The cuticular wax composition and crystal coverage of leaves and petals differ in a consistent manner between plant species.

Both leaves and petals are covered in a cuticle, which itself contains and is covered by cuticular waxes. The waxes perform various roles in plants' lives, and the cuticular composition of leaves has received much attention. To date, the cuticular composition of petals has been largely ignored. Being the outermost boundary between the plant and the environment, the cuticle is the first point of contact between a flower and a pollinator, yet we know little about how plant-pollinator interactions shape its chemical composition. Here, we investigate the general structure and composition of floral cuticular waxes by analysing the cuticular composition of leaves and petals of 49 plant species, representing 19 orders and 27 families. We show that the flowers of plants from across the phylogenetic range are nearly devoid of wax crystals and that the total wax load of leaves in 90% of the species is higher than that of petals. The proportion of alkanes is higher, and the chain lengths of the aliphatic compounds are shorter in petals than in leaves. We argue these differences are a result of adaptation to the different roles leaves and petals play in plant biology.

Fungicidal Activity of New Pyrrolo[2,3-d]thiazoles and Their Potential Action on the Tryptophan Metabolic Pathway and Wax Biosynthesis.

The main challenge in the development of agrochemicals is the lack of new leads and/or targets. It is critical to discover new molecular targets and their corresponding ligands. YZK-C22, which contains a 1,2,3-thiadiazol-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole skeleton, is a fungicide lead compound with broad-spectrum fungicidal activity. Previous studies suggested that the [1,2,4]triazolo[3,4-b][1,3,4]thiadiazole scaffold exhibited good antifungal activity. Inspired by this, a series of pyrrolo[2,3-d]thiazole derivatives were designed and synthesized through a bioisosteric strategy. Compounds C1, C9, and C20 were found to be more active against Rhizoctonia solani than the positive control YZK-C22. More than half of the target compounds provided favorable activity against Botrytis cinerea, where the EC50 values of compounds C4, C6, C8, C10, and C20 varied from 1.17 to 1.77 µg/mL. Surface plasmon resonance and molecular docking suggested that in vitro potent compounds C9 and C20 have a new mode of action instead of acting as pyruvate kinase inhibitors. Transcriptome analysis revealed that compound C20 can impact the tryptophan metabolic pathway, cutin, suberin, and wax biosynthesis of B. cinerea. Overall, pyrrolo[2,3-d]thiazole is discovered as a new fungicidal lead structure with a potential new mode of action for further exploration.

Decoding drought resilience: a comprehensive exploration of the cotton Eceriferum (CER) gene family and its role in stress adaptation.

BACKGROUND: The cuticular wax serves as a primary barrier that protects plants from environmental stresses. The Eceriferum (CER) gene family is associated with wax production and stress resistance. RESULTS: In a genome-wide identification study, a total of 52 members of the CER family were discovered in four Gossypium species: G. arboreum, G. barbadense, G. raimondii, and G. hirsutum. There were variations in the physicochemical characteristics of the Gossypium CER (GCER) proteins. Evolutionary analysis classified the identified GCERs into five groups, with purifying selection emerging as the primary evolutionary force. Gene structure analysis revealed that the number of conserved motifs ranged from 1 to 15, and the number of exons varied from 3 to 13. Closely related GCERs exhibited similar conserved motifs and gene structures. Analyses of chromosomal positions, selection pressure, and collinearity revealed numerous fragment duplications in the GCER genes. Additionally, nine putative ghr-miRNAs targeting seven G. hirsutum CER (GhCER) genes were identified. Among them, three miRNAs, including ghr-miR394, ghr-miR414d, and ghr-miR414f, targeted GhCER09A, representing the most targeted gene. The prediction of transcription factors (TFs) and the visualization of the regulatory TF network revealed interactions with GhCER genes involving ERF, MYB, Dof, bHLH, and bZIP. Analysis of cis-regulatory elements suggests potential associations between the CER gene family of cotton and responses to abiotic stress, light, and other biological processes. Enrichment analysis demonstrated a robust correlation between GhCER genes and pathways associated with cutin biosynthesis, fatty acid biosynthesis, wax production, and stress response. Localization analysis showed that most GCER proteins are localized in the plasma membrane. Transcriptome and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) expression assessments demonstrated that several GhCER genes, including GhCER15D, GhCER04A, GhCER06A, and GhCER12D, exhibited elevated expression levels in response to water deficiency stress compared to control conditions. The functional identification through virus-induced gene silencing (VIGS) highlighted the pivotal role of the GhCER04A gene in enhancing drought resistance by promoting increased tissue water retention. CONCLUSIONS: This investigation not only provides valuable evidence but also offers novel insights that contribute to a deeper understanding of the roles of GhCER genes in cotton, their role in adaptation to drought and other abiotic stress and their potential applications for cotton improvement.

