Fourth International Bemisia Workshop International Whitefly Genomics Workshop
Association of the ‘Distortion-Recovery Phenotype’ in ‘Anaheim’ Pepper Systemically Infected with the Non-Whitefly Transmissible Pepgmv-Distortion Strain (Di), with the BC1/Promoter Region
Department of Plant Sciences, The University of Arizona, Tucson, AZ, USA. Correspondence: jbrown@ag.arizona.edu
The whitefly non-transmissible strain of Pepper golden mosaic virus (PepGMV-Distortion (Di) (genus, Begomovirus) causes leaf distortion, mild mosaic, and ‘recovery’ symptoms in ‘Anaheim’ pepper Capsicum annuum L., and viral DNA is detectable by PCR in apical ‘recovered’ leaves that do not express disease symptoms. Two whitefly-transmissible mosaic strains, PepGMV-Mosaic (Mo) and PepGMV-Serano (Ser), which have both been isolated from pepper plants co-infected with PepGMV-Di, cause systemic yellow mosaic symptoms and plants do not ‘recover’ from infection. Laboratory assembled reassortants inoculated to pepper plants in all possible combinations of the PepGMV Di, Mo, and Ser DNA-A and DNA-B components were capable of causing systemic symptoms. Although the resultant phenotypes ranged from full blown, systemic ‘mosaic’ symptoms, to ‘veinal crumpling and foliar distortion’ in the inoculated and in 1–2 subsequently developing leaves, and the absence of symptoms in apical leaves, or ‘recovery’ [herein, ‘distortion-recovery’], it was clear each symptom phenotype was linked to its respective, wild type viral DNA-B component. Nucleotide and amino acid sequence comparisons for the DNA-B component of the three PepGMV strains revealed considerable variation in the BC1 ORF (movement protein) and in the putative, upstream promoter region [herein, BC1+promoter], with Mo and Ser being highly similar. To investigate the role of this region of the PepGMV genome in symptom phenotype, the sequence was amplified using strain-specific PCR primers flanking the [ORF + promoter] and existing restriction sites Nde I and Spe I to exchange the Mo and Di [ORF + promoter] into the context of the respective DNA-B component background. The resultant DNA-B chimeric mutants, Mo-Di/ and Di-Mo/, were co-inoculated with the Mo or DI DNA-A component to ‘Anaheim’ pepper seedlings using biolistic inoculation. Controls consisted of pepper seedlings inoculated with wild type, infectious PepGMV-Mo and -Di clones, and mock-inoculated pepper plants (no DNA). Pepper seedlings inoculated with PepGMV Mo and Di exhibited characteristic wild type mosaic and ‘distortion-recovery’ symptoms, respectively, whereas, the Mo-Di/ and Di-Mo/ chimeras developed symptoms associated with the respective [BC1+ promoter] in the exchanged sequence. Results suggest that the ‘recovery’ phenotype may be associated with a defective BC1 promoter and/or the BC1 coding region, or both. If so, it would be anticipated that these functionally defective sequences might make possible host innate immune system countering of infection by PepGMV-Di, leading to the observed ‘recovery phenotype’, which effectively corresponds to a latent resistance phenomenon. This is in contrast to the development of a full blow systemic infections observed for PepGMV Mo and Ser, which both appear to contain fully functional [BC1+ promoter]-regions that the host apparently cannot overcome.