Transcriptome Analysis Identifies a 140 kb Region of Chromosome 3B Containing Genes Specific to Fusarium Head Blight Resistance in Wheat

Fusarium head blight (FHB), mainly caused by Fusarium graminearum, is one of the most destructive fungal diseases of wheat (Triticum aestivum L.). Because of the quantitative nature of FHB resistance, its mechanism is poorly understood. We conducted a comparative transcriptome analysis to identify genes that are differentially expressed in FHB-resistant and FHB-susceptible wheat lines grown under field conditions for various periods after F. graminearum infection and determined the chromosomal distribution of the differentially expressed genes (DEGs). For each line, the expression in the spike (which exhibits symptoms in the infected plants) was compared with that in the flag leaves (which do not exhibit symptoms in the infected plants). We identified an island of 53 constitutive DEGs in a 140 kb region with high homology to the FhbL693b region on chromosome 3B. Of these genes, 13 were assigned to specific chloroplast-related pathways. Furthermore, one gene encoded inositol monophosphate (IMPa) and two genes encoded ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). Our findings suggest that the temporary susceptibility in locally infected spikes results from the cross-talk between RuBisCO and IMPa, which blocks secondary signaling pathways mediated by salicylic acid and induces a systemic acquired resistance in the distant leaf tissue

Differential effect of whole-ear shading after heading on the physiology, biochemistry and yield index of stay-green and non-stay-green wheat genotypes.

Two winter wheat cultivars (the functional stay-green CN12 and non-stay-green CN19) were used to investigate the effects of ear-shading on grain yield and to elucidate the differential mechanisms of different cultivars. The photosynthetic parameters, chlorophyll fluorescence, antioxidant enzyme activities, and chlorophyll contents were measured 0, 15 and 30 days after heading (DAH) under both shaded and non-shaded conditions. The final grain-yield index was also measured. Shading had a smaller effect on the net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), stomatal conductance (Gs), maximal photochemical efficiency of PSII (Fv/Fm) and coefficient of non-photochemical fluorescence quenching (qN) but a greater effect on both superoxide dismutase (SOD) and catalase (CAT) activities in CN12 than it did in CN19. Shading slightly altered the timeframe of leaf senescence in CN12 and may have accelerated leaf senescence in CN19. Moreover, shading had only a small effect on the weight of grains per spike (WGS) in CN12 compared with CN19, mainly resulting from the number of grains per spike (NGS) rather than the 1000-grain weight (SGW). In conclusion, the flag leaves of functional stay-green wheat could serve as potential "buffers" and/or "compensators" for ear photosynthesis, which is actively regulated by the antioxidant enzyme system and prevents yield loss. Thus, a functional stay-green genotype could be more tolerant to environmental stress than a non-stay-green genotype

Changes in Chlorophyll Content Between CN12 and CN19 Under Shading.

<p>(A), Chlorophyll a (<i>Chl a</i>) content; (B), chlorophyll b (<i>Chl b</i>) content; (C), total chlorophyll content; and (D), <i>Chl a</i>/<i>b</i>. Bars represent the mean ± (SE). Asterisks represent statistically significant differences, as follows: **P≤0.01 and *P≤0.05. Letters represent the probability of multiple comparisons of the means of different genotypes and treatments at each time point, as follows: capital letter, P≤0.01; lowercase letter, P≤0.05. An asterisk in the trend line represents the difference between two adjacent time points for the same genotype and treatment.</p

Changes in Antioxidant Enzyme Activity and Related Biochemical Parameters in CN12 and CN19 Under Shading.

<p>(A), superoxide dismutase (SOD); (B), catalase (CAT); (C), peroxidase (POD); and (D), malondialdehyde (MDA). The bars represent the mean ± (SE). Asterisks represent statistically significant differences, as follows: **P≤0.01 and *P≤0.05. Letters represent the probability of multiple comparisons of the means of different genotypes and treatments at each time point, as follows: capital letter, P≤0.01; lowercase letter, P≤0.05. An asterisk in the trend line represents the difference between two adjacent time points for the same genotype and treatment.</p

Changes in Chlorophyll Florescence Parameters Between CN12 and CN19 Under Shading.

