The researchers also found that plants that lacked LEAFY had high levels of gibberellin, and plants engineered to produce high levels of LEAFY had lower levels of the hormone and were also shorter with greater levels of chlorophyll characteristics of gibberellin deficiency.
"At first we were confused because gibberellin was supposed to promote all of this activity that leads to flower formation," Wagner said. "Then when we found a direct target of LEAFY that is linked to gibberellin catabolism, that gave us the clue that gibberellin must have a role in inhibiting flower formation as well."
Plants that were genetically modified to not produce gibberellin properly and plants that were treated with a gibberellin inhibitor showed signs of a delayed first transition to inflorescence but accelerated signs of flower formation. Spraying the plants with gibberellin had the opposite effect.
The results suggested that the two transition steps that lead plants to produce flowers might be regulated distinctly, both involving gibberellin. While gibberellin promotes the first transition, in which plants stop producing stems and leaves and produce an inflorescence, it inhibited the second stage, in which flowers were formed.
The mechanism, the Penn team showed, involves rising and then falling levels of gibberellin. High levels cause the plant to end the vegetative phase of development. At that point, LEAFY and ELA1 activity cause gibberellin to break down. Freed from the inhibitory effects of the hormone, a suite of proteins are activated that trigger flower formation.
"When it comes to determining the number of flowers formed and when they are formed, we think this pathway is at the forefront," Wagner said.
Farmers already use gi
|Contact: Katherine Unger Baillie|
University of Pennsylvania