Since the start of the project, we have collaborated with the group of Pierre Gladieux (PHIM, France) to identify the arsenal of MAX effectors present in the genomes of more than a hundred strains of M. oryzae capable of infecting different cereal species in a specific manner. This work has allowed us to study how MAX effectors evolve and diversify in M. oryzae. In particular, it shows that MAX effectors constitute a very dynamic compartment of the M. oryzae genome, potentially reflecting intense co-evolutionary interactions with host proteins. It also enabled the identification of MAX effectors that are present in all strains of M. oryzae, and that are potentially crucial to the infectious process.
We have also identified the MAX effectors that are deployed during the early stages of rice colonisation. Thus, we know that more than half of the MAX effectors present in a M. oryzae isolate are specifically expressed during this phase. MAX effectors are therefore largely deployed during infection.
For many of these effectors, we have identified, through several complementary experimental approaches, potential targets in the host plant, i.e. rice proteins that interact with MAX effectors and may be manipulated by the pathogen to promote infection. These targets could play a role in plant immunity or susceptibility. Our results indicate that MAX effectors interact with a wide variety of host proteins and thereby potentially target many molecular processes in rice, and potentially in other cereals. We also show that several MAX effectors appear to play redundant roles in the infection process.
We are now initiating the validation of the most interesting targets and their functional analysis in order to define their role in the establishment of the blast disease. We are also conducting, together with the group of André Padilla (CBS, France), modelling analyses of the 3D structure of MAX effectors interacting with their host targets to gain a better understanding of how MAX effectors, which have a conserved 3D structure, can interact with a wide range of host proteins.
These analyses will allow us to identify the rice proteins targeted during infection by MAX effectors and necessary for disease development. Specific modification of these targets will allow to improve rice resistance to blast.
