Minisymposium 9: Legume Biology

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Abs # M0903: Identification and cloning of a plant allantoate amidohydrolase

Presenter:	Todd, Christopher D       Contact Presenter
Authors	Todd, Christopher D (A) (B)  Polacco, Joe  (B)
Affiliations:	(A): University of Saskatchewan (B): University of Missouri

Ureides are formed in the nodules of soybean and other warm season legumes during biological nitrogen fixation. They are involved in the transport of fixed nitrogen to aerial portions of the plant through the xylem. In leaves ureides are broken down in a multi-step pathway, with all nitrogen eventually being converted to ammonia. We established that in soybean the first nitrogen-releasing step is catalyzed by the enzyme allantoate amidohydrolase. In order to better understand the regulation of ureide catabolism in legumes we sought to clone the first plant allantoate amidohydrolase using a functional genomics approach. We identified a gene from Arabidopsis thaliana that shared sequence similarity with allantoate amidohydrolase from Bacillus subtilis. Its ability to metabolize allantoate was demonstrated by expression in Saccharomyces cerevisiae and correction of a yeast dal2 mutant, unable to utilize allantoate as its sole nitrogen source. Disruption of this gene by T-DNA insertion also prevented Arabidopsis seedlings from utilizing allantoin as a nitrogen source and caused accumulation of allantoate in seedling tissue. We call this gene AtAAH (Arabidopsis thaliana Allantoate Amidohydrolase) and based on sequence similarity we have identified potential orthologs in legume EST collections, including soybean.