Branched Chain Amino Acid Metabolism in the Biosynthesis of Lycopersicon pennellii Glucose Esters

Abstract

Lycopersicon pennellii Corr. (D'Arcy) an insect-resistant, wild tomato possesses high densities of glandular trichomes which exude a mixture of 2,3,4-tri-O-acylated glucose esters that function as a physical impediment and feeding deterrent to small arthropod pests. The acyl moieties are branched C4 and C5 acids, and branched and straight chain C10, C11, and C12 acids. The structure of the branched acyl constituents suggests that the branched chain amino acid biosynthetic pathway participates in their biosynthesis.[14C]Valine and deuterated branched chain amino acids (and their oxo-acid derivatives) were incorporated into branched C4 and C5 acid groups of glucose esters by a process of transamination, oxidative decarboxylation and subsequent acylation. C4 and C5 branched acids were elongated by two carbon units to produce the branched CIO-C12 groups. Norvaline, norleucine, allylglycine, and methionine also were processed into acyl moieties and secreted from the trichomes as glucose esters. Changes in the acyl composition of the glucose esters following sulfonylurea herbicide administration support the participation of acetohydroxyacid synthetase and the other enzymes of branched amino acid biosynthesis in the production of glucose esters.

A feedback insensitive isopropylmalate synthase affects acylsugar composition in cultivated and wild tomato

“…1B). These results are consistent with previously published findings indicating the involvement of BCAA metabolism in the production of branched acyl chains in acylsugar biosynthesis Walters and Steffens, 1990). For example, virusinduced gene silencing of the E1 b-subunit of the BCKDH complex caused the reduction of acylsugar accumulation in N. benthamiana (Slocombe et al, 2008).…”

“…The acylsugars identified thus far consist of short to medium (C2-C12) chain length aliphatic acids in normal (straight chain), iso (branched at the penultimate carbon), or anteiso (branched at the antepenultimate carbon) configuration esterified to Suc or Glc ( Fig. 1A; Severson et al, 1985;Burke et al, 1987;King et al, 1990;Walters and Steffens, 1990). Acylsugars contribute to direct defense against a wide variety of insect herbivores (Rodriguez et al, 1993;Juvik et al, 1994;Chortyk et al, 1997;Puterka et al, 2003), and substitutions in either the sugar or acyl chain component alter their insecticidal activity (Puterka et al, 2003).…”

“…Feeding studies with 14 C-and 2 H-labeled amino acids showed that short, branched acyl chains (2-methylpropanoic acid [iC4], 3-methylbutanoic acid [iC5], and 2-methylbutanoic acid) on acylsugars are derived from branched-chain amino acids (BCAAs; Val, Leu, and Ile) metabolism ( Fig. 1B; Walters and Steffens, 1990). The branched acyl chains of C6 to C12 are derived from BCAAs by elongation through a fatty acid synthase-mediated mechanism or a-keto acid elongation pathway (van der Hoeven and Steffens, 2000; Kroumova and Wagner, 2003).…”

Functionally Divergent Alleles and Duplicated Loci Encoding an Acyltransferase Contribute to Acylsugar Metabolite Diversity in Solanum Trichomes

“…The branched aliphatic acyl chains are derived from branchedchain amino acid metabolism (Kandra et al, 1990;Walters and Steffens, 1990). The action of branched-chain keto acid dehydrogenase on a-keto acids gives rise to CoA esters of 2-methyl-propanoic acid (iso-C4, from Val), 3-methyl-butanoic acid (iso-C5, from Leu), and 2-methyl-butanoic acid (anteiso-C5, from Ile) (Slocombe et al, 2008).…”

Characterization of the Branched-Chain Amino Acid Aminotransferase Enzyme Family in Tomato

“…Catabolism is believed to be initiated in mitochondria, where the branched-chain keto acid (BCKA) dehydrogenase complex is located (Taylor et al, 2004). The primary fates of BCAAs in plant cells are peptide elongation, glutamate recycling, Glc-and Suc-linked branched-chain esters, branched-chain fatty acid synthesis, and respiration through the synthesis of tricarboxylic acid cycle intermediates (Kandra et al, 1990;Walters and Steffens, 1990;Kroumova et al, 1994;Daschner et al, 1999;Li et al, 2003;Beck et al, 2004;Taylor et al, 2004;Engqvist et al, 2009). BCAA catabolism likely has other functions in plant metabolism.…”