PubMed · 2026-06-08
A chemical called auxin controls how plants grow — bending toward light, growing roots, dropping leaves — and scientists have now traced how this molecule went from being a common compound found across all living things to becoming a master switch inside plants.
Auxin is not unique to plants — it is found across all domains of life (bacteria, fungi, animals), but plants uniquely evolved an intracellular system to use it as a developmental signal.
A small number of pre-existing proteins were co-opted and coordinated to assemble the auxin perception and response system, meaning the system arose from repurposing rather than invention from scratch.
The capacity to synthesize auxin internally converted what was once an environmental/ecological signal into a tightly controlled endogenous (inside-the-plant) hormone.