RtNAC081 promotes salt tolerance and plant growth linked to brassinosteroid/abscisic acid signaling in Reaumuria trigyna.

Both abscisic acid (ABA) and brassinosteroids (BRs) antagonistically regulate growth and abiotic stress responses; however, the mechanisms by which these phytohormones synergistically influence growth and salt tolerance in halophytes have not yet been fully elucidated. In this study, an NAC gene from Reaumuria trigyna, RtNAC081, was found to enhance growth and salt tolerance in transgenic poplar via the ABA and BR pathways, and its suppression led to decreased callus growth and greater sensitivity to salt stress. Under normal conditions, RtNAC081 increased wood formation and shoot growth, whereas saline conditions induced RtNAC081 transcription. RtNAC081 activated RtNCED1.1 expression and promoted BR synthesis through the RtNAC081-RtBZR1 axis, and also activated BR signaling. Synergistic interactions between ABA and BR were rapidly disrupted under extreme stress. Higher ABA levels inhibited RtBZR1 expression, causing growth retardation that improved salt tolerance through physical interaction with RtNAC081. RtNAC081 activated RtAPX5 to modulate reactive oxygen species balance and photosynthetic efficiency, which ultimately improved salt tolerance. Together, our results demonstrate the intricate interplay between the BR and ABA signaling pathways in modulating the balance between plant growth and salt stress adaptation, highlighting the pivotal role of RtNAC081 in this regulatory network.