Molecular characterization of the maize Rp1-D rust resistance haplotype and its mutants

Area of Science:

• Plant genetics
• Molecular biology
• Crop science

Background:

• Maize common rust, caused by Puccinia sorghi, is a significant agricultural disease.
• The Rp1 locus in maize is known to confer resistance to this pathogen.
• Understanding the genetic basis of resistance is crucial for developing resistant crop varieties.

Purpose of the Study:

• To identify and characterize the Rp1-D gene responsible for maize common rust resistance.
• To investigate the structure and organization of the Rp1 gene complex.
• To determine the molecular class and evolutionary relationships of the Rp1-D gene.

Main Methods:

• Gene tagging using Mutator and Dissociation transposons.
• Southern blot analysis with R gene analog probe (PIC20) and transposon probes.
• Transcript abundance analysis via Northern blotting.
• Analysis of Rp1-D mutants to identify deletions and recombination events.

Main Results:

• The Rp1-D gene was identified and confirmed through independent gene tagging experiments.
• Rp1-D belongs to the nucleotide binding site, leucine-rich repeat (NBS-LRR) class of resistance genes.
• The Rp1 gene complex comprises Rp1-D and approximately eight homologs, with deletions often arising from unequal crossing-over.
• Transcript levels of rp1 complex genes varied with leaf age but were not affected by rust inoculation.

Conclusions:

• The Rp1-D gene is a key component of maize rust resistance, belonging to the NBS-LRR family.
• The complex nature of the Rp1 locus, involving multiple gene homologs and recombination, contributes to diverse resistance specificities.
• Rp1-D's structure differs from some other rust resistance genes, lacking a specific N-terminal domain found in flax genes.