Allele-specific and Mutator-associated instability at the Rpl disease-resistance locus of maize

Abstract

The Rp1 locus of maize determines resistance to the fungal rust pathogen Puccinia sorghi. In an attempt to isolate insertion mutations at Rp1 with the Mutator transposable element system, we found that Rp1 inactivation was common both in lines with Mutator activity and in controls lacking any known transposable element activity. Some alleles of Rp1 are endogenously inactivated as frequently as one in five-hundred, whereas other alleles are over twenty times more stable. In a standard background, no mutations of the Rp1^F allele were detected in 7,339 progeny screened. In a Mutator background, 27 Rp1^F inactivations were isolated from 35,356 tested seedlings. Although most Rp1^F mutant seedlings lost resistance to all of the P. sorghi isolates tested, several retained resistance to a subset of rust biotypes. Some of the resistance specificity profiles obtained in these mutants are unlike any previously identified Rp1 alleles. These data indicate that the Rp1 locus is composed of multiple resistance factors with variable intrinsic stabilities.