Isolation and functional analysis of two CONSTANS-like 1 genes from mango

FLOWERING LOCUS T (FT) is a conserved promoter of flowering that acts downstream of various regulatory pathways, including one that mediates photoperiodic induction through CONSTANS (CO), and is expressed in the vasculature of cotyledons and leaves. A bZIP transcription factor, FD, preferentially expressed in the shoot apex is required for FT to promote flowering. FD and FT are interdependent partners through protein interaction and act at the shoot apex to promote floral transition and to initiate floral development through transcriptional activation of a floral meristem identity gene, APETALA1 (AP1). FT may represent a long-distance signal in flowering.

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 TIFY family is a novel plant-specific gene family involved in the regulation of diverse plant-specific biologic processes, such as development and responses to phytohormones, in Arabidopsis. However, there is limited information about this family in monocot species. This report identifies 20 TIFY genes in rice, the model monocot species. Sequence analysis indicated that rice TIFY proteins have conserved motifs beyond the TIFY domain as was previously shown in Arabidopsis. On the basis of their protein structures, members of the TIFY family can be divided into two groups. Transcript level analysis of OsTIFY genes in tissues and organs revealed different tempo-spatial expression patterns, suggesting that expression and function vary by stage of plant growth and development. Most of the OsTIFY genes were predominantly expressed in leaf. Nine OsTIFY genes were responsive to jasmonic acid and wounding treatments. Interestingly, almost all the OsTIFY genes were responsive to one or more abiotic stresses including drought, salinity, and low temperature. Over-expression of OsTIFY11a, one of the stress-inducible genes, resulted in significantly increased tolerance to salt and dehydration stresses. These results suggest that the OsTIFY family may have important roles in response to abiotic stresses. The data presented in this report provide important clues for further elucidating the functions of the genes in the OsTIFY family.