-mediated Expression of Family Genes is Required for Proper Timing of Flowering in

The transition to flowering is a major developmental switch in plants. In many temperate grasses, perception of indicators of seasonal change, such as changing day-length and temperature, leads to expression of () and () genes that are essential for promoting the transition to flowering. However, little is known about the upstream regulators of and genes in temperate grasses. Here, we characterize the monocot-specific gene () in and demonstrate that is a regulator of family genes. Mutations in impact the ability of the short-day (SD) vernalization, cold vernalization, and long-day (LD) photoperiod pathways to induce certain genes. is required for upregulation of () expression by the SD vernalization pathway, and overexpression of in an background can partially restore the delayed flowering phenotype of . We show that BdID1 binds in vitro to the promoter region of genes suggesting that ID1 directly activates expression. Transcriptome analysis shows that is required for , , , and expression under inductive LD photoperiods, indicating that is a regulator of the gene family. Moreover, overexpression of in the background results in rapid flowering similar to overexpressing in the wild type, demonstrating that is upstream of family genes. Interestingly, negatively regulates a previously uncharacterized gene, and we show that is a repressor of flowering. Thus, is critical for proper timing of flowering in temperate grasses.