Dephosphorylation of DPBF4 by PP2A promotes drought tolerance by regulating putrescine biosynthesis in tree peony

Drought is a major environmental factor restricting plant growth and productivity. Putrescine, a small polyamine, is known to enhance drought tolerance, but the role of key genes in the ornithine-derived pathway and their upstream regulators remains unclear. PoODC, encoding Paeonia ostii ornithine decarboxylase, was strongly upregulated under drought stress in P. ostii. Silencing PoODC reduced, while overexpression in tobacco increased putrescine accumulation and drought tolerance. Its transcription was repressed by PoDPBF4, a basic leucine zipper (bZIP) transcription factor binding to the abscisic acid response element (ABRE) element in the PoODC promoter, which negatively regulated putrescine accumulation and drought tolerance. PoDPBF4 physically interacted with PoPP2A, a drought-inducible protein phosphatase, which dephosphorylated PoDPBF4 at Ser92. This modification promoted PoDPBF4 degradation via the 26S proteasome pathway, reducing its protein stability and weakening its repression of PoODC. Also, silencing PoPP2A impaired drought tolerance, confirming its positive role in drought adaptation. These findings reveal a novel drought-responsive regulatory module in which PoPP2A dephosphorylates PoDPBF4, relieving repression of PoODC and enhancing putrescine biosynthesis. This study provides insights into the post-translational regulation of polyamine metabolism and identifies a potential genetic target for improving drought tolerance in perennial woody plants.