Genes of the circadian oscillator in Arabidopsis thaliana and homologs in other plant species discussed in this review. Ostreococcus tauri contains single homologs of CCA1 and TOC1, respectively . The PRR ortholog PPD, most similar to PRR7, in Hordeum vulgare (PPDH1)  and Triticum aestivum (PPDA1, PPDB1 and PPDD1, designated after the location they derive from)  is important for flowering time control. The PRR7-like BvBTC1 in beet (Beta vulgaris) regulates bolting time . Hordeum vulgare contains an ELF3 ortholog, EAM8 . Brassica rapa retains a suite of clock genes after polyploidization and subsequent gene loss .
Staiger et al. Genome Biology 2013 14:208 doi:10.1186/gb-2013-14-6-208