Leaf-derived ABA regulates rice seed development via a transporter-mediated and temperature-sensitive mechanism

Long-distance transport of the phytohormone abscisic acid (ABA) has been studied for similar to 50 years, yet its mechanistic basis and biological significance remain very poorly understood. Here, we show that leaf-derived ABA controls rice seed development in a temperature-dependent manner and is regulated by defective grain-filling 1 (DG1), a multidrug and toxic compound extrusion transporter that effluxes ABA at nodes and rachilla. Specifically, ABA is biosynthesized in both WT and dg1 leaves, but only WT caryopses accumulate leaf-derived ABA. Our demonstration that leaf-derived ABA activates starch synthesis genes explains the incompletely filled and floury seed phenotypes in dg1. Both the DG1-mediated long-distance ABA transport efficiency and grain-filling phenotypes are temperature sensitive. Moreover, we extended these mechanistic insights to other cereals by observing similar grain-filling defects in a maize DG1 ortholog mutant. Our study demonstrates that rice uses a leaf-to-caryopsis ABA transport-based mechanism to ensure normal seed development in response to variable temperatures.

Automated summary

The long-distance transport of the plant hormone abscisic acid (ABA) plays a crucial role in regulating rice seed development, particularly in response to temperature changes. The protein DG1 is identified as a key regulator in this process, affecting ABA efflux and ultimately influencing grain-filling phenotypes. This study not only sheds light on the mechanism behind ABA-mediated seed development in rice, but also extends the findings to other cereal crops like maize.