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Plant cuticles are a mixture of crystalline and amorphous waxes that restrict the exchange of molecules between the plant and the atmosphere. The multicomponent nature of cuticular waxes complicates the study of the relationship between the physical and transport properties. Here, a model cuticle based on the epicuticular waxes ofPetunia hybridaflower petals was formulated to test the effect of wax composition on diffusion of water and volatile organic compounds (VOCs). The model cuticle was composed of ann‐tetracosane (C₂₄H₅₀), 1‐docosanol (C₂₂H₄₅OH), and 3‐methylbutyl dodecanoate (C₁₇H₃₄O₂), reflecting the relative chain length, functional groups, molecular arrangements, and crystallinity of the natural waxes. Molecular dynamics simulations were performed to obtain diffusion coefficients for compounds moving through waxes of varying composition. Simulated VOC diffusivities of the model system were found to highly correlate within vitromeasurements in isolated petunia cuticles. VOC diffusivity increased up to 30‐fold in completely amorphous waxes, indicating a significant effect of crystallinity on cuticular permeability. The crystallinity of the waxes was highly dependent on the elongation of the lattice length and decrease in gap width between crystalline unit cells. Diffusion of water and higher molecular weight VOCs were significantly affected by alterations in crystalline spacing and lengths, whereas the low molecular weight VOCs were less affected. Comparison of measured diffusion coefficients from atomistic simulations and emissions from petunia flowers indicates that the role of the plant cuticle in the VOC emission network is attributed to the differential control on mass transfer of individual VOCs by controlling the composition, amount, and dynamics of scent emission.

 

Abstract Benzaldehyde, the simplest aromatic aldehyde, is one of the most wide-spread volatiles that serves as a pollinator attractant, flavor, and antifungal compound. However, the enzyme responsible for its formation in plants remains unknown. Using a combination of in vivo stable isotope labeling, classical biochemical, proteomics and genetic approaches, we show that in petunia benzaldehyde is synthesized via the β-oxidative pathway in peroxisomes by a heterodimeric enzyme consisting of α and β subunits, which belong to the NAD(P)-binding Rossmann-fold superfamily. Both subunits are alone catalytically inactive but, when mixed in equal amounts, form an active enzyme, which exhibits strict substrate specificity towards benzoyl-CoA and uses NADPH as a cofactor. Alpha subunits can form functional heterodimers with phylogenetically distant β subunits, but not all β subunits partner with α subunits, at least in Arabidopsis. Analysis of spatial, developmental and rhythmic expression of genes encoding α and β subunits revealed that expression of the gene for the α subunit likely plays a key role in regulating benzaldehyde biosynthesis. 

Abstract Nudix hydrolases are conserved enzymes ubiquitously present in all kingdoms of life. Recent research revealed that several Nudix hydrolases are involved in terpenoid metabolism in plants. In modern roses, RhNUDX1 is responsible for formation of geraniol, a major compound of rose scent. Nevertheless, this compound is produced by monoterpene synthases in many geraniol-producing plants. As a consequence, this raised the question about the origin of RhNUDX1 function and the NUDX1 gene evolution in Rosaceae, in wild roses or/and during the domestication process. Here, we showed that three distinct clades of NUDX1 emerged in the Rosoidae subfamily (Nudx1-1 to Nudx1-3 clades), and two subclades evolved in the Rosa genus (Nudx1-1a and Nudx1-1b subclades). We also showed that the Nudx1-1b subclade was more ancient than the Nudx1-1a subclade, and that the NUDX1-1a gene emerged by a trans-duplication of the more ancient NUDX1-1b gene. After the transposition, NUDX1-1a was cis-duplicated, leading to a gene dosage effect on the production of geraniol in different species. Furthermore, the NUDX1-1a appearance was accompanied by the evolution of its promoter, most likely from a Copia retrotransposon origin, leading to its petal-specific expression. Thus, our data strongly suggest that the unique function of NUDX1-1a in geraniol formation was evolved naturally in the genus Rosa before domestication.