TET3-Mediated Demethylation in Tomato Activates Expression of a CETS Gene that Stimulates Vegetative Growth

Expression of the mammalian DNA demethylase enzyme TET3 in plants can be used to induce hypomethylation of DNA. In tomato lines that express a TET3 transgene, we observed distinct phenotypes including an increase in the length and number of leaves of primary shoots. As these changes resemble phenotypes observed in plants with strong expression of SELF PRUNING (SP), a member of the PEBP/CETS family, we investigated in TET3 lines the expression levels of members of the PEBP/CETS gene family, which affect shoot architecture and growth of sympodial units in tomato. We did not detect any changes in SP expression in TET3 lines, but for CEN1.1, a putative family member that has not been functionally characterized, we identified changes in gene expression that corresponded to hypomethylation in the upstream region. In tomato wild type, CEN1.1 is expressed in roots, petals, and shoot apices but not in mature leaves. In contrast, in TET3 transformants, the CEN1.1 gene became hypomethylated and activated in leaves. Ectopic expression of CEN1.1 in tomato caused similar phenotypes to those seen in TET3 transformants. Vegetative growth was increased, resulting both in a delay in inflorescence development and in an instability of the inflorescences, which frequently reverted to a vegetative state. Ectopic expression of CEN1.1 in Arabidopsis thaliana also caused floral repression. Our data suggest that the phenotypes observed in TET3 lines are a consequence of ectopic activation of CEN1.1, which promotes vegetative growth, and that CEN1.1 expression is sensitive to DNA methylation changes.