LIFE & EVOLUTION
Engineered hybrid rice can clone itself
Research raises hopes of boosting crop yields more affordably
GENES & CELLS
Dads can pass on
In rare cases, kids inherit the
organelles from both parents
BY SUSAN MILIUS
After more than 20 years of dreaming,
scientists have tweaked a hybrid variety
of rice so that some of the plants produce
cloned embryos. No plant sex necessary.
The feat, described online December 12
in Nature, is encouraging for efforts to
feed an increasingly crowded world.
Crossing two good grain varieties can
make one fabulous one, combining the
best versions of genes to give crops desirable traits such as higher yields. But such
hybrids often don’t pass along the coveted
qualities to all seeds. Farmers who want
consistently higher yields have to pay for
new hybrid seeds each year. The new lab
version of hybrid rice would preserve its
qualities through self-cloning, says plant
geneticist Venkatesan Sundaresan of the
University of California, Davis.
Though more than 400 kinds of plants
naturally have self-cloning, re-creating
those pathways in crop plants has “been
BY TINA HESMAN SAEY
Some dads have broken a textbook rule.
Fathers in three unrelated families
passed mitochondria — tiny energy factories found in cells — to their children.
Scientists have long thought that children inherit mitochondria exclusively
from their mothers because mitochondria from the father’s sperm are usually
destroyed after an egg is fertilized. The
new research, published in the Dec. 18
Proceedings of the National Academy of
Sciences, suggests that in rare cases dads
contribute mitochondria too. The con-
sequences of inheriting mitochondria
from dad aren’t known.
harder than anyone expected,” says
He and colleagues discovered that
modifying two sets of genes caused the
japonica rice hybrid called Kitaake to
clone its seeds. The team found that in a
fertilized plant egg, only the male version
of a gene called BABY BOOM1 triggered
seed embryo development. Inserting a
genetic starter switch, called a promoter,
let the female version of the gene take
over spurring an egg into an embryo.
But that tweak wasn’t enough. An egg
formed through meiosis — cell division
that produces eggs and sperm — would
have only half a set of chromosomes.
A solution came from plant geneticist
Raphael Mercier of the French National
Institute for Agricultural Research. His
team had disabled three meiosis genes so
rice plants switched to asexual reproduction. Sundaresan and UC Davis colleague
Imtiyaz Khanday updated the approach,
Mitochondrial disease researcher
Paldeep Atwal spotted the paternal
signature after examining DNA from a
woman who came to the Mayo Clinic in
Jacksonville, Fla. DNA in a cell’s nucleus
is inherited equally from both parents
and contains all the genetic instructions
for building a body. Mitochondria have
their own DNA that contains some of the
genes needed for building and running
the mitochondria. The woman’s cells
weirdly contained two types of mitochondrial DNA, some from mom and
some “from elsewhere,” says Atwal, who
now runs a private clinic in Jacksonville.
With DNA from both of the woman’s
parents, the team was able to examine
the father’s mitochondrial DNA and
found that he was the source of the mystery mitochondria. The woman’s brother
also inherited their father’s mitochondria. “We thought, ‘What on Earth is
going on here?’ ” Atwal says.
Atwal got in touch with Taosheng
Plant geneticists Imtiyaz Khanday (left),
Venkatesan Sundaresan (right) and colleagues
made hybrid rice plants that clone their seeds.
using CRISPR/Cas9 gene editing.
Combining all the tweaks in Kitaake
rice let a portion of parents, about
30 percent at best, create viable seeds
with hybrid genetics intact. Plants still
needed pollen to make food for the
seeds. But those seeds sprouted into
plants that also could clone themselves,
and so could the next generation.
At scientific meetings, other teams
have unveiled proof-of-concept self-cloning crops, including sorghum and
maize, says Ueli Grossniklaus, who studies plant reproduction at the University
of Zurich. All self-cloners still have room
for improvement, he says. s
Huang, a mitochondrial disease expert at
Cincinnati Children’s Hospital Medical
Center. Huang had examined patients
from two other families in which fathers
had passed on mitochondria. All together,
the researchers found 17 people in the
three families who inherited 24 to 76 percent of their mitochondria from dad.
“It’s real and a very interesting discovery, but I’m not surprised,” says Sophie
Breton, an evolutionary biologist at the
University of Montreal. Previous studies in other animals have indicated that
males sometimes pass on mitochondria
(SN: 12/26/15, p. 4).
Breton thinks the discovery might
someday negate the need to make
“three-parent babies,” children whose
mitochondria come from donor eggs
because their mothers’ eggs carry mitochondrial diseases (SN Online: 10/18/16).
“If the mitochondria from the father can
do the job, maybe we could stick with the
two-parent baby situation,” she says. s