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.
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.]
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.
I suppose it's not entirely an accident that in my part of the Midwest, SW Missouri, and I gather a lot of it, maize and sorghum (around here called "milo") are the two most popular things to plant (the milo is fed to animals).
My mother, however, grew up on a rice farm in Louisiana. C4 rice would be very welcome as long as there's plenty of hungry mouths to feed.
As far as the biology goes, not that I'm paying any attention to the field, this is the most ambitious genetic engineering project I've ever heard of. Hope they can pull it off.
And I wonder about quinoa too, which is a complete protein, grows well in dry climates, and is also C4. And quinoa could probably substitute for rice in many recipes. The price is slightly high right now, but that's because supply has not kept with demand (due in part to the fact that it's gluten free).
Many algae already use a carbon concentrating mechanism [0] similar to C4. It works in a similar way, by concentrating CO2 around RuBisCO, the key enzyme that creates sugar from CO2. In C4 plants, the RuBisCO is kept in a wax-enclosed cell, and the CO2 is pumped in. In algae, which are single-celled, the RuBisCO aggregates together into a bubble-like structure called a pyrenoid [1], and a high CO2 concentration is maintained inside.
The pathway crosses several cells, one in which CO2 is filtered from an oxygen atmosphere and another anoxic stage where the CO2 is fixed again, this time to produce sugars which plants actually need. The two stage fixation prevents something called 'photorespiration' where existing oxygen can 'steal' some of the rubisco mollecules which would otherwise associate with CO2. So this is a multicellular process and could not be adapted to algae.
Upland rice was bred using natural variation within rice populations. C4 rice will require much more complex targeted genetic design. However, we are also harnessing natural variation, and are doing massive-scale screens of natural cultivars. The idea is that we want to do the engineering the in the most C4-like rice that exists.