<p>(A), Maximal photochemical efficiency of PSІІ in dark-adapted leaves (<i>Fv</i> /<i>Fm</i>); (B), efficiency of excitation capture by open PSII reaction centers (<i>Fv’/Fm’</i>); (C), photochemical quenching coefficient (<i>qP</i>); (D), quantum yield of photochemical energy conversion in PSII (<i>Ф</i>_PSII); and (E), regulated non-photochemical energy loss in PSII (<i>qN</i>). Bars represent the mean ± (SE). Asterisks represent statistically significant differences, as follows: **P≤0.01 and *P≤0.05. Letters represent the probability of multiple comparisons of the means of different genotypes and treatments at each time point, as follows: capital letter, P≤0.01; lowercase letter, P≤0.05. An asterisk in the trend line represents the difference between two adjacent time points for the same genotype and treatment.</p

Changes in Photosynthetic Parameters Between the Stay-Green CN12 and Non-Stay-Green CN19 Wheat Cultivars Under Shading.

<p>(A), Net photosynthetic rate (<i>Pn</i>); (B), stomatal conductance (<i>Gs</i>); (C), intercellular CO₂ concentration (<i>Ci</i>); and (D), transpiration rate (<i>Tr</i>). The bars represent the mean ± standard error (SE). Asterisks represent statistically significant differences, as follows: **P≤0.01 and *P≤0.05. Letters represent the probability of multiple comparisons of the means of different genotypes and treatments at each time point, as follows: capital letter, P≤0.01; lowercase letter, P≤0.05. An asterisk in the trend line represents the difference between two adjacent time points for the same genotype and treatment.</p

Effects of Shading Treatment on Grain Production and Weights in CN12 and CN19.

<p>Effects of Shading Treatment on Grain Production and Weights in CN12 and CN19.</p

Collinearity Analysis and High-Density Genetic Mapping of the Wheat Powdery Mildew Resistance Gene <i>Pm40</i> in PI 672538

<div><p>The wheat powdery mildew resistance gene <i>Pm40</i>, which is located on chromosomal arm 7BS, is effective against nearly all prevalent races of <i>Blumeria gram</i>inis f. sp <i>tritici</i> (<i>Bgt</i>) in China and is carried by the common wheat germplasm PI 672538. A set of the F₁, F₂ and F_2:3 populations from the cross of the resistant PI 672538 with the susceptible line L1034 were used to conduct genetic analysis of powdery mildew resistance and construct a high-density linkage map of the <i>Pm40</i> gene. We constructed a high-density linkage genetic map with a total length of 6.18 cM and average spacing between markers of 0.48 cM.<i>Pm40</i> is flanked by <i>Xwmc335</i> and <i>BF291338</i> at genetic distances of 0.58 cM and 0.26 cM, respectively, in deletion bin C-7BS-1-0.27. Comparative genomic analysis based on EST-STS markers established a high level of collinearity of the <i>Pm40</i> genomic region with a 1.09-Mbp genomic region on <i>Brachypodium</i> chromosome 3, a 1.16-Mbp genomic region on rice chromosome 8, and a 1.62-Mbp genomic region on sorghum chromosome 7. We further anchored the <i>Pm40</i> target intervals to the wheat genome sequence. A putative linear index of 85 wheat contigs containing 97 genes on 7BS was constructed. In total, 9 genes could be considered as candidates for the resistances to powdery mildew in the target genomic regions, which encoded proteins that were involved in the plant defense and response to pathogen attack. These results will facilitate the development of new markers for map-based cloning and marker-assisted selection of <i>Pm40</i> in wheat breeding programs.</p></div

Phenotypes of F₁, F₂, and F_2:3 Populations Obtained from PI 672538/L1034 with the <i>Bgt15</i> Isolate.

<p>Phenotypes of F₁, F₂, and F_2:3 Populations Obtained from PI 672538/L1034 with the <i>Bgt15</i> Isolate.</p