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Unless one is a trained fighter jet pilot, or a Formula 1 driver, humans tend not to do well at higher gravity, but tiny green moss plants seem to thrive under such conditions.

A team from Japan found that moss (Â鶹ÒùÔºcomitrium patens) exhibited increased photosynthesis under hypergravity conditions (six and 10 times Earth's gravity) due to enhanced carbon dioxide (CO₂) diffusion from the atmosphere into the chloroplasts within the plant leaves.

The plants adapt to the increased gravity by increasing the size of their chloroplasts and the number of leafy shoots of the moss (gametophores). Researchers identified for the first time the gene factor responsible for this response. They named the factor ISSUNBOSHI1 or IBSH1, a namesake of an inch-high, warrior boy from a beloved Japanese fairytale.

The findings, in Science Advances, reveal the existence of a key genetic mechanism that drove the evolutionary process, enabling plants to adapt to life on land.

Plants began their journey on Earth under water. One of the biggest environmental changes they had to adapt to was their emergence onto the land, approximately 500 million years ago.

The early plants transitioning from aquatic to terrestrial ecosystems lost their buoyancy and were now exposed to the gravitational acceleration of 1g. In the reduced gravity of water, plants didn't have to worry about carrying their own weight, but on land, they had to.

As a result, their anatomy began to shift, developing plant tissues that provided structural reinforcement and orienting the light-harvesting components of plants towards the light. Even the cell wall saw some structural changes.

Our understanding of how gravity influences photosynthesis and the genetic mechanisms behind these adaptations has been quite murky.

The researchers of this study, in a previous paper, reported that hypergravity of 10g surprisingly increased the rate of photosynthesis in Â鶹ÒùÔºcomitrium patens, but underlying anatomical and genetic mechanisms remained unexplored.

For this study, the team grew moss for eight weeks at 25°C under varying gravity levels—1g (control), 3g, 6g, and 10g—using a custom-built centrifuge with a built-in light-emitting diode (LED) for providing a photosynthetic photon.

To track the effect of hypergravity, they measured photosynthesis rates, anatomical traits like chloroplast size and gametophore number, and CO₂ conductance—the ability of small openings on leaf surfaces to let CO₂ in. They also carried out RNA sequencing to investigate if genes were expressed differently under hypergravity.

The results indicated an increased photosynthesis rate at higher gravity levels (6g and 10g) due to improved CO₂ diffusion, resulting from the presence of more leafy shoots and larger chloroplasts.

This response was linked with the upregulation of AP2/ERF transcription factors, particularly IBSH1. The researchers confirmed its role by manipulating IBSH1 in moss—overexpression reproduced the effects of hypergravity, while repression prevented these responses.

The researchers suggest that the formation of a remarkable gene network involving AP2/ERF factors may have been a key factor in enabling moss plants to adapt to life on land during the evolution of plants. They believe these findings offer pivotal insights that could one day support agricultural production in space, where gravity is vastly different from Earth's.

To fully unlock these possibilities, future research will need to extend beyond moss and investigate a broader range of plant species.

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