PRR9

PRR9, short for Pseudo-Response Regulator 9, is a gene in plants, most notably Arabidopsis thaliana, that encodes a member of the pseudo‑response regulator (PRR) family. This family includes several clock-related genes such as TOC1/PRR1, PRR3, PRR5, and PRR7, which together contribute to the plant circadian clock and daily rhythms of gene expression.

Function and role in the clock PRR9 acts as a transcriptional regulator within the plant circadian network. It is expressed after dawn and participates in the sequential, somewhat overlapping wave of PRR gene expression that helps shape the timing of downstream clock outputs. PRR9 helps repress morning-phased genes during the day, allowing the clock to progress toward evening, and it interacts genetically with other PRR family members to stabilize rhythmicity.

Expression and regulation PRR9 expression is regulated by core clock components and environmental cues such as light. In wild-type plants, its transcript levels rise after dawn, peak in the afternoon, and decline toward evening. This pattern contributes to the overall periodicity of the clock and the proper alignment of physiological processes with the day-night cycle.

Genetic and phenotypic effects Mutations that reduce PRR9 function can alter circadian period length and disrupt normal rhythmic gene expression. PRR9 often acts redundantly with closely related PRR genes; combined mutations can have stronger effects, underscoring a networked, compensatory architecture within the clock. PRR9 also influences photoperiodic responses and flowering time in some contexts.

Structure and evolution The PRR9 protein is predicted to contain an N-terminal receiver-like domain characteristic of the PRR family, with regions that mediate protein–protein interactions. PRR9 has conserved homologs across plant species, reflecting its role in the conserved plant circadian machinery.

See also: circadian rhythm, plant clock, PRR gene family.