Abstract
The cuticle plays important roles in plant development, growth and defense against biotic and abiotic attacks. Crystallized epicuticular wax, the outermost layer of cuticle, is visible as white-bluish glaucousness. In crops like barley and wheat, glaucousness is trait of adaption to the dry and hot cultivation conditions, and hentriacontane-14,16-dione (β-diketone) and its hydroxy derivatives are the major and unique components of cuticular wax in the upper parts of adult plants. But their biosynthetic pathway and physiological role largely remain unknown. In the present research, we identified a novel wax mutant in wheat cultivar Bobwhite. The mutation is not allelic to the known wax production gene loci W1 and W2, and designated as W3 accordingly. Genetic analysis localized W3 on chromosome arm 2BS. The w3 mutation reduced 99% of β-diketones, which account for 63.3% of the total wax load of the wild-type. W3 is necessary for β-diketone synthesis, but has a different effect on β-diketone hydroxylation because the hydroxy-β-diketones to β-diketone ratio increased 11-fold in the w3 mutant. Loss of β-diketones caused failure to form glaucousness and significant increase of cuticle permeability in terms of water loss and chlorophyll efflux in the w3 mutant. Transcription of 23 cuticle genes from five functional groups was altered in the w3 mutant, 19 down-regulated and four up-regulated, suggesting a possibility that W3 encodes a transcription regulator coordinating expression of cuticle genes. Biosynthesis of β-diketones in wheat and their implications in glaucousness formation and drought and heat tolerance were discussed.Key Message W3 is essential for β-diketone biosynthesis but suppresses its hydroxylation. Loss-of-function mutation w3 significantly increased cuticle permeability in terms of water loss and chlorophyll efflux.
Highlights
During transition from water to land colonization, plants developed an array of mechanisms for adaptation to the desiccation environment
To test if the mutation was due to transgene insertion, we screened 38 nonglaucous F2 individuals derived from the cross between NG1 and BW for the transformation selection marker bar gene and RNAi transgene constructs [38] by targeting at the Ubq-bar and gus-nos junctions, respectively
Result showed that eight plants were negative for both the Ubq-bar and gus-nos junctions, and 7 additional plants were negative for the gus-nos junction
Summary
During transition from water to land colonization, plants developed an array of mechanisms for adaptation to the desiccation environment. One of these mechanisms is deposition of cuticle, a hydrophobic coat, to cover the aerial organ surfaces. Cuticle consists of the fundamental framework of cutin and intracuticular wax inserted in it and epicuticular wax overlaid on them. Cutin is the cell wall-bounded ester polymer of hydroxy fatty acids [2,3,4], and waxes are the very long chain fatty acids (VLCFAs) and their derivatives including alcohols, aldehydes, alkanes, ketones and wax esters [5]. Variation in epicuticular wax composition causes changes in plant appearance: glaucous or nonglaucous. Glaucousness, the bluish-white look, is the visible form of densely arrayed wax crystals
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