The Inhibitor of wax 1 locus (Iw1) prevents formation of β‐ and OH‐β‐diketones in wheat cuticular waxes and maps to a sub‐cM interval on chromosome arm 2BS

Abstract

SUMMARYGlaucousness is described as the scattering effect of visible light from wax deposited on the cuticle of plant aerial organs. In wheat, two dominant genes lead to non-glaucous phenotypes: Inhibitor of wax 1 (Iw1) and Iw2. The molecular mechanisms and the exact extent (beyond visual assessment) by which these genes affect the composition and quantity of cuticular wax is unclear. To describe the Iw1 locus we used a genetic approach with detailed biochemical characterization of wax compounds. Using synteny and a large number of F 2 gametes, Iw1 was fine-mapped to a sub-cM genetic interval on wheat chromosome arm 2BS, which includes a single collinear gene from the corresponding Brachypodium and rice physical maps. The major components of flag leaf and peduncle cuticular waxes included primary alcohols, b-diketones and n-alkanes. Small amounts of C19-C27 alkyl and methylalkylresorcinols that have not previously been described in wheat waxes were identified. Using six pairs of BC 2 F 3 near-isogenic lines, we show that Iw1 inhibits the formation of b-and hydroxy-b-diketones in the peduncle and flag leaf blade cuticles. This inhibitory effect is independent of genetic background or tissue, and is accompanied by minor but consistent increases in n-alkanes and C 24 primary alcohols. No differences were found in cuticle thickness and carbon isotope discrimination in near-isogenic lines differing at Iw1.

A Metabolic Gene Cluster in the Wheat W1 and the Barley Cer-cqu Loci Determines β-Diketone Biosynthesis and Glaucousness

“…Conversely, alcohols, esters, and aldehydes accumulated to higher levels in leaf sheaths and peduncle of CASL*2BS, whereas these were low in these tissues of BL. In particular, the marked difference in b-diketone accumulation between the genotypes is in agreement with the accepted impact of b-diketones on glaucousness (Barber and Netting, 1968;Bianchi and Figini, 1986;Adamski et al, 2013;Zhang et al, 2013).…”

“…In particular, many Poaceae species (including wheat [Triticum spp], barley [Hordeum vulgare], rye [Secale cereale], and oat [Avena sativa]) produce very-long-chain b-diketones with characteristic structures likely formed along pathways different from those leading to more ubiquitous wax compounds (Supplemental Figure 1). Despite many years of research on b-diketone biosynthesis, particularly in barley and wheat (von Wettstein-Knowles, 1976, 1995von Wettstein-Knowles and Søgaard, 1980;Adamski et al, 2013;Zhang et al, 2013Zhang et al, , 2015, the genes and enzymes involved remain to be discovered.…”

Long noncoding miRNA gene represses wheat β-diketone waxes

“…6A and SI Appendix, Fig. S10), and the location is consistent with genetic markers from syntenic blocks from species such as Brachypodium distachyon that include the genes BRADI5G01180 and BRADI5G01160 (17,18,44). The Iw1 homology region lies within the promoter region of the Ae.…”

“…provide epistatic dominant inhibition over the W loci. In recent years, several reports have furthered the characterization of these loci, including fine-mapping of Iw1 (11), demonstrating Iw1 suppression of β-diketone wax accumulation (17), fine mapping of Iw2 in Ae. tauschii (12), comparative mapping of Iw1 and Iw2 in hexaploid wheat (18), determining the impact of W and Iw loci on glaucousness and cuticle permeability (3), and fine mapping of W1 in hexaploid wheat (19).…”

A morpho-physiological approach differentiates bread wheat cultivars of contrasting tolerance under cyclic water stress

“…Some variability of epicuticular waxes in Triticeae has already been described (Tulloch et al, 1980). More recently Adamski et al (2013) have noticed tubular/rod-shaped wax structures occurring predominantly on the abaxial leaf surface of a wheat variety.…”