BrBCAT1 mutation resulted in deficiency of epicuticular wax crystal in Chinese cabbage.

KEY MESSAGE: BrBCAT1 encoding a branched-chain amino acid aminotransferase was responsible for the glossy trait, which was verified by allelic mutants in Chinese cabbage. The glossy characteristic, thanks to the epicuticular wax crystal deficiency, is an excellent commodity character for leafy vegetables. Herein, two allelic glossy green mutants, wdm11 and wdm12, were isolated from an ethyl methane sulfonate (EMS)-mutagenized population of Chinese cabbage, and the mutant phenotype was recessive inherited. Cryo-SEM detected that epicuticular wax crystal in the mutant leaves was virtually absent. MutMap and Kompetitive allele-specific PCR analyses demonstrated that BraA06g006950.3C (BrBCAT1), homologous to AtBCAT1, encoding a branched-chain amino acid aminotransferase was the candidate gene. A SNP (G to A) on the fourth exon of BrBCAT1 in wdm11 caused the 233rd amino acid to change from glycine (G) to aspartic acid (D). A SNP (G to A) on the second exon of BrBCAT1 in wdm12 led to the 112th amino acid change from glycine (G) to arginine (R). Both of the allelic mutants had genetic structural variation in the candidate gene, which indicated that the mutant phenotype was triggered by the BrBCAT1 mutation. The expression levels of BrBCAT1 and genes related to fatty acid chain extension were decreased significantly in the mutant compared to the wild-type, which might result in epicuticular wax crystal deficiency in the mutants. Our findings proved that the mutation of BrBCAT1 induced the glossy phenotype and provided a valuable gene resource for commodity character improvement in Chinese cabbage.

Gene expression analysis of drought tolerance and cuticular wax biosynthesis in diploid and tetraploid induced wallflowers.

Whole-genome doubling leads to cell reprogramming, upregulation of stress genes, and establishment of new pathways of drought stress responses in plants. This study investigated the molecular mechanisms of drought tolerance and cuticular wax characteristics in diploid and tetraploid-induced Erysimum cheiri. According to real-time PCR analysis, tetraploid induced wallflowers exhibited increased expression of several genes encoding transcription factors (TFs), including AREB1 and AREB3; the stress response genes RD29A and ERD1 under drought stress conditions. Furthermore, two cuticular wax biosynthetic pathway genes, CER1 and SHN1, were upregulated in tetraploid plants under drought conditions. Leaf morphological studies revealed that tetraploid leaves were covered with unique cuticular wax crystalloids, which produced a white fluffy appearance, while the diploid leaves were green and smooth. The greater content of epicuticular wax in tetraploid leaves than in diploid leaves can explain the decrease in cuticle permeability as well as the decrease in water loss and improvement in drought tolerance in wallflowers. GC‒MS analysis revealed that the wax components included alkanes, alcohols, aldehydes, and fatty acids. The most abundant wax compound in this plant was alkanes (50%), the most predominant of which was C29. The relative abundance of these compounds increased significantly in tetraploid plants under drought stress conditions. These findings revealed that tetraploid-induced wallflowers presented upregulation of multiple drought-related and wax biosynthesis genes; therefore, polyploidization has proved useful for improving plant drought tolerance.

