Similarly, the deletion of a 373 bp fragment in FLM intron 1 resulted in an elevenfold reduction in FLM expression and earlier flowering by 11.5 leaves as experimentally determined. This effect size is much smaller than predicted by the linear model. However, as proposed earlier, this may likely be due to a critical lower threshold for FLM-ß to become effective (Figures 4 and 5). Intronic cis-regulatory transcription factor binding sites have been identified in other MADS-box transcription factors and interactions of enhancer and silencer elements that reside in the promoter sequence or the 3’-end of the first intron were reported (Hong et al., 2003; Schauer et al., 2009). Thus, similar mechanisms may govern the expression of FLM at intron 1 sites that may act in isolation or together with binding events at the FLM promoter.