Arabidopsis NRT1.5 Mediates the Suppression of Nitrate Starvation-Induced Leaf Senescence by Modulating Foliar Potassium Level

Abstract

Nitrogen deficiency induces leaf senescence. However, whether or how nitrate might affect this process remains to be investigated. Here, we report an interesting finding that nitrate-instead of nitrogen-starvation induced early leaf senescence in nrt1.5 mutant, and present genetic and physiological data demonstrating that nitrate starvation-induced leaf senescence is suppressed by NRT1.5. NRT1.5 suppresses the senescence process dependent on its function from roots, but not the nitrate transport function. Further analyses using nrt1.5 single and nia1 nia2 nrt1.5-4 triple mutant showed a negative correlation between nitrate concentration and senescence rate in leaves. Moreover, when exposed to nitrate starvation, foliar potassium level decreased in nrt1.5, but adding potassium could essentially restore the early leaf senescence phenotype of nrt1.5 plants. Nitrate starvation also downregulated the expression of HAK5, RAP2.11, and ANN1 in nrt1.5 roots, and appeared to alter potassium level in xylem sap from nrt1.5. These data suggest that NRT1.5 likely perceives nitrate starvation-derived signals to prevent leaf senescence by facilitating foliar potassium accumulation.

Tonoplast-localized nitrate uptake transporters involved in vacuolar nitrate efflux and reallocation in Arabidopsis

“…Leaves and roots were harvested and washed at least three times by ultrapure water for 5 min and then extracted nitrate as described 56 .…”

NRT1.5/NPF7.3 Functions as a Proton-Coupled H+/K+ Antiporter for K+ Loading into the Xylem in Arabidopsis

“…The Sensitive Phenotype of lks2 Depends on Low K + Previous reports have observed that K + transport in the nrt1.5 mutant was reduced (Lin et al, 2008;Drechsler et al, 2015;Meng et al, 2016), and this reduction was dependent on NO 3 2 (Lin et al, 2008). Our results here showed that there was no obvious phenotypic difference between wild-type and mutant plants when grown on high K + (5 mM) medium, although the NO 3 2 concentration in the medium was decreased from 5 to 0.1 mM ( Figure 3A; Supplemental Figure 5C).…”

The combination of K+ deficiency with other environmental stresses: What is the outcome?

“…Thus, NRT1.5, which belongs to a family that includes several NO 3 − transporters, was initially characterized as a transporter involved in NO 3 − release into the xylem (Lin et al ). However, it has recently been shown that this transporter also mediates K + release into the xylem and coordinates K + /NO 3 − distribution in plants (Drechsler et al , Meng et al , Li et al ).…”

“…Plant. 165,2019 recently been shown that this transporter also mediates K + release into the xylem and coordinates K + /NO 3 − distribution in plants (Drechsler et al 2015, Meng et al 2016, Li et al 2017).…”