1-MCP treatment improves the postharvest quality of Jinxiu yellow peach by regulating cuticular wax composition and gene expression during cold storage.

This study aimed to analyze the effect of 1-methylcyclopropene (1-MCP) treatment on the postharvest quality, epidermal wax morphology, composition, and gene expression of Jinxiu yellow peach during cold storage. The results showed that 1-MCP treatment could maintain the postharvest quality of peach fruit as compared to control (CK) during cold storage. The wax crystals of peach fruit were better retained by 1-MCP, and they still existed in 0.6 and 0.9 µL/L 1-MCP treated fruit at 36 days. The total wax content in all the fruit increased first and then decreased during cold storage. Meanwhile, n-alkanes and primary alcohols were the main wax components. Compared to CK, 1-MCP treatment could delay the reduction of wax content during cold storage. The correlation analysis indicated that the postharvest quality of yellow peach was mainly affected by the contents of fatty acids and triterpenoids in cuticular wax. The transcriptomics results revealed PpaCER1, PpaKCS, PpaKCR1, PpaCYP86B1, PpaFAR, PpaSS2, and PpaSQE1 played the important roles in the formation of peach fruit wax. 1-MCP treatment upregulated PpaCER1 (18785414, 18786441, and 18787644), PpaKCS (18774919, 18789438, and 18793503), PpaKCR1 (18790432), and PpaCYP86B1 (18789815) to deposit more n-alkanes and fatty acids during cold storage. This study could provide a new perspective for regulating the postharvest quality of yellow peach in view of the application of cuticular wax. PRACTICAL APPLICATION: 'Jinxiu' yellow peach fruit is favorable among consumers because of its high commercial value. However, it ripens and deteriorates rapidly during storage, leading to serious economic loss and consumer disappointment. The effect of 1-methylcyclopropene (1-MCP) treatment on the postharvest quality, epidermal wax morphology, composition, and genes regulation of 'Jinxiu' yellow peach during cold storage was assessed. Compared to control, 1-MCP treatment could retain the storage quality of yellow peach by affecting cuticular wax composition and gene expression. This study could provide new perspective for regulating the postharvest quality of yellow peach in view of the application of cuticular wax.

An upstream signaling gene calmodulin regulates the synthesis of insect wax via activating fatty acid biosynthesis pathway.

Insect wax accumulates on the surface of insect cuticle, which acts as an important protective barrier against rain, ultraviolet light radiation, pathogens, etc. The waxing behavior, wax composition and molecular mechanism underling wax biosynthesis are unclear in dustywings. Herein, the current study determined the vital developmental stage for waxing behavior in dustywings, examined the components of waxy secretions, and identified key regulatory genes for wax biosynthesis. The wax glands were mainly located on the thorax and abdomen of dustywing adults. The adults spread the waxy secretions over their entire body surface. The metabolomics analysis identified 32 lipids and lipid-like molecules, 15 organic acids and derivatives, 7 benzenoids, etc. as the main components of waxy secretions. The fatty acids represented the largest proportion of the category of lipid and lipid-like molecules. The conjoint analysis of metabolomics and transcriptomics identified two crucial genes fatty acyl-CoA reductase (CsFAR) and calmodulin (CsCaM) for wax biosynthesis. The down-regulation of these genes via nanocarrier-mediated RNA interference technology significantly reduced the amount of wax particles. Notably, the RNAi of CsCaM apparently suppressed the expression of most genes in fatty acid biosynthesis pathway, indicating the CsCaM might act as a main upstream regulator of fatty acid biosynthesis pathway.

Relationship between skin greasiness and cuticular wax in harvested "Hongro" apples.

