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• Odd-numbered primary alcohols are components of plant cuticular wax, but their biosynthesis remains unknown. • We isolated a rice wax crystal-sparse leaf 5 (WSL5) gene using a map-based cloning strategy. The function of WSL5 was illustrated by overexpression and knockout in rice, heterologous expression in Arabidopsis and transient expression in tobacco leaves. • WSL5 is predicted to encode a cytochrome P450 family member CYP96B5. The wsl5 mutant lacked crystalloid platelets on the surface of cuticle membrane, and its cuticle membrane was thicker than that of the wild-type. The wsl5 mutant is more tolerant to drought stress. The load of C23–C33 alkanes increased, whereas the C29 primary alcohol reduced significantly in wsl5 mutant and WSL5 knockout transgenic plants. Overexpression of WSL5 increased the C29 primary alcohol and decreased alkanes in rice leaves. Heterologous expression of WSL5 increased the C29 primary alcohol and decreased alkanes, secondary alcohol, and ketone in Arabidopsis stem wax. Transient expression of WSL5 in tobacco leaves also increased the production C29 primary alcohol. • WSL5 catalyzes the terminal hydroxylation of alkanes, yielding odd-numbered primary alcohols, and is involved in the formation of epidermal wax crystals on rice leaf, affecting drought sensitivity.

Previous studies have shown that wheat grain yield is seriously affected by drought stress, and leaf cuticular wax is reportedly associated with drought tolerance. However, most studies have focused on cuticular wax biosynthesis and model species. The effects of cuticular wax on wheat drought tolerance have rarely been studied. The aims of the current study were to study the effects of leaf cuticular wax on wheat grain yield under drought stress using the above-mentioned wheat NILs and to discuss the possible physiological mechanism of cuticular wax on high grain yield under drought stress. Compared to water-irrigated (WI) conditions, the cuticular wax content (CWC) in glaucous and non-glaucous NILs under drought-stress (DS) conditions both increased; mean increase values were 151.1 and 114.4%, respectively, which was corroborated by scanning electronic microscopy images of large wax particles loaded on the surfaces of flag leaves. The average yield of glaucous NILs was higher than that of non-glaucous NILs under DS conditions in 2014 and 2015; mean values were 7368.37 kg·ha and 7103.51 kg·ha . This suggested that glaucous NILs were more drought-tolerant than non-glaucous NILs ( = 0.05), which was supported by the findings of drought tolerance indices TOL and SSI in both years, the relatively high water potential and relative water content, and the low ELWL. Furthermore, the photosynthesis rate ( ) of glaucous and non-glaucous wheat NILs under DS conditions decreased by 7.5 and 9.8%, respectively; however, glaucous NILs still had higher mean values of than those of non-glaucous NILs, which perhaps resulted in the higher yield of glaucous NILs. This could be explained by the fact that glaucous NILs had a smaller reduction, a smaller reduction and a greater increase than non-glaucous NILs under DS conditions. This is the first report to show that wheat cuticular wax accumulation is associated with drought tolerance. Moreover, the leaf CWC can be an effective selection criterion in the development of drought-tolerant wheat cultivars.

Waxes are critical in limiting non-stomatal water loss in higher terrestrial plants by making up the limiting barrier for water diffusion across cuticles. Using a differential extraction protocol, we investigated the influence of various wax fractions on the cuticular transpiration barrier. Triterpenoids (TRPs) and very long-chain aliphatics (VLCAs) were selectively extracted from isolated adaxial leaf cuticles using methanol (MeOH) followed by chloroform (TCM). The water permeabilities of the native and the solvent-treated cuticles were measured gravimetrically. Seven plant species ( Camellia sinensis , Ficus elastica , Hedera helix , Ilex aquifolium , Nerium oleander , Vinca minor, and Zamioculcas zamiifolia ) with highly varying wax compositions ranging from nearly pure VLCA- to TRP-dominated waxes were selected. After TRP removal with MeOH, water permeability did not or only slightly increase. The subsequent VLCA extraction with TCM led to increases in cuticular water permeabilities by up to two orders of magnitude. These effects were consistent across all species investigated, providing direct evidence that the cuticular transpiration barrier is mainly composed of VLCA. In contrast, TRPs play no or only a minor role in controlling water loss.

