Cloning and analysis of Rdr1, a black spot resistance gene from roses.

Rdr1 is a single dominant resistance gene against black spot in roses. For positional cloning of the gene, a BAC library was constructed from a R. multiflora hybrid homozygous for Rdr1. A contig around Rdr1 covering a physical distance of about 200kb was established containing a cluster of nine highly similar resistance gene analogues (RGAs) of the nucleotide binding site (NBS)-leucine rich repeat (LRR) type. To identify the resistance gene among these candidates, expression analyses were performed. We found five of the nine RGAs to be expressed at low, probably constitutive levels in rose leaves, therefore being candidates for Rdr1. In parallel, individual RGAs subcloned into a plant transformation vector were analysed in a heterologous transient expression systems. Eight Rdr 1 homologues were found to be expressed transiently after infiltration into leaves of Nicotiana beuthamiana.