Allantoate amidohydrolase transcript expression is independent of drought tolerance in soybean

Abstract

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.

The Ureide-Degrading Reactions of Purine Ring Catabolism Employ Three Amidohydrolases and One Aminohydrolase in Arabidopsis, Soybean, and Rice

“…The relative independence of ureide-degrading activities and transcript amounts for ALN and AAH from environmental conditions, in particular the status of nitrogen fixation, had been noted earlier (Charlson et al, 2009;Alamillo et al, 2010;Díaz-Leal et al, 2012). ALN activity was independent of tissue ureide influx and ureide content, while AAH activity was only about 50% lower in soybean plants not relying on fixed nitrogen (Winkler et al, 1988;Rice et al, 1990).…”

Local inhibition of nitrogen fixation and nodule metabolism in drought-stressed soybean

“…The activity of the enzyme responsible for allantoate breakdown, allantoate amidohydrolase, was initially found to correlate to drought tolerance when cultivars with contrasting sensitivity were compared (Purcell et al ., 2000). However, in subsequent studies, differences in drought tolerance were not associated with differential transcript expression of allantoate amidohydrolase, suggesting that other factors may regulate its activity such as the post-translational regulation of the enzyme and/or the availability of Mn 2+ (Charlson et al ., 2009). Alamillo et al .…”

Breeding for improved drought tolerance in Chickpea (Cicer arietinum L.)

“…), reduction in oxygen‐binding leghaemoglobin contents (Garg and Manchanda ), suppression of N‐fixing activity (Charlson et al. ) and reduced membrane integrity of nodules (Mhadhbi et al. ).…”