We investigated the ripening and skin greasiness of "Hongro" apples during storage at 20 °C. Postharvest treatment using 100 µLL-1 ethylene accelerated ripening and increased greasiness, whereas treatment using 1 µLL-1 1-methylcyclopropene delayed ripening and reduced greasiness. Scanning electron microscopy showed changes in cuticular wax structure linked to greasiness. Metabolic analysis identified specific metabolites related to greasiness, which varied upon postharvest treatment. Greasiness was positively associated with ethylene production and butyl-9,12-octadecadienoate content. Random forest modeling predicted greasiness levels with high accuracy, with root mean square error values of 0.322 and 0.362 for training and validation datasets, respectively. These findings illuminate the complex interplay between postharvest treatment, apple ripening, wax composition, and skin greasiness. The application of predictive models exemplifies the potential for technology-driven approaches in agriculture and aids in the development of postharvest strategies to control greasiness and maintain fruit quality.

AtMYB41 acts as a dual-function transcription factor that regulates the formation of lipids in an organ- and development-dependent manner.

The plant cuticle controls non-stomatal water loss and can serve as a barrier against biotic agents, whereas the heteropolymer suberin and its associated waxes are deposited constitutively at specific cell wall locations. While several transcription factors controlling cuticle formation have been identified, those involved in the transcriptional regulation of suberin biosynthesis remain poorly characterized. The major goal of this study was to further analyse the function of the R2R3-Myeloblastosis (MYB) transcription factor AtMYB41 in formation of the cuticle, suberin, and suberin-associated waxes throughout plant development. For functional analysis, the organ-specific expression pattern of AtMYB41 was analysed and Atmyb41ge alleles were generated using the CRISPR/Cas9 system. These were investigated for root growth and water permeability upon stress. In addition, the fatty acid, wax, cutin, and suberin monomer composition of different organs was evaluated by gas chromatography. The characterization of Atmyb41ge mutants revealed that AtMYB41 negatively regulates the production of cuticular lipids and fatty acid biosynthesis in leaves and seeds, respectively. Remarkably, biochemical analyses indicate that AtMYB41 also positively regulates the formation of cuticular waxes in stems of Arabidopsis thaliana. Overall, these results suggest that the AtMYB41 acts as a negative regulator of cuticle and fatty acid biosynthesis in leaves and seeds, respectively, but also as a positive regulator of wax production in A. thaliana stems.

Divergent evolution of the alcohol-forming pathway of wax biosynthesis among bryophytes.

The plant cuticle is a hydrophobic barrier, which seals the epidermal surface of most aboveground organs. While the cuticle biosynthesis of angiosperms has been intensively studied, knowledge about its existence and composition in nonvascular plants is scarce. Here, we identified and characterized homologs of Arabidopsis thaliana fatty acyl-CoA reductase (FAR) ECERIFERUM 4 (AtCER4) and bifunctional wax ester synthase/acyl-CoA:diacylglycerol acyltransferase 1 (AtWSD1) in the liverwort Marchantia polymorpha (MpFAR2 and MpWSD1) and the moss Physcomitrium patens (PpFAR2A, PpFAR2B, and PpWSD1). Although bryophyte harbor similar compound classes as described for angiosperm cuticles, their biosynthesis may not be fully conserved between the bryophytes M. polymorpha and P. patens or between these bryophytes and angiosperms. While PpFAR2A and PpFAR2B contribute to the production of primary alcohols in P. patens, loss of MpFAR2 function does not affect the wax profile of M. polymorpha. By contrast, MpWSD1 acts as the major wax ester-producing enzyme in M. polymorpha, whereas mutations of PpWSD1 do not affect the wax ester levels of P. patens. Our results suggest that the biosynthetic enzymes involved in primary alcohol and wax ester formation in land plants have either evolved multiple times independently or undergone pronounced radiation followed by the formation of lineage-specific toolkits.

Acyl carrier protein OsMTACP2 confers rice cold tolerance at the booting stage.

