Transcription and metabolomics analysis revealed that Cyclachaena xanthiifolia exerts allelopathy effects by regulating ABA biosynthesis

Cyclachaena xanthiifolia, as an invasive weed, seriously damages the ecology and reduces crop yields, so it needs to be controlled urgently. However, its allelopathy invasion mechanism has not yet been clarified, which constitutes a key obstacle in the current control of Cyclachaena xanthiifolia. In this study, metabolomic and transcriptome were used to analyse the allelopathy differences and physiological and biochemical effects of the extract fractions of Cyclachaena xanthiifolia, and to investigate the inhibitory effects of altered metabolic pathways on seed germination and seedling growth. GC-MS detection revealed substances with allelopathy potential in the four extracts of Cyclachaena xanthiifolia, among which treatment with n-butanol extract (NE) resulted in significant inhibition of mustard seed germination and water uptake, altered the balance of endogenous seed hormones ABA and GA, disrupted the antioxidant enzyme system and caused damage to the plasma membrane. Meanwhile, combined Transcriptome and broadly targeted metabolomic analyses revealed that the Carotenoid biosynthesis pathway, an indirect pathway for ABA synthesis, was significantly enriched and it was speculated that Cyclachaena xanthiifolia allelopathy effects increased ABA synthesis and inhibited seed germination mainly by affecting the regulation of the Carotenoid biosynthesis pathway. The qPCR results showed that eight key genes involved in the ABA biosynthesis and metabolism pathway had elevated expression levels. The findings substantiated the possibility that the allelopathy impact of NE on Brassica juncea seeds may be associated with the regulatory function of the ABA signalling pathway.