Misexpression of FATTY ACID ELONGATION1 in theArabidopsisEpidermis Induces Cell Death and Suggests a Critical Role for Phospholipase A2 in This Process

Abstract

Very-long-chain fatty acids (VLCFAs) are important functional components of various lipid classes, including cuticular lipids in the higher plant epidermis and lipid-derived second messengers. Here, we report the characterization of transgenic Arabidopsis thaliana plants that epidermally express FATTY ACID ELONGATION1 (FAE1), the seed-specific b-ketoacyl-CoA synthase (KCS) catalyzing the first rate-limiting step in VLCFA biosynthesis. Misexpression of FAE1 changes the VLCFAs in different classes of lipids but surprisingly does not complement the KCS fiddlehead mutant. FAE1 misexpression plants are similar to the wild type but display an essentially glabrous phenotype, owing to the selective death of trichome cells. This cell death is accompanied by membrane damage, generation of reactive oxygen species, and callose deposition. We found that nuclei of arrested trichome cells in FAE1 misexpression plants cell-autonomously accumulate high levels of DNA damage, including double-strand breaks characteristic of lipoapoptosis. A chemical genetic screen revealed that inhibitors of KCS and phospholipase A2 (PLA2), but not inhibitors of de novo ceramide biosynthesis, rescue trichome cells from death. These results support the functional role of acyl chain length of fatty acids and PLA2 as determinants for programmed cell death, likely involving the exchange of VLCFAs between phospholipids and the acyl-CoA pool.

Patatin-like PLA<sub>2</sub> with cytotoxicity against mammalian and plant tumour cells

“…For example, pPLA and iPLA 2 share a sensitivity against BEL inhibitor (also called HELSS), showing again their close catalytic properties. Regulation of cell death is also inhibited by BEL so that the relevant protein was shown to have characteristics of a pPLA [4,43].…”

Lipid determinants of cell death

“…Overall, the level of wax was reduced to about ~80% of that in the wild type, albeit a semiglaucous phenotype was not visually apparent in the FDH:FAE1 plants. 1 Dye exclusion tests revealed that FDH:FAE1 trichomes …”

“…Although the expression of FAE1 did affect non-trichome cells (e.g., with regard to the hostpathogen interactions), cytochemical staining revealed that plasma membrane permeabilization, the accumulation of reactive oxygen species (ROS), including hydrogen peroxide, callose deposition and DNA damage only occurred in trichome cells, whereas other epidermal and non epidermal cells showed no signs of cell death. 1 The profiling of acyl-CoA and the glycerophospholipid molecular species and fatty acids revealed that the expression of FAE1 in the epidermis leads to the appearance of increasing chain-length fatty acids in various lipid classes in the plant tissues. 1 FAE1 is a β-ketoacyl-CoA synthase (KCS) which catalyzes the first rate-limiting step in the synthesis of very long-chain fatty acids (VLCFAs) that are longer than C20.…”

“…1 The profiling of acyl-CoA and the glycerophospholipid molecular species and fatty acids revealed that the expression of FAE1 in the epidermis leads to the appearance of increasing chain-length fatty acids in various lipid classes in the plant tissues. 1 FAE1 is a β-ketoacyl-CoA synthase (KCS) which catalyzes the first rate-limiting step in the synthesis of very long-chain fatty acids (VLCFAs) that are longer than C20. The topical application of sub-lethal concentrations of chloracetamide and oxoacetamide herbicides, which are capable of inactivating their KCS targets through irreversible binding, 4 rescued the trichomes from death, thereby illustrating that while the activity of FAE1 is responsible for PCD, it could be potently inhibited in planta.…”

“…The topical application of sub-lethal concentrations of chloracetamide and oxoacetamide herbicides, which are capable of inactivating their KCS targets through irreversible binding, 4 rescued the trichomes from death, thereby illustrating that while the activity of FAE1 is responsible for PCD, it could be potently inhibited in planta. 1 In our search for the molecular pathway which leads to PCD during trichome differentiation, we first investigated the role of the cuticle. Although FAE1 was active in the epidermis of transgenic plants, we found that different-chain-length fatty acids did not appear in cutin and wax.…”