Plants lengthen and bend to secure access to sunlight. Despite observing this phenomenon for centuries, scientists do not fully understand it. Now, Salk scientists have discovered that two plant factors -- the protein PIF7 and the growth hormone auxin -- are the triggers that accelerate growth when plants are shaded by canopy and exposed to warm temperatures at the same time.
In this study, the scientists compared plants growing in canopy shade and warm temperatures at the same time -- a condition that mimics high crop density and climate change. The scientists used the model plant Arabidopsis thaliana, as well as tomato and a close relative of tobacco, because they were interested to see if all three plant species were affected similarly by this environmental condition.
Across all three species, the team found that the plants grew extremely tall when simultaneously trying to avoid the shade created by neighboring plants and being exposed to warmer temperatures. On a molecular level, the researchers discovered that transcription factor PIF7, a protein that helps turn genes "on" and "off," was the dominant player driving the increased rapid growth. They also found that the growth hormone auxin increased when the crops detected neighboring plants, which fostered growth in response to simultaneous warmer temperatures. This synergistic PIF7-auxin pathway allowed the plants to respond to their environments and adapt to seek the best growing conditions.
A related transcription factor, PIF4, also stimulated stem elongation during warm temperatures. However, when shade and increased temperatures were combined, this factor no longer played an important role.
The researchers believe that there is another player, yet to be discovered, that is boosting the effect of PIF7 and auxin. They hope to explore this unknown factor in future studies. Burko's lab will also be studying how this pathway can be optimized in crop plants.
