Evolution of plant immunity and microbial pathogenicity

Dr. Remco Stam

 

Plants evolve in a constantly changing environment. This environment consists of geographical and climatic variables as well as plant pathogenic microbes of diverse lifestyles. The constant interaction between these factors and the need of both plant and pathogen fend off the infection (in the case of the plant) or to better infect (in the case of the pathogen) leads to constant adaptation to one another. This adaptation results in diversity within and between both plant and pathogen populations on different geographical locations. The degree in which plant-interacting microbes are adapted to their local host plants can lead to low or extremely high specificity of plant-microbe interactions. As such, the occurrence and severity of plant diseases mostly results from the interplay of host immunity and microbial virulence. 

There is a clear genetic interaction between host immune components and microbial virulence factors. Although this is accepted as a major driver for evolution of host resistance genes and microbial pathogenicity effectors, the actual nature, speed and relevance of co-evolution processes is little understood. We aim to understand which processes are involved in the co-evolution “arms-race”. To do so, we use genomics and population genetics to investigate genome-wide processes as well as “wet-lab” molecular biology to test the effects of the genomic changes and measure the different phenotypic outcomes that result from the genetic variation in both plant and pathogen.

The group uses both wild plant-pathosystems and data from agricultural production systems. These data and underlying evolutionary principles will enable us to better predict the occurrence and severity of disease epidemics and to explore plant gene pool plasticity for improvement of disease resistance in crop plants.

One of our models is the wild tomato S. chilense. This species grows in a wide range of habitats in Chile and Peru. In our lab we have plants from many populations throughout the species range. There are clear differences in nucleotide diversity between the different S. chilense populations. Populations from the north show higher diversity than for example populations from the south. Resistance genes (on the right) show a similar pattern, however there are many more outlier genes with very high diversity when compared to control genes (on the left). Understanding the effects of this diversity on pathogen resistance is one of our objectives (in collaboration with Prof. Dr. A. Tellier; TUM population genetics).