Screening and expression analysis of the NRAMP gene family in Kiwifruit under cadmium stress reveals the potential role of AcNRAMP7

The NRAMP gene family mediates the transport of divalent metal ions in plants and is critically involved in cadmium (Cd) accumulation and tolerance. In this study, 12 AcNRAMP genes were identified in the kiwifruit genome and phylogenetically classified into four distinct clades. Chromosomal localization analysis revealed that 11 AcNRAMP genes were unevenly distributed across seven chromosomes. Promoter cis-element analysis revealed that AcNRAMP genes contain motifs primarily associated with related to hormone responsiveness and environmental stress. Expression profiling demonstrated significant differential expression of three genes in the roots and two genes in the leaves. Based on RT-PCR analysis, we further propose a mechanistic model for AcNRAMP-mediated response to Cd stress: under high Cd conditions, transcript levels of AcNRAMP7 and AcNRAMP10 were downregulated in roots, whereas AcNRAMP6 was upregulated in leaves. This coordinated expression may limit Cd translocation into root tissues, mitigate cellular damage, and enhance plant tolerance, which was associated with reduced root growth. Our results provide valuable insights into the molecular mechanisms underlying Cd stress response in kiwifruit and establish a foundation for future functional studies on the AcNRAMP gene regulation.