Scientists sequenced the genome of the pineapple and found clues to how the fruit thrives in extremely dry environments. The findings also shed light on the evolutionary history of grasses that share a common ancestor with the pineapple. The research could help researchers discover how to introduce certain traits into other important crops, helping them adapt to drought conditions and future climate change.
Pineapple cultivation started more than 6,000 years ago and originated in what is now southwest Brazil and northeast Paraguay, the University of Illinois at Urbana-Champaign reported. Before the pineapple came to rise, common ancestors of both it and grasses such as sorghum and rice experienced multiple whole-genome duplications. The sequencing effort revealed evidence of two previously unknown whole-genome duplications in the pineapple's history and backed up past findings of three similar duplications in the history of grasses.
"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," said Ray Ming, a plant biology professor at the University of Illinois.
Pineapples employ a special type of photosynthesis called crassulacean acid metabolism (CAM) that has evolved independently and makes it the most economically valuable plant out of more than 10,000 species. Most crops use a type of photosynthesis called C3.
"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 said.
The new findings demonstrate that certain genes contributing to CAM photosynthesis are regulated by the pineapple's circadian clock genes, which allow the plant to distinguish between night and day.
"This is the first time scientists have found a link between regulatory elements of CAM photosynthesis genes and circadian clock regulation," Ming said. "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."
CAM photosynthesis allows pineapples to absorb carbon dioxide and transform it into molecules overnight. These molecules are then concentrated in the plant's leaves and released during photosynthesis in the daylight. CAM and C4 photosynthesis, which is used by the grasses with the same common ancestor, use similar enzymes to concentrate carbon dioxide in the leaves. CAM photosynthesis was found to have evolved by the reconfiguration of molecular pathways involved in C3 photosynthesis. Since all plants that use C3 photosynthesis contain the necessary genes for CAM, the findings could help scientists adapt important crops to survive droughts and even climate change.
"Drought is responsible for the majority of global crop loss, so understanding the mechanisms that plants have evolved to survive water stress is vital for engineering drought tolerance in crop species," the researchers wrote. "CAM plants can keep their stomata closed during the daytime... greatly reducing water loss."
The U.S. Department of Energy has already funded a project that aims to explore genetic mechanisms that allow for CAM photosynthesis in desert-adapted plants, and could potentially use the research to introducing those traits to potential biofuels crops.
"Higher water-use efficiency is a highly desirable trait, given the need to double food production by 2050 in the context of a changing climate," Ming concluded.
The findings were published in a recent edition of the journal Nature Genetics.