Minisymposium 5: Secondary Metabolism

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Abs # M0503: Genetic and Molecular Analyses of the Pun1 Locus and Pungency in Capsicum

Presenter:	Stewart Jr., Charles       Contact Presenter
Authors	Stewart Jr., Charles  (A)   Mazourek, Michael  (A)   Stellari, Giulia M. (A)   Fellman, Shanna  (A)   O'Connell, Mary  (B)   Jahn, Molly  (A)
Affiliations:	(A): Cornell University (B): New Mexico State University

The fiery hot sensation of heat, or pungency, produced in the fruit of certain pepper (Capsicum spp.) plants is due to the presence of capsaicin. Capsaicin is produced by the joining together of a fatty acid tail to a phenolic head group. Used as an analgesic for centuries, capsaicin is currently used to treat neurological and digestive disorders and as a chemoprotective agent during cancer treatment. Capsaicin, like other secondary metabolites, is taxonomically restricted, occurring only in the genus Capsicum. While some of the genes involved in capsaicin biosynthesis are known, regulation of this pathway is not fully understood. For nearly 500 years breeders have used the Pun1 locus to control the presence/absence of pungency in peppers. Using a candidate gene approach we isolated the Pun1 gene, identified it as a putative acyltransferase, and used virus-induced gene silencing (VIGS) to establish its function in capsaicinoid biosynthesis. The allelic diversity of this gene was examined by sequencing Pun1 from a diverse array of pepper genotypes. Three separate mutations of the Pun1 gene were identified in three disparate Capsicum species. Complementation tests and genetic inheritance studies confirmed that these mutations were alleles of Pun1 and that they consistently co-segregated with non-pungency. To date, all non-pungent peppers have a mutation in the Pun1 locus which results in non-pungency. Furthermore, comparison of gene expression profiles between pungent and non-pungent genotypes suggests that several genes implicated in capsaicin biosynthesis are coordinately regulated. This research has increased our understanding of the genetic basis of the evolution of natural plant products and how secondary metabolism can be manipulated for human use.