FAX2 Mediates Fatty Acid Export from Plastids in Developing Arabidopsis Seeds

Abstract

Vegetable oils are mainly stored in the form of triacylglycerol (TAG) in oilseeds. Fatty acids (FAs), one of the building blocks for TAG assembly, are synthesized in plastids and then exported to the endoplasmic reticulum for storage oil synthesis. A recent study demonstrated that the export of FAs from plastids was mediated by a FAX (FA export) family protein. However, the significance of FAs export from plastid during seed oil accumulation has not been investigated. In this study, we found that FAX2 was highly expressed in developing Arabidopsis seeds and the expression level was consistent with FAs synthesis activity. FAX2 mutant seeds showed an approximately 18% reduction of lipid levels compared with wild-type seeds. By contrast, overexpression of FAX2 enhanced seed lipid accumulation by up to 30%. The FAs export activity of FAX2 was confirmed by yeast mutant cell complementation analysis. Our results showed that FAX2 could interact with other proteins to facilitate FAs transport. Taken together, these results indicate that FAX2-mediated FA export from plastids is important for seed oil accumulation, and that FAX2 can be used as a target gene for increasing lipid production in oilseeds.

Plant Unsaturated Fatty Acids: Biosynthesis and Regulation

“…This can be partly achieved at the levels post transcription, possibly via protein degradation of excess subunits (Sasaki and Nagano, 2004). β-CT appears to be a quantity control factor -overexpression of β-CT (Madoka et al, 2002), but not BCCP2 (Thelen and Ohlrogge, 2002) or BC (Shintani et al, 1997), could lead to a significant rise in protein levels of all other three subunits, though their mRNA levels were not affected.…”

“…The novel FAX family consists of seven members. While FAX1 plays a prominent role in leaves and flowers (Li et al, 2015), FAX2 and FAX4 are important for seed oil accumulation (Tian et al, 2019;Li et al, 2020). Of note, FAX1 can rescue yeast (Saccharomyces cerevisiae) mutant defective in FA transport with a cargo preference for 16:0 over 18:1; however, 18:1 is the major FA exported out of plastids (Li et al, 2015).…”

Lipidomic and transcriptomic profiling of developing nodules reveals the essential roles of active glycolysis and fatty acid and membrane lipid biosynthesis in soybean nodulation

“…FAX1 located in the inner chloroplast membrane acts as an exporter of FAs from the plastid to the cytosol (Li et al ., 2015). Additionally, FAX1 homologue genes might respond to transport FAs out of the chloroplast into the cytosol to form the acyl‐CoA pool (Tian et al ., 2019). GmFAX1 and GmFAX2 were increased on average approximately 10‐fold and 2‐fold, respectively, in nodules compared to roots.…”

“…Our data showed that, during legume–rhizobia interactions and the development of nitrogen‐fixing nodules, lipid synthesis and lipid transporter genes were extensively expressed to higher levels in nodules than in roots, from GmFAX1 and its homologues on the plastid envelope (Li et al ., 2015; Tian et al ., 2019) to GmABCA1 on the ER membrane (Kim et al ., 2013), PBM‐localized STRL transporters putatively for 2‐MAG transport, and chloroplast‐localized TGD homologues responsible for ER‐plastid transport of larger lipid molecules such as PAs (Kelly et al ., 2016). These discoveries support the notion that lipid transport during nodulation is a significant event, consistent with the results of previous studies (Lei et al ., 2014; Pii et al ., 2009; Emerich and Krishnan, 2014).…”

Integrative Analysis of Lipidomics and Transcriptomics Revealed Dynamic Details of Lipids Metabolism and Accumulation in Developing Tiger Nut (Cyperus Esculentus) Tubers

“…Among those, fatty acids synthesis(PUSH), FAD2, FAD3 [11], KCSs [12]or MYB1 [13] represent the key for fatty acids composition alteration. FAX1 and FAX2 facilitate fatty acids transport from plastids for improving seed oil accumulation [14,15]. In the Kennedy pathway associated with TAG and membrane lipid synthesis (PULL), acyltransferases such as Lysophosphatidic acid acyltransferase (LPAAT) [16], diglyceride:acyltransferase (DGAT) [17],and Phospholipid diacylglycerol acyltransferase1 (PDAT1) [18] are important for TAG synthesis.…”