PRR5

PRR5, or pseudo-response regulator 5, is a gene in plants, most prominently studied in Arabidopsis thaliana. It encodes a member of the pseudo-response regulator (PRR) family, which also includes PRR3, PRR7, PRR9 and TOC1 (PRR1). PRR proteins are nuclear-localized transcriptional regulators that contribute to the plant circadian clock, helping to coordinate daily rhythms in physiology and development.

In the circadian network, PRR5 is expressed in the late day to evening and functions as a transcriptional repressor. It acts within a sequentially expressed set of PRR proteins that create a robust clock by repressing morning-phased genes, such as CCA1 and LHY, as the day progresses. This regulatory cascade establishes and maintains the approximately 24-hour rhythm that aligns internal processes with environmental light cues.

PRR5 activity is modulated by light and other environmental signals, and the protein interacts with other clock components to fine-tune the timing of gene expression. The PRR family’s characteristic structure includes a receiver-like domain, but PRR proteins are considered pseudo-receivers because they lack a conserved phosphorylation site, distinguishing them from canonical response regulators.

Biological significance of PRR5 includes its contribution to entrainment of the circadian clock to photoperiod, regulation of downstream light- and clock-controlled genes, and effects on flowering time and other date-of-day–dependent processes. Mutant or altered-expression lines can display changes in circadian period or rhythmic amplitude, highlighting PRR5’s role in temporal regulation of plant physiology.