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United States Department of Agriculture

Agricultural Research Service

Title: Identification, Characterization, and Evolution of a Large Polygalacturonase Gene Family from Rhizopus oryzae

Authors
item MERTENS, JEFFREY
item ROONEY, ALEJANDRO

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 31, 2009
Publication Date: N/A

Technical Abstract: Polygalacturonase enzymes are a valuable aid in the retting of flax for production of linens, clarification of juices, and more recently, production of value-added products from citrus wastes. A search of the recently sequenced Rhizopus oryzae strain 99-880 genome database uncovered 18 putative polygalacturonase genes, with 2 genes being identical and only 1 with any similarity to a previously reported Rhizopus endo-polygalacturonase gene. The 17 different genes possess from 1 to 3 introns and share 50% to greater than 90% identity at the nucleotide level as well as the deduced protein sequence level. The cDNA for each putative polygalacturonase was expressed in Pichia pastoris and tested for enzyme activity, with 15 of the 17 genes encoding active enzyme. Initial characterization demonstrated that some of the enzymes were endo-polygalacturonase enzymes with hydrolysis of polygalacturonic acid resulting in the production of multiple products ranging from galacturonic acid to greater than penta-galacturonic acid, while others could be considered exo-polygalacturonase enzymes as galacturonic acid was the only product obtained. More detailed biochemical understanding of the active polygalacturonase enzymes is under way with initial results demonstrating that some of the enzymes are extremely heat stable. Finally, phylogenetic analysis indicates that the genes form a distinct monophyletic group among fungal polygalacturonase enzymes and suggests that endo-polygalacturonase is the ancestral form of polygalacturonase in fungi and that exo-polygalacturonase function evolved later at least two independent times.

Last Modified: 9/10/2014
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