Low temperatures occurring at the booting stage in rice (Oryza sativa L.) often result in yield loss by impeding male reproductive development. However, the underlying mechanisms by which rice responds to cold at this stage remain largely unknown. Here, we identified MITOCHONDRIAL ACYL CARRIER PROTEIN 2 (OsMTACP2), the encoded protein of which mediates lipid metabolism involved in the cold response at the booting stage. Loss of OsMTACP2 function compromised cold tolerance, hindering anther cuticle and pollen wall development, resulting in abnormal anther morphology, lower pollen fertility, and seed setting. OsMTACP2 was highly expressed in tapetal cells and microspores during anther development, with the encoded protein localizing to both mitochondria and the cytoplasm. Comparative transcriptomic analysis revealed differential expression of genes related to lipid metabolism between the wild type and the Osmtacp2-1 mutant in response to cold. Through a lipidomic analysis, we demonstrated that wax esters, which are the primary lipid components of the anther cuticle and pollen walls, function as cold-responsive lipids. Their levels increased dramatically in the wild type but not in Osmtacp2-1 when exposed to cold. Additionally, mutants of two cold-induced genes of wax ester biosynthesis, ECERIFERUM1 and WAX CRYSTAL-SPARSE LEAF2, showed decreased cold tolerance. These results suggest that OsMTACP2-mediated wax ester biosynthesis is essential for cold tolerance in rice at the booting stage.

The Arabidopsis cytochrome P450 enzyme CYP96A4 is involved in the wound-induced biosynthesis of cuticular wax and cutin monomers.

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.

Morphology and chemical composition of Taiwan oil millet (Eccoilopus formosanus) epicuticular wax.

MAIN CONCLUSION: Taiwan oil millet has two types of epicuticular wax: platelet wax composed primarily of octacosanol and filament wax constituted essentially by the singular compound of octacosanoic acid. Taiwan oil millet (TOM-Eccoilopus formosanus) is an orphan crop cultivated by the Taiwan indigenous people. It has conspicuous white powder covering its leaf sheath indicating abundant epicuticular waxes, that may contribute to its resilience. Here, we characterized the epicuticular wax secretion in TOM leaf blade and leaf sheath using various microscopy techniques, as well as gas chromatography to determine its composition. Two kinds of waxes, platelet and filaments, were secreted in both the leaf blades and sheaths. The platelet wax is secreted ubiquitously by epidermal cells, whereas the filament wax is secreted by a specific cell called epidermal cork cells. The newly developed filament waxes were markedly re-synthesized by the epidermal cork cells through papillae protrusions on the external periclinal cell wall. Ultrastructural images of cork cell revealed the presence of cortical endoplasmic reticulum (ER) tubules along the periphery of plasma membrane (PM) and ER-PM contact sites (EPCS). The predominant wax component was a C28 primary alcohol in leaf blade, and a C28 free fatty acid in the leaf sheath, pseudopetiole and midrib. The wax morphology present in distinct plant organs corresponds to the specific chemical composition: platelet wax composed of alcohols exists mainly in the leaf blade, whereas filament wax constituted mainly by the singular compound C28 free fatty acids is present abundantly in leaf sheath. Our study clarifies the filament wax composition in relation to a previous study in sorghum. Both platelet and filament waxes comprise a protection barrier for TOM.

Larvae of Cryptolaemus montrouzieri (Coleoptera: Coccinellidae) Prioritize Secretion of Protective Wax Over Daily Consumption and Growth.

In holometabolous insects, the immature or larval stage is characterized by a high rate of food consumption. The nutrients obtained from which are directed towards the maintenance of metabolism, growth, pupation, and metamorphosis. However, when resources are scarce, the lack thereof can affect the growth rate and compromise the metamorphosis and formation of adults. Do increased energy expenditures yield outcomes similar to those resulting from restricted food intake during the larval stage? We hypothesized that removing the wax layer from the larvae of the ladybird Cryptolaemus montrouzieri Mulsant, 1850 would result in increased energy expenditure, which can compromise both larval growth and adult size. We compared the development time, feeding rate, and adult size of larvae with an intact wax layer, and those with constantly removed wax layers. We found that the production of the wax layer was continuous. Unlike the waxed larvae, the larvae of C. montrouzieri extended their development time in response to energy depletion through wax removal. The total number of mealybugs consumed by waxless larvae was higher than the total number consumed by waxed larvae; however, the daily consumption of waxless larvae was lower than that of waxed larvae. Furthermore, the adults of waxless larvae were smaller than those whose larvae had intact wax layers. This suggests that the cost associated with wax layer secretion is a pivotal factor in larval growth. Removing this layer does not get compensated by increased larval feeding or extended development time.

