A RHIZOBIUM-TROPICI DNA REGION CARRYING THE AMINO-TERMINAL HALF OF A NODD GENE AND A NOD-BOX-LIKE SEQUENCE CONFERS HOST-RANGE EXTENSION

Rhizobium tropici CIAT899 is a broad-host-range strain that, in additi on to Phaseolus, nodulates other plant legumes such as Leucaena and Ma croptilium. The narrow-host-range of Rhizobium leguminosarum biovars p haseoli(strain CE3) and trifolii(strain RS1051) can be extended to Leu caena esculenta and Phaseolus vulgaris plants, respectively, by the in troduction of a DNA fragment 521 bp long, which carries 128 amino acid s of the amino-terminal region of a nodD gene from R. tropici, as well as a putative nod-box-like sequence, divergently oriented. The 521 bp fragment, in the presence of L. esculenta or P. vulgaris root exudate s, induced a R. leguminosarum bv. viciae nodA-lacZ fusion in either a CE3 or RS1051 background, respectively.