‘Greening’ the machinery of plant life

By Amanda Garris Ph.D. ‘04
periodiCALS, Vol. 6, Issue 2, 2016

Maureen Hanson (photo by Dave Burbank)Inside every plant leaf, emerald chloroplasts harness water, light and carbon dioxide and create energy, a fundamental reaction that both is life and gives life. One of its powerhouse enzymes is the target of work to make plants radically more productive, per plant, per acre and per planet.

Although the project’s concept is straightforward—make photosynthesis more efficient by tinkering with a core enzyme—its lofty ambition is to improve on evolution. Maureen Hanson, the Liberty Hyde Bailey Professor of Plant Molecular Biology, formulated the concept as part of a team of colleagues during an “Ideas Lab” meeting of 30 experts convened in 2010 by the National Science Foundation and the United Kingdom’s equivalent, the Biotechnology and Biological Sciences Research Council (BBSRC).

“We were encouraged to focus on innovative ways to improve the system,” Hanson recalled. “A more efficient enzyme would have two main advantages: You would potentially need less acreage planted to crops, and fertilizer needs would go down.”

Here’s the logic: RuBisCO stokes a plant’s appetite for nitrogen. Thought to be the most abundant enzyme on earth, RuBisCO is fully half the protein present in leaves, and nitrogen is a core ingredient. If the enzyme was more efficient, plants would not need so much of it. Less enzyme, less nitrogen fertilizer.

“Reducing RuBisCO from 50 percent to 10 percent of the leaf protein is predicted to have an impact on a plant’s fertilizer needs,” Hanson noted.

The first step is borrowing a more productive enzyme that evolved in cyanobacteria, also known as blue-green algae. Initial successes in the project—including the first plant created through genetic engineering to process all of its carbon using the cyanobacterial enzyme—led to an infusion of nearly $1 million in NSF funding a joint NSF/BBSRC Synthetic Biology Program in July. In collaboration with Martin Parry of Lancaster University and Michael Blatt at the University of Glasgow, they are now engineering around the enzyme’s main flaw: Although it is faster, it’s also less selective and will mistakenly interact with oxygen instead of carbon dioxide, which derails the reaction.

Cyanobacteria solve the problem by cloistering the enzyme in a compartment, which creates a safe, carbon-rich blanket for the enzyme. Success will require not only the genetic engineering of the gene for the enzyme but also of the entire system: enzyme, protein shell and accessory proteins as well as a transporter to feed the carbon supply into it. Postdoctoral researcher Myat Lin handles most of the day-to-day work. He is the genetic engineer, pasting together the necessary suite of genes; the sharpshooter pulling the trigger of the gene gun to insert them into the plant; and a horticulturist tending hundreds of tiny plantlets.

“We suspect the minimum number of genes we need to insert is about ten,” Lin said, with cautious optimism. “And it’s not just the number of genes—you have to make sure they’re produced in the correct ratios and at the right concentrations.” 

Keeping watch over the full-grown experimental plants this summer was plant biology major Will Stone ’18. He was responsible for putting a number on their progress by measuring the rate of photosynthesis in the current batch of engineered tobacco plants. 

“What I like about this project is it’s a big problem and a big idea,” Stone said. “There’s a lot of different facets to wrap your mind around.” 

While the team is currently engineering the system in tobacco plants as a pilot project, the next targets will be soybean and poplar, where existing genetic tools will ease the transfer.

“This kind of project is a long shot,” Hanson mused. “But that’s what they wanted to do with this program—have scientists aim high for something that is technically challenging but potentially very valuable.”