## Revolutionary rice

Feeding the world (and saving nature) in this populous century, Jane Langdale began, depends entirely on agricultural efficiency—the ability to turn a given amount of land and sunlight into ever more food. And that depends on three forms of efficiency in each crop plant: 1) interception efficiency (collecting sunlight); 2) conversion efficiency (turning sunlight into sugars and starch); and 3) partitioning efficiency (maximizing the edible part). Of these, after centuries of plant breeding, only conversion efficiency is far short of the theoretical maximum. Most photosynthesis (called “C3“) is low-grade, poisoning its own process by reacting with oxygen instead of carbon dioxide when environmental conditions are hot and dry.

But some plants, such as corn and sugar cane, have a brilliant workaround. They separate the photosynthetic process into two adjoining cells. The outer cell creates a special four-carbon compound (hence “C4“) that is delivered to the oxygen-protected inner cell. In the inner cell, carbon dioxide is released from the C4 compound, enabling drastically more efficient photosynthesis to take place because carbon dioxide is at a much higher concentration than oxygen.

Rice is a C3 plant--which happens to be the staple food for half the world. If it can be converted to C4 photosynthesis, its yield would increase by _50%_ while using _half_ the water. It would also be drought-resistant and need far less fertilizer.

Langdale noted that C4 plants have evolved naturally 60 times in a variety of plant families, all of which provide models of the transition. “How difficult could it be?” she deadpanned. The engineering begins with reverse-engineering. For instance, the main leaves in corn are C4, but the husk leaves are C3-like, so the genes that affect the two forms of development can be studied. Langdale’s research suggests that the needed structural change in rice can be managed with about 12 engineered genes, and previous research by others indicates that the biochemical changes can be achieved with perhaps 10 genes. How much is needed for the eventual fine tuning will emerge later.

When is later? The C4 Rice project began in 2006 at the International Rice Research Institute in the Philippines, funded by the Bill & Melinda Gates Foundation. The research is on schedule, and engineering should begin in 2019, with the expectation that breeding of delicious, fiercely efficient C4 rice could be complete by 2039.

It is the kind of thing that highly focussed multi-generation science can accomplish.