A plant starts with a shoot. Everything that you see above ground is triggered in some way by the meristem. The meristem has the potential to build anything above ground, but it needs the right triggers.
Flowering is an example of an action that needs the right timing. A plant needs flowers ready when others are also ready to exchange pollen, but getting the flower ready too soon, will mean the organ is damaged before it can do its job. Flowering too late means everyone else is already finished and there’s nothing left for the flower to receive. Flowering is controlled in part by environmental cues and in part by internal signals.
A new study by Gorham and colleagues looks at these internal signals. They look at the genes HDA19 and FD and their mutant counterparts hda19 and fd. They find that hda19 causes the flowers to misform, creating stamenoid organs instead of florets. They also find fd affects the timing of building these stamens.
The authors say in JXB: “The enhancement of hda19 by fd suggests that FD also contributes to a general weakening of transcriptional repression of floral organ identity genes. It is noteworthy that this enhancement does not involve the emergence of patterning abnormalities not already seen in hda19. Instead, fd causes a temporal shift in the appearance of gene misexpression and SIA, as defects characteristic of hda19 fd IM phases 1 and 2 resemble those of hda19 IM phases 3 and 4, respectively. If SIA emergence results from reaching a threshold level of gene derepression, it is likely that loss of FD exacerbates the gene misregulation of hda19 to reach this threshold at an earlier developmental age.”