The purine metabolite allantoin enhances abiotic stress tolerance through synergistic activation of abscisic acid metabolism

Abstract

Purine catabolism is regarded as a housekeeping function that remobilizes nitrogen for plant growth and development. However, emerging evidence suggests that certain purine metabolites might contribute to stress protection of plants. Here, we show that in Arabidopsis, the intermediary metabolite allantoin plays a role in abiotic stress tolerance via activation of abscisic acid (ABA) metabolism. The aln loss-offunction of ALN, encoding allantoinase, results in increased allantoin accumulation, genome-wide up-regulation of stressrelated genes and enhanced tolerance to drought-shock and osmotic stress in aln mutant seedlings. This phenotype is not caused by a general response to purine catabolism inhibition, but rather results from a specific effect of allantoin. Allantoin activates ABA production both through increased transcription of NCED3, encoding a key enzyme in ABA biosynthesis, and through post-translational activation via high-molecularweight complex formation of BG1, a β-glucosidase hydrolysing glucose-conjugated ABA. Exogenous application of allantoin to wild-type plants also activates the two ABAproducing pathways that lead to ABA accumulation and stress-responsive gene expression, but this effect is abrogated in ABA-deficient and BG1-knockout mutants. We propose that purine catabolism functions not only in nitrogen metabolism, but also in stress tolerance by influencing ABA production, which is mediated by the possible regulatory action of allantoin.

Cell-Type-Specific H+-ATPase Activity in Root Tissues Enables K+ Retention and Mediates Acclimation of Barley (Hordeum vulgare) to Salinity Stress

“…Recently, the constitutive accumulation of allantoin was shown to improve overall plant performance under stress by activating abscisic acid signaling pathways (Wang et al, 2012), and exogenous application mitigated oxidative damage symptoms (Watanabe et al, 2014). Here, we show that pretreating barley roots with physiologically relevant concentrations of exogenously applied allantoin desensitized the root apical tissues and increased their ability to retain K + upon both salinity and ROS exposure (Fig.…”

“…Given the recent reports for the mitigating role of allantoin in oxidative stress damage in plants (Watanabe et al, 2014), we tested the effects of exogenously supplied allantoin on root ion flux responses to ROS. Root pretreatment with a physiologically relevant (1 mM) concentration of allantoin reduced the sensitivity of the root apex to both salinity and ROS stresses (Fig.…”

Allantoin, a stress-related purine metabolite, can activate jasmonate signaling in a MYC2-regulated and abscisic acid-dependent manner

“…Although not conspicuous in the GO analysis (Table 1 of Watanabe et al, 2014b), the aln mutants also showed increased expression of JA response signatures including genes involved in JA metabolism and signaling, such as 13-LIPOXYGENASE (LOX) and JASMONATE ZIM-DOMAIN (JAZ) PROTEINS (Supplementary Table S2 of Watanabe et al, 2014b). For this reason, and to improve the interpretation of the transcriptome profiles, the first step in this study was to renormalize these microarray data according to a three-parameter lognormal distribution model (Konishi, 2004).…”

“…Functional enrichment analyses of the Biological Process Gene Ontology (GO) terms were carried out using the BioMaps tool of VirtualPlant version 1.3 (Katari et al, 2010;http For quantitative transcript analysis, samples of aerial parts were collected from 2-week-old seedlings that were grown aseptically on solid 1/2MS medium with or without added allantoin (Wako Pure Chemical Industries, Ltd, Osaka, Japan) or allantoic acid (Carbosynth Limited, Berkshire, UK). RNA extraction and real-time reverse transcription quantitative PCR (RT-qPCR) were performed as described previously (Watanabe et al, 2014b). Relative gene expression levels were calculated by the 2 −∆∆Ct method (Livak and Schmittgen, 2001) after normalization to ACTIN2 expression levels.…”

“…Allantoin may function in stress protection by scavenging ROS; indeed, leaf disc assays showed that exogenous allantoin alleviated ROS accumulation and cell death (Brychkova et al, 2008). Allantoin may also activate stress responses, as its accumulation in aln mutants or supplementation of wildtype (WT) seedlings increased basal levels of the stress phytohormone abscisic acid (ABA), with concomitant activation of stress-related gene expression (Watanabe et al, 2014b).…”