Analysis of cell-to-cell and long-distance movement of a bean dwarf mosaic geminivirus-green fluorescent protein reporter in host and nonhost species: identification of sites of resistance

A bean dwarf mosaic geminivirus-green fluorescent protein (BDMV-GFP) reporter system was employed to analyze the viral infection process in host and nonhost species. Five classes of BDMV/host interaction were identified: (i) adapted hosts (susceptible Phaseolus vulgaris cultivars) permissive for systemic infection; (ii) adapted hosts (resistant P. vulgaris cv. Othello) displaying the development of a hypersensitive response (HR) associated with resistance to systemic infection; (iii) adapted (resistant P. vulgaris cv. Black Turtle Soup T-39) and nonadapted (Vigna unguiculata) hosts in which cell-to-cell, but not long-distance, movement was permitted; (iv) nonadapted hosts (Glycine max) in which systemic infection was coat protein-dependent; and (v) nonhosts (Cucurbita maxima, Gossypium barbadense, and Zea mays) in which the virus was confined to inoculated cells. Confocal laser scanning microscopy, fluorescence microscopy, and histochemical analyses were used to identify the cellular distribution of BDMV-GFP and the host response to viral infection. With this approach, the HR in P. vulgaris cv. Othello was visualized within cells of the epidermis, cortex, and phloem of inoculated hypocotyls. Infection studies performed with four begomoviruses and infectious BDMV/tomato mottle geminivirus pseudorecombinants revealed that the HR determinant(s) mapped to the BDMV DNA-B component.