Why Should Nodule Cysteine-Rich (NCR) Peptides Be Absent From Nodules of Some Groups of Legumes but Essential for Symbiotic N-Fixation in Others?

In nitrogen-fixing nodules of legumes such as pea (Pisum) and Medicago spp. the plant induces terminal differentiation in rhizobial endosymbionts by targeting nodule-specific cysteine-rich defensin-like peptides into bacteria. However, other soybean Lotus bacterial does not occur; these lack genes encoding equivalent controlling development. Here, we review effects some on rhizobia address question to how why may have evolved enslave become essential for nitrogen fixation clades but others.