DELLA proteins as hubs in signaling networks in plants

Laburpena

As sessile organism plants are extremely plastic. This feature is due their ability to integrate external and internal signals to modulate development. Therefore, understand the molecular mechanism underlying this feature is of great importance. Signals such as light, hormones and the circadian clock contribute to this plasticity. During this Thesis we use the plant model Arabidopsis thaliana to address how the circadian clock and the DELLA proteins, negative regulators of the gibberellin (GA) signaling integrate environmental signals and relay this information to transcriptional networks. We have demonstrated that the circadian clock modulate transcriptional levels of the GAs receptors GIDs, which promote the degradation of DELLA proteins, this result in a daily oscillation of DELLA proteins, which reach a minimum at the end of the night. This oscillation is key to modulate hypocotyl rhythmic growth and to control transcription of many genes. In this Thesis we present mechanisms of cross-talk among GAs and two plant hormones; ethylene and cytokinin. These mechanisms of cross-talk relies on the interaction between DELLA proteins and two transcriptional factors involved in signaling of these two hormones. The interaction with RAP2.3, prevents the transcription factor activity, this inactivation contributes to the regulation of apical hook opening by ethylene and GAs. On the contrary, the interaction with ARR1, a transcription factor that promotes cytokinin signaling, is positive for the activity of ARR1, thus contributing to the regulation of some developmental processes which are antagonistically regulated by GAs and cytokinin, for example root growth and photomorphogenesis. This interaction defines a new mechanism of DELLAs action. Additionally, by chromatin immunoprecipitation followed by massive sequencing, allowed us to show that DELLA proteins are near the promoter of many genes, this indicated that this mechanism is broad extensive. Based in these results an in the identification of more than 50 transcription factors as interactors of the DELLA GAI, we propose that DELLAs act as ¿hubs¿ in signaling networks. In particular we propose that this is the mechanism by which these proteins are key for the integration of internal signals and developmental processes.