Abstract
A plant cuticle forms a hydrophobic layer covering plant organs, and plays an important role in plant development and protection from environmental stresses. We examined epicuticular structure, composition, and a MYB-based regulatory network in two Australian wheat cultivars, RAC875 and Kukri, with contrasting cuticle appearance (glaucousness) and drought tolerance. Metabolomics and microscopic analyses of epicuticular waxes revealed that the content of β-diketones was the major compositional and structural difference between RAC875 and Kukri. The content of β-diketones remained the same while those of alkanes and primary alcohols were increased by drought in both cultivars, suggesting that the interplay of all components rather than a single one defines the difference in drought tolerance between cultivars. Six wheat genes encoding MYB transcription factors (TFs) were cloned; four of them were regulated in flag leaves of both cultivars by rapid dehydration and/or slowly developing cyclic drought. The involvement of selected MYB TFs in the regulation of cuticle biosynthesis was confirmed by a transient expression assay in wheat cell culture, using the promoters of wheat genes encoding cuticle biosynthesis-related enzymes and the SHINE1 (SHN1) TF. Two functional MYB-responsive elements, specifically recognized by TaMYB74 but not by other MYB TFs, were localized in the TdSHN1 promoter. Protein structural determinants underlying the binding specificity of TaMYB74 for functional DNA cis-elements were defined, using 3D protein molecular modelling. A scheme, linking drought-induced expression of the investigated TFs with downstream genes that participate in the synthesis of cuticle components, is proposed.
Highlights
Wheat production is highly sensitive to environmental and climatic variation
We applied SEM and GC-MS to compare the wax crystal structure and biochemical make-up of leaf blade surfaces in Kukri and RAC875, grown under well-watered and mild drought conditions. Under both well-watered (Fig. 1B) and mild drought conditions (Fig. 1D), tubule-shaped crystals, which have been suggested to result from the high content of β-diketones (Adamski et al, 2013; Zhang et al, 2013), were abundant on the abaxial side of the RAC875 flag leaves
It has been established that the primary functions of cuticle and, of the cuticular waxes is in the protection against excessive solar irradiation and conservation of internal plant water (Yeats and Rose, 2013)
Summary
Wheat production is highly sensitive to environmental and climatic variation. Crops are often subjected to the negative influences of abiotic stresses, such as limited water supply, high salinity, and heat; these significantly impair grain yields (Porter and Semenov, 2005). The worst impact of temperature increases created by global warming is predicted to occur at low latitudes, where ~100 Mha of wheat are cultivated These territories include the major wheat-cropping regions of. Understanding the biochemical and molecular mechanisms which allow plants to cope with environmental challenges has a vital significance for improvement of stress tolerance and yield (Hrmova and Lopato, 2014) Towards this aim, two Australian wheat cultivars, Kukri and RAC875, both with excellent performance and superior grain quality, but showing contrasting drought tolerance (RAC875 outyielding Kukri by 24% under cyclic drought), have been subjected to intensive physiological (Izanloo et al, 2008), genetic (Bennett et al, 2012a, b), and metabolomic (Bowne et al, 2012) investigations. Glaucousness is a bluish-white coloration of plant organs, and results from a visual reflection of light by certain epicuticular waxes accumulated in the form of wax crystals on plant surfaces
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