Shifting Routes: Plant-Specific Insert Trafficking and Function in Arabidopsis Seedlings Under Abiotic Stress

Cardosins A and B are aspartic proteinases found in cardoon that share high sequence similarity, accumulate in the vacuole, and are responsive to stress conditions. These proteins have a 100 amino acid domain termed Plant Specific Insert (PSI), responsible for their vacuolar targeting. Different PSIs mediate different routes to the vacuole: PSI from cardosin A mediates a Golgi-independent route, while PSI from cardosin B (PSI B) mediates a conventional ER-to-Golgi pathway. It is known that stress can impact protein sorting, shifting it from the conventional pathway to a Golgi-independent route. As such, in this work we investigated the expression and localization of PSI B in Arabidopsis plants overexpressing PSI B-mCherry submitted to different abiotic stress conditions (saline, hydric, oxidative and Zn). The results revealed that the plants expressing PSI B showed increased PSI B accumulation under saline stress but decreased accumulation under hydric stress. PSI B accumulation was detected in the vacuole, but also in Endoplasmic Reticulum-derived vesicles (ER bodies-rod-shaped or spindle-like compartments within the ER that store and transport proteins), indicating a shift from the conventional PSI B-mediated route. Altogether, these findings highlight the role of PSI B in promoting plant fitness and adaptation to abiotic stress by modulating protein trafficking.