Five Fatty Acyl-Coenzyme A Reductases Are Involved in the Biosynthesis of Primary Alcohols in Aegilops tauschii Leaves

Abstract

The diploid <i>Aegilops tauschii</i> is the D-genome donor to hexaploid wheat (<i>Triticum aestivum</i>) 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 <i>Ae. tauschii</i>, 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 <i>Ae. tauschii</i>. Ten putative wax biosynthetic genes encoding fatty acyl-coenzyme A reductase (FAR) were identified in the genome of <i>Ae. tauschii</i>. Five of these genes, <i>Ae.tFAR1</i>, <i>Ae.tFAR2</i>, <i>Ae.tFAR3</i>, <i>Ae.tFAR4</i>, and <i>Ae.tFAR6</i>, were found expressed in the leaf blades. Heterologous expression of the five Ae.tFARs in yeast (<i>Saccharomyces cerevisiae</i>) 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 <i>Ae.tFAR</i> paralogous genes were located on D chromosome of wheat and the wheat nullisomic-tetrasomic lines with the loss of <i>Ae.tFAR3</i> and <i>Ae.tFAR4</i> paralogous genes had significantly reduced levels of primary alcohols in the leaf blades. Collectively, these data suggest that <i>Ae.tFAR1</i>, <i>Ae.tFAR2</i>, <i>Ae.tFAR3</i>, <i>Ae.tFAR4</i>, and <i>Ae.tFAR</i>6 encode alcohol-forming FARs involved in the biosynthesis of primary alcohols in the leaf blades of <i>Ae. tauschii</i>. The information obtained in <i>Ae. tauschii</i> enables us to better understand wax biosynthesis in common wheat.