dr.ir. R (Rene) Geurts

NODULATION

René Geurts is dedicated to investigating the evolution of the nitrogen-fixing nodule rhizobium symbiosis, a trait widely recognized in legumes such as beans, soybeans, and lentils. In specialized root organs, rhizobia bacteria are hosted within cells as transient, organelle-like structures that fix nitrogen. These nodule bacteria convert atmospheric nitrogen into ammonia, a process powered by the host plant's carbohydrates. This trait not only allows legumes to thrive in soils that are deficient in nitrogen fertilizers but also enables them to maintain a protein-rich lifestyle, underscoring its significance in the realm of plant biology and agricultural science.

EVOLUTION

Research by various teams worldwide on legume crops and model species has identified hundreds of genes critical for nodule formation and functioning. It was also discovered that nodule formation is based on a much older mutualistic symbiosis—the interaction between plants and soil mycorrhizal fungi. To gain insight into the critical genetic adaptations that enable the evolution of the nodulation traits, the Geurts team established the nodulating non-legume Parasponia (from the Cannabis family) as a complementary experimental research system. Like legumes, the tropical tree species Parasponia can form nitrogen-fixing root nodules with rhizobia, despite having diverged from legumes around 100 million years ago. However, comparative genomics combined with CRISPR-Cas9-based reverse genetics in Parasponia revealed that the nitrogen-fixing nodulation trait has a single evolutionary origin. Furthermore, two genes—out of hundreds—were found to have undergone critical adaptations in the early evolution of the nodulation trait: a LysM-type receptor -named NFR5/NFP- required for the recognition of rhizobium-secreted signal molecules and the transcription factor NIN that acts as a master regulator of nodulation.

ENGINEERING

For over a hundred years, there has been speculation about the possibility of exploring the nitrogen-fixing root nodulation trait in crops other than legumes. The Geurts team has taken a step in this direction by adopting cassava as an experimental system to investigate whether rhizobium-induced nodulation can be engineered. Cassava, which thrives on marginal soils, relies on the ecosystem services of its root microbiome to obtain essential nutrients. Notably, mycorrhizal fungi play a crucial role in this process. This not only underscores the importance of cassava as a staple crop for hundreds of millions of smallholder farmers but also the plant species presents a promising opportunity for the engineering of mutualistic symbioses with nutrient-scavenging microbes.