| Circadian clock has been found to play important roles in plant growth and development. TOC1 was firstly isolated from Arabidopsis and its central role in plant circadian clock has been determined. Here three TOC1 homologs were isolated from hexaploid wheat. They were mapped in wheat chromosome 6A, 6B and 6D, respectively, and designated as TaTOC1-A, TaTOC1-B and TaTOC1-D. They were highly similar to each other and all harbored six exons and five introns. In addition, three putative protein sequences also showed somewhat similarity with Arabidopsis TOC1 and Rice OsTOC1, especially at two conserved domains, pseudo-receiver domain and CCT (CONSTANS, CONSTANS LIKE and TIMING OF CAB EXPRESSION 1) domain. It was presumed that recombination between A and B genome of TOC1 orthologs might have occurred going with the evolution of wheat by comparing sequences of TaTOC1-A, TaTOC1-B and TaTOC1-D with their orthlogs in ancestral species of wheat.The results of real-time quantitative RT-PCR experiment indicated that the transcripts of TaTOC1-A, TaTOC1-B and TaTOC1-D could be detected in all organs of wheat studied, and the expression level of each gene differed depending on the organ kinds and development stages. Meanwhile, daily oscillation of TaTOC1-A, TaTOC1-B and TaTOC1-D mRNA abundances was regulated by long-day, short-day and even continuous light conditions; whereas overall downregulation and no apparent rhythmicity of their transcripts were observed under continuous dark conditions. By analysis of upstream sequences of TaTOC1-A, TaTOC1-B and TaTOC1-D, it was shown that there were some corresponding motifs, such as the EE for rhythmicity, the MYB binding site and the light responsive elements in these regions. Interestingly, expression of TaTOC1-D, but not TaTOC1-A or TaTOC1-B, was significantly upregulated in aneuploid line N6BT6A. It was suggested that TaTOC1-D may be a target gene of TaMIR408. The mRNA abundance of TaMIR408, the precursor of TaMIR408, also oscillated. |
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