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Chloroplasts—the "light power plants" of plant cells—are increasingly the focus of synthetic biology. These organelles house the photosynthetic apparatus and host several metabolic pathways that are of great interest for engineering new traits. Gene insertion into chloroplasts is precise and carries a lower risk of transgene escape.

Despite this potential, chloroplast biotechnology remains in its infancy because standardized, scalable methods for rapid testing of diverse genetic parts have been missing. A research team from the Max Planck Institute for Terrestrial Microbiology in Marburg has now presented a micro‑algal platform that allows automated, fast, and large‑scale testing of chloroplast genetic modifications.

The study is in the journal Nature Plants.

Automated high throughput at the chloroplast level

In microbiology, optimization through repeated, rapid cycles is standard practice. This platform opens plant chloroplasts to high‑throughput applications for the first time. The researchers employed the micro‑alga Chlamydomonas reinhardtii. René Inckemann, who carried out the work in Tobias Erb's group, explains, "We succeeded in characterizing more than 140 gene‑regulatory DNA parts in the alga, covering a wide range of expression strengths. This is essential for fine‑tuning genetic circuits."

All components are compatible with common biotechnological standards, so the DNA library can be readily used in other laboratories. For example, plant scientist Felix Willmund at the neighboring Center for Synthetic Microbiology has validated the technology and is already using it to develop robust chloroplasts. The researchers have established a workflow that can generate and assay thousands of so‑called transplastomic algal lines—organisms with altered chloroplast genomes—in parallel.

Consequently, multiple genes can now be stably combined in chloroplasts and their activities predictably balanced. This is a crucial step toward identifying which modifications have real potential. By transferring only the most promising variants into more complex plant models, the development pipeline from concept to field trial is accelerated, and resources are conserved.

From chloroplasts to crop plant

As a proof of concept, the team introduced a synthetic metabolic pathway into the alga's chloroplasts. The engineered pathway enabled the alga to take up CO₂ more efficiently under stress conditions, resulting in almost double the biomass production—a "turbo‑alga." This demonstrates how targeted interventions in chloroplast metabolism can boost productivity.

The new library provides a solid foundation for a wide range of research, such as improving plant resilience to heat, drought, or excessive light, enhancing nutrient profiles, or increasing yield. It can also serve as a platform for novel carbon‑fixation routes or the production of high‑value natural compounds (e.g., pharmaceutical precursors).

"The platform we present here will play a central role in the research consortium Robust Chloroplast, as well as the Excellence Cluster Microbes‑4‑Climate, where, together with Marburg University, we aim to develop new biologically based solutions to climate change," says Erb. "Key technologies like this are essential for focused research at a pace that matches the urgency of the climate challenge."