The Plant Circadian Clock: Roles in Jasmonate Accumulation and Postharvest Plant Performance
Doctor of Philosophy
Nearly all organisms have evolved circadian clocks that allow them to anticipate and prepare for cyclical changes in their environment, such as those associated with the transitions from night to day and between seasons. The plant circadian clock functions nearly cell autonomously, regulating rhythmic behaviors in a variety of processes that range from the transcriptional level up to organismal level. Although great progress has been made in determining how the clock functions in plants, not much is known about the clock’s physiological relevance on particular plant processes. Specifically, the clock influences plant defense against Trichoplusia ni (T. ni), as well as basal rhythmic accumulation of jasmonic acid (JA), a plant hormone involved in the regulation of resistance against insect herbivores such as T. ni and necrotrophic fungi such as Botrytis cinerea (B. cinerea). Additionally, the clock affects the accumulation of glucosinolates, secondary metabolites involved in plant insect resistance, in both Arabidopsis and postharvest cabbage (Brassica oleracea). Here we show that rhythmic accumulation of basal JA may be transcriptionally regulated through clock controlled JA-biosynthesis gene transcript accumulation. Additionally, the clock may influence rhythmic accumulation of gene transcripts involved in JA biosynthesis independently of JA-positive feedback. Furthermore, while SA and JA act antagonistically, we note that decreased SA does not influence differential accumulation of JA-biosynthesis related gene transcripts. We also show that phase-entrainment dependent plant resistance to T. ni is influenced in part by aliphatic glucosinolates. Finally, we demonstrate that postharvest vegetables kept in light/dark cycles maintain appearance, tissue integrity, chlorophyll levels, and glucosinolate levels for longer periods of time when compared to postharvest vegetables stored in constant light or constant dark. Moreover, postharvest plants exhibit improved resistance to B. cinerea when kept under light/dark cycles when compared to constant light storage.