Arabidopsis xanthine dehydrogenase mutants defective in purine degradation show a compromised protective response to drought and oxidative stress

Abstract

Although generally recognized for its role in nitrogen recycling and remobilization, purine catabolism might also be involved in the plant response and adaptation to environmental stress. Previously, we demonstrated that allantoin, a major purine intermediary metabolite in stressed plants, stimulates abscisic acid production and activates stress-responsive gene expression, leading to increased tolerance to abiotic stress in Arabidopsis seedlings. Here, we show that dysfunction of purine degradation, as a result of knocking down the key enzyme xanthine dehydrogenase, severely reduced the survival of Arabidopsis under progressive drought conditions and significantly decreased the tolerance to superoxide-mediated oxidative stress. The enhanced stress sensitivity of the knockdown mutants likely resulted from defective stress responses, because the drought-induced accumulation of the cellular protectant proline was compromised in the knockdown plants, which also showed lower mRNA levels of P5CS1, the gene encoding the rate-limiting enzyme for proline biosynthesis. When exogenously applied to wild-type Arabidopsis, allantoin and its precursor urate were able to elicit expression of P5CS1 in the absence of stress. Thus, our results provide further evidence for a previously unrecognized role for purine metabolites in stress responses, supporting the possible contribution of purine degradation to plant acclimation to changing environments. © 2014 The Japanese Society for Plant Cell and Molecular Biology.