What Does It Take to Evolve A Nitrogen-Fixing Endosymbiosis?

Area of Science:

• Plant biology
• Microbiology
• Evolutionary biology

Background:

• Plant-associated nitrogen-fixing bacteria offer symbiotic opportunities.
• Nitrogen-fixing endosymbioses have evolved multiple times in angiosperms, suggesting a non-complex evolutionary path.
• Understanding the entry mechanisms of these symbionts is crucial for agricultural and ecological applications.

Purpose of the Study:

• To propose that microbe-induced cell divisions are a prerequisite for diazotrophic prokaryotes to enter plant cells.
• To explain how rhizobia and Frankia bacteria achieve this through adaptation of the common symbiosis signalling pathway.
• To discuss evolutionary adaptations enabling nitrogen-fixing root nodule endosymbiosis.

Main Methods:

• Literature review and synthesis of existing research on plant-microbe symbiosis.
• Analysis of the common symbiosis signalling pathway and its role in endosymbiosis.
• Comparative discussion of evolutionary adaptations in nitrogen-fixing root nodule symbiosis.

Main Results:

• Microbe-induced cell divisions are argued as a prerequisite for diazotrophic prokaryote entry into plant cells.
• Adaptation of the common symbiosis signalling pathway induces cell divisions for rhizobia and Frankia entry.
• The common symbiosis pathway's conservation suggests a conserved mechanism for establishing endosymbiosis.

Conclusions:

• Plant cell division, triggered by microbes, is a key step for establishing nitrogen-fixing endosymbiosis.
• The common symbiosis signalling pathway plays a conserved role in facilitating entry of beneficial microbes.
• Evolutionary pathways towards nitrogen-fixing root nodule symbiosis involve specific adaptations of this conserved pathway.