Genome-wide Analysis of AP2/ERF Genes Identifies HpERF144 As a Regulator of Salt Tolerance and Phenylpropanoid Metabolism in Herpetospermum Pedunculosum.

Salt stress disrupts plant physiology and reprograms specialized metabolism. APETALA2/ethylene-responsive factor (AP2/ERF) transcription factors integrate stress and hormone signals, but their roles in linking salt tolerance with phenylpropanoid metabolism in non-model alpine plants remain poorly understood. Here, we performed a genome-wide survey of AP2/ERF genes and functionally characterized a salt-responsive ERF in Herpetospermum pedunculosum. We identified 147 HpAP2/ERF genes, whose promoters were enriched in hormone- and stress-responsive cis-elements. Salt treatment induced widespread expression changes of HpAP2/ERF genes in roots, with HpERF144 among the most rapidly and strongly up-regulated members. Virus-induced silencing and ZYMV-mediated overexpression in H. pedunculosum, together with heterologous overexpression in Nicotiana tabacum, showed that HpERF144 positively regulates salt tolerance by modulating oxidative stress-related physiological responses. Moreover, HpERF144 silencing reduced, whereas overexpression increased, total lignin and total lignan accumulation in roots under salt stress. DAP-seq and dual-luciferase assays further indicated that HpERF144 associates with and activates selected phenylpropanoid- and cell wall-related promoters, including 4CL- and CCR-like targets. These findings identify HpERF144 as a link between salt stress signaling and phenylpropanoid-associated metabolic regulation in a lignan-rich medicinal plant.