A phosphorylation switch balances growth and stress response in cotton

Salt stress can severely affect cotton (Gossypium hirsutum) productivity, especially during early growth. Cao et al. identified a molecular switch in cotton that fine-tunes responses to salt stress and the hormone abscisic acid (ABA), based on the reversible phosphorylation of the ABA signaling phosphatase GhABI1. The authors found that GhRAF36, a Raf-like protein kinase, phosphorylates GhABI1 at two cotton-specific residues, suppressing its activity and activating ABA signaling. This promotes salt-stress responses. In contrast, GhTOPP4aD, a Type One Protein Phosphatase, counteracts this by dephosphorylating both GhRAF36 and GhABI1, thereby repressing ABA signaling. Under salt stress, GhTOPP4aD protein levels decrease, allowing GhRAF36 to dominate and drive ABA activation. Functional experiments, including gene silencing and overexpression in cotton, show that GhTOPP4aD negatively regulates salt tolerance and ABA sensitivity, while GhRAF36 enhances them. Epistasis analyses further confirm that GhRAF36 and GhABI1 operate downstream of GhTOPP4aD in this pathway. This GhTOPP4aD–GhRAF36–GhABI1 module serves as a reversible phosphorylation circuit that integrates stress signals with hormone responses. It provides new insights into how cotton balances growth and stress resilience and offers targets for improving stress tolerance in crop breeding. (Summary by Muhammad Aamir Khan @MAKNature1998)  Plant Biotechnol. J. 10.1111/pbi.70166