PubMed · 2026-05-28
During droughts, beneficial soil bacteria called Streptomyces colonize plant roots not because plants call for help, but because drought stress suppresses the plant's immune system and iron-uptake machinery, creating an opening. While some Streptomyces strains do boost plant growth, this benefit is determined by competition among Streptomyces themselves — not by the plant's distress signal.
Drought enrichment of Streptomyces in roots requires the plant to suppress both its immune defenses and iron-uptake pathways — two independent mechanisms that each gate bacterial entry.
Drought-induced suppression of iron uptake is ancient, conserved across monocots and eudicots that diverged approximately 160 million years ago, suggesting it is a deep, hardwired response rather than a recent adaptation.
Plant growth benefits from Streptomyces are real but decoupled from root enrichment levels — functional outcomes are shaped by antagonistic competition among Streptomyces strains, not by how many bacteria colonize the root.