A novel protein FK1 was discovered by Scripps Institute. In the Science report, Steve A.Kay found that FK1 suppresses a transcriptor (CDF1) which in turn suppresses CONSTANS. CONSTANS is the protein which has been identified to trigger flowering in response to changes in day length. So when spring comes along, the plants allow FK1 to destroy more CDF1. As a consequence, the elevated levels of CONSTANS allows flowering to proceed.
This is already a very straight forward case where the trigger for flowering (change in daylength) is very obvious. Wonder what exactly goes on during mast flowering?
More details found at – Scientific American: Protein Tells Flowers When Spring Starts