Disruption of theArabidopsisCGI-58 homologue produces Chanarin–Dorfman-like lipid droplet accumulation in plants

Abstract

CGI-58 is the defective gene in the human neutral lipid storage disease called Chanarin-Dorfman syndrome. This disorder causes intracellular lipid droplets to accumulate in nonadipose tissues, such as skin and blood cells. Here, disruption of the homologous CGI-58 gene in Arabidopsis thaliana resulted in the accumulation of neutral lipid droplets in mature leaves. Mass spectroscopy of isolated lipid droplets from cgi-58 loss-of-function mutants showed they contain triacylglycerols with common leaf-specific fatty acids. Leaves of mature cgi-58 plants exhibited a marked increase in absolute triacylglycerol levels, more than 10-fold higher than in wild-type plants. Lipid levels in the oil-storing seeds of cgi-58 loss-of-function plants were unchanged, and unlike mutations in β-oxidation, the cgi-58 seeds germinated and grew normally, requiring no rescue with sucrose. We conclude that the participation of CGI-58 in neutral lipid homeostasis of nonfat-storing tissues is similar, although not identical, between plant and animal species. This unique insight may have implications for designing a new generation of technologies that enhance the neutral lipid content and composition of crop plants.compartmentation | plant lipid metabolism P lants synthesize and store neutral lipids such as triacylglycerols (TAGs) primarily in cytosolic lipid droplets of maturing seeds (1, 2). In domesticated oilseeds, these stored TAGs represent a major source of calories for human and animal nutrition, an excellent feedstock for diesel fuels, and a reservoir for the deposition of industrially important fatty acids used as chemical feedstocks (3-6). Although not commonly appreciated, TAGs also are synthesized in nonseed tissues (7,8), but their abundance in these tissues is low, in part because of the metabolism of the cell and perhaps as a consequence of the continuous recycling of fatty acids for energy and membrane synthesis. Indeed, vegetative cells can incorporate radiolabeled precursors into TAG (7, 8), they express diacylglycerol acyltransferases [the only enzyme in the "Kennedy pathway" unique to TAG production (9)], and they can accumulate TAGs in β-oxidation mutants (2) and in some floral (10) and fruit (7) tissues. Thus, although plant vegetative cells appear to have the metabolic machinery to synthesize and accumulate neutral lipids, there are likely underlying regulatory mechanisms in place to minimize this process, none of which are understood.Chanarin-Dorfman syndrome is a neutral-lipid storage disease (11) caused by a defect in the protein CGI-58 (comparative gene identification-58, also called ABHD5 for α/β hydrolase-5). CGI-58 is a soluble enzyme that associates with cytosolic lipid droplets under certain metabolic conditions and appears to play a role in hydrolysis of stored lipids (11)(12)(13)(14). Several different mutations in this protein, including amino acid substitutions, premature stop codons, and defects in mRNA splicing, have been identified in various Chanarin-Dorfman patients, all of which result in a hyperac...

The SUGAR-DEPENDENT1 Lipase Limits Triacylglycerol Accumulation in Vegetative Tissues of Arabidopsis

“…Arabidopsis contains many genes that could potentially have this function (Li-Beisson et al, 2013). CGI58 is one candidate, since the protein has lipase activity (Ghosh et al, 2009) and the mutant accumulates TAG in its leaves to around 0.2% of dry weight (James et al, 2010), which is higher than we detected in sdp1. The disruption of fatty acid b-oxidation also leads to TAG accumulation in leaves (Slocombe et al, 2009;James et al, 2010), but the impact on total fatty acid content appears to be small (Yang and Ohlrogge, 2009), unless the tissue is subjected to carbohydrate starvation (Kunz et al, 2009;Slocombe et al, 2009).…”

“…Previous studies have shown that the disruption of several other genes associated with lipid catabolism can also lead to TAG accumulation in vegetative tissues, although heterotrophic tissues have not generally been investigated (Kunz et al, 2009;Slocombe et al, 2009;James et al, 2010). PXA1 is a peroxisomal ATPbinding cassette transporter that is required for fatty acid import for b-oxidation (Zolman et al, 2001), and CGI58 is an enzyme that has been reported to have lipase, phospholipase, and lysophosphatidic acid acyltransferase activities (Ghosh et al, 2009).…”

“…Lipid bodies have been observed in the leaves of many plants (Lersten et al, 2006), and oil in vegetative tissues has previously been proposed to play a role in carbon storage and membrane lipid remodeling (Murphy, 2001;James et al, 2010). Nevertheless, the oil content of leaves, stems, and roots is extremely low in all but a very few plant species (Durrett et al, 2008).…”

“…However, a number of studies have established that the oil content can be boosted by the overexpression of individual oil biosynthetic enzymes such as ACYL-COENZYME A:DI-ACYLGLYCEROL ACYLTRANSFERASE1 (DGAT1; Bouvier-Navé et al, 2000) or transcriptional "master" regulators that govern the expression of multiple enzymes in the pathway, such as WRINKLED1 (WRI1), LEAFY COTYLDON1 (LEC1), and LEC2 (Cernac and Benning, 2004;Mu et al, 2008;Andrianov et al, 2010;Sanjaya et al, 2011). In addition, several mutants have been identified that exhibit ectopic oil accumulation (Ogas et al, 1997;Xu et al, 2005;Kunz et al, 2009;Slocombe et al, 2009;James et al, 2010). Among these are pxa1 (peroxisomal ABC transporter1) and cgi58 (comparative gene identification-58), which are associated with lipid catabolism.…”

Peroxisome Function, Biogenesis, and Dynamics in Plants

“…Arabidopsis CGI-58, a homolog of a mammalian lipase activator (comparative gene identification-58), promotes PXA1 function in leaves but not in germinating seeds (Park et al, 2013), and triacylglycerol accumulates in leaf oil bodies in cgi-58 mutants (James et al, 2010). Moreover, b-oxidation of triacylglycerol from stomatal oil bodies contributes to the ATP production necessary for stomatal opening upon transfer from dark to light (McLachlan et al, 2016).…”