Efficient allocation of nitrate into vital tissues is pivotal for optimizing nitrogen utilization efficiency, fostering plant development, and enhancing stress adaptation. Despite over 90% of free nitrate being stored in vacuole, the mechanisms underlying nitrate retrieval from vacuole remains largely elusive. Through a reverse genetics approach, we have elucidated the role of VNE1 (Vacuolar Nitrate Efflux transporter) as a novel nitrate transporter in Arabidopsis, distinct from known nitrate transporter families, responsible for vacuolar nitrate efflux.
Kinetics assays of nitrate transport have revealed that VNE1-mediated nitrate transport exhibits a Km value of approximately 10 mM, comparable with vacuolar nitrate content. This suggests that VNE1 is suitable to retrieve nitrate from vacuole. The in vivo function of VNE1 is further validated by observing the accumulation of vacuolar nitrate content in the knock-out mutant vne1-1.
Furthermore, vne1-1 mutant exhibits reduced rosettes area and biomass particularly under N deficiency conditions, underscoring the critical role of efficient retrieving nitrate from vacuole in maximizing plant growth. Our findings highlight VNE1 as a novel tonoplast-localized nitrate efflux transporter, essential for optimizing nitrate utilization in Arabidopsis.