Abstract
The diploid Aegilops tauschii is the D-genome donor to hexaploid wheat (Triticum aestivum) and represents a potential source for genetic study in common wheat. The ubiquitous wax covering the aerial parts of plants plays an important role in protecting plants against non-stomatal water loss. Cuticular waxes are complex mixtures of very-long-chain fatty acids, alkanes, primary and/or secondary alcohols, aldehydes, ketones, esters, triterpenes, sterols, and flavonoids. In the present work, primary alcohols were identified as the major components of leaf cuticular wax in Ae. tauschii, with C26:0-OH being the dominant primary alcohol. Analysis by scanning electron microscope revealed that dense platelet-shaped wax crystals were deposited on leaf surfaces of Ae. tauschii. Ten putative wax biosynthetic genes encoding fatty acyl-coenzyme A reductase (FAR) were identified in the genome of Ae. tauschii. Five of these genes, Ae.tFAR1, Ae.tFAR2, Ae.tFAR3, Ae.tFAR4, and Ae.tFAR6, were found expressed in the leaf blades. Heterologous expression of the five Ae.tFARs in yeast (Saccharomyces cerevisiae) showed that Ae.tFAR1, Ae.tFAR2, Ae.tFAR3, Ae.tFAR4, and Ae.tFAR6 were predominantly responsible for the accumulation of C16:0, C18:0, C26:0, C24:0, and C28:0 primary alcohols, respectively. In addition, nine Ae.tFAR paralogous genes were located on D chromosome of wheat and the wheat nullisomic–tetrasomic lines with the loss of Ae.tFAR3 and Ae.tFAR4 paralogous genes had significantly reduced levels of primary alcohols in the leaf blades. Collectively, these data suggest that Ae.tFAR1, Ae.tFAR2, Ae.tFAR3, Ae.tFAR4, and Ae.tFAR6 encode alcohol-forming FARs involved in the biosynthesis of primary alcohols in the leaf blades of Ae. tauschii. The information obtained in Ae. tauschii enables us to better understand wax biosynthesis in common wheat.
Highlights
The outermost surfaces of land plants are covered by the cuticle, which is composed of a cutin polymer matrix and cuticular waxes
Of 12 genes, TaFAR2 and TaFAR5 are responsible for the biosynthesis of C18 and C22 primary alcohols, respectively (Wang et al, 2015c, 2016)
The results showed that the waxes from different organs consisted of the same chemical classes, including fatty acids, primary alcohols, esters, aldehydes, alkanes, hentriacontane-14, 16-dione (β-diketone), and OH-β-diketone (Table 1), the relative amount of each chemical class was quite different depending on organs
Summary
The outermost surfaces of land plants are covered by the cuticle, which is composed of a cutin polymer matrix and cuticular waxes. Cutin is a three dimensional polymer of mainly C16 and C18 hydroxy fatty acids, which are cross-linked in ester bonds directly or through a glycerol backbone (Pollard et al, 2008; Li and Beisson, 2009). Cuticular wax is a mixture of lipids, FARs in Aegilops tauschii consisting of, for example, very-long-chain fatty acids (VLCFAs, C20 to C34) and their derivatives, including alcohols, aldehydes, alkanes, ketones, and wax esters (Kunst and Samuels, 2003; Samuels et al, 2008; Lee and Suh, 2013). Cuticular wax protects plants against ultraviolet radiation, pathogen attack, and insect destruction (Eigenbrode and Espelie, 1995; Jenks et al, 2002; Solovchenko and Merzlyak, 2003; Pfündel et al, 2006)
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