Studying the genetic basis of leaf wax composition and its correlation with leaf cuticular conductance (gc) is crucial for improving crop productivity. The leaf cuticle, which comprises a cutin matrix and various waxes, functions as an extracellular hydrophobic layer, protecting against water loss upon stomatal closure. To address the limited understanding of genes associated with the natural variation of adult leaf cuticular waxes and their connection to gc, we conducted statistical genetic analyses using leaf transcriptomic, metabolomic, and physiological data sets collected from a maize (Zea mays L.) panel of ∼300 inbred lines. Through a random forest analysis with 60 cuticular wax traits, it was shown that high molecular weight wax esters play an important role in predicting gc. Integrating results from genome-wide and transcriptome-wide association studies via a Fisher's combined test revealed 231 candidate genes detected by all 3 association tests. Among these, 11 genes exhibit known or predicted roles in cuticle-related processes. Throughout the genome, multiple hotspots consisting of genome-wide association study signals for several traits from 1 or more wax classes were discovered, identifying 4 additional plausible candidate genes and providing insights into the genetic basis of correlated wax traits. Establishing a partially shared genetic architecture, we identified 35 genes for both gc and at least 1 wax trait, with 4 considered plausible candidates. Our study enhances the understanding of how adult leaf cuticle wax composition relates to gc and implicates both known and novel candidate genes as potential targets for optimizing productivity in maize.

Background It is important to explore renewable alternatives (e.g. biofuels) that can produce energy sources to help reduce reliance on fossil oils, and reduce greenhouse gases and waste solids resulted from fossil oils consumption. Camelina sativa is an oilseed crop which has received increasing attention due to its short life cycle, broader adaptation regions, high oil content, high level of omega-3 unsaturated fatty acids, and low-input requirements in agriculture practices. To expand its Camelina production areas into arid regions, there is a need to breed for new drought-tolerant cultivars. Leaf cuticular wax is known to facilitate plant development and growth under water-limited conditions. Dissecting the genetic loci underlying leaf cuticular waxes is important to breed for cultivars with improved drought tolerance. Results Here we combined phenotypic data and single nucleotide polymorphism (SNP) data from a spring C. sativa diversity panel using genotyping-by-sequencing (GBS) technology, to perform a large-scale genome-wide association study (GWAS) on leaf wax compositions. A total of 42 SNP markers were significantly associated with 15 leaf wax traits including major wax components such as total primary alcohols, total alkanes, and total wax esters as well as their constituents. The vast majority of significant SNPs were associated with long-chain carbon monomers (carbon chain length longer than C 28 ), indicating the important effects of long-chain carbon monomers on leaf total wax biosynthesis. These SNP markers are located on genes directly or indirectly related to wax biosynthesis such as maintaining endoplasmic reticulum (ER) morphology and enabling normal wax secretion from ER to plasma membrane or Golgi network-mediated transport. Conclusions These loci could potentially serve as candidates for the genetic control involved in intracellular wax transport that might directly or indirectly facilitate leaf wax accumulation in C. sativa and can be used in future marker-assisted selection (MAS) to breed for the cultivars with high wax content to improve drought tolerance.

Cooler canopy temperatures and glaucousness have both been identified as adaptive traits for improving abiotic stress tolerance in wheat. The objective of this study was to determine if glaucousness resulting from the constitutive production of leaf cuticular waxes was associated with cooler leaf and spike temperatures under heat stress and to identify associated quantitative trait loci (QTL). A set of 121 recombinant inbred lines (RILs) derived by crossing the heat tolerant wheat cultivar ‘Halberd’ and heat susceptible wheat cultivar ‘Karl92’ was utilized for QTL mapping. Flag leaf cuticular wax was extracted and quantified using a colorimetric technique at 10 days after pollination prior to initiation of the heat stress. The parental cultivars and RIL population were then subjected to a heat treatment of 38 °C and temperature depression of both leaf and spike was measured. The parental cultivar Halberd had high flag leaf wax content, and cooler leaf and spike temperatures compared to Karl92, with the RIL population showing significant genetic variation for these traits. QTL identified for leaf and spike temperature depression and leaf waxes explained 8–12 % of the phenotypic variation. Stable QTL for leaf wax content were located on chromosomes 1B and 5A with the 5A QTL region showing localization with QTL for leaf and spike temperature depression, indicating a genetic link between these traits. The results suggest that common genetic loci may influence both of these adaptive traits and could be targeted to improve adaptation to high temperature stress.

