Molecular basis and ecological genetics of hybrid incompatibilities involving a balanced NPR1 polymorphism in the genus Capsella

• Applicant: Professor Dr. Michael Lenhard
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems ; Plant Genetics and Genomics
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 290055472

• Final Report Year: 2021

Final Report Abstract

This project has provided further evidence for the notion that divergent sorting of ancestral balanced polymorphisms can promote the establishment of Bateson-Dobzhansky-Muller incompatibilities (BDMIs) and thus gene-flow barriers between incipient species. This notion was based on our previous finding of a BDMI between Capsella grandiflora and C. rubella involving the NPR1 and RPP5 genes. While C. grandiflora harbours two strongly divergent haplotypes of NPR1 that have been maintained by long-term balancing selection, only one of these is found in C. rubella. This project had three major aims, (1) to identify the causal mutations in the incompatible RPP5 haplotype, (2) to analyze the molecular basis of additional, putatively NPR1-dependent BDMIs between the two species, and (3) to investigate the mechanism of balancing selection on NPR1 in C. grandiflora. Regarding (1), we found that the incompatible RPP5 haplotype differs from several compatible ones by copy number variation of the leucine-rich repeats and three coding single-nucleotide polymorphisms. However, no single one of these differences appears to be sufficient to render an RPP5 haplotype incompatible, suggesting that more than one interacting change is required. As for aim (2), we studied two additional autoimmune-type BDMIs between C. grandiflora and C. rubella involving NPR1. In the first case, the C. grandiflora-like NPR1 haplotype interacts with a locus on chromosome 7; however, a lack of suitable recombinants hampered the identification of the causal gene. In the second case, it was the C. rubella-like NPR1 haplotype that causes an incompatible phenotype when combined with a C. grandiflora locus on chromosome 4. Here, fine-mapping identified WKRY46 and CNGC11 as plausible candidates, and their functional involvement is being validated. Regarding aim (3), a limited glasshouse experiment did not find any evidence for a strong heterozygote advantage or a trade-off between growth and basal defense in pathogen-free conditions as possible causes of the balancing selection acting on NPR1 in C. grandiflora.

Publications

• (2020) Say it with double flowers. Journal of Experimental Botany
  Abdirashid, H., Lenhard, M.