The Amino Acid Permease 5 (OsAAP5) Regulates Tiller Number and Grain Yield in Rice

Abstract

As fundamental nutrients, amino acids are important for rice (<i>Oryza sativa</i>) growth and development. Here, we identified the amino acid permease 5 (OsAAP5), that regulates tiller number and grain yield in rice. The <i>OsAAP5</i> promoter sequence differed between <i>indica</i> and <i>japonica</i> rice varieties. Lower expression of <i>OsAAP5</i> in the young leaf blade in <i>indica</i> varieties than in <i>japonica</i> varieties was associated with more tillers in <i>indica</i> than in <i>japonica</i> Down-regulation of <i>OsAAP5</i> expression in <i>japonica</i> using RNA interference (RNAi) and clustered regularly interspaced short palindromic repeats led to increases in tiller number and grain yield, whereas <i>OsAAP5</i> overexpression (OE) had the opposite effect. Both a protoplast amino acid uptake assay and HPLC analysis indicated that more basic (Lys, Arg) and neutral (Val, Ala) amino acids were transported and accumulated in the OE lines than in the wild type, but the opposite was observed in the RNAi lines. Furthermore, exogenous application of Lys, Arg, Val, and Ala in the OE lines substantially inhibited tiller bud elongation, but the effect was lost in the RNAi lines. Notably, concentrations of the cytokinins cis-zeatin and dihydrozeatin were much lower in the OE lines than in the wild type, whereas concentrations in the RNAi lines were higher. Thus, <i>OsAAP5</i> could regulate tiller bud outgrowth by affecting cytokinin levels, and knockout of <i>OsAAP5</i> could be valuable for <i>japonica</i> breeding programs seeking high yield and grain quality.