Wheat powdery mildew resistance gene Pm13 encodes a mixed lineage kinase domain-like protein.

Wheat powdery mildew is one of the most destructive diseases threatening global wheat production. The wild relatives of wheat constitute rich sources of diversity for powdery mildew resistance. Here, we report the map-based cloning of the powdery mildew resistance gene Pm13 from the wild wheat species Aegilops longissima. Pm13 encodes a mixed lineage kinase domain-like (MLKL) protein that contains an N-terminal-domain of MLKL (MLKL_NTD) domain in its N-terminus and a C-terminal serine/threonine kinase (STK) domain. The resistance function of Pm13 is validated by mutagenesis, gene silencing, transgenic assay, and allelic association analyses. The development of introgression lines with significantly reduced chromosome segments of Ae. longissima encompassing Pm13 enables widespread deployment of this gene into wheat cultivars. The cloning of Pm13 may provide valuable insights into the molecular mechanisms underlying Pm13-mediated powdery mildew resistance and highlight the important roles of kinase fusion proteins (KFPs) in wheat immunity.

Mapping of the novel powdery mildew resistance gene Pm2Mb from Aegilops biuncialis based on ph1b-induced homoeologous recombination.

KEY MESSAGE: A novel powdery mildew resistance gene Pm2Mb from Aegilops biuncialis was transferred into common wheat and mapped to chromosome 2MbL bin FL 0.49-0.66 by molecular cytogenetic analysis of 2Mb recombinants. Aegilops biuncialis, a wild relative of common wheat, is highly resistant to powdery mildew. Previous studies identified that chromosome 2Mb in Chinese Spring (CS)-Ae. biuncialis 2Mb disomic addition line TA7733 conferred high resistance to powdery mildew, and the resistance gene was temporarily designated as Pm2Mb. In this study, a total of 65 CS-Ae. biuncialis 2Mb recombinants were developed by ph1b-induced homoeologous recombination and they were grouped into 12 different types based on the presence of different markers of 2Mb-specificity. Segment sizes and breakpoints of each 2Mb recombinant type were further characterized using in situ hybridization and molecular marker analyses. Powdery mildew responses of each type were assessed by inoculation of each 2Mb recombinant-derived F2 progenies using the isolate E05. Combined analyses of in situ hybridization, molecular markers and powdery mildew resistance data of the 2Mb recombinants, the gene Pm2Mb was cytologically located to an interval of FL 0.49-0.66 in the long arm of 2Mb, where 19 2Mb-specific markers were located. Among the 65 2Mb recombinants, T-11 (T2DS.2DL-2MbL) and T-12 (Ti2DS.2DL-2MbL-2DL) contained a small 2MbL segment harboring Pm2Mb. Besides, a physical map of chromosome 2Mb was constructed with 70 2Mb-specific markers in 10 chromosomal bins and the map showed that submetacentric chromosome 2Mb of Ae. biuncialis was rearranged by a terminal intrachromosomal translocation. The newly developed 2Mb recombinants with powdery mildew resistance, the 2Mb-specific molecular markers and the physical map of chromosome 2Mb will benefit wheat disease breeding as well as fine mapping and cloning of Pm2Mb.

Wheat heat shock factor TaHsfA2d contributes to plant responses to phosphate deficiency.

Phosphate (Pi) availability has become a major constraint limiting crop growth and production. Heat shock factors (Hsfs) play important roles in mediating plant resistance to various environmental stresses, including heat, drought and salinity. However, whether members of the Hsf family are involved in the transcriptional regulation of plant responses to Pi insufficiency has not been reported. Here, we identified that TaHsfA2d, a member of the heat shock factor family, was strongly repressed by Pi deficiency. Overexpressing TaHsfA2d-4A in Arabidopsis results in significantly enhanced sensitivity to Pi deficiency, evidenced by increased anthocyanin content, decreased proliferation and elongation of lateral roots, and reduced Pi uptake. Furthermore, RNA-seq analyses showed that TaHsfA2d-4A functions through up-regulation of a number of genes involved in stress responses and flavonoid biosynthesis. Collectively, these results provide evidence that TaHsfA2d participates in the regulation of Pi deficiency stress, and that TaHsfA2d could serve as a valuable gene for genetic modification of crop tolerance to Pi starvation.

