Integrated transcriptomic and physiological analysis reveals cadmium stress responses in kiwifruit rootstock Actinidia valvata via an optimized Agrobacterium rhizogenes-mediated hairy root transformation system

Kiwifruit ( Actinidia spp.) rootstocks play a crucial role in enhancing environmental adaptability, yet the lack of efficient genetic transformation systems has limited functional genomic studies on stress resistance mechanisms. Here, we established a rapid and cost-effective Agrobacterium rhizogenes -mediated hairy root transformation system for the widely used rootstock Actinidia valvata , bypassing the need for tissue culture. This system achieved transgenic root production within 3–5 weeks and demonstrated broad applicability in both Myrica rubra and Actinidia chinensis . Utilizing GFP as a viability marker, we observed that 25 µM Cd² + markedly impaired root cell physiology within 2 h, preceding visible phenotypic changes. Transcriptomic profiling of Cd² + -treated roots identified extensive differential gene expression, with enrichment in key pathways such as “Plant hormone signal transduction” and “MAPK signaling pathway.” Hormonal quantification further revealed significant alterations in IAA, IBA, ABA, JA, SA, and GA levels under Cd² + stress. Our integrative multi-omics approach, combining transcriptomics, hormone profiling, and physiological validation, provides a comprehensive framework for decoding genotype-to-phenotype relationships in woody horticultural species. The established transformation platform not only enables efficient functional gene verification in kiwifruit roots but also provides a reliable platform for dissecting root-specific cadmium stress responses in Ericales woody species.