Over-expression of a grafting-responsive gene from hickory increases abiotic stress tolerance in Arabidopsis

A grafting response gene CcPIP1;2 was cloned from hickory plant, further functional characterization of the gene for water transport activity and abiotic stress tolerances were carried out through heterologous expression in Xenopus and Arabidopsis. Plasma membrane intrinsic proteins (PIPs) are multifunctional channel proteins belonging to the membrane intrinsic protein (MIP) family. In this study, a grafting-responsive gene from hickory (CcPIP1;2) was cloned and functionally characterized. Application of non-selective water inhibitors (HgCl₂ and phloretin) led to the death of grafted hickory plants at 30 days after grafting (DAG). Furthermore, the transcript accumulation of the selected CcPIP1;2 gene was gradually decreased from 0 to 14 DAG in the grafted samples under inhibitor treatment conditions. Transient expression analysis of the GFP-CcPIP1;2 fusion protein showed that CcPIP1;2 was located at plasma membrane. Heterologous expression of CcPIP1;2 protein in the Xenopus oocyte system helped the access of water into the cells. Over-expression of CcPIP1;2 in Arabidopsis improved the percentage of seed germination when the seeds were grown in H₂O₂-, ABA-, and mannitol-containing media, but had no effect when grown in the salt containing media. CcPIP1;2 transgenic plants grew better under drought conditions. The expression of various ABA-related stress marker genes as well as cell wall expansin marker genes was significantly higher in CcPIP1;2 over-expression Arabidopsis lines than in the wild type (WT).