Leaf cuticular waxes play an important role in reducing evapotranspiration via diffusion. However, the ability of mature trees to regulate the biosynthesis of waxes to changing conditions (e.g., drought, light exposition) remain an open question, especially during the late growing season. This holds also true for one of the most widely distributed trees in Central Europe, the European beech tree ( Fagus sylvatica L. ). In order to investigate the ongoing formation of wax constituents like alkanes and fatty acids, we conducted a 13 CO 2 pulse-chase labelling experiment on sun-exposed and shaded branches of a mature beech tree during the late summer 2018. The 13 C-label was traced via compound-specific δ 13 C isotope analysis of n -alkanes and fatty acids to determine the de-novo biosynthesis within these compound classes. We did not observe a significant change in lipid concentrations during the late growing season, but we found higher n -alkane concentrations in sun-exposed compared to shaded leaves in August and September. The n- alkane and fatty acid composition showed ongoing modifications during the late growing season. Together with the uptake and following subsequent decrease of the 13 C-label, this suggests ongoing de-novo biosynthesis, especially of fatty acids in European beech leaves. Moreover, there is a high variability in the 13 C-label among individual branches and between sun-exposed and shaded leaves. At the same time, sun-exposed leaves invest more of the assimilated C into secondary metabolites such as lipids than shaded leaves. This indicates that the investigated mature beech tree could adjust its lipid production and composition in order to acclimate to changes in microclimates within the tree crown and during the investigated period.

The objective of this study was to evaluate leaf cuticular wax constituents across a broad selection of soybean (Glycine max[L.] Merr.) cultivars and their response to drought stress. Water deficit was imposed on 18 soybean cultivars by withholding irrigation for 10 d after the postflowering stage (R2 and R3 periods), and the effect on leaf waxes and seed yield was assessed by comparison with a well‐watered control. Leaf cuticular waxes were dominated by alkanes and triterpenoids, averaging 28% and 39% of total wax amount, respectively, with primary alcohols being the next most abundant class. The components of soybean leaf cuticular waxes were quite similar, but there were quantitative differences between the cultivars studied. Compared to well‐irrigated plants, all drought‐treated cultivars except DC exhibited a significant increase in wax amount. When expressed as an average across all cultivars, drought treatment caused a 30% increase in the total wax amount, with a corresponding 59% increase in alkanes, a 16% increase in primary alcohols, a 15% increase in triterpenoids, and a 26% increase in the total of unknowns. In all cultivars, the major alkane constituents were the C27, C29, C31, and C33 homologues, whereas the major primary alcohols were the C30 and C32 homologues, and drought exposure had only minor effects on the chain length distribution within these and other wax classes. Triterpenoid constituents were identified as 3‐keto‐olean‐12‐ene, lupenone, lupeol, α‐amyrin, and β‐amyrin, and each of these showed small quantitative changes after drought. Drought stress caused a large decrease in seed yield but did not affect 100‐seed mass, showing that soybean responds to postflowering drought by reducing seed numbers but not seed size. Seed yield was inversely correlated with wax amount after drought treatment, indicating that drought induction of leaf wax deposition does not contribute directly to seed set. This study sheds new light on our understanding of the relationship between soybean leaf wax induction and seed development in a water‐limiting environment.

This chapter contains sections titled: Introduction Defenses used against pathogens Defenses used against parasitic plants Defenses used against nematodes Defenses used against herbivorous insects Defenses used against vertebrate herbivores Defenses used against neighboring plants—allelopathy Conclusions Recommended reading References