Identification and Isolation of a DNA Region Required for Tabtoxin Production: Apparent Deletion in Pseudomonas Syringae Pv Tabaci Variant ‘Angulata’ and Tox⁻Mutants

Abstract

Tabtoxin is a dipeptide pretoxin produced by several path-ovars and isolates of Pseudomonas syringae. Examples of such strains, their plant hosts, and the diseases they cause are listed in Table 1. While tabtoxin is synthesized in a biologically inactive form, it is readily cleaved by aminopep-tidases, present in either the bacteria or the plant, yielding threonine and the active moiety tabtoxinine-β-lactam (Figure 1). Cleavage of (2-serine)tabtoxin, a derivative form containing a serine molecule in place of threonine, yields T-β-L and serine. The accumulation of tabtoxinine-β-1actam (T-β-L) in planta results in a chlorotic halo surrounding the bacterial lesion and is thought to be a contributing factor in disease severity. T-β-L is an inhibitor of glutamine synthetase isolated from plants, bacteria, and fungi. The chlorosis caused by tabtoxin-producing phytobacteria has been attributed to ammonia accumulation resulting from the inhibition of glutamine synthetase by T-β-L in planta (Durbin, 1982).