Genetic Systems in the Soft Rot Erwinia Group

Abstract

The recent application of combined in vivo and in vitro techniques has led to a significant progress in the genetics of Erwinia. There are now few limitations to the genetic analysis of the role of Erwinia in phytopathogenicity.

The Erwinia Soft Rot group includes E. chrysanthemi (Echy), E. carotovora subsp. carotovora (Ecc) and E. carotovora subsp. atroseptica (Eca). The agricultural importance of this group is due to their ability to act both as plant pathogens (attacking the growing plant in the field) and as agents of biodeterioration of stored crops. The main pathogenicity determinants of the Soft Rot Erwinia group are the extracellular enzymes (pectinases, cellulases, and proteases) which macerate plant cell walls, although other factors contribute to disease (17). A study of Erwinia phytopathogenicity necessitates an investigation into the mechanisms of synthesis, regulation and export of the enzymes. This makes Erwinia a doubly important model system with which to analyze both protein translocation in Gram-negative bacteria, and the fundamental principles of plant pathogenicity.

Erwinia is a close relative of E. coli K12 and so we might reasonably expect that we could fruitfully apply “E. coli genetic techniques” to Erwinia. Previous comprehensive reviews of Erwinia genetics have shown that this rationale has allowed a gradual, but steady, progress over the past 15 years. The new combination of classical in vivo genetics and in vitro recombinant DNA techniques has now brought Erwinia genetics into a very productive era, and the purpose of this review is to highlight how recent developments have expanded the tools that are available to the Erwinia geneticist. The progress in the field up to 1982 has been well reviewed previously (4, 5, 16) and, with a few exceptions, I will not refer to work prior to that year.