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New research led by University of California, Riverside’s Professor Meng Chen shows that plants rely on multiple heat-sensing systems and that sugar — produced in sunlight — plays a central and previously unrecognized role in daytime temperature response.

“Our textbooks say that proteins like phytochrome B and early flowering 3 (ELF3) are the main thermosensors in plants,” Professor 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.”

To investigate, Professor Chen and colleagues used Arabidopsis, a small flowering plant favored in genetics labs.

They exposed seedlings to a range of temperatures, from 12 to 27 degrees Celsius, under different light conditions, and tracked the elongation of their seedling stems, known as hypocotyls — a classic indicator of growth response to warmth.

They found that phytochrome B, a light-sensing protein, could only detect heat under low light. In bright conditions that mimic midday sunlight, its temperature-sensing function was effectively shut off.

Yet, the plants still responded to heat, growing taller even when the thermosensing role of phytochrome B was greatly diminished.

“That pointed to the presence of other sensors,” Professor Chen said.

One clue came from studies of a phytochrome B mutant lacking its thermosensing function.

These mutant plants could respond to warmth only when grown in the light.

When grown in the dark, without photosynthesis, they lacked chloroplasts and did not grow taller in response to warmth.

But when the researchers supplemented the growing medium with sugar, the temperature response returned.

“That’s when we realized sugar wasn’t just fueling growth. It was acting like a signal, telling the plant that it’s warm,” Professor Chen said.

Further experiments showed that higher temperatures triggered the breakdown of starch stored in leaves, releasing sucrose.

This sugar in turn stabilized a protein known as PIF4, a master regulator of growth. Without sucrose, PIF4 degraded quickly. With it, the protein accumulated but only became active when another sensor, ELF3, also responded to the heat by stepping aside.

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

The study reveals a nuanced, multi-layered system. During the day, when light is used as the energy source to fix carbon dioxide into sugar, plants also evolved a sugar-based mechanism to sense environmental changes.

As temperatures rise, stored starch converts into sugar, which then enables key growth proteins to do their job.

The findings could have practical implications. As climate change drives temperature extremes, understanding how and when plants sense heat could help scientists breed crops that grow more predictably and more resiliently under stress.

“This changes how we think about thermosensing in plants,” Professor Chen said.

“It’s not just about proteins flipping on or off. It’s about energy, light, sugar, as well.”

“The findings also underscore, once again, the quiet sophistication of the plant world.”

“In the blur of photosynthesis and starch reserves, there’s a hidden intelligence.”

“One that knows, sweetly and precisely, when it’s time to stretch toward the sky.”

The study was published in the journal Nature Communications.

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D. Fan et al. 2025. A multisensor high-temperature signaling framework for triggering daytime thermomorphogenesis in Arabidopsis. Nat Commun 16, 5197; doi: 10.1038/s41467-025-60498-7

As humanity prepares for Mars, new research reveals that safeguarding astronaut mental health means targeting the gut, where the battle for resilience in space truly begins.

Review: Navigating mental health in space: gut–brain axis and microbiome dynamics. Image Credit: Frame Stock Footage / Shutterstock

In a recent review in the journal Experimental & Molecular Medicine, researchers collate and discuss more than 150 publications that draw parallels between human terrestrial gut-brain axis interactions and their equivalent in astronauts in space. The review emphasises that while changes in the astronaut gut microbiome are consistently observed, the magnitude, persistence, and individual-specific nature of these shifts remain areas of ongoing research. It elucidates the challenges and extreme environments to which astronauts are exposed, as well as the cascading impact on their gut–brain communication, cognition, mood, and immunity.

This review synthesizes astronaut-derived data and terrestrial stress studies examining the effects of radiation and circadian disruptions on microbial composition, immune function, and blood-brain barrier integrity. In a society eagerly reaching for Mars, it cautions us of the medical demands of long-duration space missions while providing recommendations (e.g., microbiome monitoring, personalized probiotic and prebiotic supplements) to support astronaut mental health on these extended missions. However, it also highlights that these recommendations are promising but require further validation before routine adoption.

Background

Space may present the final frontier, but it’s taking an unprecedented toll on our astronauts’ well-being. Astronauts routinely report anxiety, depression, sleep disruption, and cognitive deficits during missions, from 84-day Skylab stays to long-duration International Space Station (ISS) flights. These medical difficulties have sometimes resulted in missions being terminated early (e.g., Soyuz T14 mission), resulting in substantial economic losses.

