A novel blast resistance gene, Pi54rh cloned from wild species of rice, Oryza rhizomatis confers broad spectrum resistance to Magnaporthe oryzae
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The dominant rice blast resistance gene, Pi54 confers resistance to Magnaporthe oryzae in different parts of India. In our effort to identify more effective forms of this gene, we isolated an orthologue of Pi54 named as Pi54rh from the blast-resistant wild species of rice, Oryza rhizomatis, using allele mining approach and validated by complementation. The Pi54rh belongs to CC-NBS-LRR family of disease resistance genes with a unique Zinc finger (C3H type) domain. The 1,447 bp Pi54rh transcript comprises of 101 bp 5′-UTR, 1,083 bp coding region and 263 bp 3′-UTR, driven by pathogen inducible promoter. We showed the extracellular localization of Pi54rh protein and the presence of glycosylation, myristoylation and phosphorylation sites which implicates its role in signal transduction process. This is in contrast to other blast resistance genes that are predicted to be intracellular NBS-LRR-type resistance proteins. The Pi54rh was found to express constitutively at basal level in the leaves, but upregulates 3.8-fold at 96 h post-inoculation with the pathogen. Functional validation of cloned Pi54rh gene using complementation test showed high degree of resistance to seven isolates of M. oryzae collected from different geographical locations of India. In this study, for the first time, we demonstrated that a rice blast resistance gene Pi54rh cloned from wild species of rice provides broad spectrum resistance to M. oryzae hence can be used in rice improvement breeding programme.
KeywordsRice blast NBS-LRR Pi54 Pikh Allele mining Magnaporthe oryzae Oryza rhizomatis
TRS is thankful to ICAR and National Agricultural Innovation Project (code C4/C1071) for financial support. We thank Dr. S.R. Bhat for his help in conducting experiments on subcellular localization studies. Thanks are due to the in-charge, National Phytotron Facility, IARI, New Delhi, for providing facilities for maintaining wild species of rice and transgenic lines. We sincerely thank Dr. R. Rathour, Dr. M. Variar and Dr. U.D. Singh for providing fungal strains for phenotyping. A.D. and D.S. were supported by PG School, IARI, New Delhi in the form of fellowships for their Ph.D. and M.Sc. degrees, respectively.
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