Cutin:cutin-acid endo-transacylase (CCT), a cuticle-remodelling enzyme activity in the plant epidermis.

Anzhou Xin,Attila Molnar,Stephen C Fry,Yue Fei

doi:10.1042/bcj20200835

Abstract

Cutin is a polyester matrix mainly composed of hydroxy-fatty acids that occurs in the cuticles of shoots and root-caps. The cuticle, of which cutin is a major component, protects the plant from biotic and abiotic stresses, and cutin has been postulated to constrain organ expansion. We propose that, to allow cutin restructuring, ester bonds in this net-like polymer can be transiently cleaved and then re-formed (transacylation). Here, using pea epicotyl epidermis as the main model, we first detected a cutin:cutin-fatty acid endo-transacylase (CCT) activity. In-situ assays used endogenous cutin as the donor substrate for endogenous enzymes; the exogenous acceptor substrate was a radiolabelled monomeric cutin-acid, 16-hydroxy-[3H]hexadecanoic acid (HHA). High-molecular-weight cutin became ester-bonded to intact [3H]HHA molecules, which thereby became unextractable except by ester-hydrolysing alkalis. In-situ CCT activity correlated with growth rate in Hylotelephium leaves and tomato fruits, suggesting a role in loosening the outer epidermal wall during organ growth. The only well-defined cutin transacylase in the apoplast, CUS1 (a tomato cutin synthase), when produced in transgenic tobacco, lacked CCT activity. This finding provides a reference for future CCT protein identification, which can adopt our sensitive enzyme assay to screen other CUS1-related enzymes.

Highlights

Cutin is an extracellular polyester in the shoot epidermis of land-plants, located between the primary cell wall and the surface wax [1,2], and recently detected in root-caps [3]
Cutin occurs throughout the Embryophyta, from non-vascular [11] to vascular plants (e.g. Arabidopsis thaliana and Solanum lycopersicum) [12,13], the composition varies between taxa and even between organs in the same plant [14]
To look for the proposed cutin-fatty acid endo-transacylase (CCT) reaction within the cuticle, we devised and optimised a sensitive in-situ radiochemical assay comparable to the xyloglucan endotransglucosylase (XET) assay that is commonly used for detecting transglycosylation reactions [46]

Summary

Introduction

Cutin is an extracellular polyester in the shoot epidermis of land-plants, located between the primary cell wall and the surface wax [1,2], and recently detected in root-caps [3]. It typically constitutes 40–60% of the dry weight of the cuticle, varying between species [4,5,6]. The core structure of cutin is an aliphatic polyester of hydroxy-fatty acids (HFAs) [15,16]. In a few plants, including arabidopsis, a major component of the epidermal polyester is octadecadien-1,18-dioic acid [12,22], such components are more usually a feature of suberin rather than cutin [23]

Methods

Results

Discussion

Conclusion