Development and Characterization of Triticum aestivum-Aegilops longissima 6Sl Recombinants Harboring a Novel Powdery Mildew Resistance Gene Pm6Sl.

Powdery mildew of wheat is a foliar disease that is spread worldwide. Cultivation of resistant varieties is the most effective, economical, and environmentally friendly strategy to curb this disease. Powdery mildew resistance genes (Pm) are the primary resources for resistance breeding, and new Pm genes are in constant demand. Previously, we identified Aegilops longissima chromosome 6Sl#3 as a carrier of powdery mildew resistance and designated the resistance gene as Pm6Sl. Here, we reported the design of 24 markers specific to 6Sl#3 on the basis of the full-length cDNA sequences of 6Sl#3 donor Ae. longissma accession TA1910, and the development of wheat-Ae. longissima 6Sl#3 introgression stocks by ph1b-induced homoeologous recombination. Further, 6Sl#3 introgression lines were identified and characterized by integration analysis of powdery mildew responses, in situ hybridization, and molecular markers and Pm6Sl was mapped to a distal interval of 42.80 Mb between markers Ael58410 and Ael57699 in the long arm of 6Sl#3. Two resistant recombinants, R43 (T6BS.6BL-6Sl#3L) and T27 (Ti6AS.6AL-6Sl#3L-6AL), contained segments harboring Pm6Sl with less than 8% of 6Sl#3 genomic length, and two markers were diagnostic for Pm6Sl. This study broadened powdery mildew resistance gene resources for wheat improvement and provided a fundamental basis for fine mapping and cloning of Pm6Sl to further understand its molecular mechanism of disease resistance.

Development of Novel Wheat-Aegilops longissima 3S1 Translocations Conferring Powdery Mildew Resistance and Specific Molecular Markers for Chromosome 3S1.

Powdery mildew of wheat, caused by Blumeria graminis f. sp. tritici, is a destructive disease of common wheat. Cultivation of resistant varieties is the most cost-effective disease management strategy. Previous studies reported that chromosome 3Sl#2 present in Chinese Spring (CS)-Aegilops longissima 3Sl#2(3B) disomic substitution line TA3575 conferred resistance to powdery mildew. In this study, we further located the powdery mildew resistance gene(s) to the short arm of chromosome 3Sl#2 (3Sl#2S) by evaluating for B. graminis f. sp. tritici resistance of newly developed CS-Ae. longissima 3Sl#2 translocation lines. Meanwhile, TA7545, a previously designated CS-Ae. longissima 3Sl#3 disomic addition line, was reidentified as an isochromosome 3Sl#3S addition line and evaluated to confer resistance to powdery mildew, thus locating the resistance gene(s) to the short arm of chromosome 3Sl#3 (3Sl#3S). Based on transcriptome sequences of TA3575, 10 novel chromosome 3SlS-specific markers were developed, of which 5 could be used to distinguish between 3Sl#2S and 3Sl#3S derived from Ae. longissima accessions TL20 and TA1910 (TAM4) and the remaining 5 could identify both 3Sl#2S and 3Sl#3S. Also, CL897, one of five markers specific to both 3Sl#2S and 3Sl#3S, could be used to detect Pm13 located at chromosome 3Sl#1S from Ae. longissima accession TL01 in diverse wheat genetic backgrounds. The powdery mildew resistance genes on chromosomes 3Sl#2S and 3Sl#3S, the CS-Ae. longissima 3Sl#2 translocation lines, and the 3SlS-specific markers developed in this study will facilitate the transfer of B. graminis f. sp. tritici resistance genes into common wheat and provide new germplasm resources for powdery mildew resistance breeding.