Class I TCPs modulate cytokinin-induced branching and meristematic activity in tomato.

Arabidopsis TCPs are a family of basic helix loop helix (bHLH)-type transcription factors. Previous studies suggested that antagonistic activities of class I TCPs and class II TCPs are correlated with cell proliferation. We have recently shown that the class I TCPs AtTCP14 and AtTCP15 promote typical cytokinin (CK) responses in Arabidopsis, and proposed that they mediate the effect of CK on cell divisions. To further study the role of AtTCP14 and AtTCP15 in plant development, we expressed them in tomato plants. AtTCP14 and AtTCP15-expressing tomato plants were semi-dwarf, had a reduced apical dominance and developed ectopic meristems on leaflet petioles. CK application to tomato seedlings promoted axillary bud outgrowth and this effect was enhanced in the transgenic AtTCP14 and AtTCP15 overexpressing plants. The results of this study extend our previous suggestion that AtTCP14 and AtTCP15 modulate the plant sensitivity to CK.