Bacteria gene may help crops soak up more sun

Crops able to absorb more of the sun’s light and produce higher yields are a step closer.

Biochemists at Pennsylvania State University in the US found the gene that converts chlorophyll – the most common light-absorbing pigment used by plants to photosynthesise – to a form that absorbs wavelengths in the far red range of the light spectrum.

The discovery, which could let scientists engineer crops to better harness the sun’s energy, was published in Science.

“There is nearly as much energy in the far-red and near-infrared light that reaches the Earth from the sun as there is in visible light,” says Donald Bryant, senior author of the paper.

“Therefore, the ability to extend light harvesting in plants into this range would allow the plants to more efficiently use the energy from the sun and could increase plant productivity.”

Algae, plants and some bacteria reap energy using photosynthesis. The process if dependent on visible light – wavelengths of 400 to 700 nanometres – being absorbed by the green pigment chlorophyll. Light plus carbon dioxide is converted to sugar and oxygen through a series of reactions.

Some cyanobacteria (commonly known as blue-green algae, even though they’re bacteria) have extended their spectrum reach. They’re able to absorb light just outside the visible spectrum, around 700 to 800 nanometres, with chlorophyll f, which was discovered by Australian scientists in 2010. But how chlorophyll f was made was a mystery.

So Ming-Yang Ho and colleagues examined the genome of two cyanobacteria that naturally made chlorophyll f – and were capable of photosynthesising in far-red light – and another which could not.

They identified the enzyme responsible for making chlorophyll f, which they named chlorophyll f synthase, and the gene encoding it.

When the researchers disabled the gene that encodes for chlorophyll f synthase in the far-red-photosynthesising cyanobacteria, the bacteria were completely devoid of that form of the pigment.

And when they added chlorophyll f synthase to the cyanobacterium dependent on visible light, they found it produced chlorophyll f – albeit a small amount, and only when grown in light. This suggests chlorophyll f is connected in some way to chlorophyll a, which is the molecule plants use to absorb in the visible part of the spectrum.

But, as chlorophyll f seems to be controlled by a single gene, the researchers write it may be feasible to introduce it into plants to extend their photosynthesis wavelength range.