PagbZIP60 negatively regulates poplar salt tolerance and carbon assimilation capacity by impairing ROS scavenging and photosynthesis

Members of the bZIP transcription factor family play critical roles in plant salt adaptation. In this study, transgenic poplar lines with overexpression (OE) and RNA interference (RNAi) mediated suppression of PagbZIP60 were generated to investigate its function. Under salt stress, OE lines exhibited reduced growth, whereas RNAi lines showed improved performance. Increased superoxide dismutase (SOD) activity, electrolyte leakage rate, Na+ levels, malondialdehyde and hydrogen peroxide (H2O2) contents, but decreased peroxidase (POD) and catalase (CAT) activities, and anthocyanin content were revealed in OE lines compared with those in wild-type poplar (WT). OE lines also presented reductions in leaf number and area, increased stomatal density and aperture, and diminished photosynthetic rate and water utilization efficiency (WUE), leading to a lower capacity for carbon assimilation. PagbZIP60 was found to decrease salt tolerance and carbon sequestration capacity by impairing reactive oxygen species (ROS) scavenging and photosynthesis through negatively regulating the expression of downstream genes (TT7, PMEI, MLP, SAUR, and bZIP61). This study provides a theoretical and experimental basis for poplar germplasm development with enhanced salt tolerance and improved carbon sequestration capacity.