Virulence of Agrobacterium tumefaciens Strain A281 on Legumes

Abstract

This study addresses the basis of host range on legumes of Agrobacterium tumefaciens strain A281, an LL-succinamopine strain. We tested virulence of T-DNA and vir region constructs from this tumor-inducing (Ti) plasmid with complementary Ti plasmid re,gions from heterologous nopaline and octopine strains.Agrobacterium tumefaciens is the etiologic agent of crown gall. Oncogenic strains ofA. tumefaciens harbor large plasmids, called Ti2 plasmids (for review, see Ref. 17). Part of the Ti plasmidthe T-DNA-is transferred to the plant where it is stably maintained in the nuclear DNA (4, 5). The T-DNA contains genes that are transcribed in the plant (4) encoding enzymes for opine synthesis (29) and phytohormone synthesis (1,2,27,30 described previously (20). In some instances, Agrobacterium was grown on AT minimal medium (11). Antibiotic concentrations were as follows: for Agrobacterium: kanamycin sulfate (Sigma), 50 ,g/ml; naladixic acid (Sigma), 25 ,g/ml; tetracycline hydrochloride (Calbiochem), 10 sg/ml; carbenicillin (or ampicillin) (Sigma), 50 ug/ml; for E coli: kanamycin sulfate, 50 gg/ml; tetracycline hydrochloride (Sigma), 25 gg/ml; carbenicillin ( Scoring of Tumors. Soybean and alfalfa tumors were scored at 1-week intervals for 5 weeks after inoculation. Tumor formation was scored according to the number of inoculation sites forming tumors, then expressed as a ratio to total sites inoculated (Table II). Photographic records were also kept. RESULTS

Inheritance of Resistance to Crown Gall in Pisum sativum

“…The resistance is not specific to strain B6: with three diverse wide host range strains, tumors on Sweet Snap were consistently much smaller than on other genotypes. Strain A281 has been reported to be hypervirulent on several species, including pea (8)(9)(10), as a result of enhanced activity of vir genes due to increased expression of the transcriptional activator virG (10). Sweet Snap as well as other genotypes responded to increased vir gene activity in A28 1, but tumors induced on other genotypes were more than 100% larger than those that developed on Sweet Snap.…”

Agrobacterium -Mediated Plant Transformation: the Biology behind the “Gene-Jockeying” Tool

“…Belanger et al (23) showed that individual virA genes may be particularly suited to function in certain genetic backgrounds, and Krishnamohan et al (183) recently demonstrated that Ti plasmids may have evolved to optimize specific combinations of virA, virG, and vir boxes. As noted above, the Ti-plasmid pTiBo542 in the C58 chromosomal background is hypervirulent on certain legume species, possibly because of the associated virG gene (41, 146, 159), but not in its native Bo542 chromosomal background (143). Recent results from my laboratory indicate that vir gene induction and T-strand production by and transformation efficiency of particular Agrobacterium strains may not correlate well.…”

“…For example, the Ti plasmid pTiBo542, when in its natural host strain A. tumefaciens Bo542, directs limited tumorigenic potential when assayed on many leguminous plant species. However, when placed in the C58 chromosomal background, pTiBo542 directs strong virulence toward soybeans and other legumes (143). Finally, susceptibility to crown gall disease has a genetic basis in cucurbits (292), peas (272), soybeans (15,214,246), and grapevines (312) and even among various ecotypes of Arabidopsis thaliana (231).…”

Plant Responses at Different Ploidy Levels

“…Even within a species, different cultivars or ecotypes may show vastly different degrees of susceptibility to tumorigenesis by particular Agrobacterium strains [54][55][56]. These differences IBA 2 weeks after culture initiation.…”