A cloned cellulase gene from Erwinia carotovora subsp. carotovora is expressed in Rhizobium fredii but does not influence nodulation of cowpea

Abstract

Symbiotic rhizobia enter roots of their hosts via infection threads in root-hairs and invade the cortex, where nodules are initiated. We have transferred a cloned cellulase (Cel) gene from Erwinia carotovora subsp. carotovora into rhizobia and examined both the production of the enzyme and its impact on nodulation. Acquisition of a Cel+ plasmid allowed cultured cells of Rhizobium fredii,R. meliloti, and R. tropici to produce extracellular enzymes that degrade carboxymethylcellulose. The Cel+ plasmid was retained by R. fredii during nodulation of cowpea, and analysis of a gene fusion confirmed that the Cel promoter was active in planta. Cellulase levels in nodules nevertheless were low, and infection and nodulation were unaffected by the presence of the Cel+ plasmid. © 1994.