Characterization of <i>Arabidopsis</i> sterol glycosyltransferase <i>TTG15/UGT80B1</i> role during freeze and heat stress

Sterol glycosyltransferases regulate the properties of sterols by catalyzing the transfer of carbohydrate molecules to the sterol moiety for the synthesis of steryl glycosides and acyl steryl glycosides. We have analyzed the functional role of <i>TTG15/UGT80B1</i> gene of <i>Arabidopsis thaliana</i> in freeze/thaw and heat shock stress using T-DNA insertional <i>sgt</i> knockout mutants. Quantitative study of spatial as well as temporal gene expression showed tissue-specific and dynamic expression patterns throughout the growth stages. Comparative responses of Col-0, <i>TTG15/UGT80B1</i> knockout mutant and <i>p</i>35<i>S</i>:<i>TTG15/UGT80B1</i> restored lines were analyzed under heat and freeze stress conditions. Heat tolerance was determined by survival of plants at 42°C for 3 h, MDA analysis and chlorophyll fluorescence image (CFI) analysis. Freezing tolerance was determined by survival of the plants at -1°C temperature in non-acclimatized (NA) and cold acclimatized (CA) conditions and also by CFI analysis, which revealed that, <i>p</i>35S:<i>TTG15/UGT80B1</i> restored plants were more adapted to freeze stress than <i>TTG15/UGT80B1</i> knockout mutant under CA condition. HPLC analysis of the plants showed reduced sterol glycoside in mutant seedlings as compared to other genotypes. Following CA condition, both β-sitosterol and sitosterol glycoside quantity was more in Col-0 and <i>p</i>35<i>S</i>:<i>TTG15/UGT80B1</i> restored lines, whereas it was significantly less in <i>TTG15/UGT80B1</i> knockout mutants. From these results, it may be concluded that due to low content of free sterols and sterol glycosides, the physiology of mutant plants was more affected during both, the chilling and heat stress.