UC San Diego

To efficiently protect themselves against pests and disease, plants surveil for attacking organisms and upon recognition, activate protective inducible defenses. Here, I present my work on the regulation and function of maize inducible defenses by integrating genetic, transcriptomic and physiological approaches. This work elucidated mechanisms underlying three layers of the maize immune response, including: (1) A novel genetic locus associated with sensitivity to exogenous herbivore-associated elicitors of the fatty-acid amino-acid conjugate (FAC) family, (2) regulatory function of phytocytokines from the Plant elicitor peptide (Pep) family, and (3) biosynthesis of antibiotic specialized metabolite defenses. Early maize signaling events triggered in the context of herbivory, were probed through comparative transcriptomic analyses upon treatment with ZmPeps and FACs, indicating a largely shared signaling pathway and identifying specific genes involved in antiherbivore defense. Genetic mapping using the Intermated B73 x Mo17 mapping population derived from B73, an FAC sensitive line, and Mo17, an FAC insensitive line, identified a single locus on chromosome 4 associated with FAC sensitivity that was further fine-mapped to a region containing 19 genes. A candidate gene within this region, FAC SENSITIVITY-ASSOCIATED (FACS), was expressed at significantly lower levels in the insensitive parent line, and heterologous expression of FACS increased FAC sensitivity in Nicotiana benthamiana, suggesting a role in regulation of FAC-induced responses. Work characterizing the maize ZmPep family led to several new insights into Pep signaling mechanisms: Maize Pep precursors (PROPEPs) were found to contain multiple nested active peptides, a phenomenon not previously observed for this family. Additionally, in contrast to Peps in Arabidopsis, individual maize Peps were found to have specific activities defined by the relative magnitude of elicited responses through rheostat-like tuning of phytohormone levels. Finally, peptide structure-function analysis and physiological assays identified ZmPep5a as a potential antagonist peptide. Finally, we report on the development of an R Shiny web-application that was developed to facilitate mutual rank-based coexpression analyses integrating user-provided supporting information. The utility of this user-friendly app was demonstrated through application to define two new biosynthetic pathways for maize terpenoid antibiotics.