HEAT INDUCIBLE LIPASE1 Remodels Chloroplastic Monogalactosyldiacylglycerol by Liberating α-Linolenic Acid in Arabidopsis Leaves under Heat Stress

Abstract

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 leaves. Using thermotolerance tests, a T-DNA insertion mutant with disrupted 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 mutant. Concomitantly, the heat-induced increment of 54:9-triacylglycerol in the 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 homolog expression levels in various terrestrial plants are tightly associated with chloroplastic heat stress responses. Thus, 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 has an important role in the lipid remodeling process induced by heat stress in plants.

Lipid Dependence of Xanthophyll Cycling in Higher Plants and Algae

“…Heatstress also leads to a hydrolization of the 18:3 FAs of MGDG by a chloroplast heat-inducible lipase (HIL1), which in this way initiates and contributes to the MGDG degradation under high temperatures. The concerted action of these mechanisms explains the decreased levels of MGDG and DGDG-bound polyunsaturated FAs (PUFAs) during heat stress (Higashi et al, 2018). Interestingly, in chloroplasts, the decrease of 18:3 FAs is accompanied by an increased concentration 18:2 acyl chains in the GGLs (Higashi and Saito, 2019).…”

Lack of FIBRILLIN6 in Arabidopsis thaliana affects light acclimation and sulfate metabolism

“…This approach is based on the assumption that genes which are coexpressed (i.e. For example, transcriptome and coexpression network analyses were exploited to identify HEAT INDUCIBLE LIPASE1 (HIL1) as a remodeler of chloroplastic monogalactosyldiacylglycerol under heat stress, and to show that HIL1 homologue expression levels in various plants are tightly associated with chloroplastic heat stress responses (Higashi et al, 2018). For example, transcriptome and coexpression network analyses were exploited to identify HEAT INDUCIBLE LIPASE1 (HIL1) as a remodeler of chloroplastic monogalactosyldiacylglycerol under heat stress, and to show that HIL1 homologue expression levels in various plants are tightly associated with chloroplastic heat stress responses (Higashi et al, 2018).…”

Plastidic Δ6 fatty-acid desaturases with distinctive substrate specificity regulate the pool of c18-pufas in the ancestral picoalgaostreococcus tauri

“…Most of the following work focused on the transfer of lipid and PUFA from the ER to the chloroplast, establishing the idea that the reverse transport was negligible (Miquel & Browse, 1992; Li, N et al ., 2016). Nevertheless, the recent characterization of two Arabidopsis plastid lipases mutants highlighted that plastidic PUFA indeed contributed to PUFA remodelling of extraplastidic lipid (Wang et al ., 2017; Higashi et al ., 2018).…”