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Stresses decouple nitrate assimilation and photosynthesis through stress-initiated nitrate allocation to roots (SINAR), which is mediated by the nitrate transporters NRT1.8 and NRT1.5 and functions to promote stress tolerance. However, how SINAR communicates with the environment remains unknown. Here, we present biochemical and genetic evidence demonstrating that in Arabidopsis thaliana, ethylene (ET) and jasmonic acid (JA) affect the crosstalk between SINAR and the environment. Electrophoretic mobility shift assays and chromatin immunoprecipitation assays showed that ethylene response factors (ERFs), including OCTADECANOID-RESPONSIVE ARABIDOPSIS AP2/ERF59, bind to the GCC boxes in the NRT1.8 promoter region, while ETHYLENE INSENSITIVE3 (EIN3) binds to the EIN3 binding site motifs in the NRT1.5 promoter. Genetic assays showed that cadmium and sodium stresses initiated ET/JA signaling, which converged at EIN3/EIN3-Like1 (EIL1) to modulate ERF expression and hence to upregulate NRT1.8. By contrast, ET and JA signaling mediated the downregulation of NRT1.5 via EIN3/EIL1 and other, unknown component(s). SINAR enhanced stress tolerance and decreased plant growth under nonstressed conditions through the ET/JA-NRT1.5/NRT1.8 signaling module. Interestingly, when nitrate reductase was impaired, SINAR failed to affect either stress tolerance or plant growth. These data suggest that SINAR responds to environmental conditions through the ET/JA-NRT signaling module, which further modulates stress tolerance and plant growth in a nitrate reductase-dependent manner.
Zhang et al. (Wed,) studied this question.