Novel Plant Growth Regulator Guvermectin Promotes Root Development by Modulating Auxin Signaling.

Guvermectin (GV), a novel plant growth regulator from rhizosphere microorganism, has been officially registered as a new biopesticide in China. It plays important roles in regulating plant root growth and development, while the underlying mechanisms remain largely unknown. In this study, we demonstrate that GV induces auxin accumulation in root tips and regulates root architecture through an auxin signaling-dependent pathway. Mechanistic investigation revealed that GV activates the indole-3-pyruvic acid biosynthetic pathway of auxin biosynthesis by upregulating the expression of family genes, thereby increasing endogenous indole-3-acetic acid levels in the root tip. Concurrently, GV modulates polar auxin transport by downregulating PIN2 protein abundance, thereby reducing basipetal auxin efflux and promoting localized auxin retention. Collectively, these findings elucidate a dual regulatory mechanism whereby GV coordinates auxin biosynthesis and transport to optimize root growth. Our work bridges the gap between its agronomic application and molecular mechanism, offering a theoretical foundation for its integration into precision agriculture.