MOLECULAR CHARACTERIZATION OF PSSCDE GENES OF RHIZOBIUM-LEGUMINOSARUMBV TRIFOLII STRAIN TA1 - PSSD MUTANT IS AFFECTED IN EXOPOLYSACCHARIDESYNTHESIS AND ENDOCYTOSIS OF BACTERIA

We have identified the three genes pssCDE in Rhizobium leguminosarum b y. trifolii TA1, Even though they were almost identical to earlier ide ntified pssCDE genes of R. leguminosarum, they differed in gene length s and gene overlaps. The predicted gene products of pssCDE genes share d significant homology to prokaryotic glycosyl transferases involved i n exopolysaccharide synthesis, The Tn5 insertion in pssD created the n onmucoid mutant that induced non-nitrogen-fixing nodules, The microsco pic analysis of the nodules, induced on Trifolium pratense by the pssD 133 mutant, showed abnormally enlarged infection threads densely packe d with bacteria, which were released from the infection threads in an unusual way, The symbiosomes were observed very rarely and the nodule remained almost empty. Symbiotic phenotype of the pssD133 suggested a correlation between this mutation and defective endocytosis of bacteri a into nodule cells.