Nav: Home

Source of citrus' sour taste is identified

March 04, 2019

A team of researchers, including two from the University of California, Riverside, has identified the genes responsible for the hallmark sour taste of many citrus fruits. Published Tuesday, Feb. 25 in Nature Communications, the research could help plant breeders develop new, sweeter varieties.

Modern citrus varieties have been bred over thousands of years to generate a broad palette of sour and sweet-tasting fruits. Analyses of their pulp reveals that a single chemical element--hydrogen--is largely responsible for the difference between sour and sweet-tasting varieties, which usually have similar sugar content. The pulp from sour fruits contains more hydrogen ions, giving it a lower pH and a tangy taste that is recognized by acid-sensitive cells in our taste buds. Conversely, pulp from sweeter varieties contains fewer hydrogen ions and tastes less acidic.

Ronald Koes and colleagues at the University of Amsterdam in the Netherlands set out to untangle how some citrus varieties wind up with more acidic juice than others, a process that until now has remained a mystery. Their interest stemmed from a previous study showing that higher acidity in purple petunia flowers resulted in more petal pigmentation.

Intrigued by the Faris variety of lemon tree, which produces branches bearing both sweet and sour fruits, and white and purple-tinged flowers, Koes' team turned to UCR plant scientists Mikeal Roose and Claire Federici. Using the university's vast Citrus Variety Collection, which preserves over 1,000 living citrus and related fruit varieties, Roose and Federici selected the Faris lemon and 20 other citrus fruits ranging from wincingly sour to sugary sweet for Koes' team to analyze.

By studying the expression of genes related to those controlling acidity in petunias, Koes' team identified two citrus genes, CitPH1 and CitPH5, that are highly expressed in sour varieties and weakly expressed in sweet-tasting varieties. The CitPH1 and CitPH5 genes encode transporter proteins that pump hydrogen ions into the vacuole, a large storage compartment inside juice cells, thus increasing their overall acidity.

Next, the team turned its attention to genes that control the levels of CitPH1 and CitPH5 in juice cells. While down-regulation of CitPH1 and CitPH5 in sweeter tasting varieties arose multiple times independently in different varieties, the researchers found that mutations in genes for a handful of transcription factors (proteins that help turn specific genes on and off) were responsible for reduced expression of CitPH1 and CitPH5, and therefore a sweeter taste.

Roose, a professor of genetics in UCR's College of Natural and Agricultural Sciences, said the findings could help breeders develop better-tasting citrus fruits. However, he said breeding varieties with severe mutations in the transcription factors such as those studied in the "acidless" citrus would be "overkill," producing sugary citrus fruits with none of their popular acidic kick. Instead, plant scientists should look to target mutations that have a less dramatic effect on the production and activity of transporter proteins.

"By understanding the mechanism acidification of fruit cells, we can now look for related genes that might reduce the expression of CitPH1 and CitPH5 just enough to engineer or select for new, sweeter varieties," Roose said.
-end-
The title of the paper is "Hyperacidification of Citrus fruits by a vacuolar proton-pumping P-ATPase complex." In addition to Koes, authors at the University of Amsterdam are Pamela Strazzer, Cornelis Spelt, Shuangjiang Li, Mattijs Bliek, and Francesca Quattrocchio. Roose and Federici's work was supported by the United States Department of Agriculture (USDA)'s National Institute of Food and Agriculture.

University of California - Riverside

Related Hydrogen Articles:

Superconductivity: It's hydrogen's fault
Last summer, it was discovered that there are promising superconductors in a special class of materials, the so-called nickelates.
Hydrogen energy at the root of life
A team of international researchers in Germany, France and Japan is making progress on answering the question of the origin of life.
Hydrogen alarm for remote hydrogen leak detection
Tomsk Polytechnic University jointly with the University of Chemistry and Technology of Prague proposed new sensors based on widely available optical fiber to ensure accurate detection of hydrogen molecules in the air.
Preparing for the hydrogen economy
In a world first, University of Sydney researchers have found evidence of how hydrogen causes embrittlement of steels.
Hydrogen boride nanosheets: A promising material for hydrogen carrier
Researchers at Tokyo Institute of Technology, University of Tsukuba, and colleagues in Japan report a promising hydrogen carrier in the form of hydrogen boride nanosheets.
World's fastest hydrogen sensor could pave the way for clean hydrogen energy
Hydrogen is a clean and renewable energy carrier that can power vehicles, with water as the only emission.
Chemical hydrogen storage system
Hydrogen is a highly attractive, but also highly explosive energy carrier, which requires safe, lightweight and cheap storage as well as transportation systems.
Observing hydrogen's effects in metal
Microscopy technique could help researchers design safer reactor vessels or hydrogen storage tanks.
The 'Batman' in hydrogen fuel cells
In a study published in Nature on Jan. 31, researchers at the University of Science and Technology of China (USTC) report advances in the development of hydrogen fuel cells that could increase its application in vehicles, especially in extreme temperatures like cold winters.
Paving the way for more efficient hydrogen cars
Hydrogen-powered vehicles emit only water vapor from their tailpipes, offering a cleaner alternative to fossil-fuel-based transportation.
More Hydrogen News and Hydrogen Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Meditations on Loneliness
Original broadcast date: April 24, 2020. We're a social species now living in isolation. But loneliness was a problem well before this era of social distancing. This hour, TED speakers explore how we can live and make peace with loneliness. Guests on the show include author and illustrator Jonny Sun, psychologist Susan Pinker, architect Grace Kim, and writer Suleika Jaouad.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.