<i>P</i>. <i>triticina</i> races used in the research and their definitions based on reactions to the Thatcher <i>Lr</i> isogenic differential set.

<p>Top line with each race represents the <i>Lr</i> genes the race is avirulent to, while the bottom line represents the <i>Lr</i> genes the race is virulent to.</p

Wheat differential gene expression induced by different races of <i>Puccinia triticina</i> - Fig 2

<p>Gene expression of three wheat pathogen response (PR) genes, (A) <i>PR-1</i> (FJ815167); (B) <i>PR-2 β-1</i>,<i>3 glucanase</i> (DQ090946), and (C) <i>PR-5</i> thaumatin-like protein (AF384146) in response to six races of <i>P</i>. <i>triticina</i>.</p

Spikes responses to dehydration.

<p>Spike of BW (<i>W1W1W2W2W3W3</i>), <i>w3</i> mutant (<i>W1W1W2W2w3w3</i>), <i>w1w2</i> double recessive line (<i>w1w1w2w2W3W3</i>), and the F₁ hybrid between <i>w3</i> and <i>w1w2</i> (<i>W1w1W2w2W3w3</i>) at 0 (<b><i>A</i></b>), 6 (<b><i>B</i></b>) and 12 h of dehydration (<b><i>C</i></b>). The designations are indicated on the top. The scale bars indicate 1 cm.</p

Variation of wax homologues between BW and <i>w3</i> mutant.

<p>Carbon atom numbers of alkanes, β-diketones, primary alcohols (alkan-1-ols), fatty acids, wax esters, and aldehydes are indicated on the x-axes. Their contents are indicated on y-axes as μg per g dried tissue (dry weight, DW). The error bars indicate standard deviation of the mean calculated from five biological replicates. β-D, β-diketone; and OH-β, hydroxy-β-diketones.</p

SEM micrographs of cuticle surfaces of flag leaf sheaths.

<p>(<b><i>A</i></b>) BW and (<b><i>B</i></b>) <i>w3</i> mutant. The scale bars indicated 1 μm.</p

Genetic analysis of <i>w3</i> mutant.

<p>(<b><i>A</i></b>) The F₁ hybrid between BW and the nonglaucous mutant is intermediate between its parents in glaucousness intensity. (<b><i>B</i></b>) The F₁ hybrid between the mutant and <i>w1w2</i> double recessive line was glaucous. The scale bars indicate 1 cm.</p

Chromosomal localization of the <i>W3</i> locus.

<p>(<b><i>A</i></b>) Molecular mapping of the <i>W3</i> locus on the chromosome arm 2BS. The markers are listed at the right side of the map, and genetic distances (cM) between the marker loci are indicated at the left side of the map. The <i>W3</i> locus is indicated in bold. The top of the map is towards the telomere and the bottom is towards the centromere. (<b><i>B</i></b>) The peduncles of CS N2B-T2D (1), F₁ hybrids of NG2 with N2B-T2D (2), with deletion line 2BS-1 (3), with 2BS-2 (4), with 2BS-3 (5), with 2BS-5 (6), with 2BS-10 (7) and with 2BS-14 (8). All the flag-leaf sheaths are nonglaucous. The scale bar indicate 1 cm.</p

Phenotype of the nonglaucous mutant.

<p>(<b><i>A</i></b>) The mutant was found in a small F₂ population derived from a cross between two RNAi transgenic plants in BW background due to premature drying out. (<b><i>B</i></b>) Adult plants of BW (left) and the nonglaucous mutant (right) at anthesis. (<b><i>C</i></b>) Adult plants of BW (left) and the nonglaucous mutant (right) at grain-filling stage.</p

Analysis of cuticle permeability of BW and <i>w3</i> mutant.

<p>Cuticle permeability was evaluated by air drying at room temperature (<b><i>A</i></b>) and by chlorophyll leaching in 80% ethanol (<b><i>B</i></b>). The numbers on the x-axes represent hours of treatment. Water loss or chlorophyll leaching at each time point is represented on the y-axes as percentages of the total water content or total chlorophyll content in the tissue. Measurements taken from six individuals were averaged.</p

<i>W3</i> Is a New Wax Locus That Is Essential for Biosynthesis of β-Diketone, Development of Glaucousness, and Reduction of Cuticle Permeability in Common Wheat

<div><p>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 <i>W1</i> and <i>W2</i>, and designated as <i>W</i>3 accordingly. Genetic analysis localized <i>W3</i> on chromosome arm 2BS. The <i>w3</i> mutation reduced 99% of β-diketones, which account for 63.3% of the total wax load of the wild-type. <i>W3</i> 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 <i>w3</i> 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 <i>w3</i> mutant. Transcription of 23 cuticle genes from five functional groups was altered in the <i>w3</i> mutant, 19 down-regulated and four up-regulated, suggesting a possibility that <i>W3</i> 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.</p><p>Key Message</p><p><i>W3</i> is essential for β-diketone biosynthesis but suppresses its hydroxylation. Loss-of-function mutation <i>w3</i> significantly increased cuticle permeability in terms of water loss and chlorophyll efflux.</p></div