacks. My research program focuses on the mechanisms of both aspects, but more on understanding how pathogens handle host defenses and, in cases, how they manipulate the host's metabolism to their own advantage. Using subtractive hybridization/cDNA-AFLP, we identified several differentially expressed genes and proteins involved in the potato-V. dahliae and potato-P. infestans interactions. These included genes controlling pathogenesis or avirulence in these pathogens, as well as others potentially involved in plant resistance or susceptibility to these pathogens. We cloned and sequenced several differentially expressed transcript-derived fragments. We selected a set of corresponding genes and have been functionally characterizing them to determine their role either in pathogenesis or defense. Chasing a single gene or protein may provide information on its functional role and can be of great value in a gene-for-gene interaction, for example its deployment for plant disease resistance. In the case of polygenic resistance, the value and use of one seemingly important gene becomes a moving target as the pathogen uses adaptive strategies to balance its needs and respond to new situations. In this context, my goal is to understand each interaction in an integrated system that takes this complexity under account. My objectives for the term of this proposal are to (i) complete functional studies of genes we deemed important in plant-V. dahliae interaction, (ii) run cell and organ localization of their expression for each segment of the interaction (Response to root exudates, Infection, Colonization, and Symptom development), along with the signaling mechanisms accompanying each segment, and (iv) understanding the mechanisms of pathogenesis variations that allow pathogen adaptation over time. Integrating these findings into a pathogenesis gene distribution model will eventually lead to predicting plant and pathogen responses to clues from their counterpart and the environment. Identifying these elements and processes will be one step further towards efficiently mitigating the negative impacts of plant diseases.