MdBT2 regulates nitrogen-mediated cuticular wax biosynthesis via a MdMYB106-MdCER2L1 signalling pathway in apple.

Cuticular waxes play important roles in plant development and the interaction between plants and their environment. Researches on wax biosynthetic pathways have been reported in several plant species. Also, wax formation is closely related to environmental condition. However, the regulatory mechanism between wax and environmental factors, especially essential mineral elements, is less studied. Here we found that nitrogen (N) played a negative role in the regulation of wax synthesis in apple. We therefore analysed wax content, composition and crystals in BTB-TAZ domain protein 2 (MdBT2) overexpressing and antisense transgenic apple seedlings and found that MdBT2 could downregulate wax biosynthesis. Furthermore, R2R3-MYB transcription factor 16-like protein (MdMYB106) interacted with MdBT2, and MdBT2 mediated its ubiquitination and degradation through the 26S proteasome pathway. Finally, HXXXD-type acyl-transferase ECERIFERUM 2-like1 (MdCER2L1) was confirmed as a downstream target gene of MdMYB106. Our findings reveal an N-mediated apple wax biosynthesis pathway and lay a foundation for further study of the environmental factors associated with wax regulatory networks in apple.

Influence of Cuticular Waxes from Triticale on Rumen Fermentation: A Metabolomic and Microbiome Profiling Study.

Cuticular wax, a critical defense layer for plants, remains a relatively unexplored factor in rumen fermentation. We investigated the impact of cuticular wax on rumen fermentation using triticale as a model. In total, six wax classes were identified, including fatty acids, aldehydes, alkane, primary alcohol, alkyresorcinol, and ß-diketone, with low-bloom lines predominated by 46.05% of primary alcohols and high-bloom lines by 35.64% of ß-diketone. Low-wax addition (2.5 g/kg DM) increased the gas production by 19.25% (P < 0.05) and total volatile fatty acids by 6.34% (P > 0.05), and enriched key carbohydrate-fermenting rumen microbes like Saccharofermentans, Ruminococcus, and Prevotellaceae, when compared to non-wax groups. Metabolites linked to nucleotide metabolism, purine metabolism, and protein/fat digestion in the rumen showed a positive correlation with low-wax, benefiting rumen microbes. This study highlights the intricate interplay among cuticular wax, rumen microbiota, fermentation, and metabolomics in forage digestion, providing insights into livestock nutrition and forage utilization.

NAC transcription factor SlNOR-like1 plays a dual regulatory role in tomato fruit cuticle formation.

The plant cuticle is an important protective barrier on the plant surface, constructed mainly by polymerized cutin matrix and a complex wax mixture. Although the pathway of plant cuticle biosynthesis has been clarified, knowledge of the transcriptional regulation network underlying fruit cuticle formation remains limited. In the present work, we discovered that tomato fruits of the NAC transcription factor SlNOR-like1 knockout mutants (nor-like1) produced by CRISPR/Cas9 [clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9] displayed reduced cutin deposition and cuticle thickness, with a microcracking phenotype, while wax accumulation was promoted. Further research revealed that SlNOR-like1 promotes cutin deposition by binding to the promoters of glycerol-3-phosphate acyltransferase6 (SlGPAT6; a key gene for cutin monomer formation) and CUTIN DEFICIENT2 (SlCD2; a positive regulator of cutin production) to activate their expression. Meanwhile, SlNOR-like1 inhibits wax accumulation, acting as a transcriptional repressor by targeting wax biosynthesis, and transport-related genes 3-ketoacyl-CoA synthase1 (SlKCS1), ECERIFERUM 1-2 (SlCER1-2), SlWAX2, and glycosylphosphatidylinositol-anchored lipid transfer protein 1-like (SlLTPG1-like). In conclusion, SlNOR-like1 executes a dual regulatory effect on tomato fruit cuticle development. Our results provide a new model for the transcriptional regulation of fruit cuticle formation.

