Diallyl disulfide promotes root elongation through auxin biosynthesis involving the CsBBM2-CsYUC6 transcriptional regulation in cucumber

Intercropping cucumber with garlic is an effective agronomic practice to mitigate soil sickness in continuous cropping systems. The garlic root exudate diallyl disulfide (DADS) promotes cucumber root elongation, though the molecular mechanism remains unknown. Here, we show that 1 mM DADS enhances cucumber primary root elongation by stimulating cell expansion. Hormone quantification combined with exogenous auxin application and pharmacological inhibition demonstrated that DADS-induced root elongation is auxin-dependent. Transcriptomic and weighted gene co-expression network analyses identified a key auxin biosynthetic gene, CsYUC6 , which is up-regulated by DADS, and its upstream transcriptional regulator, CsBBM2 . Electrophoretic mobility shift and dual-luciferase assays confirmed that CsBBM2 acts as a transcriptional repressor of CsYUC6 by directly binding to its promoter. Our results suggest that DADS promotes root growth by downregulating CsBBM2 , a transcriptional repressor of the auxin biosynthesis gene CsYUC6 , thereby increasing auxin levels in cucumber roots. The result provides mechanistic insight into cucumber-garlic intercropping and supports the potential use of DADS as a sustainable agrochemical.