Gene-edited tomatoes could be a new source of vitamin D
rael-science
Tomatoes
gene-edited to produce vitamin D, the sunshine vitamin, could be a
simple and sustainable innovation to address a global health problem.
Researchers used gene editing to turn off a specific molecule in the plant's genome which increased provitamin D3 in both the fruit and leaves of tomato plants. It was then converted to vitamin D3 through exposure to UVB light.
Vitamin
D is created in our bodies after skin's exposure to UVB light, but the
major source is food. This new biofortified crop could help millions of
people with vitamin D insufficiency, a growing issue linked to higher
risk of cancer, dementia, and many leading causes of mortality. Studies
have also shown that vitamin D insufficiency is linked to increased
severity of infection by COVID-19.
Tomatoes
naturally contain one of the building blocks of vitamin D3, called
provitamin D3 or 7-dehydrocholesterol (7-DHC), in their leaves at very
low levels. Provitamin D3, does not normally accumulate in ripe tomato
fruits.
Researchers
in Professor Cathie Martin's group at the John Innes Centre used
CRISPR-Cas9 gene editing to make revisions to the genetic code of tomato
plants so that provitamin D3 accumulates in the tomato fruit. The
leaves of the edited plants contained up to 600 ug of provitamin D3 per
gram of dry weight. The recommended daily intake of vitamin d is 10 ug for adults.
When
growing tomatoes leaves are usually waste material, but those of the
edited plants could be used for the manufacture of vegan-friendly
vitamin D3 supplements, or for food fortification.
"We've
shown that you can biofortify tomatoes with provitamin D3 using gene
editing, which means tomatoes could be developed as a plant-based,
sustainable source of vitamin D3," said Professor Cathie Martin,
corresponding author of the study which appears in Nature Plants.
"Forty
percent of Europeans have vitamin D insufficiency and so do one billion
people world-wide. We are not only addressing a huge health problem,
but are helping producers, because tomato leaves which currently go to
waste, could be used to make supplements from the gene-edited lines."
Previous
research has studied the biochemical pathway of how 7-DHC is used in
the fruit to make molecules and found that a particular enzyme Sl7-DR2
is responsible for converting this into other molecules.
To
take advantage of this the researchers used CRISPR-Cas 9 to switch off
this Sl7-DR2 enzyme in tomato so that the 7DHC accumulates in the tomato
fruit.
They
measured how much 7-DHC there was in the leaves and fruits of these
edited tomato plants and found that there was a substantial increase in
levels of 7-DHC in both the leaves and fruit of the edited plants.
The 7-DHC accumulates in both the flesh and peel of the tomatoes.
The
researchers then tested whether the 7-DHC in the edited plants could be
converted to vitamin D3 by shining UVB light on leaves and sliced fruit
for 1 hour. They found that it did and was highly effective.
After
treatment with UVB light to turn the 7-DHC into Vitamin D3, one tomato
contained the equivalent levels of vitamin D as two medium sized eggs or
28g tuna—which are both recommended dietary sources of vitamin D.
The
study says that vitamin D in ripe fruit might be increased further by
extended exposure to UVB, for example during sun-drying.
Blocking
the enzyme in the tomato had no effect on growth, development or yield
of the tomato plants. Other closely related plants such as aubergine,
potato and pepper have the same biochemical pathway so the method could
be applied across these vegetable crops.
Earlier
this month the UK Government announced an official review to examine
whether food and drink should be fortified with vitamin D to address
health inequalities.
Most
foods contain little vitamin D and plants are generally very poor
sources. Vitamin D3 is the most bioavailable form of vitamin D and is
produced in the body when the skin is exposed to sunlight. In winter and
in higher latitudes people need to get vitamin D from their diet or
supplements because the sun is not strong enough for the body to produce
it naturally.
First
author of the study Dr. Jie Li said that "the COVID-19 pandemic has
helped to highlight the issue of vitamin D insufficiency and its impact
on our immune function and general health. The provitamin D enriched
tomatoes we have produced offer a much-needed plant-based source of the
sunshine vitamin. That is great news for people adopting a plant-rich,
vegetarian or vegan diet, and for the growing number of people worldwide suffering from the problem of vitamin D insufficiency."
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