The ubiquitin/26S proteasome pathway in the integration of developmental signals at the plant shoot apical meristem

Ubiquitin-mediated degradation of regulatory proteins controls key events in plant development and response to the environment. Within the framework of a Scientific and Technological Cooperation between Italy and China (MAE-MIUR) we are investigating the involvement of ubiquitin-mediated proteolysis in the integration of developmental and environmental signals exerted by Knotted1-like homeobox (KNOX) and NAM/ATAF/CUC (NAC) domain transcription factors at the plant shoot apex. KNOXs and NACs play a key role in establishing the fine equilibrium between cell differentiation and stem cell maintenance in the shoot apical meristem (SAM), a population of undifferentiated cells at the tip of the shoot axis that establishes early during plant embryogenesis and gives rise to all shoot organs throughout the plant's life. We produced transgenic Arabidopsis lines with constitutive or inducible alteration of the activity of a generic E2 UPS component and analyzed the effect on SAM function. In silico gene expression analysis and protein-protein interaction studies identified E2 and E3 enzymes putatively involved in the developmental pathways controlled by KNOX and NAC transcription factors.