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JXB Advance Access published online on January 6, 2009
Journal of Experimental Botany, doi:10.1093/jxb/ern332
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html

RESEARCH PAPER

Allantoate amidohydrolase transcript expression is independent of drought tolerance in soybean

Dirk V. Charlson1, Kenneth L. Korth2 and Larry C. Purcell1,*

1Department of Crop, Soil, and Environmental Sciences, University of Arkansas, 1366 West Altheimer Drive, Fayetteville, Arkansas 72704-6898, USA
2Department of Plant Pathology, University of Arkansas, 217 Plant Sciences, Fayetteville, Arkansas 72701,USA

* To whom correspondence should be addressed: E-mail: lpurcell{at}uark.edu

Drought is a limiting factor for N2 fixation in soybean [Glycine max (L.) Merr.] thereby resulting in reduced biomass accumulation and yield. Drought-sensitive genotypes accumulate ureides, a product of N2 fixation, during drought stress; however, drought-tolerant genotypes have lower shoot ureide concentrations, which appear to alleviate drought stress on N2 fixation. A key enzyme involved in ureide breakdown in shoots is allantoate amidohydrolase (AAH). It is hypothesized that AAH gene expression in soybean determines shoot ureide concentrations during water-deficit stress and is responsible for the differential sensitivities of the N2-fixation response to drought among soybean genotypes. The objectives were to examine the relationship between AAH transcript levels and shoot ureide concentration and drought tolerance. Drought-tolerant (Jackson) and drought-sensitive (Williams) genotypes were subjected to three water-availability treatments: well-watered control, moderate water-deficit stress, and severe water-deficit stress. Shoot ureide concentrations were examined, in addition to gene expression of AAH and DREB2, a gene expressed during water-deficit stress. As expected, DREB2 expression was detected only during severe water-deficit stress, and shoot ureide concentrations were greatest in the drought-sensitive genotype relative to the drought-tolerant genotype during water-deficit stress. However, expression of AAH transcripts was similar among water treatments and genotypes, indicating that AAH mRNA was not closely associated with drought tolerance. Ureide concentrations in shoots were weakly associated with AAH mRNA levels. These results indicate that AAH expression is probably not associated with the increased ureide catabolism observed in drought-tolerant genotypes, such as Jackson. Further study of AAH at the post-translational and enzymatic levels is warranted in order to dissect the potential role of this gene in drought tolerance.

Key words: Allantoate amidohydrolase, drought, Glycine max, manganese, nitrogen fixation, soybean, ureides, water-deficit stress

Received 29 September 2008; Revised 19 November 2008 Accepted 25 November 2008


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