S-acylated and nucleus-localized SALT OVERLY SENSITIVE3/CALCINEURIN B-LIKE4 stabilizes GIGANTEA to regulate Arabidopsis flowering time under salt stress

Abstract

The precise timing of flowering in adverse environments is critical for plants to secure reproductive success. We report a mechanism in Arabidopsis (Arabidopsis thaliana) controlling the time of flowering by which the S-acylation-dependent nuclear import of the protein SALT OVERLY SENSITIVE3/CALCINEURIN B-LIKE4 (SOS3/CBL4), a Ca2+-signaling intermediary in the plant response to salinity, results in the selective stabilization of the flowering time regulator GIGANTEA inside the nucleus under salt stress, while degradation of GIGANTEA in the cytosol releases the protein kinase SOS2 to achieve salt tolerance. S-acylation of SOS3 was critical for its nuclear localization and the promotion of flowering, but partly dispensable for salt tolerance. SOS3 interacted with the photoperiodic flowering components GIGANTEA and FLAVIN-BINDING, KELCH REPEAT, F-BOX1 and participated in the transcriptional complex that regulates CONSTANS to sustain the transcription of CO and FLOWERING LOCUS T under salinity. Thus, the SOS3 protein acts as a Ca2+- and S-acylation-dependent versatile regulator that fine-tunes flowering time in a saline environment through the shared spatial separation and selective stabilization of GIGANTEA, thereby connecting two signaling networks to co-regulate the stress response and the time of flowering.

Salinity-Induced Cytosolic Alkaline Shifts in Arabidopsis Roots Require the SOS Pathway

“…In this regard, the finding that salt-induced pHcyt changes were largely dampened in the sos3-1 mutant strongly suggests that the pHcyt-shift results from the sensory and response activity of the SOS pathway. Equal NaCl treatments result in a more severe stress in the sos3-1 mutant root than in the wild-type [ 14 , 78 ]. Consequently, a greater cytoplasmic alkalinization should be expected if that were produced only by Na + -induced ionic disturbance.…”

Designing salt stress‐resilient crops: Current progress and future challenges

“…Stress‐induced early flowering is an emergency response when plants cannot cope with adverse environmental conditions (Takeno, 2016). However, non‐lethal saline stress probably delays Arabidopsis flowering by repressing the expression of CONSTANS ( CO ) and FLOWERING LOCUS T ( FT ) (Kim et al, 2013, 2007b; Ryu et al, 2014), allowing plants to gather sufficient metabolic resources to ensure flowering and seed filling (van Zelm et al, 2020; Park et al, 2023). Under salt stress, free cytoplasmic GI is degraded, thereby releasing SOS2 to promote the salt stress response.…”

“…Under salt stress, free cytoplasmic GI is degraded, thereby releasing SOS2 to promote the salt stress response. However, nuclear GI remains stable in the presence of S ‐acylated SOS3 together with flavin‐binding, kelch repeat and F‐box 1 (FKF1), sustaining the transcription of CO and FT and eventually leading to flowering (Kim et al, 2013; Park et al, 2023). Additionally, under salt stress, early flowering 3 (ELF3), a core component of the circadian clock, negatively regulates GI stability, resulting in delayed flowering.…”

Flavin‐containing monooxygenases FMOGS‐OXs integrate flowering transition and salt tolerance in Arabidopsis thaliana

“…This complex enhances salt tolerance by phosphorylating SOS1, the primary plant Na + /H + ‐antiporter involved in salinity adaptation. The released GI is degraded, thereby delaying flowering (Park et al, 2013, Park et al, 2023). In addition, the floral repressor BFT is induced by high salinity and delays flowering by competing with FT for binding to the FD, a bZIP transcription factor, which, together with FT, can activate floral meristem identity genes, such as AP1 (Ryu et al, 2014).…”