Research

The Plant Cuticle

Land plants have to protect themselves against hostile environmental conditions, such as water loss in a low humidity environment, including during drought stress. The cuticle is a lipid-rich surface structure formed in continuation with the cell wall of above-ground organs in primary growth stage, such as leaves, fruits and floral organs. It plays an essential role as diffusion barrier protecting plants against abiotic stresses. In addition, the cuticle regulates the fluxes of signal molecules important for the communication with microorganisms and insects and gives mechanical strength to the surface of the epidermal cells.

Composition, structure and function of cutin and other cell wall polyesters

The structural component of the plant cuticle is cutin, an aliphatic polyester. The aim of our studies is to better understand the biosynthesis and assembly of cutin that has a different composition and structure in different organs and developmental stages. Furthermore, we wish to relate cutin structure to the properties of the cuticle and its role in different biological processes. Based on a genetic approach in Arabidopsis leading to the isolation of mutants having a permeable cuticle, we have characterized several genes involved in cutin formation and function. Currently, we extend our research to organs and cell types for which polyester depositions in the cell walls have not yet identified.

Towards understanding the relation between the composition, structure and the function of the plant cuticle

During recent years, we have used Arabidopsis as a model system for the identification of genes involved in the biosynthesis of cutin, the structural polyester of the cuticle. A number of Arabidopsis mutants having a permeable cuticle have been isolated using dyes that penetrate the leaves or petals only when the cuticle is disrupted. Characterization of permeable cuticle mutants lead also to a better understanding of the different roles of the plant cuticle in stress protection and plant development.

A short overview over the different research projects is given below:

(Figure to the left) caption: Transmission electron micrograph (top) and fluorol yellow staining (bottom) showing the root tip of the plants with the root cap cuticle in WT plants (left) and in its absence in transgenic plants degrading the RCC (right) The ABC transporter AtABCG32 exports cutin precursors The pec1 mutant of Arabidopsis having a knockout in AtABCG32 and respective homologues in other monocot and dicot species exhibit deficiencies in cutin formation as well as typical phenotypes associated with a permeable cuticle. AtABCG32 was localized to the outer epidermal plasma-membrane leading to the hypothesis of a function in cutin precursor export. Recently, we could show that AtABCG32 exports the cutin precursor 10, 16-diOH C16:0-2-glycerol as well as other C16:0 monomers in tobacco protoplasts as experimental system. Bessire et al., 2011 ; Chen et al, 2011 ; Fabre et al, 2016 ; Garroum et al., 2016. Elejalde-Palmett, 2021.

Transmission electron microsgraph showing the layered structure of the cuticle within the nanoridges of epidermal cells of Arabidopsis petals. Picture taken by Jean Daraspe, EMF, UniL *Connecting cutin composition and cuticle ultrastructure in Arabidopsis* petals** The ultrastructure of the cuticle varies among different plant species but also between different organs of the same plant. Characterization of the chemical composition of cutin and the ultrastructure of the cuticle in petals of Arabidopsis in numerous cuticle mutants lead to a better understanding of the relation between composition and ultrastructure and of gene functions that are essential for cutin formation in petals, such as PEC1/AtABCG32 and DEFECTIVE IN CUTICULAR RIDGES (DCR) encoding a BAHD acyltransferase. Mazurek et al, 2013; Fabre et al., 2016; Mazurek et al., 2017.
Inflorescence of a cutinase-expressing transgenic Arabidopsis plant exhibiting fusions between floral organs The role of cuticle in organ formation The formation of fusions between different plant organs early in development in many plants having a permeable cuticle lead to the hypothesis that the cuticle has an essential function during plant development. The molecular mechanisms underlying this unique phenotype are still under debate, but seem to be tightly associated with the development of the organ itself. Our publications and contributions to this topic: Sieber et al, 2000 Kurdykov et al, 2006 Voisin et al, 2009
Inoculation with Botrytis on wild type Arabidopsis plants (left) showing lesion formation and a plant having a permeable cuticle (right) being resistant The role of the cuticle in plant-pathogen interactions Although the cuticle protects plants against microbial infections, Arabidopsis plants having a permeable cuticle exhibit a strong resistance to Botrytis cinerea. This surprising phenomenon may be explained by more rapid elicitation of defense responses as well as the accumulation of antimicrobial compounds, such as aliphatic glycosinolates on the leaf surface of cuticle mutants. Chassot et al, 2007 ; Bessire et al, 2007; Dubey et al, 2020.

Figure 1: Structure of the epidermal extracellular matrix.

Figure 2: Appearance of the cuticle in wild type and cutinase-expressing plants.

Figure 3: Organs fusions in cutinase-expressing Arabidopsis plants.

Figure 4: Infection with Botrytis cinerea.

Figure 5: Calcoflour-stained leaves of Arabidopsis.

Toluidine blue diffuses quickly into the petals of the permeable cuticle1 mutant of Arabidopsis