Abstract
SummaryAmino acid transporters (AATs) play indispensable roles in nutrient allocation during plant development. In this study, we demonstrated that inhibiting expression of the rice amino acid transporter OsAAP3 increased grain yield due to a formation of larger numbers of tillers as a result of increased bud outgrowth. Elevated expression of OsAAP3 in transgenic plants resulted in significantly higher amino acid concentrations of Lys, Arg, His, Asp, Ala, Gln, Gly, Thr and Tyr, and inhibited bud outgrowth and rice tillering. However, RNAi of OsAAP3 decreased significantly Arg, Lys, Asp and Thr concentrations to a small extent, and thus promoted bud outgrowth, increased significantly tiller numbers and effective panicle numbers per plant, and further enhanced significantly grain yield and nitrogen use efficiency (NUE). The promoter sequences of OsAAP3 showed some divergence between Japonica and Indica rice, and expression of the gene was higher in Japonica, which produced fewer tillers than Indica. We generated knockout lines of OsAAP3 on Japonica ZH11 and KY131 using CRISPR technology and found that grain yield could be increased significantly. These results suggest that manipulation of OsAAP3 expression could be used to increase grain yield in rice.
Highlights
Inorganic nitrogen (N) is mainly absorbed by plants in the form of nitrate and ammonium and is converted into amino acids directly in the roots or after translocation to the leaves
Root numbers (Figure S1a-c, e) and plant height (Figure S1a-c, f) increased significantly under 1.0–8.0 mM nitrogen in Ri lines. These results indicated that RNAi-mediated down-regulation of OsAAP3 promoted bud outgrowth and seedling growth and might trigger the formation of an increased tiller number
None of the measured amino acids decreased in concentrations in grains of Ri lines (Figure 4d). These results showed that overexpression of OsAAP3 could increase the concentrations of amino acids, which inhibited the growth of plants; a reduction in expression of OsAAP3 prevented any inhibition of growth but did not affect the nutritional quality of the grain
Summary
Inorganic nitrogen (N) is mainly absorbed by plants in the form of nitrate and ammonium and is converted into amino acids directly in the roots or after translocation to the leaves. The amino acids are transported to roots, leaves, flowers, pollen and embryos (Fischer et al, 1998). (Cheng et al, 2016) These studies have shown that AAP transporters play important roles in the loading of amino acids for nitrogen sink and supply (Tegeder and Ward, 2012). In Arabidopsis, AtAAP1 regulates amino acid transport to root cells and embryos (Lee et al, 2007; Sanders et al, 2009). AtAAP8 transports amino acids to the endosperm during early embryogenesis (Schmidt et al, 2007) and was recently shown to be localized to the plasma membrane and to function in phloem loading (Santiago and Tegeder, 2016)
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