Khaled Abdallah

• Pseudomonas syringae is a phytopathogenic γ-proteobacterium that induces a wide variety of diseases on various agronomically significant crops, as well as on an unknown number of wild plant species. Virulence of the bacterial blight pathogen of soybean, P. syringae pv. glycinea PG4180, is favored by cold and humid conditions. This bacterium can synthesize the exopolysaccharide levan when it encounters moderate to high concentrations of sucrose. Although the presence of multiple alleles for levansucrase gene in P. syringae PG4180 has been the focus of many previous studies, no regulators have been described for expression of levansucrase. In the first study, the genome of P. syringae PG4180 was screened for transcriptional activators and results revealed that the prophage-borne transcriptional regulator, LscR, mediates expression of levansucrase. A lscR-deficient mutant was generated and exhibited a levan-negative phenotype when grown on a sucrose-rich medium. Furthermore, genomic analysis of the region surrounding the lscR gene revealed that LscR resides on a ~25 kb fragment of a bacteriophage origin. To determine its nature and function, the prophage region was subjected to nucleotide sequencing followed by BLAST analysis. Results showed that this region does not encode for an active phage as it only possesses genes involved in phage tail morphogenesis. In the last section of this study, we investigated a potential repressor for the transcription of lsc. Potential binding sites for the hexose metabolism repressor, HexR, were found in the PAPE region upstream of both lsc genes. A hexR mutant of P. syringae PG4180 was generated and transcriptional analysis revealed a slight increase in the expression levels of lsc. Our data proposed that genes engaged in extra-cellular sugar acquisition are co-regulated with those involved in intra-cellular energy-providing metabolic pathways in P. syringae.