RESEARCH SUMMARY

Ubiquitin conjugation to proteins is mediated by an enzymatic cascade in which E3 ubiquitin ligase enzymes provide substrate specificity. Proteins labeled with ubiquitin chains usually undergo degradation via the proteasome, although ubiquitination can also modify protein function by altering their subcellular localization, assembly into complexes or enzymatic activity.

The potential regulatory relevance of the ubiquitin pathway in plants can be realized by the fact that proteins corresponding to the ubiquitination machinery comprise 5% of the Arabidopsis proteome. Indeed, protein ubiquitination affects many key aspects of plant biology, including phytohormone synthesis and signaling, floral organ formation and transition, defence against pathogens and adaptive responses to numerous abiotic stresses.

In agreement to such regulatory potential, the number of E3 ubiquitin ligases and targets reported in the control of specific plant biological processes increases at high rate. This trend is parallel to that observed in other eukaryotic organisms in which ubiquitination is conserved. However, our knowledge on the molecular mechanisms that regulate function of the ubiquitination machinery and allow a coordinated response to different environmental stimuli and stress conditions is still limited, especially in the case of plant systems.

Despite this, several mechanisms controlling E3 activity have been reported, many of them conserved through eukaryotes, such as control of the assembly of Cullin-RING E3 ligases by neddylation/deneddylation cycles or regulation of the subcellular localization of E3 components, such as DDB1. The latter is part of protein complexes involved in chromatin signalling and DNA-damage repair, including several CUL4-RING ubiquitin ligases and ubiquitination-associated complexes.

The aim of our research is to contribute to the characterization of the molecular mechanisms that regulate the ubiquitination machinery in the control of plant development and stress responses, such as drought, high temperatures, salinity and UV radiation, associated with climate change events.