Circadian regulation and phytohormone responses of cytochrome P450 monooxygenase genes in Arabidopsis

Plant growth and development are regulated by both hormone and circadian signaling pathways. The growing number of signaling molecules whose syntheses are circadian-regulated (e.g. jasmonic acid, auxin) and the time-of-day-specific transcripts of cytochrome P450 monooxygenases (P450s) involved in their syntheses and catabolisms suggest an interactions between hormone signaling network and circadian signaling network. The first phase of my research profiled a total of 98 P450 genes in Arabidopsis thaliana as circadian-regulated at a transcriptional level under varying photoperiod and thermocycle conditions, and demonstrated that P450s involved in phenylpropanoid, carotenoid, oxylipin, glucosinolate and brassinosteroid biosynthese pathways are circadian-regulated. The next phase of my research investigated the circadian rhythms of P450 genes under different phytohormone treatments including methyl jasmonate (MeJ), salicylic acid (SA), abscisic acid (ABA) and indole-3-acetic acid (IAA). My analysis of transcript profiles of seedlings treated with individual hormones indicated the responses of many P450 genes to these hormone treatments are gated by circadian clock. And different hormone inductions also provided feedback to the circadian clock of P450 gene expressions by affecting their phase, amplitude, period and precision. In silico cis-element analyses of co-regulated promoters in different pathways identified that many known elements including Evening Element, CCA1 Binding Site and G-Box variant elements, as well as some novel elements including JA1 and TRP1 were over-represented and likely to be important in circadian regulation and/or hormone induction. The third phase of my research focused on the bHLH transcription factor MYC2, which plays a critical role in JA signaling and its crosstalk with many other stresses. Analysis of myc2 knockout plants confirmed that MYC2 positively regulated the JA pathway and negatively regulated the IG pathway, and that the MeJ responses of JA signaling genes were only moderately reduced in the mutant seedlings. The work suggests that there are transcription factors other than MYC2 playing a major role in regulating the responses to MeJ. Three closely related genes MYC3, MYC4 and MYC5 were found to bind to the same DNA binding sites as MYC2, which might play different roles, in concert with MYC2 in the integration of JA-signaling to control both circadian and hormone response processes.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2013

Author dc:creator

• Pan, Yinghong

Contributors dc:contributor

• Schuler, Mary A.
• Zielinski, Raymond E.
• Ming, Ray R.
• Clough, Steven J.

• phytohormones
• Arabidopsis
• cytochrome P450s
• circadian

Statement dc:rights

• Copyright 2012 Yinghong Pan

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/42197

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/42197