MdDEWAX decreases plant drought resistance by regulating wax biosynthesis.

Apple epidermal wax protects plants from environmental stresses, determines fruit gloss and improves postharvest storage quality. However, the molecular mechanisms underlying the biosynthesis and regulation of apple epidermal waxes are not fully understood. In this study, we isolated a MdDEWAX gene from apple, which localized in the nucleus, expressed mainly in apple fruit, and induced by drought. We transformed the MdDEWAX gene into Arabidopsis, and found that heterologous expression of MdDEWAX reduced the accumulation of cuticular waxes in leaves and stems, increased epidermal permeability, the rate of water loss, and the rate of chlorophyll extraction of leaves and stems, altered the sensitivity to ABA, and reduced drought tolerance. Meanwhile, overexpression or silencing of the gene in the epidermis of apple fruits decreased or increased wax content, respectively. This study provides candidate genes for breeding apple cultivars and rootstocks with better drought tolerance.

A 3-Ketoacyl-CoA Synthase 10 (KCS10) Homologue from Alfalfa Enhances Drought Tolerance by Regulating Cuticular Wax Biosynthesis.

Cuticular wax, forming the first line of defense against adverse environmental stresses, comprises very long-chain fatty acids (VLCFAs) and their derivatives. 3-Ketoacyl-CoA synthase (KCS) is a rate-limiting enzyme for VLCFA biosynthesis. In this study, we isolated KCS10, a KCS gene from alfalfa, and analyzed the effect of gene expression on wax production and drought stress in transgenic plants. MsKCS10 overexpression increased compact platelet-like crystal deposition and promoted primary alcohol biosynthesis through acyl reduction pathways in alfalfa leaves. Overexpression of MsKCS10 induced the formation of coiled-rodlet-like crystals and increased n-alkane content through decarbonylation pathways in tobacco and tomato fruits. Overexpression of MsKCS10 enhanced drought tolerance by limiting nonstomatal water loss, improving photosynthesis, and maintaining osmotic potential under drought stress in transgenic tobacco. In summary, MsKCS10 plays an important role in wax biosynthesis, wax crystal morphology, and drought tolerance, although the mechanisms are different among the plant species. MsKCS10 can be targeted in future breeding programs to improve drought tolerance in plants.

Fine-tuning the activities of ß-KETOACYL-COA SYNTHASE 3 (KCS3) and KCS12 in Arabidopsis is essential for maintaining cuticle integrity.

The plant cuticle, consisting of wax and cutin, is involved in adaptations to various environments. ß-Ketoacyl-CoA synthases (KCSs) usually serve as a component of the fatty acid elongation complex that participates in the production of very long-chain fatty acids and provides precursors for the synthesis of various lipids, including wax; however, we recently reported that KCS3 and KCS12 negatively regulate wax biosynthesis. In this current study, we observed that unlike KCS3-overexpressing (OE) lines, KCS12-OE lines had fused floral organs because of abnormal cuticle biosynthesis. This prompted us to compare the functions of KCS3 and KCS12 during cuticle formation. Mutation of KCS3 caused greater effects on wax production, whereas mutation of KCS12 exerted more severe effects on cutin synthesis. The double-mutant kcs3 kcs12 had significantly increased wax and cutin contents compared to either single-mutant, suggesting that KCS12 and KCS3 have additive effects on cuticle biosynthesis. Cuticle permeability was greater for the double-mutant than for the single mutants, which ultimately led to increased susceptibility to drought stress and floral-organ fusion. Taken together, our results demonstrate the regulatory roles of KCS3 and KCS12 during cuticle biosynthesis, and show that maintaining KCS3 and KCS12 expression at certain levels is essential for the formation of a functional cuticle layer.