3',5'-cAMP in plants: an integrated view of homeostasis, effectors, and physiological functions

3',5'-cAMP is a ubiquitous signaling molecule across kingdoms. Although cAMP was identified early in plants, its significance remained underappreciated. Recent discoveries revealed that nuclear auxin receptors (TIR1/AFBs) possess intrinsic adenylyl cyclase (AC) activity. Crucially, the cAMP produced can participate in transcriptional regulation semi-independently of canonical receptor function, transforming our understanding of the regulatory roles of cAMP in plants. This review systematically synthesizes: (i) the molecular basis of cAMP homeostasis; (ii) identification and functions of downstream effectors; and (iii) the role of cAMP in plant development, stress responses, and hormone interactions. We further highlight critical knowledge gaps, including the evolutionary rationale for moonlighting ACs, precise signal transduction mechanisms, and functions of non-canonical cyclic nucleotides. This review provides a conceptual framework for advancing plant cAMP research.