
What is C4 rice? - iwwr
http://c4rice.irri.org/index.php/component/content/article/19-about/56-what-is-c4-rice
======
Blahah
PhD student working on the C4 rice project here. On the road right now but
happy to answer questions when I can find a moment.

I genuinely think C4 rice the best shot we've got at alleviating a huge chunk
of world hunger in one (extremely difficult) move.

Some key points:

\- C4 plants (like maize and sugarcane) are generally about 50% more efficient
at biomass accumulation than C3 plants (like rice and wheat). C4 rice could
mean a yield increase for rice of up to 50% _with no increase in inputs_

\- RuBisCO is by far the most abundant protein in plants. It accounts for the
majority of the nitrogen required by C3 plants, and the inefficiency of C3 is
the reason we have to use so much nitrogen fertiliser. C4 rice would require
considerably less fertiliser than C3 rice.

\- C4 plants use CO2 much more efficiently that C3 plants. This allows them to
keep their stomata closed much more of the time, so they lose less water
through transpiration. This makes C4 plants much more water efficient - C4
rice could require much less water than C3 rice, meaning it could be grown on
land that is currently unsuitable for rice production.

\- C4 is probably the most interesting example of convergent evolution we know
about. It has evolved over 70 times independently. This is quite amazing -
it's a complex trait that requires dozens of proteins to be organised in a
particular temporal and spatial pattern, and needs a new cell type to be made.
Yet it has evolved 70+ times.

\- We are using the recurrent evolution pattern as our 'way in' to the problem
of figuring out how to control C4 at the molecular level. We analyse gene
expression on a massive scale in C4 and C3 sister species from all the
evolutionary origins of the trait.

\- This involves a lot of interesting software challenges that hn might be
interested in. For example, we're working with so many species that we can't
sequence all their genomes. But we can sequence their _transcriptomes_, which
is all the genes that are expressed at a given time. The sequencing technology
produces millions of tiny fragments of the original sequences, which have to
be pieced back together to be useful (an NP-hard problem).

~~~
sdabdoub
> we're working with so many species that we can't sequence all their genomes

Are you talking about sequencing enough to get adequate coverage for
reconstruction?

Also, what do you think of the criticism that it is difficult to know the
potential effects of GMO on their ecosystems in the wild?

~~~
Blahah
> Are you talking about sequencing enough to get adequate coverage for
> reconstruction?

Yes. Assembling a genome requires a lot of sequencing data or different kinds,
and is expensive. Genomes (especially in plants) can be huge. We're only
interested, at least in this specific example, in the things that are
expressed. These make up a small proportion of the genome, and so we sequence
only those things.

> Also, what do you think of the criticism that it is difficult to know the
> potential effects of GMO on their ecosystems in the wild?

Agriculture in general has a vast impact on the environment. This is true
across the board - including organic, GMOs, 'conventional', etc. By its very
nature agriculture is about shaping the environment so we can control a piece
of it to optimise it for food production. Our responsibility is to try to
predict and minimise the effects that might cause problems.

So far, GMOs have proven to have relatively little effect on the environment
(compared to other drivers of agricultural productivity, like pesticide and
herbicide use, for example).

In the case of C4 rice we can predict what the major potential issue might be:
C4 rice plants might perform so well that they outcompete wild plants outside
the field setting. `There are some technological tricks we can use to try to
ensure plants don't do well outside the field.

~~~
ptaipale
When you say "relatively little", what does that mean? I can't see why there
would be any difference at all that comes from some (plant) being GMO in
itself.

Some plants developed with GMO technology might of course behave differently
from other variants of same species; for instance if some GMO variantg grows
up faster than previous seeds and is harvested faster and you can grow another
crop in the same season and get a better yield, then there is of course more
need for fertilizing etc. But that in itself does not come from something
being GMO.

~~~
Blahah
Well, with first-generation GMOs, a single gene was inserted into a crop. This
is totally unlike all previous crop breeding, where changes were complex and
no single gene was likely to control the trait. So before GMOs, there was
basically no chance that a trait bred into crops could escape into the wild by
gene flow, but with first-gen GMOs that became a real possibility. It has
indeed been recorded happening a bunch of times, leading to, for example,
herbicide resistance in weeds.

I should point out that herbicide resistance in weeds was widespread before
GMOs by other mechanisms, and in fact the switch to glyphosate has been a
great thing because we've massively reduced the application of harmful
chemicals, while glyphosate is benign. But the fact remains that GMOs do carry
their own specific risks that are a result of the technology and methodology,
rather than the specific application.

