For decades, science has understood the basics of photosynthesis, the process by which plants turn sunlight into food. However, photosynthesis occurs on uniquely specialized membranes that we have only begun to understand. These must be continually assembled, remodeled and repaired as plants grow and respond to stress.
Now, a team of researchers at the University of Nebraska–Lincoln has mapped a new region within chloroplasts that serves as the assembly line for photosynthetic membranes. The study, recently published in Nature Communications, identifies a specific area within the cell where the machinery of life is built, repaired and maintained.
The discovery is the culmination of a career-long ambition for Rebecca Roston, an associate professor in the Center for Plant Innovation and the Department of Biochemistry.
"The idea that we knew where every atom of a photosystem was, but had no idea how its structures were actually built, fascinated me as a graduate student," Roston said. "I dreamed that if I ever had my own lab, I would try to figure it out."
The path to the discovery, however, was anything but linear. The project relied on a team of researchers who persevered through extraordinary personal challenges.
Graduate student Evan LaBrant led the initial charge, screening dozens of proteins to see where they existed within the cell. Despite facing multiple personal tragedies that nearly led him to leave graduate school, LaBrant returned to the lab to develop a strategy using fluorescent tagging. His brilliance and command of the literature were absolutely critical to the project’s success, as was his trainee, Joslin Ishimwe. Together, they identified several key protein candidates that appeared in specialized regions inside the chloroplast. Ishimwe piloted a new machine learning technique to quantify the thousands of microscopy images Evan made.
To prove these proteins were responsible for building membranes, Cailin Smith joined the team. Smith’s rigorous experiments showed that when certain proteins (like TVPFP or PMFP) were missing, the plant's photosynthetic membranes became disorganized. Teaming up with expert microscopist Bara Altartouri, Smith showed that in tvpfp mutants, membrane contact regions were markedly extended, while in pmfp mutants, contact site density was reduced. A team of blinded undergraduate researchers (Lauren Litterer and Allan Tullis) led by Smith quantified the images. Those findings linked these previously uncharacterized proteins to the organization of the photosynthetic membrane and support the idea that chloroplasts contain specialized regions dedicated to membrane maintenance.
The final piece of the puzzle required a massive proteomic analysis. Alondra Torres-Genera, who joined Roston’s lab after searching for the right research fit, worked with proteomic expert Michael Naldrett to profile the proteins. Fan Huang teamed up with Torres-Genera to perform parallel proteomic analyses. This approach revealed a “light thylakoid” intermediate-density fraction with a distinctive functional signature: it was enriched in lipid transport, lipid metabolism and other processes associated with membrane remodeling and organelle maintenance. The fraction also contained multiple proteins with homology to known membrane contact site factors, supporting the idea that it captures a structured interface rather than simple contamination from neighboring membranes.
Understanding how plants build and repair their unique membrane structures that support photosynthesis has important implications for the future of agriculture and renewable energy. In agriculture, photosynthetic membranes are a major target of stress — temperature extremes, drought and intense sunlight damage them, reducing yield. A better understanding of how plants assemble and repair structures supporting photosynthesis could help researchers identify new levers to improve resilience — a long-standing goal for crop improvement.
At the same time, photosynthetic membranes represent one of nature’s most effective solar-energy conversion systems. By clarifying how plants build robust photosynthetic membranes and maintain their architecture, the work also offers concepts and molecular parts lists that could inform the design of bio-inspired, biomimetic or bio-hybrid membranes for renewable energy applications, such as solar-to-fuel or solar-to-electricity technologies.
The study involved a cross-disciplinary effort utilizing the UNL Proteomics and Metabolomics Facility and the Morrison Microscopy Core Research Facility. Both LaBrant and Smith successfully defended their dissertations following the completion of the work.
"This paper is more than a scientific discovery," Roston said. "It is a testament to the resilience of young researchers who did incredible science while navigating immense adversity."
