Castor RcnsLTPC Confers Salt Tolerance in Yeast and Tobacco with Synergistic Enhancement by ZnO-NPs Priming

Soil salinity severely restricts castor (Ricinus communis L.) seed germination, yet the molecular basis of this trait remains poorly understood. Here, we identified and functionally characterized RcnsLTPC, a nonspecific lipid transfer protein gene strongly induced by salt stress, which encodes a plasma membrane-localized nsLTP1 protein. Promoter analyses indicated that RcnsLTPC is responsive to stress-, hormone-, and light-related signals, supporting its potential role in environmental adaptation. Heterologous expression in Saccharomyces cerevisiae and overexpression in Nicotiana tabacum consistently demonstrated that RcnsLTPC acts as a positive regulator of salt tolerance, improving germination, root development, biomass accumulation, antioxidant capacity, and ion homeostasis under NaCl stress. Notably, ZnO-NPs priming further amplified the protective effects of RcnsLTPC, suggesting a synergistic interaction between nanopriming and gene-mediated stress adaptation. Collectively, these findings establish RcnsLTPC as a key regulator of salt tolerance in castor and provide a conceptual basis for combining nanotechnology with genetic enhancement to improve crop performance on saline soils.