Arabidopsis flippase ALA3 is required for adjustment of early subcellular trafficking in plant response to osmotic stress

To compensate for their sessile lifestyle, plants developed several responses to exogenous changes. One of the previously investigated and not yet fully understood adaptations occurs at the level of early subcellular trafficking, which needs to be rapidly adjusted to maintain cellular homeostasis and membrane integrity under osmotic stress conditions. To form a vesicle, the membrane needs to be deformed, which is ensured by multiple factors, including the activity of specific membrane proteins, such as flippases from the family of P4-ATPases. The membrane pumps actively translocate phospholipids from the exoplasmic/luminal to the cytoplasmic membrane leaflet to generate curvature, which might be coupled with recruitment of proteins involved in vesicle formation at specific sites of the donor membrane. We show that lack of the AMINOPHOSPHOLIPID ATPASE3 (ALA3) flippase activity caused defects at the plasma membrane and trans-Golgi network, resulting in altered endocytosis and secretion, processes relying on vesicle formation and movement. The mentioned cellular defects were translated into decreased intracellular trafficking flexibility failing to adjust the root growth on osmotic stress-eliciting media. In conclusion, we show that ALA3 cooperates with ARF-GEF BIG5/BEN1 and ARF1A1C/BEX1 in a similar regulatory pathway to vesicle formation, and together they are important for plant adaptation to osmotic stress. The interplay of P4-ATPase ALA3, ARF BEX1, and ARF-GEF BEN1 controls vesicle formation at the plasma membrane/trans -Golgi network and the subsequent vesicle trafficking important for the plant response to osmotic stress.

Automated summary

To compensate for their sessile lifestyle, plants have developed adaptations at the level of subcellular trafficking to maintain cellular homeostasis and membrane integrity under osmotic stress conditions. The activity of flippases, such as P4-ATPases, is crucial for the formation of vesicles, which are involved in processes like endocytosis and secretion. Lack of flippase activity leads to defects in membrane and Golgi network, resulting in impaired vesicle formation and movement, and decreased intracellular trafficking flexibility, thereby affecting plant adaptation to osmotic stress.