Gibberellin-dependent brassinosteroid signaling modulates plant growth by optimizing nitrogen levels during salinity stress

Low nitrogen (LN) and high salt stress are major constraints for plant growth and development. Under LN stress, plants typically show root elongation to increase nitrogen foraging from the rhizosphere, whereas high salt levels cause inhibition of root growth to avoid salinity stress-induced toxicity. To date, mechanisms and strategies of root adaptations in plants under combined LN and high salt stress remain poorly defined. Here, we provide evidence that Arabidopsis plants under LN stress show increased brassinosteroid (BR) signaling activity, which in turn suppresses salt stress-responsive pathways but improves nitrogen foraging. BR signaling, through its transcriptional regulators, activates and represses nitrogen and salt-responsive genes, respectively. In contrast, salinity stress represses gibberellin (GA) signaling and leads to the accumulation of DELLA proteins. High levels of DELLAs inhibit BZR1-dependent nitrogen-responsive growth to facilitate plant adaptation under high salt stress condition. Our data suggest that GA-promoted root elongation under combined LN and high salt stress is associated with BZR1-DELLA and Salt Overly Sensitive 3 (SOS3) protein stoichiometry. Specifically, DELLAs interact with SOS3, and high levels of SOS3 in turn facilitate tolerance to salt stress by adjusting DELLA-dependent BZR1 function and nitrogen homeostasis. Taken together, our findings highlight the adaptive responses plants exert to mitigate variable nitrogen and high salt stress conditions and appear essential for balancing growth and stress response.