Role of TCP transcription factors in seedling development leaf morphogenesis and senescence in Arabidopsis thaliana

Abstract

The TCP gene family encodes non-canonical bHLH transcription factors that act as key regulatory molecules in diverse developmental processes in plants including organ morphogenesis, plant architecture, leaf maturation, and flowering transition. In this study, we assign a number of new functions to the CINCINNATA-like TCP (CIN-TCP) proteins throughout the life of Arabidopsis thaliana starting from light-mediated seedling morphogenesis, regulation of simple leaf architecture, and hormone homeostasis during leaf senescence. PART-I: Role of TCP transcription factors in light-mediated Arabidopsis seedling development Plant growth and morphogenesis rely heavily on the coordination between external and internal cues to cope with the ever-changing surroundings. In Arabidopsis seedlings grown under low light intensity, the embryonic stem (hypocotyl) elongates more in an attempt to reach the light source, a process called skotomorphogenesis. By contrast, seedlings grown under sufficient light grow shorter (photomorphogenesis). We had earlier shown that the CIN-TCPs promote cell elongation during photomorphogenesis. Here we show that this effect of CIN-TCPs is abolished in darkness, suggesting that CIN-TCP-mediated cell elongation is dependent on the light-signaling pathway. By analyzing hypocotyl elongation under various light qualities, we show that TCP4-mediated hypocotyl cell elongation is dependent on phytochrome B (PhyB) photoreceptor under diverse light conditions. Using various biochemical and genetic assays, we demonstrate that TCP4 activation leads to the stabilization of several phytochrome-interacting factor (PIF) proteins through protein-protein interaction. Enhanced PIF level leads to the destabilization of PhyB and indirectly represses the HFR1 protein to promote hypocotyl elongation. Thus, CIN-TCP functions as a major negative regulator of photomorphogenic seedling growth together with PIF...