Plants elongate and bend to provide access to sunlight. Despite having observed this phenomenon for centuries, scientists do not fully understand it.

Now, scientists at the Salk Institute in California, USA have discovered that two plant factors, the protein PIF7 and the growth hormone auxin, are the triggers that accelerate growth when plants are shaded and exposed to warm temperatures at the same time.

The findings, published in Nature Communications they will help scientists predict how plants will respond to climate change and increase crop productivity despite yield-damaging global temperature increases.

How do plants respond to light and temperature?

“We currently grow crops at certain densities, but our findings indicate that we will need to reduce these densities to optimize growth as our climate changes,” says lead author Professor Joanne Chory, Director of the Cell Biology Laboratory and Plant Molecular at Salk and a Howard Hughes Medical Institute investigator.

“Understanding the molecular basis of how plants respond to light and temperature will allow us to fine-tune crop density in a specific way that leads to the best yields.”

Plants return to the sun

During germination, plants quickly elongate their stems to pierce the soil to capture sunlight as quickly as possible. Normally, the stem slows its growth after exposure to sunlight. But the stem can quickly lengthen again if the plant competes with surrounding plants for sunlight or in response to warm temperatures to increase the distance between the hot soil and the plant’s leaves.

In all three species, the team found that the plants grew extremely tall when they simultaneously tried to avoid the shade created by neighboring plants and were exposed to warmer temperatures. At the molecular level, the researchers found that the transcription factor PIF7, a protein that helps turn genes “on” and “off,” was the dominant player driving the rapid growth. They also found that the growth hormone auxin increased when the crops detected neighboring plants, which stimulated growth in response to simultaneous warmer temperatures, indicates Eurek Alert.

This synergistic PIF7-auxin pathway allowed 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.

Another key factor associated with this symbiosis

“We were surprised to find that PIF4 did not play a major role, as previous studies have shown the importance of this factor in associated growth situations,” says first author Yogev Burko, a Salk researcher and assistant professor in the Agricultural Research Organization at the Volcani Institute from Israel. “The fact that PIF7 is the dominant driving force behind the growth of this plant was a real surprise. With this new knowledge, we hope to fine-tune this growth response in different crop plants to help them adapt to climate change.”

The researchers believe there is another player, as yet undiscovered, that boosts the effect of PIF7 and auxin. They hope to explore this unknown factor in future studies. Burko’s lab will also study how this pathway can be optimized in crop plants.

“Global temperatures are rising, so we need food crops that can thrive in these new conditions,” says Chory, who specializes in Salk’s Harnessing Plants. “We have identified key factors that regulate plant growth during warm temperatures, which will help us develop better performing crops to feed future generations.”

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