Abstract
Rice includes 93 nitrate and peptide transporters family (NPF) members that facilitate the soil uptake and internal reallocation of nitrogen for growth and development. This study demonstrated that OsNPF7.7 had two splicing variants, and altered expression of each variant could regulate shoot branching and nitrogen utilization efficiency (NUtE) in rice. The expression of both variants was down-regulated in the buds by increased nitrogen level in the Japonica rice variety ZH11. The expression level of long-variant OsNPF7.7-1 was higher in panicles at reproductive stage, however, the expression level of short-variant OsNPF7.7-2 was higher in buds and leaves at vegetative stage compared to each other in ZH11. OsNPF7.7-1 was localized in the plasma membrane, whereas OsNPF7.7-2 was localized in the vacuole membrane. Furthermore, the results indicated that the expression level of each variant for OsNPF7.7 determined axillary bud outgrowth, and then influenced the rice tiller number. Overexpression of OsNPF7.7-1 could promote nitrate influx and concentration in root, whereas overexpression of OsNPF7.7-2 could improve ammonium influx and concentration in root. RNAi and osnpf7.7 lines of OsNPF7.7 showed an increased amount of amino acids in leaf sheaths, but a decreased amount in leaf blades, which affected nitrogen allocation and plant growth. The elevated expression of each variant for OsNPF7.7 in ZH11 enhanced NUtE using certain fertilization regimes under paddy field conditions. Moreover, overexpression of each variant for OsNPF7.7 in KY131 increased significantly the filled grain number per plant. Thus, increased each variant of OsNPF7.7 has the potential to improve grain yield and NUtE in rice.
Highlights
The application of nitrogen is one possible measure to obtain higher yield, and China applies more nitrogen fertilizers than any other country in the world (Narits, 2010)
We found that OsNPF7.7 in the OsNPF family has two splicing variants with different exons (Figure 1A)
The newly found two variants of gene OsNPF7.7 in the nitrate and peptide transporters family (NPF) family could be assigned by nitrogen sources, and the level of each variant depended on the concentration of external nitrogen source
Summary
The application of nitrogen is one possible measure to obtain higher yield, and China applies more nitrogen fertilizers than any other country in the world (Narits, 2010). A potential solution to this issue could be the increase of nitrogen use efficiency (NUE) in crop plants, including rice (Xu et al, 2012). NUE is a crucial strategy to increase the grain yield, which is mainly controlled by tiller number per plant, grain number per panicle, and thousand-grain weight in rice (Li et al, 2003; Liang et al, 2014). Plants have evolved multiple transport systems to facilitate nitrogen uptake from the soil and internal reallocation involving in growth and development including rice tiller number (Rentsch et al, 2007; Tsay et al, 2007; Hu et al, 2015). Overexpression of the splicing gene OsPTR9 (OsNPF8.202) enhances tiller number and NUtE in rice (Fang et al, 2013)
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