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      Rapidly evolving R genes in diverse grass species confer resistance to rice blast disease.

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          Abstract

          We show that the genomes of maize, sorghum, and brachypodium contain genes that, when transformed into rice, confer resistance to rice blast disease. The genes are resistance genes (R genes) that encode proteins with nucleotide-binding site (NBS) and leucine-rich repeat (LRR) domains (NBS-LRR proteins). By using criteria associated with rapid molecular evolution, we identified three rapidly evolving R-gene families in these species as well as in rice, and transformed a randomly chosen subset of these genes into rice strains known to be sensitive to rice blast disease caused by the fungus Magnaporthe oryzae. The transformed strains were then tested for sensitivity or resistance to 12 diverse strains of M. oryzae. A total of 15 functional blast R genes were identified among 60 NBS-LRR genes cloned from maize, sorghum, and brachypodium; and 13 blast R genes were obtained from 20 NBS-LRR paralogs in rice. These results show that abundant blast R genes occur not only within species but also among species, and that the R genes in the same rapidly evolving gene family can exhibit an effector response that confers resistance to rapidly evolving fungal pathogens. Neither conventional evolutionary conservation nor conventional evolutionary convergence supplies a satisfactory explanation of our findings. We suggest a unique mechanism termed "constrained divergence," in which R genes and pathogen effectors can follow only limited evolutionary pathways to increase fitness. Our results open avenues for R-gene identification that will help to elucidate R-gene vs. effector mechanisms and may yield new sources of durable pathogen resistance.

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          Author and article information

          Journal
          Proc Natl Acad Sci U S A
          Proceedings of the National Academy of Sciences of the United States of America
          Proceedings of the National Academy of Sciences
          1091-6490
          0027-8424
          Nov 12 2013
          : 110
          : 46
          Affiliations
          [1 ] State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing 210093, China.
          Article
          1318211110
          10.1073/pnas.1318211110
          3831948
          24145399
          7b440b9e-92c6-46b6-9a6c-e00dbede9bef
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