Rob McClung

215 Gilman Hall

Genetics And Molecular Genetics Of Plant Circadian Rhythms

 

The ability of an organism to measure time is the product of a cellular biological clock.  Many phenomena controlled by the biological clock cycle on a daily basis and are called circadian rhythms.  My goal is to understand the genetic and biochemical mechanisms by which an organism measures time and uses that temporal information to regulate gene expressionand cellular physiology.  The circadian clock is an endogenous oscillator that drives rhythms with periods of approximately 24 hours.  By definition, these circadian (from the Latin, circa, approximately; dies, day) rhythms persist in constant conditions and reflect the activity of an endogenous biological clock.  Plants are richly rhythmic and the circadian clock regulates a number of key metabolic pathways and stress responses.  In addition, the circadian clock plays a critical role in the photoperiodic regulation of the transition toflowering in many species.  Circadian rhythms in plants have been the subject of a number of recent reviews, including several from my lab (Salomˇ and McClung, 2004, 2005a; McClung, 2006, 2008; McClung and Gutiˇrrez, 2010).  It is worth noting that two of these were largely taken from the introduction to Patrice SalomˇÕs Ph.D. thesis.

 

CURRENT PROJECTS

1.  Mutational Analysis of the Arabidopsis Circadian Clock.  We have identified a number of loci which, when mutated, alter circadian rhythmicity (period or phase is altered, or the plants are arrhythmic).  These studies include novel genes identified in forward genetic screens as well as defined genes identified through a candidate gene (reverse genetics) approach.  The genetic and molecular biological analysis of these mutations offers a number of thesis projects (Michael et al., 2003; Salomˇ and McClung, 2005b, a; Hong et al., 2010; Salomˇ et al., 2010).

 

2. Post-transcriptional Regulation by the Arabidopsis Circadian Clock.  The biochemical function of the PRR proteins is not yet understood.  However, it has become clear that the stability of each is tightly regulated.  For example, TOC1 and PRR5 are targeted for proteasomal degradation through interaction with the F-box protein ZTL.  Each PRR is phosphorylated and this phosphorylation is implicated in their regulated stability (Fujiwara et al., 2008). For example, the more highly phosphorylated forms of PRR5 and TOC1 interact best with ZTL.  This suggests that phosphorylation may be an important step in the regulated proteolysis of the PRRs.  What kinases are important for clock function? 

 

3. Evolutionary and Quantitative Analysis of the Brassica rapa Circadian Clock. We have started a new collaboration, with colleagues at Wyoming and Wisconsin, to look at clocks in a crop species, Brassica rapa (Chinese cabbage, turnip). We are measuring clock parameters (again, by leaf movement) in order to map QTLs that contribute to period, phase and amplitude.  The study is ongoing, but we already have identified multiple QTLs.  To date, we have focused on a period QTL on chromosome A9 and are testing candidate loci, including the B. rapa GIGANTEA gene.  In addition, we will map genes that contribute to temperature entrainment and temperature compensation.  We have developed a transgenic tissue culture system to allow the measurement of circadian clock regulated gene expression in B. rapa (Xu et al., 2010).  We have observed the colocalization of QTLs affecting circadian period with QTLs for water use efficiency.  We will explore the possible link between these two phenotypes through fine-mapping and cloning of these QTLs.  Finally, we are collaborating with colleagues at Wyoming, UC Davis, and Kansas State in a genetic study to use computational models that combine recent advances in ecophysiological crop models with genomic network inference, including environmental dependencies of network behavior to address the ability to predict phenotype from genotype (G→P) in heterogeneous field environments.

 

RECENT PUBLICATIONS

Fujiwara, S., Wang, L., Han, L., Suh, S.S., Salomˇ, P.A., McClung, C.R., and Somers, D.E. (2008). Post-translational regulation of the circadian clock through selective proteolysis and phosphorylation of pseudo-response regulator proteins. J. Biol. Chem. 283, 23073-23083.

Hong, S., Song, H.-R., Lutz, K., Kerstetter, R.A., Michael, T.P., and McClung, C.R. (2010). Type II Protein Arginine Methyltransferase PRMT5 is required for circadian period determination in Arabidopsis thaliana. Proc. Natl. Acad. Sci. USA 107, 21211-21216.

McClung, C.R. (2006). Plant circadian rhythms. Plant Cell 18, 792-803.

McClung, C.R. (2008). Comes a time. Curr. Opin. Plant Biol. 11, 514-520.

McClung, C.R., and Gutiˇrrez, R.A. (2010). Network news: prime time for systems biology of the plant circadian clock. Curr. Opin. Genet. Dev. 20, 588-598.

Michael, T.P., Salomˇ, P.A., Yu, H.J., Spencer, T.R., Sharp, E.L., Alonso, J.M., Ecker, J.R., and McClung, C.R. (2003). Enhanced fitness conferred by naturally occurring variation in the circadian clock. Science 302, 1049-1053.

Salomˇ, P.A., and McClung, C.R. (2004). The Arabidopsis thaliana clock. J. Biol. Rhythms 19, 425-435.

Salomˇ, P.A., and McClung, C.R. (2005a). What makes Arabidopsis tick: Light and temperature entrainment of the circadian clock. Plant Cell Environ. 28, 21-38.

Salomˇ, P.A., and McClung, C.R. (2005b). PSEUDO-RESPONSE REGULATOR 7 and 9  are partially redundant genes essential for the temperature responsiveness of the Arabidopsis circadian clock. Plant Cell 17, 791-803.

Salomˇ, P.A., Weigel, D., and McClung, C.R. (2010). The role of the Arabidopsis morning loop components CCA1, LHY, PRR7 and PRR9 in temperature compensation. Plant Cell 22, 3650-3661.

Xu, X., Xie, Q., and McClung, C.R. (2010). Robust circadian rhythms of gene expression in Brassica rapa tissue culture Plant Physiol. 153, 841-850.

  updated December 29, 2010