Physical, Chemical, Developmental, and Genetic Factors that Modulate the Agrobacterium-Vitis Interaction

Abstract

Tumor formation in Vitis species and hybrids, incited by Agrobacterium tumefaciens, was altered by chemical, physical, developmental, and genetic variables. Knowledge of the effect of these variables was used to develop a stringent in vitro assay system to select parents for a study of genetic factors that modulate tumor formation. Tumor formation was reduced by short day preconditioning of assay plants and by inoculation of the morphological apex of isolated stem segments. Pretreatment of plants with auxin or cytokinin altered specificity in various combinations of strains and host genotypes. All Vitis species and hybrids formed tumors in response to strains designated as limited host range, but some displayed a necrotic reaction (cell death at and below site of inoculation) or a null response (same as the response to inoculation with an avirulent strain) to strains designated as wide host range (VC Knauf, CG Panagopoulos, EW Nester [1982] Phytopathology 72: 1545-1549). Screens of F1 progeny, derived from crosses of null, necrotic, and tumor-producing phenotypes, demonstrated that the null and the necrotic phenotypes were modulated by dominant and recessive host genes. The extent of cellular necrosis in the necrotic phenotype was modified by the morphological location of the inoculation site, by the presence of buds on the host stem, and by deletion of the tryptophane monooxygenase locus gene of the Ti-plasmid.The tumor-inducing plasmid ofAgrobacterium tumefaciens contains two regions, termed the virulence (vir) and tumorinducing DNA (T-DNA), that coordinately participate in the excision of DNA from the pathogen and its transfer into the host genome (11,17). The current model for infection of host cells by Agrobacterium predicts that phenolic metabolites produced by wounded plant cells activate plasmid vir genes of the bacterium (22). Once activated, the genes modulate the excision and packaging of T-DNA and facilitate its transfer into the host plant genome (17,22). Expression of T-DNA in host cells alters the endogenous levels of auxin, cytokinin, and ethylene (6,11,17), which results in the loss of cellular totipotency (11,17 3,17,27). Bacterial host range and virulence determinants have been attributed to structural and organizational differences in T-DNA loci (1,17,21,(27)(28)(29)30) and to structural differences in at least two vir loci (30,31). Some investigators suggest that chromosomal loci might also modulate host selectivity (17,25). The role of the host genome in Agrobacterium-host compatibility has not received as much consideration as that of the pathogen. However, intergeneric (3,12,25,26,29,30) and intraspecific and cultivar variations (1, 2, 7-9, 19, 23, 24, 27) in hostresponse to WHR and/or LHR strains have been reported. A preliminary analysis of Vitis hybrids showed that resistance to A. tumefaciens was a heritable trait (23).The primary goal of our research was to develop a system to study the interactions of bacterial virulence genes and host genes so that the molecular and bioch...

Agrobacterium-mediated genetic transformation of plants: The role of host

“…Even within a species, different cultivars or ecotypes may show different degrees of susceptibility to tumorigenesis by particular Agrobacterium strains. These differences have been noted in maize (Ritchie et al 1993), various legumes (Hood et al 1987, Owens andCress 1984), aspen (Beneddra et al 1996), pine (Bergmann and Stomp 1992), tomato (Van Roekel et al 1993), Arabidopsis (Nam et al 1997) and grape (Lowe and Krul 1991). The ability of particular Agrobacterium strains to transform plant cells is defined by mechanisms necessary for attachment and DNA-transfer, and the ability of plants to produce different inducer molecules.…”

Reasons for lower transformation efficiency in indica rice using Agrobacterium tumefaciens-mediated transformation: lessons from transformation assays and genome-wide expression profiling

“…Genetic analysis of crosses between susceptible cultivars/ecotypes and resistant cultivars/ecotypes indicated that the phenotype was transmitted to progenies as a heritable trait controlled by dominant (Szegedi and Kozma 1984;Lowe and Krul 1991), recessive (Mauro et al 1995) or semidominant genes (Nam et al 1997). The inheritance of these traits are determined by a single gene or a single major contributing locus (Szegedi and Kozma 1984;Nam et al 1997), or by quantitative trait loci (Bailey et al 1994).…”

“…It has long been noted that different species (Anderson and Moore 1979) and cultivars of the same species may differ remarkably in their susceptibility to Agrobacterium infection (Nam et al 1997;Bailey et al 1994;Lowe and Krul 1991;Smarrelli et al 1986). Genetic analysis of crosses between susceptible cultivars/ecotypes and resistant cultivars/ecotypes indicated that the phenotype was transmitted to progenies as a heritable trait controlled by dominant (Szegedi and Kozma 1984;Lowe and Krul 1991), recessive (Mauro et al 1995) or semidominant genes (Nam et al 1997).…”

Plant Responses at Different Ploidy Levels

“…have been noted in rice [57], maize [58], various legumes [55], aspen [56], cucurbits [59], Pinus species [60], tomato [61], Arabidopsis [62], grape [63], and other species. Although some differences in transformation frequency may be attributed to environmental or physiological factors, a genetic basis for susceptibility has clearly been established in a few plant species [62,[64][65][66].…”