Identification of voruscharin biosynthetic genes through differential gene expression analysis of Asclepias species

Cardiac glycosides are secondary metabolites produced in plants as toxic defenses against herbivorous insects. They have evolved independently at least twelve times in different plant families, and function by inhibiting the NA+/K+ ATPase enzyme in animal cells, making the plants that produce them toxic. Despite their ecological importance, many steps of the biosynthetic pathways of cardiac glycosides remain unknown. Milkweed species in the genus Asclepias are optimal candidates to investigate cardiac glycoside biosynthesis due to tremendous variation among species. Different species not only synthesize different cardiac glycosides but also vary greatly in cardiac glycoside concentrations. There are a small number of cardiac glycosides containing nitrogen and sulfur, making their biosynthetic pathways ideal for studying. Voruscharin is one such cardiac glycoside; it is present in Asclepias curassavica (tropical milkweed). Thus, the A. curassavica genome may be compared to that of a closely related species, Asclepias incarnata (swamp milkweed), that does not produce voruscharin. Asclepias syriaca (common milkweed) also produces a nitrogen and sulfur-containing cardiac glycoside that is not present in a close relative species, Asclepias tuberosa (butterfly weed). A. curassavica and A. syriaca are expected to use similar enzymes in this process. I performed the preparations for the assembly of the A. tuberosa and A. incarnata transcriptomes in order to compare differential expression under stress in species pairs. Genes that are upregulated in both A. curassavica and A. incarnata or both A. syriaca and A. tuberosa as a defense response are not likely to be involved in voruscharin biosynthesis.

My summer in the Jander lab gave me insight into what it would be like to perform research full-time. I was able to learn new lab protocols and techniques as well as how to manage my time spent doing it. Since I only had a mentor for the first few weeks, I became more confident in asking various lab members and BTI staff for help. As a result, I was also able to develop closer relationships with the people I was working alongside. Through the weekly seminar series, I not only learned new science but also how to communicate science. I am incredibly grateful to have had the opportunity to participate in the BTI REU and look forward to continuing research in plant science.