The transcription factor PpTGA9 improves salt tolerance by interacting with PpATP1 in peach

Salt stress hinders plant growth and development by affecting the ability of plant roots to absorb water, in turn affecting photosynthetic capacity and other metabolic processes, and ultimately reducing yield and quality. Peach (Prunus persica) is a salt-sensitive species, but the mechanism of peach adaptation to salt stress is not clear. We previously screened 50 basic leucine zipper (bZIP) transcription factors (TFs) in peach and found that the PpbZIP30 TF has several conserved functions. The gene encoding this TF was found to be highly homologous (75.19 % similarity) to Arabidopsis thaliana AtTGA9, so it was named PpTGA9. Expression of PpTGA9 was induced by exogenous application of NaCl after different treatments of exogenous signals in peach seedlings, and overexpressed PpTGA9 in Arabidopsis plants enhanced resistance to salt stress. To clarify the role of PpbZIP30/PpTGA9 in salt resistance, PpATP1 was screened using a yeast two-hybrid cross and further validated by bimolecular fluorescence complementation (BiFC), pull down, and subcellular localization to show that the two interacted with each other in vitro and in the nucleus. To investigate the mechanism of interaction between PpTGA9 and PpATP1, we divided PpTGA9 into five segments and cotransformed them with PpATP1. We found that two glutamic acid (Gln)-rich structural domains (Q1 and Q2) were essential in the interaction between PpTGA9 and PpATP1, however, the N and bZIP regions did not have significant roles in this interaction. Further study revealed that PpATP1 protein interacts with itself to form homodimers and PpATP1 expression specificity analysis showed that it can rapidly respond to salt stress signals. These findings suggest that PpATP1 interacts with two Gln-rich structural domains (Q1 and Q2) of PpTGA9 and simultaneously forms homodimers. The two also form a PpTGA9/PpATP1 complex that has an active role in improving salt tolerance in peach.