The Parastagonospora nodorum necrotrophic effector SnTox3 likely evolved from a duplication event of SnTox5

Authors: KARIYAWASAM, GAYAN - North Dakota State University; Wyatt, Nathan; LIU, ZHAOHUI - North Dakota State University; STUKENBROCK, EVA - Max Planck Institute For Evolutionary Biology; Faris, Justin; Friesen, Timothy

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/9/2021
Publication Date: 3/15/2022
Citation: Kariyawasam, G.K., Wyatt, N.A., Liu, Z., Stukenbrock, E.H., Faris, J.D., Friesen, T.L. 2022. The Parastagonospora nodorum necrotrophic effector SnTox3 likely evolved from a duplication event of SnTox5. In: Fungal Genetics Conference, Mar. 15-20,2022, Pacific Grove, CA.

Interpretive Summary:

Technical Abstract: Parastagonospora nodorum is a destructive foliar pathogen of wheat that causes septoria nodorum blotch. The fungus follows an inverse gene-for-gene model and releases multiple necrotrophic effectors that elicit programmed cell death (PCD) in the presence of the corresponding host susceptibility genes. Five genes, SnToxA, SnTox1, SnTox267, SnTox3, and SnTox5 that encode for five distinct necrotrophic effectors have been cloned and functionally characterized. SnTox5 is the latest gene to be cloned and it encoded a protein with a signal peptide and a pro-sequence. The mature SnTox5 was 16.26 kDa in size and showed 45.13% sequence homology and 98% structural similarity to SnTox3. Functional characterization using confocal microscopy showed that SnTox5 facilitated the colonization of leaf mesophyll tissue and may suppress the host defense response prior to the induction of PCD, suggesting functional similarity to SnTox3. Therefore, to evaluate the hypothesis that SnTox3 is a result of a duplication of the SnTox5 genomic region, we evaluated the genomic regions of SnTox3 and SnTox5. SnTox5 showed 63.13% homology to SnTox3 at the nucleotide level. Furthermore, repeat annotation showed a TcMar-Fot1, a DNA transposable element 748 bp upstream of SnTox5. BlsatN analysis of the TcMar-Fot1 element showed 44.25 % homology to a region 532 bp upstream of SnTox3. Furthermore, eight repeat induced polymorphisms were identified in the TcMar-Fot1 homolog upstream of SnTox3. Therefore, these evidences suggest that SnTox5 and SnTox3 are two genes likely evolved from a single duplication event. To evaluate the direction of the duplication event we evaluated whole genome sequences of 387 P. nodorum isolates acquired from different wheat growing regions of the world. The presence/absence of SnTox5 and SnTox3 was initially evaluated, and it was shown that 48 isolates lacked both genes, 179 isolates harbored both genes, and 133 isolates had only SnTox5, whereas only 27 isolates had just SnTox3. Haplotype analysis showed that SnTox5 had 27 haplotypes that encoded for 21 protein isoforms, whereas SnTox3 had only 12 haplotypes that encoded for only four protein isoforms. Therefore, high prevalence and haplotype diversity of SnTox5 relative to SnTox3 suggests that SnTox3 likely evolved through a duplication of SnTox5. Therefore, it is possible that both SnTox3 and SnTox5 target similar vulnerabilities of the host to induce PCD in the presence of Snn3 and Snn5, respectively.