A multinational team of scientists has sequenced genomes of a wild pineapple relative, the red pineapple (Ananas bracteatus), and two cultivated varieties of the pineapple (Ananas comosus).
Pineapple (Ananas comosus), on sale on Reunion Island. Image credit: David Monniaux / CC BY-SA 3.0.
Christopher Columbus arrived in Guadeloupe on November 4, 1493, during his second voyage to the New World. At a Carib village, he and his sailors encountered pineapple plants and fruit, with the astonishing flavor and fragrance delighting them then and us today.
At that time, pineapple was already cultivated on a continent-wide scale following its initial domestication in northern South America, about 6,000 years before the present.
Today, more than 85 countries produce about 25 million metric tons of pineapple fruit each year, with a gross production value approaching $9 billion.
Like many plants, the ancestors of pineapple and grasses experienced multiple doublings of their genomes. Tracking the remnants of these whole-genome duplications in different plant species helps genetic scientists trace their evolutionary histories.
“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,” explained team leader Prof Ray Ming, of the University of Illinois.
Prof Ming and his colleagues from the United States, China, Canada, Taiwan, Australia and the United Kingdom, uncovered evidence of two whole-genome duplications in the pineapple’s history, and validated previous findings of three such duplications in grasses.
Photosynthesis converts solar energy to chemical energy, allowing plants to build the tissues that sustain life on Earth.
Pineapple makes use of a special type of photosynthesis, called crassulacean acid metabolism (CAM), which has evolved independently in more than 10,000 plant species.
“Pineapple is the most economically valuable plant among those 10,000 species,” Prof Ming explained. “Most crop plants use a different type of photosynthesis, called C3.”
“CAM plants use only 20% 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.”
A closer look at the pineapple genome revealed that some genes that contribute to CAM photosynthesis are regulated by the plant’s circadian clock genes, which allow plants to differentiate day and night and adjust their metabolism accordingly.
“This is the first time scientists have found a link between regulatory elements of CAM photosynthesis genes and circadian clock regulation,” Prof. 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.”
The scientists also discovered that CAM photosynthesis evolved by reconfiguring molecular pathways involved in C3 photosynthesis.
“All plants contain the necessary genes for CAM photosynthesis, and the evolution of CAM simply requires rerouting of pre-existing pathways,” Prof. Ming said.
“Understanding the evolution of these different types of photosynthesis will help scientists in their efforts to develop more productive, drought-tolerant varieties of essential crops.”
The results were published online in the journal Nature Genetics on October 2, 2015.
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Ray Ming et al. The pineapple genome and the evolution of CAM photosynthesis. Nature Genetics, published online November 02, 2015; doi: 10.1038/ng.3435
