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

Abstract

There has been considerable interest recently in the prospect of engineering crops to produce triacylglycerol (TAG) in their vegetative tissues as a means to achieve a step change in oil yield. Here, we show that disruption of TAG hydrolysis in the Arabidopsis (Arabidopsis thaliana) lipase mutant sugar-dependent1 (sdp1) leads to a substantial accumulation of TAG in roots and stems but comparatively much lower TAG accumulation in leaves. TAG content in sdp1 roots increases with the age of the plant and can reach more than 1% of dry weight at maturity, a 50-fold increase over the wild type. TAG accumulation in sdp1 roots requires both ACYL-COENZYME A:DIACYLGLYCEROL ACYLTRANSFERASE1 (DGAT1) and PHOSPHATIDYLCHOLINE: DIACYLGLYCEROL ACYLTRANSFERASE1 and can also be strongly stimulated by the provision of exogenous sugar. In transgenic plants constitutively coexpressing WRINKLED1 and DGAT1, sdp1 also doubles the accumulation of TAG in roots, stems, and leaves, with levels ranging from 5% to 8% of dry weight. Finally, provision of 3% (w/v) exogenous Suc can further boost root TAG content in these transgenic plants to 17% of dry weight. This level of TAG is similar to seed tissues in many plant species and establishes the efficacy of an engineering strategy to produce oil in vegetative tissues that involves simultaneous manipulation of carbohydrate supply, fatty acid synthesis, TAG synthesis, and also TAG breakdown.

Arabidopsis Lipins, PDAT1 Acyltransferase, and SDP1 Triacylglycerol Lipase Synergistically Direct Fatty Acids toward β-Oxidation, Thereby Maintaining Membrane Lipid Homeostasis

“…Previous studies have shown that SDP1 and SDP1L have overlapping functions in TAG hydrolysis in germinating seeds of Arabidopsis (Eastmond, 2006;Kelly et al, 2013). To test whether this is also the case in leaves, we constructed a triple mutant impaired in both SDP1 and SDP1L functions in the tgd1-1 mutant background.…”

“…Based on double mutant analysis, it has been shown that PXA1 is epistatic to SDP1 in regulating TAG content in roots (Kelly et al, 2013). To determine the genetic relationship between these two genes in TAG accumulation in leaves, we generated the triple mutant tgd1-1 sdp1-4 pxa1-2.…”

“…Recent genetic studies have demonstrated a role for SDP1 in TAG breakdown in vegetative tissues of Arabidopsis (Kelly et al, 2013). To determine the role of SDP1 in FA turnover in leaves of transgenic plants overexpressing PDAT1, genetic crosses were conducted between the PDAT1 overexpressor 3 and sdp1-4 (Eastmond, 2006), and plants expressing the PDAT1 transgene in the sdp1-4 genetic background were subsequently obtained.…”

“…In plants and yeast, the major pathway for metabolic breakdown of FAs is b-oxidation in peroxisomes (Graham, 2008;Theodoulou and Eastmond, 2012), and FAs as CoA esters are transported into this organelle by PEROXISOMAL TRANSPORTER1 (PXA1) in Arabidopsis (De Marcos Lousa et al, 2013). Recent genetic studies have implicated PXA1, SDP1, and SDP1L in TAG breakdown in nonseed tissues (Slocombe et al, 2009;Kelly et al, 2013), but the physiological function of TAG turnover and the regulatory aspects of the FA b-oxidation pathway in leaves remain largely unknown.…”

Peroxisome Function, Biogenesis, and Dynamics in Plants

“…Various mutants defective in b-oxidation, the glyoxylate cycle, or NADH reduction display peroxisomes clustered near oil bodies after oil bodies are depleted in wild type (Germain et al, 2001;Eastmond, 2007;Pracharoenwattana et al, 2007;Cassin-Ross and Hu, 2014;Rinaldi et al, 2016). Moreover, diphenyl methylphosphonate confers triacylglycerol retention (Brown et al, 2013) similar to sdp1 and pxa1 mutants (Eastmond, 2006;Slocombe et al, 2009;Kelly et al, 2013). The mechanism through which peroxisomal enzyme dysfunction feeds back to prevents triacylglycerol mobilization is unknown.…”