On salt stress, PLETHORA signaling maintains root meristems

Salt stress is one of the unfavorable environmental factors to affect plants. Salinity represses root growth, resulting in reduced biomass of agricultural plants. Little is known about how plants maintain root growth to counteract salt stress. The AP2-domain transcription factors PLETHORA1/2 (PLT1/2) act as master regulators in root meristem maintenance in Arabidopsis. In this study, we report that the salt overly sensitive (SOS) pathway component SOS2 regulates PLT1/2 at the post-transcriptional level. Salt-activated SOS2 interacts and phosphorylates PLT1/2 through their conserved C-terminal motifs to stabilize PLT1/2, critical for root apical meristem maintenance under salt stress. The phospho-mimetic version of PLT1/2 restored meristem and primary root length reduction of sos2-2 and plt1-4 plt2-2 mutants on salt treatment. Moreover, SOS2-mediated PLT1/2 phosphorylation improves root growth recovery after salt stress alleviation. We identify a SOS2-PLT1/2 core protein module that is required for protecting primary root growth and meristem maintenance from salt stress. [Display omitted] •Root meristem maintenance is critical for plant salt stress tolerance•SOS2 phosphorylates and stabilizes PLT1/2 proteins under salt stress•Phosphorylated PLT modulates cell division to maintain root growth under salt stress•PLT1/2 promotes recovery growth from salt alleviation Hao et al. report that salt signaling in Arabidopsis activates SOS2 to stabilize PLT1/2 proteins via phosphorylation, and phosphorylated PLT1/2 maintains meristem activity under both salt stress and recovery of root growth after stress alleviation.