CLONING OF A PECTATE LYASE GENE FROM XANTHOMONAS-CAMPESTRIS PV MALVACEARUM AND COMPARISON OF ITS SEQUENCE RELATIONSHIP WITH PEL GENES OF SOFT-ROT ERWINIA AND PSEUDOMONAS

The cotton blight pathogen, Xanthomonas campestris pv, malvacearum str ain B414, produces an extracellular pectate lyase (PeI) with an estima ted M(r) of 41,000 and pI of 9.7, The gene coding for this enzyme init ially identified in a 1.8-kb PstI genomic DNA fragment was cloned, The nucleotide sequences of this 1.8-kb fragment and two pel genes previo usly cloned from Pseudomonas fluorescens and P. viridiflava were deter mined, These pel genes encoded pre-Pel proteins consisting of 377 to 3 80 amino acids (a.a.), A signal peptide consisting of 26 to 29 a,a, wa s present at the amino-terminus of each pre-Pel, Multiple sequence ana lysis revealed that Pel proteins of non-Erwinia phytopathogens includi ng Xanthomonas, Pseudomonas, and Bacillus constituted a distinct clust er, which showed 20 to 43% a,a. identity to the four established Pel f amilies of Erwinia. Homologous pel sequences were detected in various pathovars or strains of X, campestris. All of these xanthomonads produ ced an alkaline Pel and were capable of causing soft-rot in potato tub er slices and green pepper fruits.