Abstract
BackgroundSoil salinity is a critical threat to global agriculture. In plants, the accumulation of xanthine activates xanthine dehydrogenase (XDH), which catalyses the oxidation/conversion of xanthine to uric acid to remove excess reactive oxygen species (ROS). The nucleobase-ascorbate transporter (NAT) family is also known as the nucleobase-cation symporter (NCS) or AzgA-like family. NAT is known to transport xanthine and uric acid in plants. The expression of MdNAT is influenced by salinity stress in apple.ResultsIn this study, we discovered that exogenous application of xanthine and uric acid enhanced the resistance of apple plants to salinity stress. In addition, MdNAT7 overexpression transgenic apple plants showed enhanced xanthine and uric acid concentrations and improved tolerance to salinity stress compared with nontransgenic plants, while opposite phenotypes were observed for MdNAT7 RNAi plants. These differences were probably due to the enhancement or impairment of ROS scavenging and ion homeostasis abilities.ConclusionOur results demonstrate that xanthine and uric acid have potential uses in salt stress alleviation, and MdNAT7 can be utilized as a candidate gene to engineer resistance to salt stress in plants.
Highlights
Soil salinity is a critical threat to global agriculture
All nucleobase-ascorbate transporters contain 13–14 transmembrane segments, with a highly conserved signature motif ([Q/E/P]-N-X-G-X-X-X-X-T-[R/K/G]), which is pivotal for the NAT feature (Fig. 1a)
Plant growth and root elongation were inhibited under salt condition, while the addition of X and uric acid (UA) alleviated this inhibition (Fig. 3a)
Summary
Soil salinity is a critical threat to global agriculture. The accumulation of xanthine activates xanthine dehydrogenase (XDH), which catalyses the oxidation/conversion of xanthine to uric acid to remove excess reactive oxygen species (ROS). NAT is known to transport xanthine and uric acid in plants. Ionic stress induces excess Na+ to accumulate in leaves. During periods of high salt stress, the uptake of Na+ competes with that of K+, resulting in excess sequestration of cytoplasmic Na+ rather than Cl− within the cells [4]. In the roots of plants, K+ absorption from soil is primarily mediated by K+ channels or transporters. The transcription and activities of these K+ channels or transporters could be induced in response to K+ deficiency [9]. The SOS3-SOS2 protein complex activates the SOS1 protein, a plasma membrane Na+/H+ antiporter that induces the efflux of Na+ [11].
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