In nature, plants must adapt their development to multiple environmental challenges involving numerous plant pathogens and suboptimal growth conditions related to drought, heat or salinity, among the most prevalent. Plant survival to these challenges is associated with significant changes in post-translational modifications (PTMs) of plant proteins. PTMs are among the earliest and most rapid plant responses to changes in the environment and trigger downstream molecular and cellular responses influencing plant growth and survival in a precise and timely manner. PTMs, either constitutive or reversible, determine the function of proteins and expand the diversity of the cellular proteome. PTMs induce changes in protein activity, turnover, subcellular localization, and interactions with other molecules, enabling a fine-tuning of cellular responses.
SUMO (Small Ubiquitin-like MOdifer) is an essential PTM belonging to the Ubl family of modifiers. In plants, SUMO regulates multiple biological processes, ranging from development to responses arising from environmental challenges. This biological versatility of plant SUMOylation offers novel opportunities for improving agricultural productivity. SUMO modulates protein activity through regulation of subcellular localization, protein activity and stability, and protein-protein interactions. Several studies point to a nuclear enrichment of SUMO conjugation machinery, which is consistent with a preferential nuclear localization of the SUMO targets. Nonetheless, non–nuclear targets exist and the molecular mechanisms that mediate their modification remain elusive. Dr Lois’s group has uncovered a novel regulatory mechanism consisting of the processing of the C-terminus of the SUMO E1-activating enzyme large subunit, SAE2. Processed SAE2 partially localizes to the cytosol and the processing activity is prominent at the transition between embryo growth and seed maturation. Accumulation of SAE2 in the cytosol promotes cytosolic SUMOylation and behave as a signal for growth arrest, suggesting that SAE2 processing could contribute to finalizing embryogenesis. SUMOCell aims to uncover the signals that trigger SAE2 cytosolic localization and the cellular responses activated by cytosolic SUMOylation. First, with Duke University partner, we will study SAE2 subcellular dynamics using super-resolution microscopy, under hormone treatments and stress challenges. Second, we will study the physiological processes regulated by SAE2 localization to the cytosol. For that, we will perform single-cell RNAseq studies from cells enriched in cytosolic SAE2. Bioinformatics analysis will be carried out by a placement at Sequentia SL. Finally, we will analyse physiological parameters related to seed quality. Data obtained from cell studies, transcriptomics and seed performance will be integrated in a signalling model to understand the role of cytosolic SUMO conjugation in seed development, providing a multidisciplinar training program.
