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Map-based cloning of the gene Pm21 that confers broad-spectrum resistance to wheat powdery mildew by Dr. Huagang He

Common wheat (Triticum aestivum) is one of the most widely cultivated cereal crops providing ~20% of the calories consumed by humans. However, wheat production is constantly challenged by powdery mildew disease, which occurs globally and is caused by the biotrophic fungal pathogen Blumeria graminis f. sp. tritici (Bgt). Utilization of powdery mildew resistance (Pm) genes is the most effective and economical way to control Bgt infection. Pm21 originating from the Triticeae grass Dasypyrum villosum (2n = 2x = 14, VV) confers high resistance or immunity to all tested Bgt races. The wheat-D. villosum translocation line T6AL.6VS harboring Pm21 has been widely used in wheat breeding in China since 1995. Nevertheless, the genetic basis of the broad-spectrum resistance conferred by Pm21 remains unclear. Due to the lack of recombination between 6VS and wheat homoeologous counterpart, conventional map-based cloning strategy depending on genetic mapping in wheat background is not effective for isolating Pm21.

In the previous study, we made a significant progress in molecularly mapping Pm21 based on the discovery and utilization of diverse D. villosum accessions that differed in the response to Bgt infection. Using the genetic population developed by crossing resistant and susceptible D. villosum accessions, Pm21 was successfully mapped to a 0.01 cM interval. One resistance gene analog (RGA) marker within the mapped interval co-segregated with Pm21. However, Stpk-V, formerly reported as a key member of Pm21, is outside the interval.

Recently, we reported the cloning and functional validation of Pm21. Our data showed that DvRGA2, located in the mapped interval and encoding a typical CC-NBS-LRR protein, is Pm21. The key result supporting our claim is that we identified a large number of mutations in DvRGA2 that changed Bgt resistance to susceptibility. More importantly, we found that the transgenic wheat lines expressing the cloned Pm21 exhibited strong resistance to diverse Bgt isolates and mixed cultures, thus confirming the functionality of Pm21 as broad-spectrum Bgt resistance at the molecular level. We also obtained several additional sets of data, i.e., expression profile of DvRGA2 and virus inducing silencing of DvRGA2, which all support the conclusion that DvRGA2 is Pm21. Interestingly, our evolutionary analysis revealed that Pm21 is a conserved gene in Triticeae, but its orthologs in wheat and closely related species were all disrupted by retrotransposon insertions.

In conclusion, we have cloned Pm21 and validated its function as a broad-spectrum Bgt resistance gene through transgenic expression. The cloned Pm21 is valuable for efficient development of Bgt resistant wheat crops through molecular breeding. Since Pm21 and its wheat orthologs have different evolutionary fates, it may also aid further analysis of the different mechanisms underlying the evolution of important disease resistance genes in Triticeae plants.


Publications

1. Huagang He*, Shanying Zhu, Renhui Zhao, Zhengning Jiang, Yaoyong Ji, Jian Ji, Dan Qiu, Hongjie Li and Tongde Bie. Pm21, encoding a typical CC-NBS-LRR protein, confers broad-spectrum resistance to wheat powdery mildew disease. Molecular Plant. 2018 (online).

2. Shanying Zhu, Yaoyong Ji, Jian Ji, Tongde Bie, Anli Gao and Huagang He*. Fine physical bin mapping of the powdery mildew resistance gene Pm21 based on chromosomal structural variations in wheat. International Journal of Molecular Sciences. 2018, 19: 643.

3. Huagang He*, Yaoyong Ji, Shanying Zhu, Bin Li, Renhui Zhao, Zhengning Jiang and Tongde Bie. Genetic, physical and comparative mapping of the powdery mildew resistance gene Pm21 originating from Dasypyrum villosum. Frontiers in Plant Science. 2017, 8: 1914.

4. Huagang He*, Shanying Zhu, Zhengning Jiang, Yaoyong Ji, Feng Wang, Renhui Zhao and Tongde Bie. Comparative mapping of powdery mildew resistance gene Pm21 and functional characterization of resistance-related genes in wheat. Theoretical and Applied Genetics. 2016, 129: 819-829.

5. Tongde Bie, Renhui Zhao, Shanying Zhu, Shulin Chen, Bo Cen, Boqiao Zhang, Derong Gao, Zhengning Jiang, Tiantian Chen, Ling Wang, Ronglin Wu, Huagang He*. Development and characterization of an efficient breeding-practical marker MBH1 simultaneously tagging Pm21 and PmV genes conferring resistance to wheat powdery mildew. Molecular Breeding. 2015, 35: 189.

6. Tongde Bie, Renhui Zhao, Zhengning Jiang, Derong Gao, Boqiao Zhang, Huagang He*. Efficient marker-assisted screening of structural changes involving Haynaldia villosa chromosome 6V using a double-distal-marker strategy. Molecular Breeding. 2015, 35: 34.

7. Huagang He*, Shanying Zhu, Weihong Sun, Derong Gao and Tongde Bie. Efficient development of Haynaldia villosa chromosome 6VS-specific DNA markers using a CISP-IS strategy. Plant breeding. 2013, 132(3): 290-294.


 

Returns〗 Hits: Date:2018-04-11
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