Plants use sugar in ways we never imagined

For many years, scientists believed that plants sensed heat using proteins active mostly at night. But recent findings reveal something far more complex.

A new study led by Professor Meng Chen from the University of California, Riverside, shows that during the day, plants rely on sugar and a combination of thermal signals to detect warmth and adjust their growth.

The research reshapes long-standing views. The results uncover how plants integrate sunlight, sugar, and internal signals to regulate daytime thermomorphogenesis, the growth response triggered by warmth.

Plants sense heat differently by day

“Our textbooks say that proteins like phytochrome B and early flowering 3 (ELF3) are the main thermosensors in plants,” Chen said. “But those models are based on nighttime data.”

“We wanted to know what’s happening during the day, when light and temperature are both high because these are the conditions most plants actually experience.”

Previous models focused on phytochrome B (phyB) and ELF3, both of which are responsive at night. But in strong sunlight, phyB becomes constantly activated, shutting down its heat-sensing role.

The research team tested Arabidopsis plants under a range of temperatures and red-light intensities, including conditions mimicking midday sun.

The paper shows two clear heat responses. One operates between 12 and 21 °C and depends on phyB. The other, active between 21 and 27 °C, does not rely on phyB. This second, sugar-driven response remains active even under intense light.

Sugar helps plants detect daytime heat

The study reveals that sugar is more than just a fuel. It is a heat signal during daylight. “That’s when we realized sugar wasn’t just fueling growth,” Chen said. “It was acting like a signal, telling the plant that it’s warm.”

Under high temperatures, chloroplasts break down stored starch into sucrose. This sugar then stabilizes PIF4, a protein that drives growth.

Without sugar, PIF4 degrades. With sugar, PIF4 sticks around, so long as another protein, ELF3, also lifts its repressive control.

The study confirms that adding sucrose to mutant plants restores growth, even in darkness. This shows sugar acts independently from light and provides a thermal cue during the day.

Plant growth needs both sugar and heat

“PIF4 needs two things,” Chen explained. “Sugar to stick around, and freedom from repression. Temperature helps provide both.”

This dual system operates like an “AND” gate in electronics. Both sucrose and the release from ELF3 inhibition are required for full thermoresponsive growth. Sucrose promotes PIF4 stability, while high temperature relieves ELF3’s suppression.

When either cue is missing, plants fail to elongate properly. But when both are present, like sugar and warmth, PIF4 can trigger auxin-related genes that stretch the plant upwards.

Protein blocks growth until it’s warm

Interestingly, ELF3 inhibits PIF4 in two ways. It blocks its production and its activity. High temperatures disable ELF3, freeing PIF4 to act. This insight flips older beliefs that ELF3 only worked at night.

The microscopy images and data on page 8 reveal that even without ELF3, plants can respond to sugar and still grow taller. But only with both sugar and heat do PIF4 targets like IAA19 and YUC9 become active.

Engineering stronger crops

“This changes how we think about thermosensing in plants,” Chen said. “It’s not just about proteins flipping on or off. It’s about energy, light, sugar, as well.”

Understanding these systems has practical value. As global temperatures rise, crops need to grow reliably. Knowing that starch breakdown and sugar signaling help regulate growth can help scientists design better, more heat-resilient plants.

Researchers also illustrate how the three thermosensors, phyB, ELF3, and chloroplast-sucrose, work together. This multisensor setup allows plants to fine-tune growth, even under extreme conditions.

Plants use sugar smartly to grow

Plants live silent lives, but their internal machinery buzzes with complex decisions. In the heat of the day, they don’t just react, they calculate.

By using sugars to sense their environment, they respond with a quiet precision that helps them grow exactly when conditions are right. This study doesn’t just add to our knowledge. It rewrites it.

The study is published in the journal Nature Communications.

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