MOLECULAR CLONING OF CRR1A, A GENE FOR RESISTANCE TO CLUBROOT DISEASE (PLASMODIOPHORA BRASSICAE WORONIN) IN BRASSICA RAPA L.

Clubroot disease, caused by the obligate biotrophic protist Plasmodiophora brassicae Woronin, is one of the most economically important diseases of Brassica crops in the world. Although many clubroot resistance (CR) loci have been identified through genetic analysis and QTL mapping, the molecular mechanisms underlying P. brassicae-host interactions remain unknown. Here we report the map-based cloning of Crr1a, a gene conferring resistance to clubroot in Brassica rapa. Crr1a^G004 encoded a Toll-Interleukin-1 receptor / nucleotide-binding site / leucine-rich repeat (TIR-NB-LRR) protein expressed mainly in the stele or cortex of hypocotyl and roots, in leaves, and in apical meristem, but not in root hairs. Compared with the resistant allele Crr1a^G004, the susceptible allele Crr1a^A9709 appeared to encode a truncated NB-LRR protein lacking more than half of the TIR domain. Transgenic Arabidopsis harboring Crr1a^G004 cDNA showed pathotype-specific resistance to P. brassicae isolates similar to that of untransformed B. rapa with a homozygous Crr1 locus. This study provides a basis for further analysis of molecular mechanisms underlying Brassica-P. brassicae interactions and contributes significantly to breeding of highly resistant cultivars of Brassica vegetables.