OsbZIP40 and OsbZIP12 interact with OsMFT1 to repress Ehd1 expression and delay flowering in rice

Flowering time (or heading date) is a crucial agronomic trait for the adaptation of rice to specific growing regions and seasons. Although many flowering time-related rice genes have been identified and functionally characterized, continuing in-depth research is revealing how transcription of these genes is regulated. In this study, we determined that a basic leucine zipper transcription factor (OsbZIP40) and its homologous protein (OsbZIP12) participate in the control of flowering time. Overexpression of OsbZIP40 delayed flowering. Double mutants in which both OsbZIP40 and OsbZIP12 were knocked out exhibited an early-flowering phenotype under both long-day and short-day conditions. However, there was no difference in the heading date between the wild-type and each single mutant. These results suggest that OsbZIP40 functions as a flowering suppressor. Both OsbZIP40 and OsbZIP12 bound directly to the Ehd1 promoter and repressed its expression. Furthermore, MOTHER OF FT AND TFL1 (OsMFT1) interacted with OsbZIP40/OsbZIP12 and enhanced their repressive effects on Ehd1 expression. Based on the data, we present a transcriptional regulatory mechanism in which OsbZIP40 and OsbZIP12 interact with OsMFT1 and modulate Ehd1 expression to delay flowering. Our findings provide relevant insights into the molecular mechanisms regulating flowering time in rice.