Rice nitrate transporter OsNPF7.2 positively regulates tiller number and grain yield

Jie Wang,Qisen Zeng,Zhongming Fang,Bowen Wu,Haipeng Nie,Junjie Qian,Kai Lu

doi:10.1186/s12284-018-0205-6

Jie Wang, Qisen Zeng + Show 5 more

Open Access

https://doi.org/10.1186/s12284-018-0205-6

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Abstract

BackgroundRice tiller number is one of the most important factors that determine grain yield, while nitrogen is essential for the crop growth and development, especially for tiller formation. Genes involved in nitrogen use efficiency processes have been identified in the previous studies, however, only a small number of these genes have been found to improve grain yield by promoting tillering.ResultsWe constructed over-expression (OX) lines and RNA-interference (Ri) lines, and selected a mutant of OsNPF7.2, a low-affinity nitrate transporter. Our analyses showed that rice tiller number and grain yield were significantly increased in OX lines, whereas Ri lines and mutant osnpf7.2 had fewer tiller number and lower grain yield. Under different nitrate concentrations, tiller buds grew faster in OX lines than in WT, but they grew slower in Ri lines and mutant osnpf7.2. These results indicated that altered expression of OsNPF7.2 plays a significant role in the control of tiller bud growth and regulation of tillering. Elevated expression of OsNPF7.2 also improved root length, root number, fresh weight, and dry weight. However, reduced expression of OsNPF7.2 had the opposite result on these characters. OsNPF7.2 OX lines showed more significantly enhanced influx of nitrate and had a higher nitrate concentration than WT. The levels of gene transcripts related to cytokinin pathway and cell cycle in tiller bud, and cytokinins concentration in tiller basal portion were higher in OX lines than that in WT, suggesting that altered expression of OsNPF7.2 controlled tiller bud growth and root development by regulating cytokinins content and cell cycle in plant cells. Altered expression of OsNPF7.2 also was responsible for the change in expression of the genes involved in strigolactone pathway, such as D27, D17, D10, Os900, Os1400, D14, D3, and OsFC1.ConclusionOur results suggested that OsNPF7.2 is a positive regulator of nitrate influx and concentration, and that it also regulates cell division in tiller bud and alters expression of genes involved in cytokinin and strigolactone pathways, resulting in the control over rice tiller number. Since elevated expression of OsNPF7.2 is capable of improving rice grain yield, this gene might be applied to high-yield rice breeding.

Highlights

Rice tiller number is one of the most important factors that determine grain yield, while nitrogen is essential for the crop growth and development, especially for tiller formation
Over-expression of OsNPF7.2 improves rice tiller number and grain yield OsNPF7.2 is mainly expressed in the roots of seedlings, and its protein transports nitrate at vacuolar membrane (Hu et al 2016)
We found that tiller number increased in three OX lines at reproductive stage (Fig. 1b-d, r) compared to that in wild-type (WT) ZH11 (Fig. 1a, r), but it dramatically decreased in three Ri lines (Fig. 1e-g, r) and mutant osnpf7.2 (Fig. 1h, r)

Summary

Introduction

Rice tiller number is one of the most important factors that determine grain yield, while nitrogen is essential for the crop growth and development, especially for tiller formation. Afterwards, other NPFs were explored, such as SP1 (OsNPF4.1) and OsPTR9 (OsNPF8.20), their substrates remain unclear (Lin et al 2000; Fang et al 2013), Recently, OsNPF2.4, OsNPF2.2, and OsNPF7.2 have been reported to serve as low-affinity nitrate transporters functioning under high nitrate concentrations (Li et al 2015; Xia et al 2015; Hu et al 2016). Allelic differences in the dual-affinity nitrate transporter NRT1.1B (OsNPF6.5) have been reported between indica and japonica cultivars with high nitrogen-use efficiency and grain yield in the NRT1.1B– indica allele (Hu et al 2015). OsPTR7 (OsNPF8.1) shows dimethylarsenate (DMA) transport activity and is involved in the long-distance translocation of DMA into rice grain (Tang et al 2017)

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