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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Functional Characterization of Allantoinase Genes from Arabidopsis and a Nonureide-Type Legume Black Locust¹

Department of Forestry, Michigan State University, East Lansing, Michigan 48824

The availability of nitrogen is a limiting factor for plant growth in most soils. Allantoin and its degradation derivatives are a group of soil heterocyclic nitrogen compounds that play an essential role in the assimilation, metabolism, transport, and storage of nitrogen in plants. Allantoinase is a key enzyme for biogenesis and degradation of these ureide compounds. Here, we describe the isolation of two functional allantoinase genes, AtALN (Arabidopsis allantoinase) and RpALN (Robinia pseudoacacia allantoinase), from Arabidopsis and black locust (Robinia pseudoacacia). The proteins encoded by those genes were predicted to have a signal peptide for the secretory pathway, which is consistent with earlier biochemical work that localized allantoinase activity to microbodies and endoplasmic reticulum (Hanks et al., 1981). Their functions were confirmed by genetic complementation of a yeast mutant (dal1) deficient in allantoin hydrolysis. The absence of nitrogen in the medium increased the expression of the genes. In Arabidopsis, the addition of allantoin to the medium as a sole source of nitrogen resulted in the up-regulation of the AtALN gene. The black locust gene (RpALN) was differentially regulated in cotyledons, axis, and hypocotyls during seed germination and seedling growth, but was not expressed in root tissues. In the trunk wood of a mature black locust tree, the RpALN gene was highly expressed in the bark/cambial region, but had no detectable expression in the sapwood or sapwood-heartwood transition zone. In addition, the gene expression in the bark/cambial region was up-regulated in spring and fall when compared with summer, suggesting its involvement in nitrogen mobilization.

¹ This work was supported by the U.S. Department of Agriculture (grants to the Eastern Hardwood Utilization Program at Michigan State University, nos. 98-34158-5995, 00-34158-9236, and 01-34158-11222).

^* Corresponding author; e-mail hanky{at}msu.edu; fax 517-432-1143.

Received October 10, 2003; returned for revision November 10, 2003; accepted December 6, 2003.

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