Evolution of serine carboxypeptidase-like acyltransferases in the monocots

Abstract

The serine carboxypeptidases are a large family of proteases. in higher plants some members of this family have diversified and adopted new functions as acyltransferases required for the synthesis of natural products. we recently reported the first serine carboxypeptidase-like (scpl) acyltransferase enzyme to be characterized from monocotyledonous plants. This enzyme, AsSCPL1, is required for acylation of antimicrobial terpenes (avenacins) that are produced in the roots of oat (Avena spp.) and that provide protection against soil-borne pathogens. The SCPL acyltransferase enzyme family has undergone substantial expansion following the divergence of monocots and dicots. Here we discuss the evolution of this SCPL enzyme family in monocots, their contribution to metabolic diversity, and the roles of these enzymes in biotic and abiotic stress tolerance.

Figure 1

Evolutionary relationships across the plant SCPL protein family. SCPL protein sequences from P. patens (20 sequences) and C. reinhardtii (9 sequences) were identified using www.phytozome.net and aligned with sequences from A. thaliana (50 sequences), O. sativa (31 sequences) and selected sequences for characterized SCPL acyltransferases from other plant species using Muscle 3.6. Phylogeny was reconstructed using Mega 4.0, regions corresponding to the predicted signal peptide and internal spacer were removed prior to tree construction (sequence alignments are included as Suppl. materials online) as described in ref. 1. Characterized SCPL acyltransferase enzymes included in the tree are from Arabidopsis: (SCT: sinapoyl:choline transferase; SMT : sinapoyl:malate transferase; SST: sinapoyl:sinapoyl transferase; SAT : sinapoyl:anthocyanin transferase); oat: (AsSCPL1 acyltransferase; FJ475130 circled in red); Solanum pennellii glucose acyltransferase (GAC; AAF64227); and Brassica napus sinapoyl:choline transferase (SCT; AAQ91191). Characterized serine carboxypeptidase sequences included are from barley (Hordeum vulgare): SCPI (P07519), CPDWII (P55748) and SCPIII (P21529); wheat (Triticum aestivum): CPDWII (P08819); yeast (Saccharomyces cerevisiae): CPY (NP_014026). Also included were the sorghum (Sorghum bicolour) HNL1 nitrile-lyase enzyme (CAD12888), and the Brachypodium distachyon BdSCPL1 sequence (encoded by Bd3g21550). The rice homologue of AsSCPL1, encoded by Os10g01134, is indicated by an arrow. The scale bar indicates 0.1 substitutions per site. Bootstrap support (%) is shown for selected branches.