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Title: DETECTION AND SEQUENCE ANALYSIS OF AN ALTERED PECTATE LYASE GENE IN PSEUDOMONAS SYRINGAE PV. GLYCINEA AND RELATED BACTERIA

Author
item LIAO, CHING HSING
item FETT, WILLIAM
item TZEAN, SEAN-SHONG - NATIONAL TAIWAN UNIV.
item HOFFMAN, GABRIEL

Submitted to: Canadian Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2006
Publication Date: 10/1/2006
Citation: Liao, C., Fett, W.F., Tzean, S., Hoffman, G. 2006. Detection and sequence analysis of an altered pectate lyase gene in pseudomonas syringae pv. glycinea and related bacteria. Canadian Journal of Microbiology. 52:1051:1059.

Interpretive Summary: “Pectate lyase” is an important tissue-macerating enzyme responsible for the spoilage (soft-rot) of a large proportion of fresh vegetables and fruits. This enzyme is produced by a wide variety of bacteria naturally associated with plants. These bacteria and the enzyme they produce can favor the survival and growth of human pathogens such as Salmonella on fresh produce. In this study, we have examined the structure of bacterial genes in relation to the enzymatic function or non-function of their protein products. We have also identified two mechanisms possibly accounting for the inactivity of the protein products produced by several disease-causing bacteria of plants that do not cause soft rot. A better understanding of molecular structure and function of this important cell wall-degrading enzyme may lead to the development of an innovative strategy to reduce the spoilage caused by this enzyme and to minimize the proliferation of human pathogens in soft-rotted plant tissue. The new knowledge generated during the study is also useful for the development of novel pectin-degrading enzymes for food processing and other industrial applications by protein engineering technologies.

Technical Abstract: Pectate lyase (PL) is a potent cell wall-degrading enzyme and is believed to play a role in microbial infection of plants. The gene (pel) coding for this enzyme has been isolated from a wide variety of microorganisms, especially the bacteria capable of causing soft rot. We report here the detection of pel gene homologs in the genomes of three non-pectolytic pathovars of Pseudomonas syringae and the cloning of a pel homolog from a non-pectolytic strain of P. s. pv. glycinea. The P. s. pv. glycinea pel gene was predicted to encode a PL-like protein sharing 70-90% identity in amino acid (a.a.) sequence with the functional PLs produced by pectolytic pseudomonads and xanthomonads. A series of sequence analyses presented show that: (a) the defective P. s. pv. glycinea PL contains two regions in the a.a. sequence which may affect the formation of a '-helix tertiary structure important for enzymatic activity, and (b) the defective P. s. pv. glycinea pel sequence contains a single- and double-base insertion and a 18-bp deletion not found in the functional pel. The defective pel sequences were detected by PCR and nucleotide sequencing in the genomes of non-pectolytic pv. phaseolicola and pv. tagetis, but not in the genomes of pectolytic pv. lachrymans and pv. tabaci. Occurrence of a defective pel gene is common among strains of P. s. pv. glycinea, P. s. pv. phaseolicola, and P. s. pv. tagetis, suggesting that production of an active PL is not essential for the induction of diseases by these foliar pathogens.