HEAT INDUCIBLE LIPASE1 Remodels Chloroplastic
Monogalactosyldiacylglycerol by Liberating α-Linolenic Acid in
Arabidopsis Leaves under Heat Stress
Journal: Plant Cell Impact factor: 9.618 Published date: 2018
Published by: Kanagawa Sustainable Resources Science Center, Japan
Under heat stress, polyunsaturated acyl groups, such as α-linolenate (18:3) and hexadecatrienoate (16:3), are removed from chloroplastic glycerolipids in various plant species.
Here, we showed that a lipase designated HEAT INDUCIBLE LIPASE1 (HIL1) induces the catabolism of monogalactosyldiacylglycerol (MGDG) under heat stress in Arabidopsis thaliana leaves. Using thermotolerance tests, a T-DNA insertion mutant with disrupted HIL1 was shown to have a heat stress-sensitive phenotype. Lipidomic analysis indicated that the decrease of 34:6-MGDG under heat stress was partially impaired in the hil1 mutant. Concomitantly, the heat-induced increment of 54:9-triacylglycerol in the hil1 mutant was 18% lower than that in the wild-type plants. Recombinant HIL1 protein digested MGDG to produce 18:3-free fatty acid (18:3-FFA), but not 18:0- and 16:0-FFAs. A transient assay using fluorescent fusion proteins confirmed chloroplastic localization of HIL1. Transcriptome coexpression network analysis using public databases demonstrated that the HIL1 homolog expression levels in various terrestrial plants are tightly associated with chloroplastic heat stress responses. Thus, HIL1 encodes a chloroplastic MGDG lipase that releases 18:3-FFA in the first committed step of 34:6 (18:3/16:3)-containing galactolipid turnover, suggesting that HIL1 has an important role in the lipid remodeling process induced by heat stress in plants.
Figure 1 HIL1 homologous genes are evolutionarily conserved in plant species and HIL1-like proteins have an indispensable role in terrestrial plants
Figure 2 Gene expression analysis of HIL1 found that it is closely related to CLPB3 and DGD1, and is present in soybean, tomato and other plants
Figure 3 Recombinant HIL1 proteolytically hydrolyzes MGDG to release 18:3Y. Higashia et al., HEAT INDUCIBLE LIPASE1 Remodels Chloroplastic Monogalactosyldiacylglycerol by Liberating α-Linolenic Acid in Arabidopsis Leaves under Heat Stress. The Plant Cell, Vol. 30: 1887–1905, August 2018
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