Nitrate transporter NRT1.1 and anion channel SLAH3 form a functional unit to regulate nitrate-dependent alleviation of ammonium toxicity

Ammonium(NH4~+) and nitrate(NO3~-) are major inorganic nitrogen(N) sources for plants.When serving as the sole or dominant N supply,NH4~+often causes root inhibition and shoot chlorosis in plants,known as ammonium toxicity.NO3~-usually causes no toxicity and can mitigate ammonium toxicity even at low concentrations,referred to as nitrate-dependent alleviation of ammonium toxicity.Our previous studies indicated a NO3~-efflux channel SLAH3 is involved in this process.However,whether additional components contribute to NO3~--mediated NH4~+ detoxification is unknown.Previously,mutations in NO3~-transporter NRT1.1 were shown to cause enhanced resistance to high concentrations of NH4~+.Whereas,in this study,we found when the high-NH4+medium was supplemented with low concentrations of NO3~-,nrt1.1 mutant plants showed hyper-sensitive phenotype instead.Furthermore,mutation in NRT1.1 caused enhanced medium acidification under high-NH4~+/Iow-NO3~-condition,suggesting NRT1.1 regulates ammonium toxicity by facilitating H+uptake.Moreover,NRT1.1 was shown to interact with SLAH3 to form a transporter-channel complex.Interestingly,SLAH3 appeared to affect NO3~-influx while NRT1.1 influenced NO3~-efflux,suggesting NRT1.1 and SLAH3 regulate each other at protein and/or gene expression levels.Our study thus revealed NRT1.1 and SLAH3 form a functional unit to regulate nitrate-dependent alleviation of ammonium toxicity through regulating NO3~-transport and balancing rhizosphere acidification.