How SFR2 is regulated to confer freezing tolerance of the chloroplast envelope membrane

Internal cellular membranes must have their lipid composition remodeled for plants to survive low temperatures. One mechanism necessary for freezing tolerance of the chloroplast envelope membranes is well defined. An enzyme named “Sensitive to Freezing 2” (SFR2) changes monogalactolipid into oligogalactolipids at temperatures below freezing. Interestingly, SFR2 activity does not respond to initial cool temperatures, it only responds to barely tolerable freezing temperatures. Here, we show that SFR2 is post‐translationally regulated by modifications and changes to cytosolic acidification. We show that freezing increases cytosolic acidification and that proton pumps at both the plasma and vacuolar membranes participate in maintaining the acidification during low temperatures. Finally, quantitative measurements of SFR2’s product in a large number of plant species with diverse phylogenetic backgrounds shows that SFR2 is likely responding to membrane damage in some, if not all species. We conclude that plant low temperature sensing and response is likely a continuum rather than a switch, and that internal cellular membranes have systems set up to respond to damage in a diverse set of abiotic stresses.