Disruption of the rice nitrate transporter OsNPF2.2 hinders root-to-shoot nitrate transport and vascular development

Abstract

Plants have evolved to express some members of the nitrate transporter 1/peptide transporter family (NPF) to uptake and transport nitrate. However, little is known of the physiological and functional roles of this family in rice (Oryza sativa L.). Here, we characterized the vascular specific transporter OsNPF2.2. Functional analysis using cDNA-injected Xenopus laevis oocytes revealed that OsNPF2.2 is a low-affinity, pH-dependent nitrate transporter. Use of a green fluorescent protein tagged OsNPF2.2 showed that the transporter is located in the plasma membrane in the rice protoplast. Expression analysis showed that OsNPF2.2 is nitrate inducible and is mainly expressed in parenchyma cells around the xylem. Disruption of OsNPF2.2 increased nitrate concentration in the shoot xylem exudate when nitrate was supplied after a deprivation period; this result suggests that OsNPF2.2 may participate in unloading nitrate from the xylem. Under steady-state nitrate supply, the osnpf2.2 mutants maintained high levels of nitrate in the roots and low shoot:root nitrate ratios; this observation suggests that OsNPF2.2 is involved in root-to-shoot nitrate transport. Mutation of OsNPF2.2 also caused abnormal vasculature and retarded plant growth and development. Our findings demonstrate that OsNPF2.2 can unload nitrate from the xylem to affect the root-to-shoot nitrate transport and plant development.

Identification of arbuscular mycorrhiza-inducible Nitrate Transporter 1/Peptide Transporter Family (NPF) genes in rice

“…Growth condition-dependent modulation of transcriptional induction by AMF colonization is also known for several AM marker genes, including PT11 and AMT3.1 (Vallino et al 2014). While NPF1.3 is still not functionally characterized, Li et al (2015) demonstrated that the NPF2.2/ PTR2 protein functions as a low-affinity, pH-dependent nitrate transporter, which unloads NO 3 − from the xylem, is involved in nitrate transport from root to shoot and affects plant development. Hence, the AM-specific upregulation of NPF2.2/PTR2 in rice roots suggests that upon symbiosis NO 3 − , unloading from the xylem is enhanced.…”

Nitrogen Use Efficiency in Rice

“…Elevated expression of OsNPF7.3 promoted rice growth through increasing ammonium transporter expression and glutamine synthetase activity [34]. Recently, OsNPF2.4 [35] and OsNPF2.2 [36] involved in long-distance root-to-shoot nitrate transport have been identified. Knockout of OsNPF2.4 impaired potassium (K)-coupled nitrate upward transport and nitrate redistribution from old leaves to other organs [35].…”

“…Knockout of OsNPF2.4 impaired potassium (K)-coupled nitrate upward transport and nitrate redistribution from old leaves to other organs [35]. OsNPF2.2 can unload nitrate from the xylem affecting the root-to-shoot nitrate transport and plant development [36]. In addition, a tonoplast-localized low-affinity nitrate transporter OsNPF7.2 has been characterized playing a pivotal role in intracellular allocation of nitrate in roots [37].…”

Superexpressão do transportador OsNPF4.11 (OsNRT1.2) afeta teor de nitrato, parâmetros radiculares e crescimento de arroz

“…Estudos anteriores demonstraram que o nocaute de transportadores envolvidos no carregamento do xilema, pode alterar a translocação de NO 3 -a longa distância, acarretando em um acúmulo de NO 3 -nas raízes e uma redução no crescimento das plantas (Lin et al, 2008;Tang et al, 2012;Li et al, 2015), desta forma o aumento na expressão do OsNPF4.11 pode ter influenciado na expressão de transportadores envolvidos no carregamento do xilema, acarretando assim no fenótipo observado.…”