Consequently, a growing body of research aims to unravel the underlying risk factors associated with the unique stressors of space travel (e.g., cosmic radiation, disruptions to the light-dark cycle) and their impact on astronaut mental health outcomes. Unfortunately, while the impacts of space stressors on astronauts’ physical well-being have been extensively researched, the consequences of these stressors on astronauts’ mental health remain poorly understood.

Simultaneously, laboratory studies on Earth demonstrate a robust association between gut microbes and the brain, known as the “gut-brain axis.” Gut microbiota produce metabolites (e.g., short-chain fatty acids, neurotransmitters, and immune modulators) that significantly influence mood, immunity, stress resilience, and even cognition. A similar understanding tailored to life in space would help inform future neurological care for this rare breed of humans. Importantly, the review notes that while these associations are well established terrestrially, causality and precise mechanisms in space remain to be determined.

About the review

The present review aims to leverage this terrestrial-derived data to inform astronaut care, simultaneously highlighting gaps in the literature, the unique challenges of space, and their extrapolated impacts on astronaut health, as well as how we can address potential gut microbial perturbations to ensure optimal neurological outcomes.

The narrative review integrates diverse data streams from more than 150 publications (n = 152) and National Aeronautics and Space Administration (NASA) datasets, comprising astronaut health records, terrestrial analog studies, animal models, and microbiome sequencing. It focuses on: 1. Crew microbiome data (gut and saliva samples), 2. Crew psychological and neurological assessments (objective measurements), 3. Controlled studies (impact assessments of certain stressors on specific health outcomes), and 4. Molecular assays (biochemical investigations).

Patterns observed in terrestrial studies were juxtaposed onto similar space scenarios, allowing for correlation-based stress, microbial community changes, and depression estimations. For example, they used evidence from how actors like reduced microbial diversity, loss of short-chain fatty acids (SCFA), increased gut permeability, and microglial activation correlate with mood and cognitive outcomes, and then evaluated the magnitude of those outcomes when faced with cosmic radiation, reduced gravity, and disrupted circadian rhythms. The review repeatedly notes that most links between microbiome shifts and neuropsychological outcomes, especially in astronauts, are correlational and not yet causally established.

Key findings

The review highlights several crucial points for space agencies and medical professionals:

1. Limited evidence suggests that astronaut gut microbial diversity often reduces mid-flight, with Bifidobacterium and Faecalibacterium bacteria especially affected. This, in turn, results in reduced anti-inflammatory metabolites and SFCA secretions, which may potentially contribute to suboptimal mood and neurological outcomes.
2. Animal models suggest that exposure to incident cosmic radiation and prolonged light exposure independently cause dysbiosis, increased gut permeability, systemic cytokine release, and disruption of markers of blood-brain barrier integrity. Carefully monitoring these parameters is essential to counter any potential imbalances before they exacerbate.
3. Gut microbiome estimations have revealed that gut microbial imbalances are correlated with elevated anxiety, sleep disturbances, and cognitive decline in astronauts. Notably, gut microbial dysbiosis has been found to disrupt immune signaling and weaken gut-brain barriers, allowing inflammatory molecules to influence neural circuits and mood. The review also discusses how some microbial and immune changes observed in astronauts are transient, reversing post-flight, while others may persist for months after return, underscoring both short- and long-term health implications.
4. Finally, some studies have demonstrated the beneficial and dysbiosis-reversing effects of pre- and probiotic supplementation on terrestrial and space-bound humans, a cause for relief and additional metabolomic and epidemiological research. Nutrition may also play a significant role in astronauts’ quality of life (QoL), as fiber-rich diets and fermented foods have been seen to maintain gut integrity in terrestrial clinical trials. However, the review cautions that more research is needed to confirm the efficacy and optimal protocols for these interventions in space.

Conclusions

The present review establishes a strong associative link between space travel, gut microbial alterations, and neuropsychological outcomes. It postulates a model in which space-related stressors lead to dysbiosis, which then triggers immune activation and subsequent biochemical changes in the brain, ultimately resulting in suboptimal mental health outcomes. Nevertheless, the authors emphasise that mechanistic details and direct causality remain incompletely understood.

While underscoring the job-associated hazards of an astronaut’s life, this review calls for the formal integration of microbiome monitoring and nutritional interventions (probiotics, prebiotics, and diet) to ensure optimal QoL outcomes, especially against the contextual backdrop of our potential collective resilience on Mars.

Further, they recommend integrating both noninvasive (microbiome and psychological assessments) and invasive (biomarker and hormone analysis) monitoring to enable early detection and management of neuropsychological risks.