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

Cyclic adenosine 3',5'-monophosphate (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 cAMP's regulatory roles in plants. This review systematically synthesizes: i) 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 (cNMPs). This review provides a conceptual framework for advancing plant cAMP research.