Sunday, November 22, 2015

Drought-resistant pineapple has clues for drought resistance in other crops

Drought is responsible for most of the world’s crop losses, and researchers say that new work on drought-resistant pineapple is providing clues.

“Understanding the mechanisms that plants have evolved to survive water stress is vital for engineering drought tolerance in crops,” write the authors of a new study  in the journal Nature Genetics.

(Image: Pineapple [Ananas comosus {L.} Merr.]. Source: University of Hawai`i.)

Pineapple, the world’s second most important tropical fruit after bananas, is a member of the bromeliad family—the only bromeliad to produce a commercially important fruit. The bromeliads and the grasses are descended from a common ancestor.

An international team of researchers, including two from the University of Hawai`i at Mānoa, sequenced the pineapple genome. The two are Nancy Jung Chen and Robert Paull, with the university’s Department of Tropical Plant and Soil Sciences in the College of Tropical Agriculture and Human Resources. The project’s leader, Ray Ming, is a former University of Hawai`i researcher who is now with the University of Illinois.

They sequenced wild pineapple as well as two commercial species—an old high acid variety used in canned pineapple and a newer low-acid variety used primarily for fresh fruit sales. Pineapple has the scientific name Ananas comosus.

The researchers are looking at flower metabolism, sugar production and other features, but an important research objective is understanding pineapple’s drought tolerance, according to the University of Hawai`i’s press release on the project. 

“The plant possesses an alternate photosynthetic pathway that concentrates carbon dioxide during the night when water loss is less. This reduced water loss leads to high water-use efficiency,” the release says.

The name scientists use for this process is crassulacean acid metabolism or CAM.

Pineapples convert carbon-dioxide into malic acid at night , and then use it in the daytime while they keep their stomata closed to preserve moisture.

Here’s how the scientists say that: “CAM plants can keep their stomata closed during the daytime while the stored malic acid is decarboxylated and the carbon dioxide released is refixed through the Calvin-Benson cycle, greatly reducing water loss through evapotranspiration.”

Stomata are plant pores from which gases, including moisture, can be exchanged. Closing them in daylight can prevent moisture loss during hot, dry, sunny periods. Malic acid is an organic acid found in all fruits,.

The authors suggest that the drought resistance of pineapple could be conveyed via genetic engineering into other crops: “This work provides the first detailed analysis of the expression and regulation patterns of genes associated with CAM and could ultimately be used to engineer better (water-use efficiency) and drought tolerance in crop plants.”

Drought tolerance has been a key goal of crop plant breeding and genetic engineering worldwide.

Pineapple is originally a Central American plant, first reported by Europeans on Christopher Columbus' voyage. It once was one of Hawai`i's economic mainstays, second to sugar.

"Today, pineapple is cultivated on 1.02 million hectares of land in over 80 countries worldwide, and 24.8 million metric tonnes of fruit are produced annually with a gross production value approaching $9 billion. Pineapple has outstanding nutritional and medicinal properties," the paper's authors write.

© Jan TenBruggencate 2015

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