Secretory Circuits of Symbiosis in Medicago truncatula
New Commentary · MPMI 39:325–326
Tiwari, R. & Singh, J. 2026
How does a legume know to switch on the right machinery only inside its root nodules? In our latest Commentary — written with Ruby Tiwari — we unpack a neat piece of molecular wiring behind nitrogen-fixing symbiosis.
Think of a root nodule as a tiny factory where the plant houses nitrogen-fixing bacteria. To keep that factory running, the plant must deliver special proteins to exactly the right place, using a delivery crew called the signal peptidase complex (SPC). The study we highlight shows that the plant flips this crew "on" only in nodules, using a short DNA tag called SOLE. Remove that switch — or knock out the key SPC18 gene with CRISPR — and the nodules turn white and stop fixing nitrogen. Strikingly, the very same tag is read by NIN, the master switch of nodulation — tying the plant's protein-delivery system directly into its symbiotic program.
A tiny DNA tag (SOLE) decides where the cell's protein-delivery machinery switches on — and without it, nitrogen fixation fails.
