Stress-associated proteins in plants: Structural diversity, evolutionary diversification, and mechanistic roles in abiotic stress tolerance

Stress-associated proteins (SAPs) are a class of plant zinc-finger proteins that are primarily characterized by the canonical A20-AN1 domain architecture. In contrast, proteins containing only AN1 domains, repeated AN1 domains, or additional expanded domains are more appropriately classified as SAP-like variants. Across land plants, SAP-related genes have undergone lineage-specific expansion, whereas the canonical A20-AN1 configuration remains the predominant structural form.Available functional evidence indicates that perturbation of specific SAPs under drought and osmotic stress, salinity, temperature stress, oxidative stress, and heavy-metal stress is repeatedly associated with three major biological output layers: ubiquitin-proteasome-related proteostasis, hormone-associated signaling pathways, particularly abscisic acid (ABA)-related responses, and redox/ion homeostasis. These recurring outputs should not be interpreted as evidence for a single conserved mechanistic model across the entire SAP family. Current evidence instead supports a context-dependent framework in which SAP function is shaped by paralog identity, tissue context, developmental stage, interaction partners, and stress type. SAPs may function as either positive or negative regulators, making broad family-level generalizations unreliable.Direct biochemical evidence is currently available for only a limited subset of SAP members. For most SAP proteins, native substrates, in planta interaction networks, and stress-dependent post-translational regulatory mechanisms remain unresolved. In this review, we synthesize SAP biology within an evidence-weighted framework that integrates structural classification, evolutionary diversification, phenotype-level function, and mechanistic links to proteostasis, hormone signaling, and redox/ion homeostasis. We further propose that systematic substrate identification, post-translational modification (PTM)-resolved proteomics, proximity-labeling-based interactomics, and causal genetic analyses under multi-environment stress conditions will be essential for the development of paralog- and context-resolved SAP models. Such advances are expected to provide a stronger basis for identifying SAP targets with translational potential in breeding and genome-editing strategies aimed at improving climate resilience.