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Implication of an Aldehyde Dehydrogenase Gene and a Phosphinothricin N-Acetyltransferase Gene in the Diversity of Pseudomonas cichorii Virulence
Genes 2012, 3(1), 115-137; doi:10.3390/genes3010115

Genomic Distribution and Divergence of Levansucrase-Coding Genes in Pseudomonas syringae

School of Engineering and Science, Jacobs University Bremen, Bremen 28759, Germany
* Author to whom correspondence should be addressed.
Received: 2 January 2012 / Revised: 19 January 2012 / Accepted: 3 February 2012 / Published: 10 February 2012
(This article belongs to the Special Issue Genes and Genomes of Plant Pathogenic Bacteria)
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In the plant pathogenic bacterium, Pseudomonas syringae, the exopolysaccharide levan is synthesized by extracellular levansucrase (Lsc), which is encoded by two conserved 1,296-bp genes termed lscB and lscC in P. syringae strain PG4180. A third gene, lscA, is homologous to the 1,248-bp lsc gene of the bacterium Erwinia amylovora, causing fire blight. However, lscA is not expressed in P. syringae strain PG4180. Herein, PG4180 lscA was shown to be expressed from its native promoter in the Lsc-deficient E. amylovora mutant, Ea7/74-LS6, suggesting that lscA might be closely related to the E. amylovora lsc gene. Nucleotide sequence analysis revealed that lscB and lscC homologs in several P. syringae strains are part of a highly conserved 1.8-kb region containing the ORF, flanked by 450-452-bp and 49-51-bp up- and downstream sequences, respectively. Interestingly, the 450-452-bp upstream sequence, along with the initial 48-bp ORF sequence encoding for the N-terminal 16 amino acid residues of Lsc, were found to be highly similar to the respective sequence of a putatively prophage-borne glycosyl hydrolase-encoding gene in several P. syringae genomes. Minimal promoter regions of lscB and lscC were mapped in PG4180 by deletion analysis and were found to be located in similar positions upstream of lsc genes in three P. syringae genomes. Thus, a putative 498-500-bp promoter element was identified, which possesses the prophage-associated com gene and DNA encoding common N-terminal sequences of all 1,296-bp Lsc and two glycosyl hydrolases. Since the gene product of the non-expressed 1,248-bp lscA is lacking this conserved N-terminal region but is otherwise highly homologous to those of lscB and lscC, it was concluded that lscA might have been the ancestral lsc gene in E. amylovora and P. syringae. Our data indicated that its highly expressed paralogs in P. syringae are probably derived from subsequent recombination events initiated by insertion of the 498-500-bp promoter element, described herein, containing a translational start site.
Keywords: levansucrase; phage-associated promoter element; Pseudomonas syringae; Erwinia amylovora; pro-phage levansucrase; phage-associated promoter element; Pseudomonas syringae; Erwinia amylovora; pro-phage
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Srivastava, A.; Al-Karablieh, N.; Khandekar, S.; Sharmin, A.; Weingart, H.; Ullrich, M.S. Genomic Distribution and Divergence of Levansucrase-Coding Genes in Pseudomonas syringae. Genes 2012, 3, 115-137.

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