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Coevolutionary Dynamics of Rice Blast Resistance Gene Pi-ta and Magnaporthe oryzae Avirulence Gene AVR-Pita 1

Jia, Yulin, Zhou, Erxun, Lee, Seonghee, Bianco, Tracy
Phytopathology 2016 v.106 no.7 pp. 676-683
Magnaporthe oryzae, alternative splicing, blast disease, coevolution, defense mechanisms, disease resistance, exons, fungi, gene expression, genes, genetic markers, genome-wide association study, haplotypes, loci, marker-assisted selection, pathotypes, plant protection, promoter regions, proteins, quantitative trait loci, rice, sequence analysis, transposons, varieties, yield components, United States
The Pi-ta gene in rice is effective in preventing infections by Magnaporthe oryzae strains that contain the corresponding avirulence gene, AVR-Pita1. Genome sequencing and mapping studies demonstrated that AVR-Pita1 is highly unstable, and diverse haplotypes of AVR-Pita1 have been identified from isolates of M. oryzae from rice production areas in the US and worldwide. DNA sequencing, expression analysis, and QTL mapping of the Pi-ta locus reveal the complex of evolutionary mechanisms in Pi-ta mediated resistance. A single resistance Pi-ta haplotype was associated with a transposable element at the promoter region, suggesting that a transposon mechanism can play an important role in Pi-ta gene expression. Several Pi-ta transcripts were identified, most of which are probably derived from alternative splicing and exon skipping, which could produce functional resistance proteins that support a new concept of coevolution of Pi-ta and AVR-Pita1. User friendly DNA markers for Pi-ta have been developed to support marker assisted selection, and development of new rice varieties with the Pi-ta markers. Genome-wide association studies revealed a link between Pi-ta mediated resistance and yield components suggesting that rice has evolved a complicated defense mechanism against the blast fungus. Pyramiding of more than one major blast resistance gene in any single rice variety provides resistance to an overlapping spectra of pathotypes, and is recommended for effective crop protection.