Combined toxicity and mechanism of cadmium and neonicotinoid insecticide to rice (Oryza sativa L.): reduced antioxidant defence mediated by flavonoid

Abstract

The combined pollution of heavy metals and organics in agricultural soils has become a global environmental issue, threatening ecosystem health and agricultural product safety. Our previous study evidenced that exposure to combined pollutants of cadmium and neonicotinoid insecticides (Cd-NIs) can influence Cd accumulation in rice tissues through chelation interactions. However, their combined toxicity to rice metabolism and the underlying molecular mechanisms remain poorly understood. The field experiments demonstrated that three representative NIs, including imidacloprid, thiamethoxam, and clothianidin, significantly reduced the Cd accumulation in rice (Oryza sativa L.) grains (> 3.50% of single Cd) while increased NIs accumulation in leaves (up to 136.08 mg/kg). The increased NIs accumulation inhibited flavonoid metabolism in rice, leading to a significant decrease in flavonoid content (4.01%–9.67%), consequently weakening the antioxidant capacity of rice (4.44%–35.32%). Proteomics and RT-qPCR confirmed that Cd-NIs downregulated the expression of glutathione S-transferase (GST), multidrug and toxin extrusion (MATE), and ATP-binding cassette (ABC) transporters involved in flavonoid transport, with the most pronounced downregulation in ABC transporters. Phylogenetic analysis revealed that the differentially expressed ABC transporters were mainly enriched in the ABCG, ABCI, and ABCB subfamilies, with ABCG containing the most members (6) and the greatest downregulation (> 40%). Molecular simulation suggested that Cd-NIs may compete with flavonoids for binding to ABCG34, potentially diminishing flavonoid accumulation, thereby blocking flavonoid-mediated antioxidant pathways. This study revealed ABCG transporter competition as a novel mechanistic target mediating Cd-NIs-induced disruption of flavonoid metabolism, providing a critical theoretical basis for environmental risk assessment of combined pollutants.

Graphical abstract

Keywords

Combined pollutants / Cd / Neonicotinoid insecticides / Flavonoid / Rice

Highlight

	● Cd-NIs exacerbated rice protein degradation in storage.
	● Cd-NIs blocked flavonoid-mediated antioxidant pathways.
	● Reduced flavonoids resulted from disrupted ABCG transport, not biosynthesis.
	● Cd-NIs and flavonoids compete for ABCG transporter binding sites.

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