Osre1 Interacts With Osrip1 To Regulate Rice Heading Date By Finely Modulatingehd1expression

Heading date is a key agronomic trait affecting crop yield. In rice, Early heading date 1 (Ehd1) is an important B-type response regulator in determination of heading date. Although many regulatory factors ofEhd1expression have been functionally characterized, the direct regulators ofEhd1largely remain to be identified. Here, we identified a new regulator ofEhd1, OsRE1, that directly binds to the A-box motif in theEhd1promoter.Osre1confers an early heading phenotype due to elevated expression levels ofEhd1. OsRE1 is a nucleus-localized bZIP transcription factor with a diurnal rhythmic expression pattern. Furthermore, we identified an OsRE1-interacting protein, OsRIP1, and demonstrated that OsRIP1 can repress the transcript expression ofEhd1in an OsRE1-dependent manner. Our genetic data showed that OsRE1 and OsRIP1 may function upstream ofEhd1in regulating heading date. Together, our results suggest that OsRE1 functions cooperatively with OsRIP1 to regulate heading date through finely modulating the expression ofEhd1. In addition, OsRE1 and OsRIP1 are two minor heading date regulators, which are more desirable for fine-tuning heading date to improve rice regional adaptability.