Plants have evolved a sophisticated internal timing system—the circadian clock—to adapt to the diurnal and seasonal changes of light and temperature. This system enables plants to maintain a dynamic balance between growth and defense responses. Pseudo-Response Regulators (PRRs) are central components of the core oscillator in plant circadian clock, and play vital roles in regulating circadian rhythms, photoperiod-induced flowering, and abiotic stress responses. Systematic characterization of the PRR gene family will deepen our understanding of the molecular mechanisms underlying circadian clock regulation in plants and provide theoretical insights for improving crop agronomic traits such as stress tolerance and yield.

PRR proteins typically contain a relatively conserved N-terminal PR domain and a C-terminal CCT domain. Based on phylogenetic analyses, PRR family members are classified into three subclades: TOC1/PRR1, PRR7/3 and PRR9/5. Although PRRs have been identified in rice, wheat, barley, sorghum, and soybean, researches on the molecular mechanisms of PRRs in regulating plant circadian clock have been conducted primarily in Arabidopsis. The core circadian clock oscillator is composed of interconnected morning, central and evening feedback loops, with PRRs serving as key regulators. Studies have demonstrated that PRRs play crucial roles in regulating plant developmental processes spanning from seed germination, hypocotyl elongation to flowering time. In addition, PRRs also modulate plant responses to various abiotic stresses such as drought, cold, and salinity. Recent studies in wheat, rice and soybean have provided crucial theoretical foundations for crop genetic improvement. For example, TaPRR95 in wheat functions as a negative regulator of flowering and thus represents a promising genetic target for enhancing wheat yield. Similarly, GmPRR3b from soybean negatively regulates drought response, offering a novel candidate gene for breeding stress-tolerant crops.

Although progress has been made in PRRs research, several questions remain elusive. First, the functional conservation and diversification of PRRs in plant species beyond Arabidopsis requires systematic investigation. Second, the biological functions, regulatory networks, and potential applications of PRRs in plant biotic stress responses remain unclear. Third, the upstream regulators and downstream components of PRR-regulated pathways have not been fully characterized.

Future research should focus on three directions: Elucidating the functional conservation and species-specific roles of PRRs across diverse plant species; utilizing gene editing technologies to precisely manipulate PRR expression and evaluate their potential applications for breeding stress-resistant crops; characterizing the core functions and regulatory mechanisms of PRRs in plant biotic stress responses to expand our understanding of PRRs functions.