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Wax biosynthesis is closely controlled by many regulators under different environmental conditions. We have previously shown that the module miR156–SQUAMOSA PROMOTER BINDING PROTEIN-LIKE9 (SPL9)–DEWAX is involved in the diurnal regulation of wax production; however, it was not determined whether other SPLs are also involved in wax synthesis. Here, we report that SPL13 also regulates drought-induced wax production, by directly and indirectly affecting the expression of the two wax biosynthesis genes ECERIFERUM1 (CER1) and CER4 , respectively. In addition, we show that SPL13 together with SPL9 redundantly regulates wax accumulation under both normal and drought stress conditions, and that simultaneous mutation of both genes additively increases cuticle permeability and decreases drought tolerance. However, in contrast to SPL9, SPL13 does not seem to participate in the DEWAX-mediated diurnal regulation of wax production. [ABSTRACT FROM AUTHOR]

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]

We report here the development of an inexpensive and engaging laboratory-based activity that can help students learn about the scientific method and the role of plant epicuticular waxes and surfactant function on waxy plant leaves as real life example in the agricultural industry. Three each of nontreated collard leaves ("Brassica oleraceae" L. Acephala group) and brushed-leaves were sprayed with water to demonstrate hydrophobicity of epicuticular waxes. Another set of three nontreated collard leaves was sprayed with Tween 20 containing water to demonstrate function of surfactant. Then, water retention rate was calculated by subtracting between before and after spray treatments. Water contact angles were measured by ImageJ software from nontreated and brushed-leaves from pictures taken by students' smartphones. This lab activity provides a foundation for instruction on the importance of the plant epicuticular waxes that is the outermost hydrophobic barrier in agrochemical applications and the function of surfactant on waxy leaf surface.

Epicuticular wax forms an outer coating on the aerial surfaces of many crop plants and is implicated in tolerance to several environmental stresses including drought. Advances in knowledge of biosynthesis and secretion of these leaf surface waxes could lead to improvements in crop-stress tolerance. To study the genetics of epicuticular wax deposition, we screened for bloomless (bm) and sparse-bloom (h) mutants with reduced glaucousness of abaxial sheath surfaces within chemically mutagenized populations of Sorghum bicolor (L.) Moench. We screened over 3974 segregating [M.sub.2] head rows with over 160,000 plants and identified 38 putative recessive epicuticular wax mutant alleles. We grouped 31 of these into allelic groups associated with one existing and 18 new epicuticular wax loci. The overall epicuticular wax mutation frequency was 0.88%. In addition, analysis of the mutant segregation frequencies within the [M.sub.2] rows allowed us to calculate the existence of five target meristem cells in a dormant ([M.sub.0]) seed embryo. The high epicuticular wax mutation rate and identification of 19 epicuticular wax loci indicate the presence of a complex genetic system of epicuticular wax production in sorghum as has been shown in other species. The new bloomless and sparse-bloom mutants identified here have a wide range of phenotypes and constitute a valuable resource for studies of the genetics and biosynthesis of epicuticular waxes and their effects on tolerance to environmental stresses such as drought.