Connecting the Molecular Structure of Cutin to Ultrastructure and Physical Properties of the Cuticle in Petals of Arabidopsis.

The plant cuticle is laid down at the cell wall surface of epidermal cells in a wide variety of structures, but the functional significance of this architectural diversity is not yet understood. Here, the structure-function relationship of the petal cuticle of Arabidopsis (Arabidopsis thaliana) was investigated. Applying Fourier transform infrared microspectroscopy, the cutin mutants long-chain acyl-coenzyme A synthetase2 (lacs2), permeable cuticle1 (pec1), cyp77a6, glycerol-3-phosphate acyltransferase6 (gpat6), and defective in cuticular ridges (dcr) were grouped in three separate classes based on quantitative differences in the ν(C=O) and ν(C-H) band vibrations. These were associated mainly with the quantity of 10,16-dihydroxy hexadecanoic acid, a monomer of the cuticle polyester, cutin. These spectral features were linked to three different types of cuticle organization: a normal cuticle with nanoridges (lacs2 and pec1 mutants); a broad translucent cuticle (cyp77a6 and dcr mutants); and an electron-opaque multilayered cuticle (gpat6 mutant). The latter two types did not have typical nanoridges. Transmission electron microscopy revealed considerable variations in cuticle thickness in the dcr mutant. Different double mutant combinations showed that a low amount of C16 monomers in cutin leads to the appearance of an electron-translucent layer adjacent to the cuticle proper, which is independent of DCR action. We concluded that DCR is not only essential for incorporating 10,16-dihydroxy C16:0 into cutin but also plays a crucial role in the organization of the cuticle, independent of cutin composition. Further characterization of the mutant petals suggested that nanoridge formation and conical cell shape may contribute to the reduction of physical adhesion forces between petals and other floral organs during floral development.

Cuticular Defects in Oryza sativa ATP-binding Cassette Transporter G31 Mutant Plants Cause Dwarfism, Elevated Defense Responses and Pathogen Resistance.

The cuticle covers the surface of the polysaccharide cell wall of leaf epidermal cells and forms an essential diffusion barrier between plant and environment. Homologs of the ATP-binding cassette (ABC) transporter AtABCG32/HvABCG31 clade are necessary for the formation of a functional cuticle in both monocots and dicots. Here we characterize the osabcg31 knockout mutant and hairpin RNA interference (RNAi)-down-regulated OsABCG31 plant lines having reduced plant growth and a permeable cuticle. The reduced content of cutin in leaves and structural alterations in the cuticle and at the cuticle-cell wall interface in plants compromised in OsABCG31 expression explain the cuticle permeability. Effects of modifications of the cuticle on plant-microbe interactions were evaluated. The cuticular alterations in OsABCG31-compromised plants did not cause deficiencies in germination of the spores or the formation of appressoria of Magnaporthe oryzae on the leaf surface, but a strong reduction of infection structures inside the plant. Genes involved in pathogen resistance were constitutively up-regulated in OsABCG31-compromised plants, thus being a possible cause of the resistance to M. oryzae and the dwarf growth phenotype. The findings show that in rice an abnormal cuticle formation may affect the signaling of plant growth and defense.

The ABCG transporter PEC1/ABCG32 is required for the formation of the developing leaf cuticle in Arabidopsis.

The cuticle is an essential diffusion barrier on aerial surfaces of land plants whose structural component is the polyester cutin. The PERMEABLE CUTICLE1/ABCG32 (PEC1) transporter is involved in plant cuticle formation in Arabidopsis. The gpat6 pec1 and gpat4 gapt8 pec1 double and triple mutants are characterized. Their PEC1-specific contributions to aliphatic cutin composition and cuticle formation during plant development are revealed by gas chromatography/mass spectrometry and Fourier-transform infrared spectroscopy. The composition of cutin changes during rosette leaf expansion in Arabidopsis. C16:0 monomers are in higher abundance in expanding than in fully expanded leaves. The atypical cutin monomer C18:2 dicarboxylic acid is more prominent in fully expanded leaves. Findings point to differences in the regulation of several pathways of cutin precursor synthesis. PEC1 plays an essential role during expansion of the rosette leaf cuticle. The reduction of C16 monomers in the pec1 mutant during leaf expansion is unlikely to cause permeability of the leaf cuticle because the gpat6 mutant with even fewer C16:0 monomers forms a functional rosette leaf cuticle at all stages of development. PEC1/ABCG32 transport activity affects cutin composition and cuticle structure in a specific and non-redundant fashion.

ABCG transporters export cutin precursors for the formation of the plant cuticle.

The plant cuticle is deposited on the surface of primary plant organs, such as leaves, fruits, and floral organs, forming a diffusion barrier and protecting the plant against various abiotic and biotic stresses. Cutin, the structural polyester of the plant cuticle, is synthesized in the apoplast. Plasma-membrane-localized ATP-binding cassette (ABC) transporters of the G family have been hypothesized to export cutin precursors. Here, we characterize SlABCG42 of tomato representing an ortholog of AtABCG32 in Arabidopsis. SlABCG42 expression in Arabidopsis complements the cuticular deficiencies of the Arabidopsis pec1/abcg32 mutant. RNAi-dependent downregulation of both tomato genes encoding proteins highly homologous to AtABCG32 (SlABCG36 and SlABCG42) leads to reduced cutin deposition and formation of a thinner cuticle in tomato fruits. By using a tobacco (Nicotiana benthamiana) protoplast system, we show that AtABCG32 and SlABCG42 have an export activity for 10,16-dihydroxy hexadecanoyl-2-glycerol, a cutin precursor in vivo. Interestingly, also free ω-hydroxy hexadecanoic acid as well as hexadecanedioic acid were exported, furthering the research on the identification of cutin precursors in vivo and the respective mechanisms of their integration into the cutin polymer.