------
iwwr
Specifically, it's a serious project to adapt the C4 carbon fixation pathway
to rice, which is a C3 plant. C4 fixation is much more efficient in drier
climates like the ones more prevalent in developing nations. C4 plants while
small as a percentage of plant biomass (5%) produce about 30% of carbon
fixation among plants.

~~~
gus_massa
More details about C4 from Wikipedia:
[http://en.wikipedia.org/wiki/C4_carbon_fixation](http://en.wikipedia.org/wiki/C4_carbon_fixation)

> _About 7,600 plant species use C4 carbon fixation, which represents about 3%
> of all terrestrial species of plants._

> _These include the food crops maize, sugar cane, millet, and sorghum_

(The section
[http://en.wikipedia.org/wiki/C4_carbon_fixation#C4_leaf_anat...](http://en.wikipedia.org/wiki/C4_carbon_fixation#C4_leaf_anatomy)
is easier to read because it's not so technical.)

Is it easier to transform the rice in a C4 plant or to transfprm the rice
fields to maize fields? [Disclaimer: My family is from the north of Argentina
and we really like maize.]

~~~
Blahah
Most of asia uses rice as a staple, and it has a cultural history going back
over 2000 years. _Many_ governments and other groups have tried to explore
encouraging dietary change away from rice as a staple, but it has so far not
made any difference.

A 50% yield increase in rice could alleviate starvation for the most starving
continent on the planet.

------
ciconia
The background section does not mention the fact that a substantial part of
crops is used to feed animals in the meat/dairy industry, which is then
consumed mostly in developed countries. Another part of agricultural
production is used for manufacturing bio-diesel (1).

In light of this, it should be questioned whether the use of optimized crop
variants could be the right answer to the problem of feeding billions of
people, and whether it can be a _sustainable_ solution. OK, let's say we can
increase yield by 50%. What comes after that? (2)

I know it is a controversial and touchy subject, and also somewhat off-topic,
but personally I'm quite convinced that the answer to current food shortages
is not increased production, but rather the reduction of (over)consumption.

[1] The UNEP reports that "today, nearly half of the world’s cereals are being
used for animal feed." \-
[http://www.unep.org/pdf/FoodCrisis_lores.pdf](http://www.unep.org/pdf/FoodCrisis_lores.pdf)

[2] It is interesting that the same UNEP report, among the seven options it
proposes for dealing with food shortage (pp. 92-93), does not once mention GM
crops or increasing yields as a possible solution.

~~~
Blahah
You're absolutely right in the first part - a huge proportion of arable land
is used to feed animals.

However, this doesn't change the optimal strategy for feeding people in the
medium term, for a bunch of reasons:

1\. The arable land used for feeding animals would not necessarily be
available for feeding people who are hungry now if it were to be freed up.

2\. In general the world's poorest people grow their own food on small plots
of land and don't produce a lot of meat. They care about the productivity of
their plot of land.

3\. Changing the world's eating habits is a gargantuan task. Are you
suggesting we stop trying to feed people in the medium term using technology,
and allow them to starve while we try to convince westerners not to eat meat?
I know this is not what you're suggesting - but it serves to show that we
should of course be pursuing all the available routes to alleviating hunger.

> OK, let's say we can increase yield by 50%. What comes after that?

That's enough to meet the entire calorific intake increase for rice-eating
countries by the time population stabilises. By around 2050 the world
population will have stopped growing. So what comes after that is that
everyone is fed, and we can enjoy a world where very few people go hungry
while we fix the much more difficult problems of economics and society.

Finally, the UNEP report doesn't talk about the potential for GM crops because
it's out of scope - the report is about environmental factors in food
production. They do say that their projections could be affected by
improvements in GM technology.

------
jqm
I've always wondered if it would be possible to incorporate carbon fixation
schemes similar to those used by cactus into food plants (Grains might be
difficult, but maybe different types of fruit and vegetables, citrus, which I
understand is distantly related to cactus, for instance?).

Sure, growth rates would be slow, but the lack of need for irrigation and
ability to utilize tracts of arid land might offset this.

I'm sure somebody at some point has looked into this. Any insight OP?

~~~
Blahah
Fly-by comment: C4 is very similar to CAM, the scheme that cacti use. So the
C4 rice project is essentially what you're thinking of, except that the
reactions are separated spatially in C4 instead of temporally in CAM.

------
meepmorp
I wonder how this will fare against the tide of anti-GMO silliness that seems
to be prevalent these days. Even something unquestionably useful like golden
rice has been met with fear mongering and paranoia.

~~~
Moru
I don't want to play the devils advocate but I was just watching "I, robot" on
TV... What ever could go wrong playing with nature? :-)

~~~
meepmorp
> What ever could go wrong playing with nature? :-)

No offense (seriously), but this argument is the biggest load of bullshit.

Do you think there are any major food sources that just developed, as is,
naturally? Pretty much every vegetable, fruit, grain, or pulse - has been
selectively developed by humans, many over the course of thousands of years.
The bananas we eat can't even reproduce without our direct intervention.
Animals, too, both livestock and pets - that dachshund wasn't running wild in
the forest before we tamed it.

We've been playing with nature as long as we've been able to do so. Genetic
engineering is just a better set of tools for it. Somehow, though, people have
convinced themselves that the selective breeding process is safer than direct
genetic manipulation. Because, of course, breeding crops based on taste or
visual appeal makes for safer and better development of crops - why pick the
specific traits you want when you can just fumble about for generations
without a clear idea of what you're gonna get?

Should we be careful? Sure, in this as in all things we do; but the fact that
the technology is new isn't the reason why.

