PoWRKY17 promotes drought tolerance in Paeonia ostii by modulating lignin accumulation

Drought is a detrimental environmental factor limiting sustainable agricultural development worldwide. Paeonia ostii, an oil-producing woody crop, while its endogenous mystery underlying this tolerance remains largely elusive to scholars. Herein, we reported that PoWRKY17, a WRKY transcription factor from IId subgroup, positively functioned in face of drought stress in P. ostii. PoWRKY17 expressed in significantly higher abundance when drought was applied. Silencing of PoWRKY17 substantially reduced drought resistance, with decreased leaf water content and protective enzyme activities, increased relative electric conductivity (REC), malondialdehyde (MDA) content, and reactive oxygen species (ROS) accumulation. On the contrary, overexpression of PoWRKY17 endowed plants with higher drought tolerance with opposite drought-relevant physiological indices. Notably, both PoWRKY17-silenced P. ostii and PoWRKY17-overexpressing plants showed changes in lignin content under drought stress. Based on this clue, we quantified the expression of lignin biosynthetic caffeoyl-CoA O-methyl-transferase (CCoAOMT) gene in PoWRKY17-silenced P. ostii and found that PoCCoAOMT expression was significantly repressed. Next, protein-gene interaction assays showed that PoWRKY17 interacted with PoC-CoAOMT promoter by targeting the W-box element and activated PoCCoAOMT expression under drought stress, which has been early verified to act as a positive participant in P. ostii drought tolerance. This study broadens our understanding of WRKY-mediated lignin biosynthesis regulation in response to drought stress in plants.