Genomic organization, induced expression and promoter activity of a resistance gene analog (PmTNL1) in western white pine (Pinus monticola)

Abstract

Cronartium ribicola causes white pine blister rust (WPBR) in subgenus Strobus. Various genetic and molecular approaches were used to detect white pine genes contributing to host resistance. The molecular role of the NBS-LRR family is highly related to plant immuno-activity against various pathogens and pests. In the present study, genomic organization of a resistance gene analog (RGA), designated as PmTNL1, and its allelic variants were characterized in Pinus monticola. PmTNL1 showed high identity with TIR-NBS-LRR proteins from other plants. qRT-PCR revealed that the PmTNL1 transcript was expressed at low basal levels in different tissues and exhibited similar patterns during compatible and incompatible interactions of P. monticola with C. ribicola at early stages post inoculation. In comparison, PmTNL1 was up-regulated significantly in diseased P. monticola tissues with WPBR symptoms. Expression of the PmTNL1 promoter::GUS fusion gene in transgenic Arabidopsis demonstrated that GUS signal appeared only inside phloem tissues of young seedlings and at hydathodes and branching and organ-connecting points in mature Arabidopsis plants. Similar to the endogenous expression pattern for this gene in pine, GUS activity was up-regulated significantly around vascular tissues locally at pathogen infection sites, but little or no induction was observed in response to abiotic stresses. A DNA marker was developed based on variation of the LRR-coding region, and PmTNL1 was mapped to one genetic linkage group using a pedigree with major dominant gene (Cr2) conferring HR resistance to C. ribicola. These results suggest that PmTNL1 may play an important role in white pine partial resistance against C. ribicola.