Roles of Arabidopsis PSEUDO-RESPONSE REGULATOR (PRR) genes in the opposite controls of flowering time and organ elongation under long-day and continuous light conditions

Abstract

The circadian clock regulates a wide variety of processes including the control of photoperiodic flowering and organ elongation in higher plants. Arabidopsis is a facultative long-day (LD) plant and flowers much earlier under LD and continuous light (LL) than short-day (SD) conditions. Although many of the genes required for the control of photoperiodic flowering have been identified, the precise mechanisms underlying the recognition of critical day or night lengths required for photoperiodic responses have not been fully clarified. To address this issue, we investigated circadian outputs in the loss- of-function of PSEUDO-RESPONSE REGULATOR (PRR) genes, which are believed to be clock components, under LD and LL. Here we report that prr9 flowered earlier under LL but later under LD compared to wild-type plants, which showed an opposite control of flowering response under these conditions. Although flowering times under LD and LL were similar, prr9;prr7;prr5 mutant plants showed an opposite control of petiole elongation under LD and LL. Under LL, the prr9;prr7;prr5 mutant plants had shorter petioles but longer hypocotyls than those of wild-type plants. Based on our results, we propose some models to explain the organ-specific effect caused by mutations in Arabidopsis clock genes.