PCR-Amplified Resistance Gene Analogs Link to Resistance Loci in Rice

Abstract

Products of disease resistance genes cloned from several plant species share structural motifs such as a nucleotide binding site (NBS) and leucine-rich repeats. The presence of conserved domains in resistance genes anabled the cloning of nunrerous additional resistance gene analogs from rice using a polymerase chain reaction (PCR) with degenerate oligonucleotide primers to the NBS motifs. Ten resistance gene analogs (RGAs) were amplified from rice varieties Aichiasahi and Toride-1. The sequences coded open reading frames with additional sequences characteristic of NBSs. A hounology search through a database revealed significant similarities to known resistance genes. Southern blot analysis of eight rice varieties probed with RGAS demonstrated that most of them were single copy genes with diverse restriction fragment length polymorphisms (RFLPs). RFLPs Were observed between japonica and indica type rice in some RGAs and within bothjaponica and indica varieties. Some of their map positions were linked to known true resistance loci and some to field resistance (quantitative trait) Ioci. The transcription for RGAs could be detected by RT-PCR; however, their transcription levels were extremely low and varied with the variety.