Genetic mapping of a novel recessive allele for non-glaucousness in wild diploid wheat Aegilops tauschii: implications for the evolution of common wheat

Cuticular wax in wheat: biosynthesis, genetics, and the stress response

All terrestrial plants possess a hydrophobic cuticle in the outermost layer of their aerial organs that is composed of cutin and wax. The cuticle serves as the first barrier between the plant and the surrounding environment and plays a key role in the resistance of plants to abiotic and biotic stressors. Additionally, they are closely associated with plant growth and development. Cuticular wax has attracted considerable attention as the main mediator of cuticular functions. In this review, we summarize the advances in the research investigating wheat cuticular wax, focusing on three aspects that include biosynthesis, genetics, and stress responses. Additionally, we discuss the applications of cuticular wax in wheat breeding.

Lipidomic, Transcriptomic, and BSA-660K Single Nucleotide Polymorphisms Profiling Reveal Characteristics of the Cuticular Wax in Wheat

Plant epidermal wax helps protect plants from adverse environmental conditions, maintains the function of tissues and organs, and ensures normal plant development. However, the constituents of epidermal wax and the regulatory mechanism of their biosynthesis in wheat have not been fully understood. Wheat varieties with different wax content, Jinmai47 and Jinmai84, were selected to comparatively analyze their waxy components and genetic characteristics, using a combination of lipidomic, transcriptomic, and BSA-Wheat 660K chip analysis. Through lipidomic analysis, 1287 lipid molecules were identified representing 31 lipid subclasses. Among these, Diacylglycerols (DG), (O-acyl)-ω-hydroxy fatty acids (OAHFA), wax ester (WE), Triacylglycerols (TG), and Monoradylglycerols (MG) accounted for 96.4% of the total lipids in Jinmai84 and 94.5% in Jinmai47. DG, OAHFA, and WE were higher in Jinmai84 than in Jinmai47 with the content of OAHFA 2.88-fold greater and DG 1.66-fold greater. Transcriptome sequence and bioinformatics analysis revealed 63 differentially expressed genes related to wax biosynthesis. Differentially expressed genes (DEGs) were found to be involved with the OAHFA, DG, and MG of synthesis pathways, which enriched the wax metabolism pathway. Non-glaucous and glaucous bulks from a mapping population were used to identify single nucleotide polymorphisms (SNP) via 660K chip analysis. Two loci centered on chromosomes 2D and 4B were detected and the locus on 4B is likely novel. These data improve understanding of complex lipid metabolism for cuticular wax biosynthesis in wheat and lay the foundation for future detailed investigation of mechanisms regulating wax metabolism.

Phenotypic characterization of the glossy1 mutant and fine mapping of GLOSSY1 in common wheat (Triticum aestivum L.)

A novel wax locus GLOSSY1 was finely mapped to an approximately 308.1-kbp genomic interval on chromosome 2DS of wheat. The epicuticular wax, the outermost layer of aerial organs, gives plants their bluish-white (glaucous) appearance. Epicuticular wax is ubiquitous and provides an essential protective function against environmental stresses. In this study, we identified the glossy1 mutant on the basis of its glossy glume from an EMS population in the elite wheat (Triticum aestivum L.) cultivar Jimai22. The mutant had a dramatically different profile in total wax load and composition of individual wax constituents relative to the wild type, resulting in the increased cuticle permeability of glumes. The glossy glume phenotype was controlled by a single, semidominant locus mapping to the short arm of chromosome 2D, within a 308.1-kbp genomic interval that contained ten annotated protein-coding genes. These results pave the way for an in-depth analysis of the underlying genetic basis of wax formation patterns and enrich our understanding of mechanisms regulating wax metabolism.

The semidominant mutation w5 impairs epicuticular wax deposition in common wheat (Triticum aestivum L.)

The semidominant EMS-induced mutant w5 affects epicuticular wax deposition and mapped to an approximately 194-kb region on chromosome 7DL. Epicuticular wax is responsible for the glaucous appearance of plants and protects against many biotic and abiotic stresses. In wheat (Triticum aestivum L.), β-diketone is a major component of epicuticular wax in adult plants and contributes to the glaucousness of the aerial organs. In the present study, we identified an ethyl methanesulfonate-induced epicuticular wax-deficient mutant from the elite wheat cultivar Jimai22. Compared to wild-type Jimai22, the mutant lacked β-diketone and failed to form the glaucous coating on all aerial organs. The mutant also had significantly increased in cuticle permeability, based on water loss and chlorophyll efflux. Genetic analysis indicated that the mutant phenotype is controlled by a single, semidominant gene on the long arm of chromosome 7D, which was not allelic to the known wax gene loci W1-W4, and was therefore designated W5. W5 was finely mapped to an ~ 194-kb region (flanked by the molecular markers SSR2 and STARP11) that harbored four annotated genes according to the reference genome of Chinese Spring (RefSeq v1.0). Collectively, these data will broaden the knowledge of the genetic basis underlying epicuticular wax deposition in wheat.