Abstract
In plants, fatty acids are primarily synthesized in plastids and then transported to the endoplasmic reticulum (ER) for synthesis of most of the complex membrane lipids, including glycerolipids and sphingolipids. The first step of sphingolipid synthesis, which uses a fatty acid and a serine as substrates, is critical for sphingolipid homeostasis; its disruption leads to an altered plant growth. Phospholipase As have been implicated in the trafficking of fatty acids from plastids to the ER. Previously, we found that overexpression of a patatin-related phospholipase, pPLAIIIβ, resulted in a smaller plant size and altered anisotropic cell expansion. Here, we determined the content and composition of sphingolipids in pPLAIIIβ-knockout and overexpression plants (pPLAIIIβ-KO and -OE). 3-keto-sphinganine, the product of the first step of sphingolipid synthesis, had a 26% decrease in leaves of pPLAIIIβ-KO while a 52% increase in pPLAIIIβ-OE compared to wild type (WT). The levels of free long-chain base species, dihydroxy-C18:0 and trihydroxy-18:0 (d18:0 and t18:0), were 38 and 97% higher, respectively, in pPLAIIIβ-OE than in WT. The level of complex sphingolipids ceramide d18:0–16:0 and t18:1–16:0 had a twofold increase in pPLAIIIβ-OE. The level of hydroxy ceramide d18:0–h16:0 was 72% higher in pPLAIIIβ-OE compared to WT. The levels of several species of glucosylceramide and glycosylinositolphosphoceramide tended to be higher in pPLAIIIβ-OE than in WT. The total content of the complex sphingolipids showed a slightly higher in pPLAIIIβ-OE than in WT. These results revealed an involvement of phospholipase-mediated lipid homeostasis in plant growth.
Highlights
Lipids are structural components of membrane bilayers and play important metabolic and regulatory roles in plant growth, development, and stress responses
The total content of complex sphingolipids tended to be slightly higher in β-OE than in wild type (WT) (Figure 7D). These data show that overexpression of pPLAIIIβ results in a 52% increase and knockout mutant has a 26% decrease of 3-KS, the www.frontiersin.org product of the first step of sphingolipid synthesis
Overexpression of pPLAIIIβ leads to increase of several complex sphingolipid species with saturated long chain base and saturated fatty acid chains, such as Cer d18:0–16:0 (90%), Cer t18:0–16:0 (112%), hCer d18:0–h16:0 (72%), GlcCer d18:0–h20:0 (379%), and GIPC t18:0–h16:0 (24%)
Summary
Lipids are structural components of membrane bilayers and play important metabolic and regulatory roles in plant growth, development, and stress responses. Overexpressing pPLAIIIβ alters sphingolipid composition (Chen et al, 2006), while LCB2 is encoded by two functionally redundant genes, LCB2a and LCB2b (Dietrich et al, 2008). Partial RNA interference suppression of LCB1 results in reduced cell expansion, a smaller plant, and elevated levels of saturated sphingolipid LCBs (Chen et al, 2006).
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