Plant scientists are continuously in a race against time to develop
crops with higher yields in order to feed the projected 9 billion people
on the planet by 2050. A study led by Dr. Maureen Hanson from Cornell
University describes their work in putting elements from cyanobacteria
into crop plants for more efficient photosynthesis.

Rubisco's reaction to both carbon dioxide and oxygen in the air is a
hurdle in improving photosynthesis. Such reaction to air creates toxic
byproducts, slows photosynthesis, and thereby lowers crop yields.
However, in cyanobacteria, Rubisco is contained within microcompartments
called carboxysomes that shield Rubisco from oxygen. Carboxysome allows
cyanobacteria to concentrate carbon dioxide so Rubisco can use it for
faster carbon fixation. "Crop plants don't have carboxysomes, so the
idea is to eventually put in the entire carbon-concentrating mechanism
from cyanobacteria into crop plants," Hanson said.

For this system to work in crop plants, scientists must remove carbonic
anhydrase, a naturally occurring enzyme, from the chloroplasts,
organelles in plant cells where photosynthesis occurs. The researchers
usedCRISPR-Cas9to disablegenesthat express two carbonic anhydrase
enzymes that are present in chloroplasts. In the past, another research
group used a different method to remove 99 percent of the anhydrase
enzyme's activity, and the plants grew normally. When Hanson's team
removed 100 percent of the enzyme's activity, the plants barely grew.
"It showed that plants need this enzyme to make bicarbonate that is used
in pathways to make components of leaf tissue," Hanson said. Experiments
showed that the absence of carbonic anhydrase did not interfere with
photosynthesis, contrary to previously held views.

Scientists take step to improve cropsâ?? photosynthesis, yields | Cornell
Chronicle
[news.cornell.edu]