For more than 6,000 years, humans have cultivated pineapples, which thrive in water-limited environments. In order to better understand how the fruits grow to be so juicy under such dry environmental conditions, researchers from the University of Illinois at Urbana-Champaign took a closer look at the plant's genes and genetic pathways. 

To their surprise, they found that pineapples share a distant ancestor with grasses, such as sorghum and rice. Like many plants, the genomes of these ancestors diversified, or doubled, over time so researchers tracked these "whole-genome duplications" to better understand the plant's evolutionary history.

"Our analysis indicates that the pineapple genome has one fewer whole genome duplication than the grasses that share an ancestor with pineapple, making pineapple the best comparison group for the study of cereal crop genomes," Ray Ming, leader of the study and a plant biology professor from the University of Illinois, said in a news release.

Essentially, researchers found that pineapples have undergone two whole-genome duplications, and confirmed previous studies that indicated related grasses experienced three such duplications, according to the release.

They also discovered that pineapples actually use a special type of photosynthesis, known as crassulacean acid metabolism (CAM), which they believe evolved independently. Most other crops use a photosynthesis called C3, a basic photosynthesis that converts solar energy into chemical energy, which the plants utilize for life-sustaining functions. 

"CAM plants use only 20 percent of the water used by typical C3 crop plants, and CAM plants can grow in dry, marginal lands that are unsuited for most crop plants," Ming explained in the release.

Researchers also found that pineapples have genes that allow them to differentiate between day and night and adjust their metabolism accordingly. This means they can easily protect themselves from intense solar rays during the day and reserve energy during the night.  

"This is the first time scientists have found a link between regulatory elements of CAM photosynthesis genes and circadian clock regulation," Ming added in a statement. "This makes sense, because CAM photosynthesis allows plants to close the pores in their leaves during the day and open them at night. This contributes to pineapple's resilience in hot, arid climates, as the plant loses very little moisture through its leaves during the day."

At night the plants also absorb and "fix" carbon dioxide into molecules they are able to release the next day during CAM photosynthesis. Researchers explained that CAM photosynthesis evolved through genetic processes of reconfiguring molecular pathways involved in C3 photosynthesis. Ultimately, plants may have undergone such a genetic evolution in order to adapt to warming temperatures.

This study will help researchers better understand drought conditions and crop loss. Using this information could lead to the development of drought-tolerant crop species. Their findings were recently published in the journal Nature Genetics. 

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