Abstract
<title>Abstract</title> <p>Cadmium (Cd) is a primary contaminant deteriorating agricultural soil quality in China. Pepper (Capsicum annuum L.) is a vegetable crop capable of accumulating high levels of Cd. Combined application of Cd-resistant plant growth-promoting rhizobacteria and biochar is a promising strategy to reduce Cd uptake. Here, we developed a biochar-immobilized Burkholderia pyrrocinia P10 inoculant (PC) and investigated its effects on Cd resistance mechanisms in pepper through integrated physiological and transcriptomic analyses. Under Cd stress (10–70 mg kg⁻¹), PC treatment consistently enhanced pepper growth and Cd tolerance throughout the growth period, as reflected by increased plant biomass and antioxidant enzyme activities and decreased malondialdehyde content. PC also significantly improved fruit yield and nutritional quality, while markedly reducing Cd levels in soil, plants, and fruits. These beneficial effects were superior to those of bacterial inoculation or biochar application alone. Root transcriptomic profiling at the full-fruiting stage revealed that PC triggered a multifaceted molecular response, including upregulation of lignin and membrane lipid synthesis-related genes and ABCG transporter genes to reinforce Cd sequestration in the cell wall and efflux, enhanced expression of auxin and brassinosteroid biosynthesis genes to promote plant growth, induction of base excision repair, spliceosome, and heat shock protein genes to alleviate Cd-induced molecular damage and maintain protein homeostasis, and activation of glutathione and ascorbate metabolism to scavenge reactive oxygen species. These findings elucidate the molecular basis of the superior efficacy of biochar-immobilized bacterial agent in enhancing Cd tolerance and reducing Cd accumulation in pepper.</p>