RESISTANCE GENE ANALOGS IN SUGAR PINE

¹ Institute of Forest Genetics, USDA Forest Service, Department of Environmental Horticulture, One Shields Way, University of California, Davis, CA 95616

² Institute of Forest Genetics, USDA Forest Service, 2480 Carson Road, Placerville, CA 95667

³ Institute of Forest Genetics, USDA Forest Service, Pacific Southwest Research Station, 800 Buchanan St., Albany, California 94707

White pine blister rust (causal agent Cronartium ribicola) is an epidemic fungal disease to which all North American white pines are susceptible. Our laboratory is endeavoring to isolate a rare gene from sugar pine (Pinus lambertiana) that confers major gene resistance to the disease. Recently, genes conferring resistance to a wide variety of plant pathogens and pests have been isolated from diverse species. The majority can be placed into groups that share regions of sequence homology. Members of the largest group, class I resistance genes, share a nucleotide binding site (NBS) motif and a leucine-rich repeat (LRR) domain. An additional conserved region with the amino acid sequence GLPLAL is located between the NBS and LRR regions. We used degenerate PCR primers corresponding to the P-loop domain of the NBS site and the GLPLAL region to amplify resistance gene analogs (RGAs) from sugar pine genomic DNA and from a resistant tissue cDNA library. Southern analyses indicate that multiple copies of class I RGAs are present in the genomes of sugar pine and other gymnosperms. Our work suggests that class I RGAs predate the angiosperm-gymnosperm divergence.