A novel OsHB5-OsAPL-OsMADS27/OsWRKY102 regulatory module regulates grain size in rice

Grain size, a crucial trait that determines rice yield and quality, is typically regulated by multiple genes. Although numerous genes controlling grain size have been identified, the precise and dynamic regulatory network governing grain size is still not fully understood. In this study, we unveiled a novel regulatory module composed of OsHB5, OsAPL and OsMADS27/OsWRKY102, which plays a crucial role in modulating grain size in rice. As a positive regulator of grain size, OsAPL has been found to interact with OsHB5 both in vitro and in vivo. Through chromatin immunoprecipitation-sequencing, we successfully mapped two potential targets of OsAPL, namely OsMADS27, a positive regulator in grain size and OsWRKY102, a negative regulator in lignification that is also associated with grain size control. Further evidence from EMSA and chromatin immunoprecipitation-quantitative PCR experiments has shown that OsAPL acts as an upstream transcription factor that directly binds to the promoters of OsMADS27 and OsWRKY102. Moreover, EMSA and dual-luciferase reporter assays have indicated that the interaction between OsAPL and OsHB5 enhances the repressive effect of OsAPL on OsMADS27 and OsWRKY102. Collectively, our findings discovered a novel regulatory module, OsHB5-OsAPL-OsMADS27/OsWRKY102, which plays a significant role in controlling grain size in rice. These discoveries provide potential targets for breeding high-yield and high-quality rice varieties.

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

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.