Crops that Can Grow in the Dark? Not Yet, But It’s a Step

It's not exactly plants that grow in the dark, but new research points that way to more sunlight-efficient crops.

by Michael Byrne
Jul 7 2016, 6:00pm

Image: Mark Sadowski/Flickr

There's really no question that we don't have enough to eat. If we are to keep Earth's ever-advancing population from famines so severe that they will make 2016 look like it was raining hamburgers, we will need to produce more food, like, yesterday. How much more food, exactly, varies depending on the study, but the required increase could be as much as 110 percent. And yet, at the same time, around 40 percent of all land on Earth is already currently used for agriculture, which is nearly all of the planet's arable land, or land that can be used for agriculture in the first place.

While crop yields are currently increasing by a rate of around 1 percent per year, this isn't nearly enough to meet food demands circa 2050. Eating bugs will help, sure, but agriculture needs breakthroughs. We need crops that can grow on less land and with longer growing seasons. How can we minimize agricultural downtime? Similarly, how can we maximize the free solar energy bathing half the planet at any given time of day? We might start by looking to blue-green algae, aka cyanobacteria.

As described in a paper published Thursday in Science, a group of researchers led by Pennsylvania State University biochemist Donald Bryant has uncovered a key enzyme used by cyanobacteria to produce the biomolecule chlorophyll f.

It's this variant of chlorophyll, the stuff employed by plants to convert sun energy into sugar energy, that allows the bacteria to harvest energy from the near-red spectrum of light—that is, radiation just at the edge of the visible spectrum that goes mostly unused in the more typical photosynthesis variant employed by green plants.

Being able to harvest infrared light doesn't mean being able to grow in the dark so much as it does being able to grow in otherwise prohibitive shade and conditions of "strongly filtered light." This is partially what enables them to grow in the huge macroscale mats that earned them the blue-green algae misnomer (algae is a plant, bacteria is bacteria). An individual bacterium can survive even glopped together with a bunch of other bacteria that may be hogging all of the direct sunlight.

Chlorophyll f is itself a very recent discovery and was first described in a 2010 paper in Science, which suggested that it may have implications for bioenergy applications. Bryant's paper is the first to identify the enzyme responsible for the production of the infrared variant, a process known as far-red light photoacclimation (FaRLiP).

FaRLiP involves 20 specific genes, three of which are responsible for the signalling cascade that results in the process of photoacclimation itself. To find the enzymes responsible for the expression of the needed genes, Bryant and his group employed reverse genetics. Essentially, they took the suspect enzymes and tried plugging them into cyanobacteria that don't normally synthesize chlorophyll f. With the new enzymes, they were able to accomplish this, but only in the presence of visible light, which suggests a fundamental connection to chlorophyll a, which is how plants absorb more usual wavelengths of visible radiation spanning from violet-blue to orange-red light.

Unfortunately, getting a plant to suddenly start utilizing chlorophyll f in the same way that bacteria do isn't quite as simple as it sounds. "In principle putting a single gene into a plant is no big deal," Bryant told me. "Getting it to make an adequate level of chlorophyll f so that it would make a difference for the plant and getting the chlorophyll f bound to proteins that would normally bind [chlorophyll a or b], which are the two types of chlorophyll that plants usually have, that's a tougher problem."

In other words, it's not a given that something useful in bacteria is going to be useful in a plant, at least without some tweaking. This is the problem facing Bryant and his team now: How to make plants with the chlorophyll f enzyme make enough of the stuff for it to really matter.

"We've already been successful in increasing the amount of chlorophyll f synthesis by about a factor of two," Bryant said. "That doesn't sound like a lot but it's more than zero. You have to go in small steps. We have many other experiments in progress that we hope will get us an equivalent increases and if we get multiplication of those factors then maybe we'll [see] a hundredfold increase."

In the meantime, we'll just have to make do with the sunlight we can see.