Pm67, a new powdery mildew resistance gene transferred from Dasypyrum villosum chromosome 1V to common wheat(Triticum aestivum L.)

Powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici(Bgt), is a global disease that poses a serious threat to wheat production. To explore additional resistance gene, a wheatDasypyrum villosum 1 V#5(1 D) disomic substitution line NAU1813(2 n = 42) with high level of seedling resistance to powdery mildew was used to generate the recombination between chromosomes 1 V#5 and1 D. Four introgression lines, including t1 VS#5 ditelosomic addition line NAU1815, t1 VL#5 ditelosomic addition line NAU1816, homozygous T1 DL·1 VS#5 translocation line NAU1817, and homozygous T1 DS·1 VL#5 translocation line NAU1818 were developed from the selfing progenies of 1 V#5 and 1 D double monosomic line that derived from F1 hybrids of NAU1813/NAU0686. All of them were characterized by fluorescence in situ hybridization, genomic in situ hybridization, 1 V-specific markers analysis, and powdery mildew tests at different developmental stages. A new powdery mildew resistance gene named Pm67 was physically located in the terminal bin(FL 0.70–1.00) of 1 VS#5. Lines with Pm67 exhibited seedling stage immunity and tissue-differentiated reactions at adult plant stage. The sheaths, stems, and spikes of the Pm67 line were still immune, but the leaves showed a low degree of susceptibility.Microscopic observation showed that most penetration attempts were stopped in association with papillae on the sheath, and colonies cannot form conidia on the susceptible leaf of Pm67 line at adult plant stage, suggesting that the defence layers of the Pm67 line is tissue-differentiated. Thus, the T1 DL·1 VS#5 translocation line NAU1817 provides a new germplasm in wheat breeding for improvement of powdery mildew resistance.

Pm21 from Haynaldia villosa Encodes a CC-NBS- LRR Protein Conferring Powdery Mildew Resistance in Wheat

Dear Editor Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici （Bgt）, is a destructive disease of wheat throughout the world. One of the most important environmental-friendly and economical methods to reduce wheat loss caused by Bgt is to develop highly resistant varieties （Kuraparthy et al., 2007）. Pm21 from the wild species Haynaldia villosa （also known as Dasypyrum villosum） confers high resistance to Bgt in wheat throughout all growth stages. It has now become one of the most highly effective genetic loci introgressed into wheat from wild species, and the commercial varieties harboring Pm21 have been widely used in wheat production with more than 4 million hectares in China.

Characterization of a Putative New Semi-Dominant Reduced Height Gene, Rht_NM9, in Wheat(Triticum aestivum L.)

Plant height is an important agronomic trait in cereal crops, and can affect both plant architecture and grain yield. New dwarfing genes are required for improving the genetic diversity of wheat. In this study, a novel dwarf mutant, NM9, was created by treating seeds of the wheat variety NAU9918 with ethyl methanesulfonate （EMS）. NM9 showed obvious phenotypic changes, which were distinct from those caused by other dwarfing genes, especially the reduced plant height, increased effective tiller number, and elongated spike and grain length. The reduced plant height in NM9 was attributable to a semi-dominant dwarfing gene Rht__NM9, which was flanked by two closely linked SNP markers, SNP34 and SNP41, covering an 8.86-Mb region on the chromosome arm 2AS. The results of gibberellic acid （GA） sensitivity evaluation, comparative genomics analysis and allelism test indicated that RhtNM9 was neither allelic to Rht7 and Rht21 nor homoe- oallelic to Rht8, so Rht_NM9 was proposed to be a new dwarfing locus on the homoeologous group 2 chromosomes of wheat. Rht_NM9 has a negative effect on plant height and positive effects on effective tiller number and grain size, thus, Rht_NM9 could be used for elucidating the mechanisms underlying plant architecture and grain development.

Competitive Expression of Endogenous Wheat CENH3 May Lead to Suppression of Alien ZmCENH3 in Transgenic Wheat × Maize Hybrids

Uniparental chromosome elimination in wheat × maize hybrid embryos is widely used in double haploid production of wheat. Several explanations have been proposed for this phenomenon, one of which is that the lack of cross-species CENH3 incorporation may act as a barrier to interspecies hybridization. However, it is unknown if this mechanism applies universally. To study the role of CENH3 in maize chromosome elimination of wheat x maize hybrid embryos,？cos, maize ZmCENH3 and wheat aTaCENH3-B driven by the constitutive CaMV35S promoter were transformed into wheat variety Yangmai 158. Five transgenic lines for ZmCENH3 and six transgenic lines for ctTaCENH3-B were identified. RT-PCP analysis showed that the transgene could be transcribed at a low level in all ZmCENH3 transgenic lines, whereas transcription of endogenous wheat CENH3 was significantly up-regulated. Interestingly, the expression levels of both wheat CENH3 and ZmCENH3 in the ZmCENH3 transgenic wheat × maize hybrid embryos were higher than those in the non-transformed Yangmai 158 × maize hybrid embryos. This indicates that the alien ZmCENH3 in wheat may induce competitive expression of endogenous wheat CENH3, leading to suppression of ZmCENH3 over-expression. Eliminations of maize chromosomes in hybrid embryos of ZmCENH3 transgenic wheat ×maize and Yangmai 158 x maize were compared by observations on micronuelei presence, by marker analysis using maize SSRs （simple sequence repeats）, and by FISH （fluorescence in situ hybridization） using 45S rDNA as a probe. The results indicate that maize chromosome elimination events in the two crosses are not sigmficantly different. Fusion protein ZmCENH3- YFP could not be detected in ZmCENH3 transgenic wheat by either Western blotting or immnunostaining, whereas accumulation and loading of the αTaCENH3-B-GFP fusion protein was normal in aTaCENH3-B transgenic lines. As ZmCENH3-YFP did not accumulate after AM114 treatment, we speculate that low levels of ZmCENH3 protein in transgenic wheat may be one of the factors that lead to failure of suppression of maize chromatin elimination in ZmCENH3 transgenic wheat × maize hybrids.