A flowering shrub in California鈥檚 Death Valley is one of the most heat-tolerant plants known to science and could hold clues for engineering crops that can cope with rising temperatures.
Most agricultural crops are unable to withstand temperatures above 35掳C (95掳F), meaning our food sources could be affected as climate change worsens.
at Michigan State University and her colleagues wondered whether crops could be made more heat-resilient by incorporating traits from those that naturally like hot conditions.
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Rhee became interested in a flowering shrub called Tidestromia oblongifolia after a colleague who had studied it in the 1970s mentioned it in a talk she attended. The plant is native to California鈥檚 Death Valley and appears to flourish in the famously hot desert. Death Valley is where the hottest-recorded temperature on Earth 鈥� 56.7掳C (134掳F) 鈥� was measured in 1913, and it reached 53.3掳C (127.9掳F) last month. 鈥淲hen I heard about this plant, I thought, 鈥榃ow, that鈥檚 amazing, I can鈥檛 imagine any organism being able to survive under those conditions, let alone thrive鈥�,鈥� says Rhee.
She and her colleagues studied the plant by growing it in a chamber in their laboratory, first at moderate temperatures, then in conditions mimicking summer in Death Valley. As a comparison, they also grew a closely related plant that is native to Mexico called Amaranthus hypochondriacus.
Under the Death Valley conditions, A. hypochondriacus ceased growing altogether within a few days, but T. oblongifolia flourished, tripling its biomass in 10 days. Even at 50掳C, the upper limit of the chamber, T. oblongifolia still exhibited effective photosynthesis. The researchers have just built a new chamber that can be ramped up to 60掳C to see how far they can push the plant.
A closer look at T. oblongifolia when it was grown in the Death Valley conditions revealed some of the nifty tricks it deploys to cope with extreme heat. For example, its leaf cells became smaller, increasing the density of its chloroplasts, where photosynthesis occurs. At the same time, many of the leaves鈥� mitochondria, which provide energy, moved closer to the chloroplasts. Together, these processes may have increased the plant鈥檚 ability to photosynthesise in the harsh conditions, says Rhee.
Similarly, under increasing heat, the plant鈥檚 chloroplasts morphed from a standard disc shape into a highly unusual cup shape. This may have allowed them to hold on to carbon dioxide and prevent leakages more effectively while they were carrying out photosynthesis, whereby CO2 is converted to sugars, says Rhee.
The researchers also identified thousands of genes in the plant that increased or decreased in expression as temperatures rose. By comparing them with similar genes that have been studied in other plants, they deduced that many were probably involved in boosting photosynthesis, protecting against heat stress and carrying out detoxification and repair mechanisms.
The team is now trying to pinpoint the most important genes responsible for the plant鈥檚 heat tolerance in the hope of transferring them to agricultural crops.
at Macquarie University in Sydney, Australia, and his colleagues have previously showed that a conventional short-grain rice variety can be made more heat-tolerant by inserting a gene that they discovered in a species of Australian wild rice called Oryza australiensis. The gene evolved in the wild rice to help it photosynthesise in Australia鈥檚 hot tropical north.
When grown at 45掳C in a lab, conventional rice that had a copy of the wild gene , which struggled to grow in the heat. This opens up the possibility of making other crops more resilient to hotter climates by transferring genes from O. australiensis, T. oblongifolia or other heat-loving plants, says Atwell.
bioRxiv
