Minisymposium 20: Photomorphogenesis

Abs # 41005: Roles of the Pseudo Response Regulator genes in the Arabidopsis circadian clock

Presenter:	McClung, C Robertson, c.robertson.mcclung@dartmouth.edu
Authors	McClung, C Robertson (A)   Salomé, Patrice A. (A)   Jamai, Aziz  (A)   Song, Hae-Ryong  (A)   Abernathey, Elizabeth J. (A)   Amato, Katherine R. (A)   Hacker, Kathryn E. (A)   Choi, Seung Hyuk  (A)
Affiliations:	(A): Dartmouth College
Web Site:	http://www.dartmouth.edu/~rmcclung/index.html

The TIMING OF CAB EXPRESSION 1 (TOC1, also known as PRR1 or APRR1) clock gene defines a small family of genes related to the response regulators of two-component signaling systems. Typically, a sensor histidine kinase autophosphorylates and that phosphate is transferred to a conserved Asp residue in the cognate response regulator, activating the response. Pseudo-Response Regulators (PRRs) lack this Asp and so are unlikely to participate in conventional phospho-relays, but nonetheless are thought to play signaling roles. Loss of function mutations of each of the five Arabidopsis PRR genes affect either circadian period or phase (Michael et al., Science 302:1049-1053, 2003), implicating them in input pathways by which environmental information is transmitted to the circadian clock. However, the phenotypes of the prr mutants are modest, except for the 3 hr period shortening and conditional arrhythmicity (in red light) associated with toc1/prr1 loss of function (Más et al., Plant Cell 15:223-236, 2003). prr3 and prr5 mutations shorten the period of the leaf movement rhythm during entrainment to light-dark but not to temperature cycles, implicating these genes in light input to the clock. In contrast, the long period of prr7 and lagging phase of prr9 mutants are seen during either light-dark or temperature entrainment, indicating roles in both light and temperature input pathways, or directly in oscillator function. These analyses are being extended to examine effects of the prr mutations on the clock itself through analysis of luciferase fusions driven by promoters of the clock component genes CCA1, LHY and TOC1/PRR1. GFP-tagged versions of the PRR proteins localize to the nucleus, consistent with roles in signal transduction and gene regulation. The modest phenotypes associated with these prr mutants suggest that PRR functions may be redundantly specified; this is being tested by analysis of double mutants. We are further testing whether the circadian clock contributes to evolutionary fitness. Considerable genetic variation at the PRR7 locus exists among natural accessions; three alleles are evident among a collection of 20 accessions. We are using molecular analysis of this sequence diversity to test whether this locus is evolving in a nonneutral fashion and whether PRR7 sequence variation is associated with differences in circadian function observed among natural accessions. This work is supported by grants (MCB-0091008 and 0343887) from the NSF to CRM.