Investigating insect defense systems in groundcherry as a model for related Physalis species

Physalis is a genus of fruit plants native to Central and South America. Goldenberry (Physalis peruviana) has abundant nutritional and medicinal properties that make it desirable for large-scale agricultural production. However, it is susceptible to insect herbivory, which reduces fruit yield and poses a challenge to growers. A close relative of P. peruviana, groundcherry (Physalis grisea), is more resistant to insect herbivores. Its leaves produce specialized metabolites called withanolides that confer insect resistance in other plant species. Withanolide content in P. peruviana may be manipulated to make it more viable for large-scale production. To further explore the application of withanolides as a defense mechanism against insect herbivory, through deterrent or toxic effects, we used CRISPR gene editing to alter withanolide accumulation in P. grisea leaf tissue. We targeted two branch points in the withanolide biosynthetic pathway: BETA-AMYRIN SYNTHASE (PgꞵAS) and STEROL METHYLTRANSFERASE 2 (PgSMT2). Three mutant lines with unique alleles for each gene were recovered. We used these lines in a no-choice insect bioassay in which Trichoplusia ni neonate larvae were placed individually in a petri dish with one leaf disc. The larvae did not exhibit a significant feeding preference for wild type P. grisea or any edited line, and the larvae had similar survival rates on all lines. This may be due to T. ni being a generalist species and having an acute sensitivity to withanolides. Future bioassays will investigate the effect of withanolides on Lema daturphila beetles, which are Physalis specialists and can likely tolerate higher levels of withanolides.

This summer, I had the opportunity to work in Joyce Van Eck’s lab at BTI, using chemical ecology to study insect defense mechanisms in groundcherry as a part of the Physalis Improvement Project. I was closely mentored by Savanah Dale who gave me the freedom to think independently and the support I needed as I delved into a new project. Through my work and the weekly seminar series, I’ve learned about a plethora of plant research projects and their practical applications. Understanding how scientists can use their research to improve crops has enriched my love of plant science and has sparked my interest in plant breeding as a career path.