HIPP26L-NF-YC9-SRMT module regulates drought response in poplar

Drought severely limits the growth and development of perennial trees, which activate the abscisic acid (ABA) signaling pathway to cope with this condition. Despite its importance, the transcriptional regulatory mechanisms associated with ABA in poplars remain poorly understood. In this study, we identified HIPP26-like (HIPP26L), a heavy-metal-associated isoprenylated plant protein gene in poplar, which localizes to the cytomembrane, cytoplasm, and nucleus under normal conditions but accumulates in the nucleus in response to ABA and mannitol treatment. Overexpression of HIPP26L increased drought tolerance in poplar, whereas silencing the gene reduced drought resistance. Biochemical assays, double-transgenic analysis, and multi-omics approaches revealed that the HIPP26L-SRMT (salt-responsive MYB transcription factor [TF]) complex modulates the transcription of ABA- and drought-responsive genes. Moreover, nuclear factor Y subunit C9 (NF-YC9) is required for ABA- and mannitol-induced translocation of HIPP26L. These findings demonstrate that the HIPP26L-NF-YC9-SRMT module plays a critical role in ABA signaling and transcriptional regulation, offering new molecular insights into poplar's adaptive responses to drought.