Genome-Wide Identification and Expression Analysis of Pseudo-Response Regulators (PRRs) in the Tea Plant Camellia sinensis (L.) O. Kuntze

The circadian clock plays a vital role in facilitating plant adaptation to rhythmically changing environmental factors. Pseudo-response regulators (PRRs) are key components regulating the plant circadian clock and have been extensively characterized in model plants. However, the PRRs in the tea plant have not been comprehensively studied. In this study, seven CsPRRs were cloned from the tea plant. Domain, phylogenetic evolution, gene structure, motifs, and cis-acting element analysis revealed their sequence characters and suggested that the first subgroup members, CsPRR1a, 1b, 5a, 5b, 7, and 37, may be responsible for circadian rhythm regulation and abiotic stress responses, while the second subgroup member, CsPRR2, may be involved in development and chloroplast function regulation. Most CsPRRs showed relatively higher expression in flowers, implying their potential roles in photoperiod-regulated flower induction. Moreover, rhythmic expression of CsPRR7, 5b, 5a, 37, 1b, and 1a was observed under long-day conditions in a sequential manner. Additionally, CsPRRs were differently induced/inhibited by cold, heat, and drought stresses in tissue-specific and photoperiod-related manners. A stronger cold induction of CsPRRs was observed under long-day conditions than under short-day conditions. And, among the two tested tissues, changes in the expression of CsPRRs caused by various stresses were more obvious in young shoots. Studies using a floriferous cultivar (FDDB) and an oliganthous cultivar (PYTZ) implied that CsPRRs also played crucial roles in tea-plant flower induction. This study presents the first comprehensive analysis of CsPRRs in the tea plant, providing vital information for further elucidation of CsPRR functions. It also suggests that tissue type and photoperiod conditions should be taken into consideration when conducting gene function studies in the tea plant.