Date Available

12-7-2018

Year of Publication

2016

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department/School/Program

Plant and Soil Sciences

First Advisor

Dr. Ling Yuan

Abstract

For millennia humans have utilized plant specialized metabolites for health benefits, fragrances, poisons, spices, and medicine. Valued metabolites are often produced in small quantities and may command high prices. Understanding when and how the plant synthesizes these compounds is important for improving their production. Phytohormone signaling cascades, such as jasmonate (JA) activate or repress transcription factors (TF) controlling expression of metabolite biosynthetic genes. TFs regulating specialized metabolite biosynthetic genes can be manipulated to engineer plants with increased metabolite production.

WRKY transcription factor are known components of both JA signaling cascades and regulation of specialized metabolism. The presence of WRKY binding sites in promoters of several terpene indole alkaloids suggested their involvement in regulating biosynthesis of these compounds. A phylogenetic analysis was used to compare Arabidopsis and Catharanthus WRKY TFs families. Gene expression analysis identified WRKY TFs induced by JA in both Arabidopsis and Catharanthus, providing candidates for future characterization. WRKY TFs suggest a possible conserved regulatory network of TFs downstream of JA signaling cascades.

The origin and conservation of JA signaling in plants remain ambiguous. Identification of the first algal TIFY factor helped determine when JA signaling appeared. The charophyte, Klebsormidium flaccidum does not possess genes encoding key green-plant JA signaling components, including CORONATINE INSENSTIVE1, JASMONATE-ZIM DOMAIN, NOVEL INTERACTOR OF JAZ, and the JAZ-interacting bHLH factors, yet their orthologs are present in the moss. A molecular clock analysis dated the evolution of JA signaling evolution to during the early Ediacaran to late Cambrian periods 628 to 491 million years ago – a time corresponding to rapid diversification of animal predators.

The plant Mediator complex is a core component of gene expression. Conservation of the MED25 subunit in plants, and its known involvement in JA signaling implicates this factor in regulation of specialized metabolism. MED25 is involved in anthocyanin accumulation, but how it functions remains unknown. Characterization of MED25 in Arabidopsis revealed it interacts with the transcription factor GL3 as well as the JAZ1 repressor. Importantly, the interaction of JAZ1 with MED25 reveals a new mechanism by which JAZ proteins regulate gene expression, improving our understanding of JA signaling.

Digital Object Identifier (DOI)

https://doi.org/10.13023/ETD.2016.451

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