Abstract
BackgroundAmino acids, which are transported by amino acid transporters, are the major forms of organic nitrogen utilized by higher plants. Among the 19 Amino Acid Permease transporters (AAPs) in rice, only a small number of these genes have been reported to influence rice growth and development. However, whether other OsAAPs are responsible for rice growth and development is unclear.ResultsIn this study, we demonstrate that OsAAP4 promoter sequences are divergent between Indica and Japonica, with higher expression in the former, which produces more tillers and higher grain yield than does Japonica. Overexpression of two different splicing variants of OsAAP4 in Japonica ZH11 significantly increased rice tillering and grain yield as result of enhancing the neutral amino acid concentrations of Val, Pro, Thr and Leu. OsAAP4 RNA interference (RNAi) and mutant lines displayed opposite trends compared with overexpresing (OE) lines. In addition, exogenous Val or Pro at 0.5 mM significantly promoted the bud outgrowth of lines overexpressing an OsAAP4a splicing variant compared with ZH11, and exogenous Val or Pro at 2.0 mM significantly enhanced the bud outgrowth of lines overexpressing splicing variant OsAAP4b compared with ZH11. Of note, the results of a protoplast amino acid-uptake assay showed that Val or Pro at different concentrations was specifically transported and accumulated in these overexpressing lines. Transcriptome analysis further demonstrated that OsAAP4 may affect nitrogen transport and metabolism, and auxin, cytokinin signaling in regulating rice tillering.ConclusionOur results suggested that OsAAP4 contributes to rice tiller and grain yield by regulating neutral amino acid allocation through two different splicing variants and that OsAAP4 might have potential applications in rice breeding.
Highlights
Amino acids, which are transported by amino acid transporters, are the major forms of organic nitrogen utilized by higher plants
The Expression Level of OsAAP4 Positively Correlated with Rice Tillering and Grain Yield between Indica and Japonica Overall, 533 rice accessions according to Rice Variation Map v2.0 were used in this study (Chen et al 2014)
Tiller number per plant were higher in seedlings of Indica accessions that carried Hap2 compared to Japonica accessions carrying Hap5 (Fig. 1h). These results demonstrated that Indica accessions with Hap2 more highly expressed OsAAP4, which was accompanied by higher tiller numbers and grain yield, than Japonica accessions, indicating that OsAAP4 expression levels are positively correlated with both tiller development and grain yield in rice
Summary
Amino acids, which are transported by amino acid transporters, are the major forms of organic nitrogen utilized by higher plants. Higher plants take up inorganic nitrogen, including nitrate and ammonium; this is followed by nitrogen assimilation into amino acids, the main form of organic nitrogen transport, in the root and transport and reallocation from source organs to sinks via the xylem and phloem (Xu et al 2012; Tegeder and Masclaux-Daubresse, 2018). Amino acid transporters play an important role in the transmembrane transport of amino acids, which are involved directly or indirectly in processes of nitrogen metabolism that are crucial for plant growth and development. Such processes include assimilation and partition of amino acids within the cell, translocation of amino acids over short and long distances, and uptake and usage of amino acids by sink organs (Tegeder, 2014; Tegeder and Masclaux-Daubresse, 2018). Recent studies have shown that increasing phloem and embryo loading with amino acids may increase biomass and seed yield (Zhang et al 2015; Perchlik and Tegeder, 2017; Tegeder and Masclaux-Daubresse, 2018)
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