PRR5PRR5L

PRR5PRR5L is a designation used in plant genomics to refer to the pair of genes PRR5 and the PRR5-like gene (PRR5L), both members of the pseudo-response regulator (PRR) family that participate in the plant circadian clock. PRR genes act as transcriptional repressors that accumulate in a daily rhythm and help shape the timing and output of clock signals.

Proteins in the PRR family typically contain a conserved receiver-like domain and a CCT-related domain, but PRR proteins are considered pseudo-receivers because they lack key phosphorylation residues. PRR5 and PRR5L share substantial sequence similarity and are thought to have arisen through gene duplication. They are expressed in a diurnal pattern, often peaking in the afternoon, and function to repress morning-phased genes, contributing to the proper sequencing of clock outputs. Through their regulatory interactions, they help modulate the expression of core clock components such as CCA1, LHY, and TOC1, helping to maintain a ~24-hour cycle.

In many species, including Arabidopsis thaliana and related plants, both PRR5 and PRR5L are present and may have overlapping or partially redundant roles. In some genome annotations, the PRR5 and PRR5L loci are labeled as PRR5-PRR5L due to close proximity or a readthrough annotation, while in other annotations they are identified as separate genes. The PRR5-PRR5L pair is considered part of the broader PRR gene family that stabilizes circadian timing and influences downstream processes such as flowering time and metabolism.