The DUF641 family protein PtCOST3 manipulates shoot growth and salt stress response in poplar

DUF641 family proteins have important functions in regulating plant growth and responses to environmental stress. To understand how they regulate the switch between the normal growth and salt response in woody tree, we investigated the biological role of PtCOST3, a DUF641 family protein encoding gene, in transgenic polar. Phenotypic analyses indicated that PtCOST3 expression promoted shoot growth with increased plant height, leaf area and stem diameter, and salt sensitivity with more Na+ and less K+ accumulation in transgenic plants. The content of reactive oxygen species, malondialdehyde and proline was significantly increased, whereas the activity of antioxidant enzymes was significantly decreased, in PtCOST3 transgenic plants. Further sub-cellular location and protein interaction studies demonstrated that PtCOST3 co-localized and directly interacted with the autophagy protein ATG8e in the autophagosomes, and PtCOST3 expression reduced the autophagy activity, as indicated by the decreased autophagosome number, in transgenic plants under both normal and stress conditions. Our results demonstrate that PtCOST3 positively regulates the normal growth but negatively modulates the salt tolerance by precisely manipulating the autophagy switch in plants.