Related Arabidopsis Serine Carboxypeptidase-Like Sinapoylglucose Acyltransferases Display Distinct But Overlapping Substrate Specificities

Abstract

The Arabidopsis (Arabidopsis thaliana) genome encodes 51 proteins annotated as serine carboxypeptidase-like (SCPL) enzymes. Nineteen of these SCPL proteins are highly similar to one another, and represent a clade that appears to be unique to plants. Two of the most divergent proteins within this group have been characterized to date, sinapoyl-glucose (Glc):malate sinapoyltransferase and sinapoyl-Glc:choline sinapoyltransferase. The fact that two of the least related proteins within this clade are acyltransferases rather than true serine carboxypeptidases suggests that some or all of the remaining members of this group may have similar activities. The gene that encodes sinapoyl-Glc:malate sinapoyltransferase (sinapoyl-Glc accumulator1 [SNG1]: At2g22990) is one of five SCPL genes arranged in a cluster on chromosome 2. In this study, an analysis of deletion mutant lines lacking one or more genes in this SCPL gene cluster reveals that three of these genes also encode sinapoyl-Glcdependent acyltransferases. At2g23000 encodes sinapoyl-Glc:anthocyanin acyltransferase, an enzyme that is required for the synthesis of the sinapoylated anthocyanins in Arabidopsis. At2g23010 encodes an enzyme capable of synthesizing 1,2-disinapoyl-Glc from two molecules of sinapoyl-Glc, an activity shared by SNG1 and At2g22980. Sequence analysis of these SCPL proteins reveals pairwise percent identities that range from 71% to 78%, suggesting that their differing specificities for acyl acceptor substrates are due to changes in a relatively small subset of amino acids. The study of these SCPL proteins provides an opportunity to examine enzyme structure-function relationships and may shed light on the role of evolution of hydroxycinnamate ester metabolism and the SCPL gene family in Arabidopsis and other flowering plants.

Comprehensive Flavonol Profiling and Transcriptome Coexpression Analysis Leading to Decoding Gene–Metabolite Correlations inArabidopsis

“…The positive correlation between MYB12 and UGT84A1 (r = 0.781) and the negative correlation of MYB12/UGT84A1 and SNG1 (r = 20.357/20.323) tends to support this hypothesis. 1-O-Sinapoylglucose is also a substrate for anthocyanin sinapoyltransferase (Fraser et al, 2007), and anthocyanins accumulate with UV exposure and high sucrose stress. Arabidopsis may thus coregulate 1-O-sinapoylglucose with the flavonoids for prompt responses to stress.…”

“…Thirty-five flavonoid biosynthetic genes, including genes encoding 12 transcription factors, 10 structural enzymes, and 10 modification enzymes, have been identified (Tohge et al, 2005Lepiniec et al, 2006;Fraser et al, 2007;Luo et al, 2007;Stracke et al, 2007;Yonekura-Sakakibara et al, 2007), but even in this highly studied species, the full details of the flavonoid pathway, including modification, are still unknown. The major flavonoid structures in Arabidopsis suggest that there are as yet unidentified modification enzyme genes and pathways in flavonoid metabolism.…”

A Serine Carboxypeptidase-Like Acyltransferase Is Required for Synthesis of Antimicrobial Compounds and Disease Resistance in Oats

“…Since some dicot SCPL proteins are known to have acyltransferase functions (Lehfeldt et al, 2000;Li and Steffens, 2000;Shirley et al, 2001;Fraser et al, 2007;Weier et al, 2008), and Sad7 is known to be genetically linked to Sad1 and Sad2, SCPL1 became a candidate avenacin acyltransferase gene. We sequenced the SCPL1 gene in mutants #376 and #616 and identified a single nucleotide polymorphism (SNP) in each.…”

“…Members of the BAHD family are involved in the synthesis of important natural products, including the anticancer drugs vinblastine (St Pierre et al, 1998) and taxol (Kingston 1994;Walker et al, 2002). More recently, serine carboxypeptidase-like (SCPL) proteins have emerged as a new group of acyltransferase enzymes that are able to modify plant natural products (Lehfeldt et al, 2000;Li and Steffens, 2000;Shirley et al, 2001;Fraser et al, 2007;Weier et al, 2008). These two different classes of acyltransferases operate by distinct mechanisms.…”

“…The SCPL acyltransferases that have been cloned and characterized to date are all of dicot origin (Lehfeldt et al, 2000;Li and Steffens, 2000;Shirley et al, 2001;Fraser et al, 2007;Weier et al, 2008). Oats (monocots belonging to the genus Avena) produce acylated defense compounds known as avenacins.…”