This project focuses on capsaicin biosynthesis and the genes that define and regulate the pathway in Capsicum. Apart from portions of the biosynthetic pathway common to other primary metabolic pathways, the remainder of the pathway remains unknown. Of particular interest among the enzymes uncharacterized to date is the terminal acyltransferase, capsaicin synthase (CS), which joins the alkaloid moiety of the capsaicin molecule derived from phenylpropanoid biosynthesis to the fatty acid moiety. Preliminary results have identified three novel putative acyltransferases (ATs) that are highly up-regulated during capsaicin accumulation. Based on genetic studies in this laboratory, AT3 is Pun1 (formerly the C locus), the genetic determinant long known as the on/off switch for this pathway. AT3 will be evaluated as a candidate for CS activity through biochemical experiments designed to characterize the CS enzyme and show CS activity is inherently linked to the presence of the AT3 protein. In the event that AT3 is not CS, it is still clear that the enzyme encoded by the Pun1 locus is critical for expression of the pathway. Experiments will be undertaken to gain insight as to the identity of this enzyme, if it is not CS. The second objective focuses on AT3 as a regulator of pungency. Preliminary data indicate that extreme transcript down-regulation occurs for many of the genes required for biosynthesis when the pun1 allele, which possesses a large deletion of the promoter and the first exon, is homozygous.
Broader Impact: Finally, capsaicin biosynthesis represents an ideal focus for a project aimed at integrating educational and research objectives because of the popularity and familiarity of products containing capsaicin and its rapidly growing economic significance in a wide array of food products, in medicine, industry, law enforcement, and pest control (it has become a leading insect repellent in organic agriculture and is the active ingredient in many of the most effective deer and rodent repellents). Well-developed alliances with Alcorn State University in Mississippi, Texas A&M at Kingsville, and New Mexico State allow for recruitment of underrepresented minorities for summer and graduate opportunities and assistance in providing resources for their own research programs.
