Integrated physiological and transcriptomic analyses reveal that HmPIF1 overexpression confers lead stress tolerance in Hydrangea.

key messageTransient overexpression assays and RNA sequencing (RNA-seq) showed that the transcription factor HmPIF1 enhances lead (Pb) tolerance in Hydrangea by improving antioxidant capacity and altering transporter protein expression. Lead (Pb) soil contamination has caused serious ecological and environmental issues. Hydrangea represents a promising candidate species for phytoremediation, whereas research on its Pb-tolerant genes remains relatively limited. This study aimed to explore the Pb tolerance function of HmPIF1 at the physiological and transcriptional levels. Results showed that Pb stress significantly upregulated the expression of HmPIF1. Subcellular localization and transcriptional autoactivation assays demonstrated that HmPIF1 is a nuclear-localized transcription factor without transcriptional autoactivation activity. Transient overexpression experiments confirmed that eight substances, including glutathione reductase, superoxide dismutase, and total protein, were key physiological factors for HmPIF1-enhanced Pb tolerance in Hydrangea leaves, while transcriptomic analysis identified "photosynthesis" and "glutathione metabolism" as likely the core regulatory pathways. Furthermore, HmPIF1 overexpression promoted Pb accumulation in leaves, accompanied by differential expression of ion transporter proteins. Taken together, HmPIF1 positively regulates plant Pb tolerance and enhances Pb uptake in leaves, which may be achieved through multiple regulatory pathways including photosynthesis, antioxidation and ion transporter-mediated processes. These findings provide a theoretical basis for subsequent related research.