PHASEOLUS ENOD40 IS INVOLVED IN SYMBIOTIC AND NON-SYMBIOTIC ORGANOGENETIC PROCESSES - EXPRESSION DURING NODULE AND LATERAL ROOT DEVELOPMENT

ENOD40 is an early nodulin gene, recently isolated from legume species forming nodules either after Rhizobium infection or spontaneously. EN OD40 cDNAs from Phaseolus plants were isolated and nucleotide sequence determination revealed a 85% and 88.5% homology with the reported soy bean cDNA clones. The putative polypeptide deduced coincides with the soybean one but a stop codon, almost in the middle of the respective O RF, renders it much shorter. This polypeptide was overexpressed as a f usion protein in Escherichia coli. Although the spatial expression pat tern of the gene in the root pericycle and nodule primordium at early stages of development as well as in the pericycle of the vascular bund les and uninfected cells in mature nodules is comparable to the gene's expression pattern in soybean, differences in developmental regulatio n are evident. We have shown that ENOD40 transcripts are also detected at very early stages of lateral root development, in the dividing per icycle cells of the root stele that give rise to the lateral root prim ordia. The presence of Rhizobium causes an enhancement of the gene's e xpression and also induction of the gene in the vascular tissues of de veloped lateral roots. Interestingly, a discrimination on the gene's e xpression level in adventious and acropetal incipient lateral root pri mordia, emerging in infected and uninfected roots, is observed. This i ndicates that the gene's product may be involved in the hormonal statu s of the plant and that ENOD40 may be used as a molecular marker in la teral root initiation.