Overexpression of Plant Specific Insert from Cardosin B (PSI B) in Arabidopsis Correlates with Cell Responses to Stresses

Under abiotic stress, several changes occur in plant cells both regarding their physiology and cellular and molecular mechanisms. These are reflected in cell division, growth and differentiation of new structures. Plants have developed sophisticated mechanisms to overcome stress conditions, specifically modifications in the production and trafficking of proteins, and remodelling of endomembranes. Cardosins A and B are aspartic proteinases present in the thistle flower that have emerged as model systems to study intracellular trafficking due to the presence of a 100 amino acid domain named Plant Specific Insert (PSI), that is able to mediate transport to the vacuole. It is known that stress situations can alter the targeting of proteins to the vacuole shifting their transport towards more unconventional, Golgi-independent, routes. Given that PSIs may mediate such routes, our goal was to evaluate if transgenic Arabidopsis plants overexpressing PSI B respond differently when subjected to different abiotic stresses (osmotic, oxidative, salt, and metal). We analyzed biometric parameters, the expression of PSIB by qRT-PCR and the localization of PSI B-mCherry, in seedlings grown under stress. The results obtained point to a differential expression of PSI B-mCherry depending on the type of stress. Confocal microscopy observations showed a higher accumulation of PSI B m-Cherry in vacuoles from plants under hydric stress and a decrease of cellular and cytoplasmatic movement in all stress situations. In summary, PSI B overexpression seems to be correlated with the stress response of plant cells, suggesting that it might mediate adaptation/defense mechanisms against adverse conditions.