EAGER: Self-incompatibility in elderberry

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Roughly half of the approximately 352,000 species of flowering plants on earth possess mechanisms that favor cross-pollination. This reproductive strategy is crucial for generating and sustaining the genetic diversity that plants need to survive and adapt. Humans rely on plant diversity both directly, for crop improvement, and indirectly, for ecosystem support. Many plants have evolved ways to recognize and reject self-pollen and pollen from close relatives. These so-called “self-incompatibility systems” are among the most common and effective mechanisms that prevent self-pollination and favor cross-pollination. To date, the genes controlling self-incompatibility, called S-genes, have been identified in only three systems that operate in a handful of plant families. This project will identify S-genes in elderberry, an emerging specialty crop rich in antioxidants that is used in wine, supplements, and other products. Candidate genes were identified using a novel approach prioritizing DNA sequence differences that could relate to pollen recognition as well as expression data. Experiments will evaluate these candidate genes by testing whether the presence or absence of particular S-genes reliably predicts what types of pollen are accepted or rejected. Other experiments will identify additional S-gene variants. The approach used to identify elderberry S-genes may be applied to additional self-incompatibility systems and, thus, further contribute to understanding maintenance of plant diversity. Self-incompatibility (SI) systems are among the most important genetic mechanisms plants use to control mating. Typically, the genes controlling SI, S-genes, have numerous allelic variants, and, basically, SI allows plants to reject pollen from potential mates with similar alleles. SI species are obligate outcrossers because self-pollen always has the same S-alleles as the pistil. Notwithstanding their outsized importance for plant diversity, evolution and adaptability, S-genes have only been identified in a handful of SI systems. Here, the overall goals are to elucidate a new SI system, identify the controlling S-genes, and facilitate their use in the scientific and agriculture communities. We characterized SI in elderberry (Sambucus canadensis) and used RNASeq to identify candidate S-genes. Genetic experiments will ascertain whether these candidate S-genes truly control SI in elderberry. Four populations segregating for distinct S-allele candidates will be genotyped and test pollinated to determine whether they reject pollen from plants bearing the same alleles. Elderberry is an emerging specialty crop valued for potential health benefits, and additional S-alleles will be identified in elderberry and related plants to support the elderberry improvement community. Specifically, the project will allow breeders and producers to predict the crossing behavior of commercial varieties. Project activities related to elderberry production and improvement will be broadly disseminated via presentations, video, and Extension publications. The project also will contribute to human resource development by providing undergraduate research training in both laboratory- and field-based plant science.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.