Evidence of local adaptation and regional effector repertoires in Parastagonospora nodorum

Authors: RICHARDS, JONATHAN - North Dakota State University; STUKENBROCK, EVA - Christian Albrechts University; LIU, ZHAOHUI - North Dakota State University; Cowger, Christina; Faris, Justin; Friesen, Timothy

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 1/13/2020
Publication Date: 1/13/2020
Citation: Richards, J.K., Stukenbrock, E.H., Liu, Z., Cowger, C., Faris, J.D., Friesen, T.L. 2020. Evidence of local adaptation and regional effector repertoires in Parastagonospora nodorum [abstract]. Plant and Animal Genome Conference. W502.

Interpretive Summary: .

Technical Abstract: Septoria nodorum blotch (SNB) is caused by the necrotrophic fungal pathogen Parastagonospora nodorum and continues to threaten wheat production internationally. Within the continental United States, P. nodorum has adapted to diverse environmental conditions due to the wide geographic range of wheat acreage planted. P. nodorum utilizes specialized effector proteins to elicit a programmed cell death response to facilitate disease development. Currently, little is known about differences in effector diversity or genomic regions that are under positive selection between discrete P. nodorum populations. Whole-genome sequences of 197 P. nodorum isolates collected from spring, durum, and winter wheat production regions of the United States were developed to test the hypothesis that regional environmental and host factors have driven the selection of beneficial genes, including potential effectors. A total of 1,026,859 polymorphisms were identified within the natural population. Population structure analyses classified two major populations corresponding to the Upper Midwest and the Southeastern United States. Selective sweep analyses identified 10 and 19 non-overlapping regions of positive selection specific to the Upper Midwest and Southeastern populations, respectively, and co-localized with 92 genes. The number and size of sweep regions in the Southeastern population was greater than the Upper Midwest population, likely indicating more recent selection events. A selective sweep was detected at the SnToxA locus specific to the Upper Midwestern population. Further analysis of individual isolates indicated that 96% of isolates from that population harbored a functional SnToxA compared to only 6% of isolates in the Southeastern population. This appears to reflect the frequency of the matching host sensitivity gene Tsn1 in wheat germplasm of the two regions. Additionally, as evidenced by pN/pS ratios, different suites of effectors were diversifying in a population-specific manner. Overall, effector genes were under greater diversifying selection when compared to genes encoding non-secreted proteins or secreted non-effectors. Genes confined to a small accessory chromosome were also observed to be more rapidly evolving. Combined, this study sheds light onto local adaptation and genomic mechanisms of diversification in an economically important pathogen of wheat.