<p>List of primers used in RT‑qPCR.</p>

Synteny analysis identified whole-genome or segmental duplication as the primary driving force for the expansion of this family, with all of the duplicated gene pairs having undergone strong purifying selection. Based on interspecies synteny analysis, <i>F. suspensa</i> and <i>F. viridissima</i> exhibited the highest degree of NHX gene family homology. Expression analysis revealed that the <i>F. suspensa</i> NHX gene family exhibits distinct and tissue-specific responses to drought, salt, and exogenous ABA stress.

Among the NHX members, FsNHX3 and FsNHX6 exhibited the most pronounced and sustained transcriptional upregulation across the three stress treatments, suggesting their potential involvement in stress response. These findings provide valuable insights for the further exploration of the functions and molecular mechanisms of the NHX gene family in <i>Forsythia</i> under salt and drought stress, offering valuable candidate genetic resources for breeding <i>Forsythia</i> varieties with enhanced tolerance to salinity and dehydration.</p></div>