Plants are highly elongated, bending to allow access of sunlight to each of their leaves. Despite observing this phenomenon for centuries, scientists do not fully understand it. Now scientists at the Salk Institute have discovered that two plant factors — the protein PIF7 and the growth hormone auxin — are triggers that speed up growth when plants are in the shade and exposed to high temperatures at the same time. official website of the institute.
The findings, published in the journal Nature Communications on August 29, 2022, will help scientists predict how plants will respond to climate change and increase yields despite global warming damaging crops.
"Right now, we're growing crops at a certain density, but our results indicate that we'll need to lower that density to optimize plant growth as climate changes," says senior author Professor Joanne Chory, director of the Salk Institute's Plant Molecular and Cell Biology Laboratory and Howard, researcher at the Hughes Medical Institute. "Understanding the molecular basis of how plants respond to light and temperature will allow us to fine-tune planting density to produce the best yields."
During germination, seedlings quickly lengthen their stems to break through the soil and capture sunlight as quickly as possible. Normally, the stem slows down its growth after exposure to sunlight. But the stem can quickly elongate again if the plant competes with surrounding plants for sunlight or increases the distance between the hot ground and the plant's leaves in response to rising temperatures. While both environmental conditions - shading and high temperatures - stimulate stem growth, they also reduce yields.
In this study, the scientists compared plants growing in the shade and warm temperatures at the same time — conditions that mimic high planting densities and climate change. The scientists used the model plant Arabidopsis thaliana, as well as the tomato and a close relative of tobacco, because they were interested to see if all three plant species were equally affected by these environmental conditions.
In all three species, the team of researchers found that the plants grew extremely tall when they simultaneously tried to avoid the shade created by neighboring plants and were exposed to higher temperatures. At the molecular level, the researchers found that the PIF7 transcription factor, a protein that helps turn genes on and off, helped boost growth. They also found that levels of auxin, a growth hormone, increased when crops found neighboring plants, which promoted growth in response to simultaneous higher temperatures. This synergistic PIF7-auxin pathway allowed plants to respond to their environment and adapt in search of the best growing conditions.
A related transcription factor, PIF4, also stimulated stem elongation at high temperatures. However, with a combination of shade and elevated temperatures, this factor no longer played an important role.
"We were surprised to find that PIF4 does not play an important role because previous studies have shown the importance of this factor in related growth situations," says study first author Yogev Burko, a research fellow at the Salk Institute and an associate professor at the Organization for Agricultural Research at the Israel Volcanoes Institute. “The fact that PIF7 is the dominant growth driver for this plant was a real surprise. With this new knowledge, we hope to fine-tune the growth response of various crops to help them adapt to climate change.”
The researchers believe there is another factor yet to be discovered that amplifies the effect of PIF7 and auxin. They hope to explore this unknown factor in future studies. Berko's lab will also study how this pathway can be optimized in crops.
“Global temperatures are rising, so we need food crops that can grow in these new conditions,” says Chori, co-leader of the Salk Plant Use Initiative and Howard H. and Maryam R. Newman Chair of Plant Biology. “We have identified the key factors that regulate plant growth at high temperatures, which will help us grow more productive crops to feed future generations.”