Pseudo-Response Regulator (PRR) Homologues of the Moss Physcomitrella patens: Insights into the Evolution of the PRR Family in Land Plants

The pseudo-response regulators (PRRs) are the circadian clock component proteins in the model dicot Arabidopsis thaliana. They contain a receiver-like domain (RLD) similar to the receiver domains of the RRs in the His–Asp phosphorelay system, but the RLDs lack the phosphoacceptor aspartic acid residue invariably conserved in the receiver domains. To study the evolution of PRR genes in plants, here we characterize their homologue genes, PpPRR1, PpPRR2, PpPRR3 and PpPRR4, from the moss Physcomitrella patens. In the phylogenetic analysis, PpPRRs cluster together, sister to an angiosperm PRR gene subfamily, illustrating their close relationships with the angiosperm PRRs. However, distinct from the angiosperm sequences, the RLDs of PpPRR2/3/4 exhibit a potential phosphoacceptor aspartic acid–aspartic acid–lysine (DDK) motif. Consistently, the PpPRR2 RLD had phosphotransfer ability in vitro, suggesting that PpPRR2 functions as an RR. The PpPRR1 RLD, on the other hand, shows a partially diverged DDK motif, and it did not show phosphotransfer ability. All PpPRRs were expressed in a circadian and light-dependent manner, with differential regulation between PpPRR2/4 and PpPRR1/3. Altogether, our results illustrate that PRRs originated from an RR(s) and that there are intraspecific divergences among PpPRRs. Finally, we offer scenarios for the evolution of the PRR family in land plants

Evolutionary relationships among barley and <i>Arabidopsis</i> core circadian clock and clock-associated genes

The circadian clock regulates a multitude of plant developmental and metabolic processes. In crop species, it contributes significantly to plant performance and productivity and to the adaptation and geographical range over which crops can be grown. To understand the clock in barley and how it relates to the components in the Arabidopsis thaliana clock, we have performed a systematic analysis of core circadian clock and clock-associated genes in barley, Arabidopsis and another eight species including tomato, potato, a range of monocotyledonous species and the moss, Physcomitrella patens. We have identified orthologues and paralogues of Arabidopsis genes which are conserved in all species, monocot/dicot differences, species-specific differences and variation in gene copy number (e.g. gene duplications among the various species). We propose that the common ancestor of barley and Arabidopsis had two-thirds of the key clock components identified in Arabidopsis prior to the separation of the monocot/dicot groups. After this separation, multiple independent gene duplication events took place in both monocot and dicot ancestors. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00239-015-9665-0) contains supplementary material, which is available to authorized users