OsAPL controls the nutrient transport systems in the leaf of rice (Oryza sativa L.)

Main conclusion OsAPL positively controls the seedling growth and grain size in rice by targeting the plasma membrane H+-ATPase-encoding gene, OsRHA1, as well as drastically affects genes encoding H+-coupled secondary active transporters. Nutrient transport is a key component of both plant growth and environmental adaptation. Photosynthates and nutrients produced in the source organs (e.g., leaves) need to be transported to the sink organs (e.g., seeds). In rice, the unloading of nutrients occurs through apoplastic transport (i.e., across the membrane via transporters) and is dependent on the efficiency and number of transporters embedded in the cell membrane. However, the genetic mechanisms underlying the regulation of these transporters remain to be determined. Here we show that rice (Oryza sativa L., Kitaake) ALTERED PHLOEM DEVELOPMENT (OsAPL), homologous to a MYB family transcription factor promoting phloem development in Arabidopsis thaliana, regulates the number of transporters in rice. Overexpression of OsAPL leads to a 10% increase in grain yield at the heading stage. OsAPL acts as a transcriptional activator of OsRHA1, which encodes a subunit of the plasma membrane H+-ATPase (primary transporter). In addition, OsAPL strongly affects the expression of genes encoding H+-coupled secondary active transporters. Decreased expression of OsAPL leads to a decreased expression level of nutrient transporter genes. Taken together, our findings suggest the involvement of OsAPL in nutrients transport and crop yield accumulation in rice.