A single-nucleotide insertion in Rxp confers durable resistance to bacterial pustule in soybean

Area of Science:

• Plant genetics and breeding
• Molecular biology
• Plant pathology

Background:

• Bacterial pustules, caused by Xanthomonas axonopodis pv. glycines, significantly reduce soybean yield and cause defoliation.
• The recessive rxp allele of the Rxp gene confers durable resistance to bacterial pustules in soybean.
• This resistance was crucial for eliminating bacterial pustules in the USA ~70 years ago.

Purpose of the Study:

• To isolate and identify the historical Rxp gene responsible for bacterial pustule resistance in soybean.
• To characterize the Rxp gene and its alleles, including the resistance-conferring rxp allele.

Main Methods:

• Positional cloning was employed to narrow down the genomic region containing the Rxp gene.
• Complementation tests were performed to confirm the gene's identity.
• Six different alleles of the Rxp gene were obtained and analyzed.

Main Results:

• The Rxp gene, Glyma.17g090500, was successfully isolated to an 11.1 kb region.
• The resistance allele, rxp, was identified to contain a T insertion, leading to a truncated protein.
• Loss-of-function mutations in Rxp were found to decrease bacterial pustule lesions.

Conclusions:

• The Rxp gene encodes a bHLH transcription factor with an ACT-like domain.
• The rxp allele confers durable resistance to bacterial pustules by producing a truncated protein.
• Understanding the Rxp gene provides valuable insights for soybean disease resistance breeding.