Heat-inducible lipase HIL1 mitigates heat stress in Arabidopsis

Higashi et al. investigate the function of a heat-inducible lipase in Arabidopsis thaliana. Plant Cell (2018). https://doi.org/10.1105/tpc.18.00347

By Yasuhiro Higashi and Kazuki Saito

Background: Land plants suffer from high-temperature stress, exacerbated by climate changes in recent years. Heat stress can cause membrane damage, and plants have developed a mechanism to change the membrane lipid composition and stabilize the membranes in response to high temperature. Under heat stress, various plants remove polyunsaturated fatty acids, such as α-linolenic acid (18:3), from chloroplastic glycerolipids. The biosynthetic pathway of the chloroplastic glycerolipids in Arabidopsis thaliana has been relatively well characterized. However, the catabolic process of their turnover under stress conditions is still unknown.

Question: We studied membrane lipid remodeling under heat stress. In particular, we aimed to identify the particular genes responsible for releasing unsaturated fatty acids from chloroplastic glycerolipids.

Findings: Transcriptome analysis identified a candidate gene that is involved in chloroplastic membrane lipid remodeling under heat stress. We characterized a T-DNA insertion mutant that disrupted a gene named HEAT INDUCIBLE LIPASE1 (HIL1) by investigating compositional changes of membrane lipids under heat stress. The hil1 mutant leaves partially impaired the remodeling of 18:3-containing glycerolipids, and the mutant plants were sensitive to heat stress. The purified HIL1 recombinant protein catalyzed the liberation of 18:3-free fatty acid from monogalactosyldiacylglycerol. Our results suggest that this gene encodes a lipase that participates in plant heat stress responses via the lipid remodeling process.

Next steps: Gene coexpression analysis revealed a conserved network associated with HIL1 in various plant species. We are interested in discovering the function of the HIL1 homologous genes in major crop species. In addition, we wish to investigate the suborganelle localization and details of HIL1 protein function. We hope our knowledge about HIL1 might aid the development of heat stress-tolerant plant varieties.

Keywords: Heat stress, lipase, lipidomic analysis, lipid remodeling, gene coexpression network.

Yasuhiro Higashi, Yozo Okazaki, Kouji Takano, Fumiyoshi Myouga, Kazuo Shinozaki, Eva Knoch, Atsushi Fukushima and Kazuki Saito. (2018). A lipase gene, HEAT INDUCIBLE LIPASE1, is involved in remodeling chloroplastic monogalactosyldiacylglycerol by liberating α-linolenic acid in Arabidopsis leaves under heat stress. Plant Cell 30: 1887-1905. https://doi.org/10.1105/tpc.18.00347.