UC Davis

Jasmonic acid (JA) signaling controls many aspects of plant growth, development, and defense, as well as the plant’s ability to adapt to various environmental and abiotic stressors. JASMONATE-ZIM DOMAIN (JAZ) proteins are negative regulators of JA signaling and are increasingly being observed as regulatory links in phytohormone signaling crosstalk, allowing tight regulation of these plant processes. However, specific molecular functions of JAZ4 and other JAZs is poorly understood, highlighting the need to further address mechanistic underpinnings of these signaling networks, ultimately contributing to the generation of enhanced plant health and production in economically important crops. Therefore, in Chapter 1, I review evidence of JAZ4 biological function in Arabidopsis thaliana in comparison with other known JAZ functions in the context of specificity and redundancy within canonical JA signaling or interconnection with alternative signaling nodes. Furthermore, alternative splicing of JAZ pre-mRNAs has been previously demonstrated to produce truncated isoforms with varying levels of JA-insensitive phenotypes. This observation provided the framework for Chapter 2, in which I determined naturally-occurring JAZ4 isoforms in planta and respective spatiotemporal expression and splicing patterns. These findings unveiled organ-specific roles of JAZ4 in root growth and development through differential regulation of ethylene and auxin signaling pathways. Finally, in Chapter 3, I observed pathogenesis and growth phenotypes utilizing reverse genetics, and performed yeast one-hybrid screening and RNA-sequencing analysis to establish JAZ4 biological function and regulatory networks up- and down-stream of JAZ4, respectively. These findings uncovered JAZ4 as a negative regulator of plant growth and defense, predominantly through an auxin-mediated negative feedback mechanism. Altogether, my work has significantly advanced the scientific knowledge behind jasmonate signaling specificity and the interconnection with alternative signaling networks controlling the plant host’s ability to regulate growth and defense to optimize plant health and production.