A Land-Plant-Specific Glycerol-3-Phosphate Acyltransferase Family in Arabidopsis: Substrate Specificity, sn-2 Preference, and Evolution    

Abstract

Arabidopsis (Arabidopsis thaliana) has eight glycerol-3-phosphate acyltransferase (GPAT) genes that are members of a plantspecific family with three distinct clades. Several of these GPATs are required for the synthesis of cutin or suberin. Unlike GPATs with sn-1 regiospecificity involved in membrane or storage lipid synthesis, GPAT4 and -6 are unique bifunctional enzymes with both sn-2 acyltransferase and phosphatase activity resulting in 2-monoacylglycerol products. We present enzymology, pathway organization, and evolutionary analysis of this GPAT family. Within the cutin-associated clade, GPAT8 is demonstrated as a bifunctional sn-2 acyltransferase/phosphatase. GPAT4, -6, and -8 strongly prefer C16:0 and C18:1 v-oxidized acyl-coenzyme As (CoAs) over unmodified or longer acyl chain substrates. In contrast, suberin-associated GPAT5 can accommodate a broad chain length range of v-oxidized and unsubstituted acyl-CoAs. These substrate specificities (1) strongly support polyester biosynthetic pathways in which acyl transfer to glycerol occurs after oxidation of the acyl group, (2) implicate GPAT specificities as one major determinant of cutin and suberin composition, and (3) argue against a role of sn-2-GPATs (Enzyme Commission 2.3.1.198) in membrane/storage lipid synthesis. Evidence is presented that GPAT7 is induced by wounding, produces suberin-like monomers when overexpressed, and likely functions in suberin biosynthesis. Within the third clade, we demonstrate that GPAT1 possesses sn-2 acyltransferase but not phosphatase activity and can utilize dicarboxylic acyl-CoA substrates. Thus, sn-2 acyltransferase activity extends to all subbranches of the Arabidopsis GPAT family. Phylogenetic analyses of this family indicate that GPAT4/6/8 arose early in land-plant evolution (bryophytes), whereas the phosphatase-minus GPAT1 to -3 and GPAT5/7 clades diverged later with the appearance of tracheophytes.

MYB107 and MYB9 Homologs Regulate Suberin Deposition in Angiosperms

“…Indeed, the signature metabolites for suberin formation were also identified in the russeted apple surface. These included an increase of ferulates (Serra et al, 2010) and dicarboxylic fatty acids (Kolattukudy, 2001;Compagnon et al, 2009;Yang et al, 2012) and an increase in chain length of the modified FAs (Kolattukudy, 2001;Compagnon et al, 2009). Furthermore, large-scale expression analysis performed in both tomato and apple material confirmed the metabolic shift occurring in the suberized fruit surfaces, corresponding to the reduction in cutin polymer and its replacement with suberin.…”

Cuticle Biosynthesis in Tomato Leaves Is Developmentally Regulated by Abscisic Acid

“…S10A). Of particular note, the expression levels of CD3 and GLYCEROL-3-PHOSPHATE ACYLTRANSFEREASE6 (GPAT6), which catalyze cutin monomer formation (Shi et al, 2013;Yang et al, 2012), were significantly lower (2-to 4.5-fold) in the ABA-deficient mutants than in their respective wild-type genotypes (Supplemental Fig. S10A).…”

Apoplastic Diffusion Barriers in Arabidopsis

“…Interestingly, in vitro biochemical studies revealed that these GPATs catalyze the acyl transfer to the sn-2 position of glycerol in contrast to the classical GPAT-catalyzed sn-1 acylation (Yang et al, 2010). Therefore, an important branch point between membrane lipid synthesis and polyester synthesis may have evolved within the GPAT family (Yang et al, 2012). In addition, differences in the activity of the GPAT4/8 and GPAT5 are hypothesized to be critical for the synthesis of cutin and suberin; these enzymes are discussed in detail below (Yang et al, 2012).…”

“…Therefore, an important branch point between membrane lipid synthesis and polyester synthesis may have evolved within the GPAT family (Yang et al, 2012). In addition, differences in the activity of the GPAT4/8 and GPAT5 are hypothesized to be critical for the synthesis of cutin and suberin; these enzymes are discussed in detail below (Yang et al, 2012).…”