Arabidopsis defective in the phospholipid:sterol acyltransferase (AtPSAT) is chilling sensitive

A gene encoding a sterol ester synthesizing enzyme was identified in Arabidopsis. The gene belongs to the LCAT/PDAT family and is the only intracellular enzyme so far found which catalyzes an acyl CoA-independent sterol ester formation. It catalyzes a transacylation of acyl groups from phospholipids to sterols. When this gene was knocked out the content of sterol esters were reduced by about 70% in the plant tissue. No difference in the phenotype between the AtPSAT knock out plants and their null segregants was detected at room temperature. However, when the plants were subjected to 2 or 6 degree Celsius, older leaves of the knockout plants started to die off. Signs of this were visible already after 2 – 3 weeks in the 6 degree Celsius and later in the 2 degree treatment. The results presented implicate a role for AtPSAT in regulating both the amount and the quality of the free sterols in the membrane. They also suggest an involvement of AtPSAT in plant cold resistance