The top 20 up-regulated transcription factor genes in leaves of the severe chlorosis line Ldn/KU-2111, as identified by microarray analysis.

<p>The top 20 up-regulated transcription factor genes in leaves of the severe chlorosis line Ldn/KU-2111, as identified by microarray analysis.</p

Genetic mapping of <i>Hch1</i> to the short arm of chromosome 7D.

<p>Genetic distances (cM) are shown on the left and markers on the right.</p

Comparison of photosynthetic activity of WT and chlorosis lines based on chlorophyll fluorescence.

<p>Each plant was grown at 23°C for 2 to 4 weeks. Mean values with the same letters were not significantly different (<i>P</i> < 0.05) (Tukey-Kramer’s HSD test).</p

Accelerated Senescence and Enhanced Disease Resistance in Hybrid Chlorosis Lines Derived from Interspecific Crosses between Tetraploid Wheat and <i>Aegilops tauschii</i>

<div><p>Hybrid chlorosis, a type of hybrid incompatibility, has frequently been reported in inter- and intraspecific crosses of allopolyploid wheat. In a previous study, we reported some types of growth abnormalities such as hybrid necrosis and observed hybrid chlorosis with mild or severe abnormalities in wheat triploids obtained in crosses between tetraploid wheat cultivar Langdon and four <i>Ae</i>. <i>tauschii</i> accessions and in their derived synthetic hexaploids. However, the molecular mechanisms underlying hybrid chlorosis are not well understood. Here, we compared cytology and gene expression in leaves to characterize the abnormal growth in wheat synthetics showing mild and severe chlorosis. In addition, we compared disease resistance to wheat blast fungus. In total 55 and 105 genes related to carbohydrate metabolism and 53 and 89 genes for defense responses were markedly up-regulated in the mild and severe chlorosis lines, respectively. Abnormal chloroplasts formed in the mesophyll cells before the leaves yellowed in the hybrid chlorosis lines. The plants with mild chlorosis showed increased resistance to wheat blast and powdery mildew fungi, although significant differences only in two, third internode length and maturation time, out of the examined agricultural traits were found between the wild type and plants showing mild chlorosis. These observations suggest that senescence might be accelerated in hybrid chlorosis lines of wheat synthetics. Moreover, in wheat synthetics showing mild chlorosis, the negative effects on biomass can be minimized, and they may show substantial fitness under pathogen-polluted conditions.</p></div

The top 19 up-regulated transcription factor genes in leaves of the mild chlorosis line Ldn/IG47202, as identified by microarray analysis.

<p>The top 19 up-regulated transcription factor genes in leaves of the mild chlorosis line Ldn/IG47202, as identified by microarray analysis.</p

Hypersensitive reaction (upper) and hyphal growth (lower) in epidermal cells of synthetic hexaploid wheat lines 48 h after inoculation with Br48, observed under a bright field (left) or fluorescence field (right).

<p>Each plant was grown at 23°C for 1 to 3 weeks. App; appressoria, HR; hypersensitive reaction, IH; infection hyphae.</p

Comparative TEM ultrastructure of chloroplast structures in the mesophyll cells of the WT and chlorosis lines.

<p>(A) Leaf phenotypes in the WT and severe chlorosis lines. In the chlorosis line, two types of leaves were represented, before and after appearance of chlorosis. (B) Chloroplasts in synthetic hexaploid wheat lines showing WT appearance and hybrid chlorosis. (C) The average area of chloroplasts in mesophyll cells of three leaves examined. (D) Ratio of the grana and plastoglobuli in chloroplasts of mesophyll cells. (E) Number of plastoglobuli. The values were expressed as means ± SD from three technical replicates, in each of which at least 25 mesophyll cells were observed. Student’s <i>t</i>-test was used to evaluate statistical significance (**<i>P</i> < 0.01) of differences between lines.</p

Synthetic hexaploid wheat plants exhibiting hybrid chlorosis.

<p>(A) Phenotypes of the normal growth (WT, Ldn/KU-2126), severe chlorosis (Ldn/KU-2111) and mild chlorosis (Ldn/IG47202) lines. The plants with mild chlorosis were grown for two months after sowing and showed lighter yellowish symptoms than those with severe chlorosis. (B) The first leaf phenotypes of plants with WT and with hybrid chlorosis. Each plant was grown at 23°C for 2 to 4 weeks.</p

List of the top 20 up-regulated carbohydrate metabolism genes in leaves of the severe chlorosis line Ldn/KU-2111 identified by microarray analysis.

<p>List of the top 20 up-regulated carbohydrate metabolism genes in leaves of the severe chlorosis line Ldn/KU-2111 identified by microarray analysis.</p

Summary of results from microarray analysis.

<p>(A) Venn diagram of genes differentially expressed between plants with severe chlorosis, mild chlorosis and type III necrosis. (B) Number of up- and down-regulated genes in leaves of the Ldn/KU-2111 and Ldn/IG47202 lines. Genes up- and down-regulated in the chlorosis line (Ldn/KU-2111) and (Ldn/IG47202) relative to WT were categorized into 18 functional groups.</p