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SUMMARY: The plant cuticle is composed of cuticular wax and cutin polymers and plays an essential role in plant tolerance to diverse abiotic and biotic stresses. Several stresses, including water deficit and salinity, regulate the synthesis of cuticular wax and cutin monomers. However, the effect of wounding on wax and cutin monomer production and the associated molecular mechanisms remain unclear. In this study, we determined that the accumulation of wax and cutin monomers in Arabidopsis leaves is positively regulated by wounding primarily through the jasmonic acid (JA) signaling pathway. Moreover, we observed that a wound‐ and JA‐responsive gene (CYP96A4) encoding an ER‐localized cytochrome P450 enzyme was highly expressed in leaves. Further analyses indicated that wound‐induced wax and cutin monomer production was severely inhibited in the cyp96a4 mutant. Furthermore, CYP96A4 interacted with CER1 and CER3, the core enzymes in the alkane‐forming pathway associated with wax biosynthesis, and modulated CER3 activity to influence aldehyde production in wax synthesis. In addition, transcripts of MYC2 and JAZ1, key genes in JA signaling pathway, were significantly reduced in cyp96a4 mutant. Collectively, these findings demonstrate that CYP96A4 functions as a cofactor of the alkane synthesis complex or participates in JA signaling pathway that contributes to cuticular wax biosynthesis and cutin monomer formation in response to wounding. Significance Statement: Plant cuticle is a lipidic barrier composed of cuticular wax and cutin polymers. Cuticle plays a critical role in protecting plants from various biotic and abiotic stresses. Wounds due to mechanical damage or insect feeding are common and are potentially harmful to plants. However, the effect of wounding on plant cuticular wax and cutin monomer biosynthesis remains unclear. In our study, the findings present the validation that the Arabidopsis cuticle development was positively regulated by wounding mainly through the jasmonic acid (JA) signaling pathway. We also characterized the wound‐ and JA‐responsive gene CYP96A4, which is required for wound‐ and JA‐induced synthesis of cuticular wax and cutin monomer. [ABSTRACT FROM AUTHOR]

Summary: Genetic signature of climate adaptation has been widely recognized across the genome of many organisms; however, the eco‐physiological basis for linking genomic polymorphisms with local adaptations remains largely unexplored.Using a panel of 218 world‐wide Arabidopsis accessions, we characterized the natural variation in root suberization by quantifying 16 suberin monomers. We explored the associations between suberization traits and 126 climate variables. We conducted genome‐wide association analysis and integrated previous genotype–environment association (GEA) to identify the genetic bases underlying suberization variation and their involvements in climate adaptation.Root suberin content displays extensive variation across Arabidopsis populations and significantly correlates with local moisture gradients and soil characteristics. Specifically, enhanced suberization is associated with drier environments, higher soil cation‐exchange capacity, and lower soil pH; higher proportional levels of very‐long‐chain suberin is negatively correlated with moisture availability, lower soil gravel content, and higher soil silt fraction. We identified 94 putative causal loci and experimentally proved that GPAT6 is involved in C16 suberin biosynthesis. Highly significant associations between the putative genes and environmental variables were observed.Roots appear highly responsive to environmental heterogeneity via regulation of suberization, especially the suberin composition. The patterns of suberization–environment correlation and the suberin‐related GEA fit the expectations of local adaptation for the polygenic suberization trait. [ABSTRACT FROM AUTHOR]

Summary: Iso‐branched wax compounds are well known in plants, but their biosynthetic pathways are still mostly unknown. It has been speculated that branched waxes are derived from branched‐chain amino acid (BCAA) catabolism, but the evidence for this is very limited.Gas chromatography‐flame ionisation detection (GC‐FID) analysis revealed that mutations in two subunits of the branched‐chain ketoacid dehydrogenase (BCKDH) complex, a key enzyme complex in the degradation of BCAAs, significantly decreased the amounts of branched wax compounds, indicating that BCAA degradation may be integral to the synthesis of iso‐branched wax. Substrate feeding studies further revealed that the metabolic precursor of iso‐branched wax compounds is isobutyric acid (iBA), which is derived from valine degradation in Arabidopsis.We also isolated a novel mutant and found that its branched wax deficient phenotype could not be rescued by iBA. Map‐based cloning together with complementation analysis revealed that mutation in ACYL‐ACTIVATING ENZYME 9 (AAE9) is responsible for this phenotype.Genetic and enzyme activity analysis demonstrated that AAE9 is located downstream of the BCAA degradation pathway, and that it activates iBA to isobutyryl‐CoA for use on branched wax synthesis. Taken together, our study demonstrates that AAE9 is a key factor connecting BCAA catabolism with branched wax biosynthesis. [ABSTRACT FROM AUTHOR]

The plant cuticle is a complex structure composed primarily of wax and cutin, but also contains cutan, glycerolipids, phenolics, polysaccharides and proteins. The cuticle plays an important protective role as barrier between plants and their environment. In this paper, 4‐week‐old leaves produced either on the rosette or on the inflorescence stem of the model extremophyte Thellungiella salsuginea were examined using scanning electron microscopy, cuticle permeability assays and chemical composition analysis. Results showed that stem leaves (SL) had more abundant cuticle lipids and lower cuticle permeability than rosette leaves (RL). SL were dominated by alkanes, especially the C29 and C31 homologs, whereas in RL the most abundant wax class was free very long‐chain acids. The major cutin monomers for both leaf types were C18:2 dioic acids and 18‐OH C18:2 acids. We performed Illumina high‐throughput sequencing for SL and RL, and 3577 differentially expressed genes were identified. Sixty‐five genes possibly involved in cuticular lipid biosynthesis, transport, or regulation was selected for further analysis. Many cuticle‐associated genes exhibited differential expression levels that could be associated with compositional differences between these two leaf types. Furthermore, transcription factors and other regulatory proteins previously associated with cuticle production were expressed at higher levels in SL than in RL. The associations between gene expression and characteristics of this extremophile's leaf cuticles sheds new light on cuticle as an adaptive trait in extreme environments, and contributes new information that may guide efforts to modify crop cuticles for improved stress tolerance. [ABSTRACT FROM AUTHOR]

Populus euphratica is an important native tree found in arid regions from North Africa and South Europe to China, and is known to tolerate many forms of environmental stress, including drought. We describe cuticle waxes, cutin and cuticle permeability for the heteromorphic leaves of P. euphratica growing in two riparian habitats that differ in available soil moisture. Scanning electron microscopy revealed variation in epicuticular wax crystallization associated with leaf type and site. P. euphratica leaves are dominated by cuticular wax alkanes, primary-alcohols and fatty acids. The major cutin monomers were 10,16- diOH C16:0 acids. Broad-ovate leaves (associated with adult phase growth) produced 1.3- and 1.6-fold more waxes, and 2.1- and 0.9-fold more cutin monomers, than lanceolate leaves (associated with juvenile phase growth) at the wetter site and drier site, respectively. The alkane-synthesis-associated ECERIFERUM1 (CER1), as well as ABC transporter- and elongase-associated genes, were expressed at much higher levels at the drier than wetter sites, indicating their potential function in elevating leaf cuticle lipids in the dry site conditions. Higher cuticle lipid amounts were closely associated with lower cuticle permeability (both chlorophyll efflux and water loss). Our results implicate cuticle lipids as among the xeromorphic traits associated with P. euphratica adult-phase broad-ovate leaves. Results here provide useful information for protecting natural populations of P. euphratica and their associated ecosystems, and shed new light on the functional interaction of cuticle and leaf heterophylly in adaptation to more arid, limited-moisture environments. [ABSTRACT FROM AUTHOR]