Setaria viridis as a model for translational genetic studies of jasmonic acid-responsive insect defenses in Zea mays

Authors: Hunter, Charles; Block, Anna; Christensen, Shawn; Li, Qin-Bao; Rering, Caitlin; Alborn, Hans

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2019
Publication Date: 2/1/2020
Citation: Hunter III, C.T., Block, A.K., Christensen, S.A., Li, Q., Rering, C.C., Alborn, H.T. 2020. Setaria viridis as a model for translational genetic studies of jasmonic acid-responsive insect defenses in Zea mays. Plant Science. 291, February 2020, 110329. https://doi.org/10.1016/j.plantsci.2019.110329.
DOI: https://doi.org/10.1016/j.plantsci.2019.110329

Interpretive Summary: Molecular genetics is a valuable tool for helping scientists protect U.S. agricultural crops and products. Molecular genetics experiments can be conducted in model organisms before applying gained insights to species of real-world relevance. The utilization of model plants is also beneficial due to their faster growth rate in a greenhouse setting, thus easier to study. Setaria viridis has emerged as a good model species for grasses such as Zea mays (corn), but almost nothing is known about the chemical defense pathways in S. viridis. Here we examine a subset of chemical defense responses to caterpillar feeding in both corn and S. viridis, with the purpose of determining whether S. viridis would serve as an effective model species for corn in the context of chemical defense responses. ARS scientists at the CMAVE in Gainesville, FL studied the defense chemicals and defense gene expression responses after subjecting plants to caterpillar damage or caterpillar regurgitant. By doing so, they showed that many of the core chemical defense signaling pathways are maintained between corn and S. viridis, and thus show that S. viridis would serve as an effective model species for examining these pathways. However, we also show that many of the defense chemicals that corn makes are absent in S. viridis, suggesting that these particular chemical pathways must be studied in the species of interest directly. Knowledge of these defense responses can then be used in other studies to help strengthen the plant’s ability to fight off attack by insect pests.

Technical Abstract: Little is known regarding insect defense pathways in Setaria viridis, a model system for panicoid grasses, including Zea mays (maize). It is thus of great interest to compare herbivory responses in S. viridis and maize. Here we use metabolic, phylogenetic, and gene expression analyses to measure a subset of jasmonic acid (JA)-related defense responses to leaf-chewing caterpillars. Phylogenetic comparisons of known defense-related maize genes were used to identify putative orthologs in S. viridis, and candidates were tested by qPCR to determine transcriptional responses to insect challenge. Our findings show that while much of the core JA-related metabolic and genetic responses appear conserved between S. viridis and maize, production of downstream secondary metabolites such as benzoxazinoids and herbivore-induced plant volatiles are dissimilar. The high degree of genetic similarity and ease of orthologous gene identification between S. viridis and maize make S. viridis an excellent species for translational genetic studies, but the species specificity of downstream insect defense chemistry make some pathways unamenable to cross species comparisons. The diversity of chemical defenses and gene families involved in secondary metabolism among grasses presents new opportunities for cross species engineering.