39 North Innovation District Plan Unveiled
The Science in Our Food
How does C3 photosynthesis differ from C4?
C3 is the pathway used by most plants (eg. rice, wheat, barley) to fix carbon. The primary product of this kind of photosynthesis is C3 – as the enzyme RuBisCO adds CO2 to a five-carbon molecule, transforming it into a six carbon molecule which breaks down into two three-carbon molecules (hence the name C3). However, as RuBisCO is a very slow and inefficient enzyme that reacts with oxygen to produce a cytotoxic substance, many plants have developed a two-step photosynthetic process to improve efficiency, known as C4. When CO2 enters the cell, it enters an oxygen-rich environment and where it is fixed into a C4 acid by PEPC. The cell will then move that acid into an inner-cell type, which is protected from atmospheric oxygen and capable of decarboxylating the acid in the vicinity of RuBisCO, creating an artificially high level of CO2 that effectively eliminates the oxygenase reaction of the enzyme and therefore photorespiration.
What benefits might C4 crops bring for growers?
When plants are grown under hot, dry conditions, photorespiration can utilise about 30 per cent of the photosynthetic capacity of the plant, thereby reducing productivity. This is not the case in C4. C4 photosynthesis therefore endows plants with more nitrogen- and water-use efficiency. My group seeks to engineer C4 traits into C3 crops like rice. No one has been able to do this so far, or understand the genes and networks which dictate the differentiation of C4.
Why is maize so valuable on both US and international markets?
In the US, maize is used primarily as a commodity for animal feed, with most of the remainder being used for ethanol – although a relatively small amount of the maize crop is produced for human consumption. In China, growing demand for pork has increased maize grain consumption by animals – so now their number one crop is maize. They grow more corn than rice or wheat and have become the second largest producer behind the US. Argentina grows a lot of corn as well. Because there is a great demand in both the feed and energy sectors, the goal is to increase yield with fewer inputs (ie. nitrogen fertilisers and water). This is a priority for the biotech and seed companies.
How do you expect innovation in plant research will help propel genetics?
One factor that is rapidly transforming our field right now is cheap high-throughput sequencing. The ability to sequence an entire genome can now be accessible to individual research groups like ours, enabling us to compare sequences across related grasses, and identify points of divergence. It also allows us to clone genes much more quickly, to isolate genes knocked out with our transposons much faster than before, and enables us to explore natural variation within a species at a resolution we have not previously had. For instance, we may have a line of corn that grows very well under dry conditions and another that only grows well under wet conditions: having a DNA sequence of both plants allows us to explore the factors that make it more suitable. Traditionally it would take decades to clone some of these genes, but now it can be achieved in a year.