Abstract
Arsenic (As) pollution poses serious threats to soil ecosystems and plant growth. Arbuscular mycorrhizal fungi (AMF) have been confirmed to enhance As tolerance in host plants, making mycorrhizal-assisted phytoremediation a promising and practical strategy for remediating As-contaminated soils. Populus tomentosa Carr. (Chinese white poplar) is a native fast-growing woody species suitable for phytoremediation in East Asia. However, comprehensive transcriptomic analyses focusing on the molecular mechanisms by which AMF improve As tolerance in this species remain limited. In this study, a pot-based experiment was performed on P. tomentosa seedlings using a two-factor experimental design with four treatments: non-inoculated seedlings under non-As stress (CK0), non-inoculated P. tomentosa seedlings under As stress (CK100), Rhizophagus irregularis-inoculated seedlings under non-As stress (Ri0), and R. irregularis-inoculated seedlings under As stress (Ri100). Plant-growth measurements, root morphological assessment, and Illumina RNA-seq transcriptomic analysis were applied to characterize seedling responses. Our results revealed that As stress significantly inhibited AMF colonization rate, suppressed seedling growth, and disrupted root morphological architecture. Nevertheless, R. irregularis inoculation substantially alleviated As-induced growth repression, increasing plant height, shoot and root dry biomass, as well as key root morphological parameters under As exposure. Transcriptome profiling identified large sets of differentially expressed genes (DEGs) triggered by AMF symbiosis and As stress. Functional enrichment indicated that signal transduction of jasmonate (JA) biosynthesis and metabolism represented the dominant response pathways. AMF symbiosis dynamically rewrote the transcriptional patterns of core JA biosynthesis and metabolism genes in P. tomentosa seedlings under As stress. Weighted gene co-expression network analysis further highlighted hub transcription factors, including GATA5 and WRKY57, which were tightly co-expressed with JA-synthesis-related genes and potentially bridged mycorrhizal symbiotic signals and downstream defense responses. These findings illustrated that AMF enhanced As tolerance in P. tomentosa seedlings by reprogramming JA-associated transcriptional regulatory networks. This study provided novel mechanistic insights for understanding AMF-wood plant-As interactions, and offered theoretical support for developing AMF-assisted poplar phytoremediation technology in As-contaminated soils.