A flowering desert shrub that thrives in blistering heat stumped researchers for decades — until a recent discovery at the cellular level revealed a striking adaptation. Siddhant Pusdekar reports for SN on how the Arizona honeysweet’s shapeshifting insides helps it flourish in extreme climates.

🎋 Photosynthetic acclimation

The Arizona honeysweet (Tidestromia oblongifolia) grows best in blistering heat. In 1972, researchers demonstrated that this plant’s ability to perform photosynthesis — the vital process of converting sunlight into energy — peaks at over 116° Fahrenheit (47° Celsius), marking the highest known peak-performance temperature for any plant. But they didn’t know why this was the case.

In a paper published this past November in the journal Current Biology, another team of researchers investigated T. oblongifolia’s photosynthesis rates in the lab. They kept plants for eight weeks at nearly 89° F (31° C) before turning the heat up for some to over 116° F (47° C). Plants in the hotter setting tripled in size over another eight days. The researchers call this adaptation “photosynthetic acclimation.”

But the team didn’t stop there — they looked under the microscope at the shrubs’ chloroplasts, or the cell organelles that perform photosynthesis. While most plants’ chloroplasts sustain damage in such heat, T. oblongifolia’s remained intact. But also, the chloroplasts in specialized leaf cells that convert carbon dioxide to sugar had taken on a novel, cup shape. Arizona honeysweet displayed other adaptations, too, like growing smaller leaves with smaller cells, activating damage repair genes and rehabilitating a photosynthesis enzyme.

🧬 Heat-proofing plants

This paper also reveals that heat-proofing a plant isn’t as simple as adjusting a gene here and a protein there. Still, understanding how T. oblongifolia acclimates could serve as inspiration for heat-proofing other plants as temperatures rise around the world. Most greens aren’t like the Arizona honeysweet; they perform heat-limited photosynthesis, and in temperatures higher than what they’re used to, they may not grow as well, or even suffer on the cellular level. Investing in technology that can help plants all over the planet adapt now can mean preserving more species — including those that may be key to our diet or pollination — as longer, hotter seasons become the norm.

🌱 Companies planting ideas

Here are a few companies whose technology seeks to make plants more climate-resilient, if not bequeath them photosynthetic acclimation:

• Plantik Biosciences: This Paris-based, seed-stage company develops technology that enables plants’ resilience during heatwaves. Founded in 2019, they’ve raised $100,000 so far.
  
• Inari: This Cambridge, Massachusetts–based Series G company is designing seeds that need less water and fertilizer and have higher crop yields. By building a trove of plant gene data and honing the ability to edit multiple genes with multiple techniques at once, they aim to produce more resilient strains. This past January they raised $144 million, bringing their total funding to $753 million.
  
• Tropic Biosciences: Founded in 2016, this London-based Series C startup uses gene editing tech to create disease- and climate-resilient tropical crops by promoting or suppressing certain genes in coffee, bananas and rice. Over four funding rounds they’ve raised over $73 million, counting Temasek Holdings and Aliment Capital among their lead investors.

This science may help seed the future of more heat-resilient plants.

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