The Evolution of CONSTANS-Like Gene Families in Barley, Rice, and Arabidopsis

Abstract

The CO (CONSTANS) gene of Arabidopsis has an important role in the regulation of flowering by photoperiod. CO is part of a gene family with 17 members that are subdivided into three classes, termed Group I to III here. All members of the family have a CCT (CO, CO-like, TOC1) domain near the carboxy terminus. Group I genes, which include CO, have two zinc finger B-boxes near the amino terminus. Group II genes have one B-box, and Group III genes have one B-box and a second diverged zinc finger. Analysis of rice (Oryza sativa) genomic sequence identified 16 genes (OsA-OsP) that were also divided into these three groups, showing that their evolution predates monocot/dicot divergence. Eight Group I genes (HvCO1-HvCO8) were isolated from barley (Hordeum vulgare), of which two (HvCO1 and HvCO2) were highly CO like. HvCO3 and its rice counterpart (OsB) had one B-box that was distantly related to Group II genes and was probably derived by internal deletion of a two B-box Group I gene. Sequence homology and comparative mapping showed that HvCO1 was the counterpart of OsA (Hd1), a major determinant of photoperiod sensitivity in rice. Major genes determining photoperiod response have been mapped in barley and wheat (Triticum aestivum), but none corresponded to CO-like genes. Thus, selection for variation in photoperiod response has affected different genes in rice and temperate cereals. The peptides of HvCO1, HvCO2 (barley), and Hd1 (rice) show significant structural differences from CO, particularly amino acid changes that are predicted to abolish B-box2 function, suggesting an evolutionary trend toward a one-B-box structure in the most CO-like cereal genes.The control of flowering by photoperiod is an important adaptive characteristic in plants. Studies of the model dicot Arabidopsis have shown that the CO (CONSTANS) gene, isolated by Putterill et al. (1995), has an important role in the photoperiod pathway, which is one of four regulatory pathways controlling the timing of flowering (for review, see Mouradov et al., 2002;Simpson and Dean, 2002). CO acts between the circadian clock and genes controlling meristem identity (Samach et al., 2000;Suárez-Ló pez et al., 2001). In Arabidopsis, CO belongs to a family of 17 putative transcription factors defined by two conserved domains (Putterill et al., 1995;Robson et al., 2001). The first is a zinc finger region near the amino terminus that resembles B-boxes, which regulate protein-protein interactions in several animal transcription factors (Borden, 1998;Torok and Elkin, 2000). The second is a region of 43 amino acids near the carboxy terminus termed the CCT (CO, CO-like, TOC1) domain (Strayer et al., 2000;Robson et al., 2001). Studies using green fluorescent protein fusions show that the CCT domain is involved in nuclear localization of the CO protein but must have an additional role because the late-flowering co-7 mutant, which has an altered CCT domain, correctly localizes the protein .Previous analysis of CO-like genes in Arabidopsis showed that the family is subdivided int...

An extensive microarray analysis of AAL-toxin-induced cell death in Arabidopsis thaliana brings new insights into the complexity of programmed cell death in plants

“…Equally unclear is the link between the CONSTANS family of transcription factors and PCD. The CONSTANS genes in Arabidopsis have an important role in the regulation of flowering by photoperiod [39,40]. A recent analysis of H 2 O 2 -induced cell death gene expression in tobacco also identified WRKY, NAM and MYB transcription factors as among the earliest genes induced [41].…”

Molecular characterization of the allelic variation at the VRN-H2 vernalization locus in barley

“…Comparison of the CCT domains of these three sequences with the CCT domains from other grass genes (Griffiths et al 2003) demonstrated that ZCCT-Hc belongs to the ZCCT group ( Figure 5). Inclusion of ZCCT-Hc within the ZCCT cluster was confirmed using alternative clustering methods (Kumar et al 2001): UPGMA ( Figure 5), Neighbor Joining, Minimum Evolution and Maximum parsimony (data not shown).…”

“…In barley, within the dominant Vrn-H1 class, we found no significant differences in flowering time between the plants carrying the recessive vrn-H2 or the dominant Vrn-H2 alleles. On the (Griffiths et al 2003). Os = Oryza sativa, Hv = Hordeum vulgare, Tm = Triticum monococcum.…”

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