Tag Archives: adaptation

Local adaptation and the accessory genome in an endemic plant-pathogen

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Genetic variation is fodder for evolution, and microbial plant-pathogens have it in spades. The Pseudomonas syringae genome is characterized by many rare “accessory” genes that co-occur with “core” genes found in all individuals. In fact, accessory genes outnumber core genes 2:1, even though accessory genes are not essential for survival. Moreover, there is tremendous variation in the gene content of P. syringae; isolates from different crop species, for example, differ in gene content by ~32% (Karasov et al. 2017). Whether these strain-specific genes have adaptive potential remains unknown; they may simply be a consequence of high rates of mutation and lateral gene transfer, even if purifying selection to remove deleterious variants is strong. Another, not mutually exclusive possibility is that accessory genes are maintained by positive selection as pathogens adapt to alternative hosts. Indeed, local adaptation has been hypothesized to explain the presence of rare alleles in P. syringae, which causes major agricultural loss in multiple crop species each year. To address these hypotheses, I have paired a set of P. syringae isolates with their original hosts of isolation. I first test for local adaptation by comparing the in planta fitness of each isolate in its own, and in each other’s, native host. Next, I ask to what degree strain-specific genes influence adaptive patterns by using Tn-seq to track the in planta gene frequencies of each pathogen over the course of infection in each host. From this combination of experiments, we will learn to what extent host ecology influences genome evolution and virulence in P. syringae; this is important not only to inform our understanding of the selective process, but also to fields concerned with the emergence and spread of infectious disease. 

Local adaptation in Swedish beach populations of A. thaliana

Local adaptation in Swedish beach populations of A. thaliana

Beaches are marginal environments for plants, as they tend to have low nutrient sandy soil and poor water availability, as well as other physical stresses like salt spray and wind. Populations of Arabidopsis growing on gravelly beaches on the Baltic coast display different, more extreme phenotypes than inland conspecifics. The project focuses on quantifying phenotypic differences in a panel of Swedish accessions including beach lines and identifying genes underlying these differences. Studies of this type provide insight into plant adaptation to specific local conditions across their range. Additionally, the physical stressors on beaches are similar to those faced by plants in marginal agricultural environments, thus, adaptation to such environments may involve the same genes.