Shifting Routes: Plant Specific Insert trafficking and function in Arabidopsis seedlings under abiotic stress

Due to plants' inability to escape adverse conditions, they must adapt and adjust their endomembrane system through protein sorting and distribution. Cardosins A and B are key models for studying intracellular trafficking. They are aspartic proteinases in thistle flowers that mediate different vacuolar pathways despite sharing high sequence similarity, and both are responsive to stress conditions. The Plant Specific Insert (PSI) is a 100 amino acid domain found in these proteins. It is known that stress can impact protein sorting, shifting it from the conventional pathway (ER-Golgi) to a Golgi-independent route. In this work we assessed changes in the expression and localization of PSI from Cardosin B (PSI B) in Arabidopsis plants overexpressing PSI B-mCherry submitted to different abiotic stress conditions (saline, hydric, oxidative, metals). Aside from potential PSI B localization changes, we focused on characterizing the homozygous line, alongside assessing several biometric parameters and biochemical endpoints. The results revealed that the PSI B line responded differently depending on the stress conditions. Biometric and biochemical analyses emphasized the roles of PSI B in enhancing plant fitness and supporting adaptation to abiotic stress. Besides, confocal microscopy allowed us to find PSI B accumulation in Endoplasmic Reticulum-derived vesicles (ER bodies), indicating a shift from the common PSI B-mediated route. These findings underscore the role of PSI B in enhancing plant fitness and adaptation to abiotic stress through altered protein trafficking.