The evolution and function of the PSEUDO RESPONSE REGULATOR gene family in the plant circadian clock

Abstract

PSEUDO-RESPONSE PROTEINS (PRRs) are a gene family vital for the generation of rhythms by the circadian clock. Plants have circadian clocks, or circadian oscillators, to adapt to a rhythmic environment. The circadian clock system can be divided into three parts: the core oscillator, the input pathways, and the output pathways. The PRRs have a role in all three parts. These nuclear proteins have an N-terminal pseudo receiver domain and a C-terminal CONSTANS, CONSTANS-LIKE, and TOC1 (CCT) domain. The PRRs can be identified from green algae to monocots, ranging from one to >5 genes per species. Arabidopsis thaliana, for example, has five genes: PRR9, PRR7, PRR5, PRR3 and TOC1/PRR1. The PRR genes can be divided into three clades using protein homology: TOC1/PRR1, PRR7/3, and PRR9/5 expanded independently in eudicots and monocots. The PRRs can make protein complexes and bind to DNA, and the wide variety of protein-protein interactions are essential for the multiple roles in the circadian clock. In this review, the history of PRR research is briefly recapitulated, and the diversity of PRR genes in green and recent works about their role in the circadian clock are discussed.

The Roles of the PSEUDO-RESPONSE REGULATORs in Circadian Clock and Flowering Time in Medicago truncatula

“…Our study showed that MtPRRs can be grouped into the PRR5/9 clade, PRR3/7 clade, and TOC1 clade, which is highly conserved in many species, such as Arabidopsis, rice, Brassica rapa, and rose [18,54,55]. According to the previous study, there are five members of clock PRR genes in Arabidopsis thaliana, Sorghum bicolour, and Oryza sativa, all including one TOC1/PRR1 member gene, two genes in the PRR5/9 clade, and two genes in the PRR3/7 clade [41,56]. However, seven PRR genes were shown in the Medicago truncatula genome, including two genes in the TOC1/PRR1 clade, three members in the PRR5/9 clade, and two PRR3/7 members.…”

“…However, seven PRR genes were shown in the Medicago truncatula genome, including two genes in the TOC1/PRR1 clade, three members in the PRR5/9 clade, and two PRR3/7 members. This is mainly because PRRs were expanded in M. truncatula during evolution, and the duplication event tends to happen in the TOC1/PRR1 clade and PRR5/9 clade, which is also seen in the PRR family of Populus trichocarpa and Vitis vinifera [56]. Like the PRR proteins in Arabidopsis, rice, sorghum, and other plants, the PRRs in M. truncatula are also nuclear-localized with an N-terminal PR domain followed by the C-terminal CCT motif, and the structure and location similarity imply their potential functional conservation in monocot and dicot species.…”

“…According to the previous study, PRRs also act by forming protein complexes [49,54,56,57]. To verify the conservation of regulatory mechanism, protein interactions among MtPRRs were performed.…”

Loss of daylength sensitivity by splice site mutation in Cannabis

“…Photoperiod insensitive genotypes of cannabis were found to contain a splice site mutation in CsPRR37. CsPRR37 is homologous to other PRR family genes within the PRR3/7 clade (Hotta et al, 2022), many of which have been confirmed as bona fide timekeepers such as PRR7 in Arabidopsis , and PRR37 in rice. CsPRR37 contains both PR and CCT domains which are signature features of pseudo-response regulators.…”