Martin Jonikas receives new grant to boost crop yields by introducing an algal organelle into plants

With world population projected to exceed eight billion people by 2025, food security is already a pressing global problem.  Part of the solution will come from efforts to increase the yields of current food crops, but the global need for food only continues to grow, and may soon outpace farmers’ ability to increase production via conventional means such as breeding, application of fertilizers, and improved land management.  Martin Jonikas, an Assistant Professor in Princeton’s Department of Molecular Biology, is collaborating with Alistair McCormick from the University of Edinburgh, Luke Mackinder from the University of York and Howard Griffiths from Cambridge University on a novel approach to boost crop productivity.

During photosynthesis, chloroplasts transmute light energy into chemical energy by converting carbon dioxide (CO₂) and water into sugar.  The chloroplasts of all photosynthetic eukaryotes – from the single-celled green algae to the massive sycamore – use an enzyme called Rubisco to extract carbon atoms from CO₂ in the air and incorporate them into starches.  In many crop plants, this process (known as carbon fixation) is slow and limits growth because Rubisco catalysis runs very slowly. But algae don’t face this limitation because their chloroplasts contain a structure called a pyrenoid, which feeds densely packed Rubisco with concentrated CO₂, making the enzyme run faster.

“The algal CO₂ concentrating mechanism contributes significantly to global carbon fixation and has the potential to enhance crop productivity if successfully introduced into higher plant chloroplasts,” notes Jonikas.  Thanks to a grant jointly awarded by the U.S. National Science Foundation and the British Biotechnology and Biological Sciences Research Council, Jonikas and colleagues now plan to do just that, by expressing the genes essential for a functional pyrenoid in Arabidopsis thaliana, a small flowering plant commonly used in studies of plant biology.  

 “We hypothesize that a minimal algal-type CO₂ concentrating mechanism can be produced in a higher plant such as Arabidopsis by expressing as few as six already known algal proteins,” says Jonikas.

The effort to engineer a CO₂ concentrating mechanism into higher plants builds on discoveries the team has made over the past 10 years, which have transformed our understanding of pyrenoid protein composition, structure and biogenesis.  The work will be guided by a computational model of pyrenoid function being developed in Jonikas’ lab.  The researchers plan to begin by investigating whether Rubisco clusters can be created in Arabidopsis.  Next, it will be important to show that chloroplasts can be further engineered to supply their new Rubisco clusters with concentrated CO₂, and that this improves plant growth.  Jonikas and colleagues expect that this work will set the stage for future efforts to add a pyrenoid to crop plants, and also lead to new revelations about how the pyrenoid functions and how it is regulated in algae.

Figure 1. The chloroplast of the alga Chlamydomonas reinhardtii contains an organelle called the pyrenoid that improves cell growth. The pyrenoid is spherical and has three sub-compartments: a matrix packed with the CO₂-fixing enzyme Rubisco, surrounded by a starch  sheath, and traversed by membranous structures called pyrenoid tubules.

Figure 2. Princeton researcher Martin Jonikas and colleagues plan to investigate whether the introduction of a synthetic pyrenoid into higher plants will boost the plant’s growth, with the ultimate goal of increasing crop yields.

This work will be supported by grant MCB-1935444 from the U.S.’s National Science Foundation to Martin Jonikas, and by grant BB/S015337/1 from the United Kingdom’s Biotechnology and Biological Sciences Research Council to Luke Mackinder from University of York, Alistair McCormick from University of Edinburgh, and Howard Griffiths from Cambridge University.