Class I TCP-DELLA Interactions in Inflorescence Shoot Apex Determine Plant Height

Regulation of plant height, one of the most important agronomic traits, is the focus of intensive research for improving crop performance [1]. Stem elongation takes place as a result of repeated cell divisions and subsequent elongation of cells produced by apical and intercalary meristems. The gibberellin (GA) phytohormones have long been known to control stem and internodal elongation by stimulating the degradation of nuclear growth-repressing DELLA proteins; however, the mechanism allowing GA-responsive growth is only slowly emerging [2]. Here, we show that DELLAs directly regulate the activity of the plant-specific class I TCP transcription factor family, key regulators of cell proliferation [3]. Our results demonstrate that class I TCP factors directly bind the promoters of core cell-cycle genes in Arabidopsis inflorescence shoot apices while DELLAs block TCP function by binding to their DNA-recognition domain. GAs antagonize such repression by promoting DELLA destruction and therefore cause a concomitant accumulation of TCP factors on promoters of cell-cycle genes. Consistent with this model, the quadruple mutant tcp8 tcp14 tcp15 tcp22 exhibits severe dwarfism and reduced responsiveness to GA action. Altogether, we conclude that GA-regulated DELLA-TCP interactions in inflorescence shoot apex provide a novel mechanism to control plant height. •DELLA growth repressors restrain cell proliferation in inflorescence shoot apices•DELLA proteins physically interact with class I TCP transcription factors•DELLAs block the DNA-binding capacity of class I TCPs on cell-cycle gene promoters•The quadruple mutant tcp8 tcp14 tcp15 tcp22 exhibits severe dwarfism Davière et al. address how the nuclear growth-repressing DELLA proteins restrain plant height. They show that DELLAs interact with and block the ability of class I TCP transcription factors to bind promoters of core cell-cycle genes in Arabidopsis inflorescence shoot apices. In this way, DELLAs repress cell proliferation driving plant growth.