Molecular cloning, functional verification, and evolution of TmPm3, the powdery mildew resistance gene of Triticum monococcum L.

Powdery mildew (Pm) is one of the most harmful diseases in wheat. Three Pm-resistance genes, Pm3, Pm21, and Pm8, have been cloned but most Pm3/Pm8 alleles have lost their resistance to Pm in hexaploid wheat. In this study, a new Pm3 homolog gene (TmPm3) was isolated from Triticum monococcum L. using a homology-based cloning strategy, being the first report of a functional Pm3 homolog gene from a diploid wheat species. The transient expression of TmPm3 in leaf epidermal cells showed that over-expressed TmPm3 could significantly inhibit the penetration of Blumeria graminis f. sp tritici conidia spores and the formation of haustoria. Sequence analysis of Pm3 alleles shed new light on the evolution of Pm3 genes, providing a better understanding of the molecular basis of disease resistance. This study also suggested that homology-based cloning of resistance genes is a feasible method for the isolation of functional resistance genes from wheat germplasm.

Cloning and characterization of leaf cDNAs that are differentially expressed between wheat hybrids and their parents.

Previous studies have shown that heterosis is associated with differential gene expression between hybrids and their parents. In this study, we performed a screen for genes that are differentially expressed between wheat hybrids and their parents in jointing-stage leaves and flag leaves using the differential display technique. Twenty-four differentially expressed cDNA were cloned and sequenced, and their expression patterns were confirmed by reverse-Northern blotting. Sequence analysis and database searches revealed that among the genes that showed differential expression between hybrid and parents were transcription factor genes and genes involved in metabolism, signal transduction, disease resistance, and retrotransposons. These results indicate that hybridization between two parental lines can cause changes in the expression of a variety of genes, and it is concluded that the altered pattern of gene expression in the hybrid may be responsible for the observed heterosis.

[Molecular tagging of a major powdery mildew resistance gene MlG in wheat derived from wild Emmer by using microsatellite marker].

Powdery mildew caused by Erysiphe graminis f. sp. tritici is one of the most important wheat diseases in many regions of the world. Breeding for resistant cultivars has been proved to be an effective and environmentally safe method to control diseases in wheat production. It is necessary to search for more resistance genes for the diversification of resistance genes in wheat breeding. An Isreali wild emmer wheat (Triticum dicoccoides) accession "G-305-M" was found resistant to the prevailing E. graminis f. sp. tritici isolate Race No. 15 in Beijing region. The powdery mildew resistance has been transferred from G-305-M into common wheat by crossing and backcrossing (G-305-M/781//Jing 411* 3). Genetic analysis showed that the resistance was controlled by a single dominant gene at the seedling stage. A segregating BC2F3 family of the cross "G-305-M/781//Jing 411* 3" with 167 plants was chosen for SSR analysis. Totally 96 wheat microsatellite primer pairs were screened, only one primer pair WMS570 could generate polymorphic DNA fragments between the resistant and susceptible plants. After evaluating this polymorphic marker in the segregating population, the microsatellite locus Xgwm570 mapped on chromosome 6AL was found to be linked to the resistance gene, with the estimated genetic distance of 14.9 +/- 3.0 cM. Based on the origin and chromosomal location of the gene, it is suggested that the resistance gene derived from G-305-M should be a novel Pm gene and is temporarily designated MlG.

[Relationship between differential expression patterns of multigene families and heterosis in a wheat diallel crosses].

In order to understand molecular basis of heterosis, the patterns of differential gene expression of multigene families between wheat hybrids and their parents in seedling leaves were analyzed by using mRNA differential display. Relationships between differential gene expression patterns, heterosis and F1 hybrid performance were determined. Four patterns of differential gene expression were observed, which include: (1) bands observed in both parents but not in the F1; (2) bands occurring in only one parent but not in the F1 or the other parent; (3) bands detected in only the F1 but neither of the parents; (4) bands present in one parent and F1 but absent in the other parent. The analysis showed that patterns of differential gene expression were not correlated with the F1 hybrid performance for all the eight agronomic traits. However, differentially expressed fragments that occurred only in the F1 but neither of the parents were found to be positively correlated with heterosis. On the contrary, fragments observed in both parents but not in the F1 were negatively correlated with heterosis. It is concluded that the differential expression of regulatory genes plays an important role in heterosis.