Molecular Evolution and Related Defense Response of Pi-ta Gene in Wild Rice (Oryza rufipogon)
Date Issued
2011
Date
2011
Author(s)
Huang, Chun-Lin
Abstract
Rice blast disease is caused by the fungal pathogen Magnaporthe grisea. The resistant response is triggered by a physical interaction between the protein products of the host R (Resistance) gene Pi-ta and the pathogen Avr (Avirulence) gene AVRpita. The genotype variation and resistant/susceptible phenotype at the Pi-ta locus of wild rice (Oryza rufipogon), the ancestor of cultivated rice (O. sativa), was surveyed in 36 locations worldwide to study the molecular evolution and functional adaptation of the Pi-ta gene. The low nucleotide polymorphism in the Pi-ta gene of O. rufipogon was similar to that of O. sativa, but greatly differed from what has been reported for other O. rufipogon genes. The haplotypes can be subdivided into two divergent haplogroups named H1 and H2. H1 is derived from H2, with nearly no variation and at a low frequency. H2 is common and the ancestral form. The LRR domain has a high πnon/πsyn ratio and the low polymorphism of Pi-ta gene might cause primarily by recurrent selective sweep and constraint by other putative physiological function. Meanwhile, we provide data to show the amino acid, Ala-918, of H1 in the leucine-rich repeat (LRR) domain has close relationship with resistant phenotype. H1 might arise recently during rice domestication, and associate with the scenario of the blast pathogen host shift from Italian millet to rice.
To identify early induced and repressed defense genes involved in broad-spectrum resistance to rice blast, microarray is used to compare differentially expressed in AVRpita-resistant and -susceptible wild rice O. rufipogon. Receptor-like kinase (RLK), cytochrome P450, and WRKY transcription factor are the majority gene families induced. In addition, some genes that participate in ROS, signal transduction, and tryptophan pathway are discussed. Further functional validation and analysis of these genes will enhance our understanding of the molecular mechanism of broad-spectrum resistance in rice.
Subjects
Disease resistance
wild rice
rice blast
Pi-ta gene
polymorphism
microarray
Type
thesis
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