Biogenesis and downstream effects of 3',5' and 2',3' cAMP isomers in plants Cyclic adenosine monophosphate (cAMP) is a fundamental second messenger involved in diverse signaling pathways across both animals and plants. While the role of 3′,5′-cAMP has been extensively characterized, the biological significance of its structural isomer, 2′,3′-cAMP, remains largely unexplored, particularly in plants. Here, we show that 2′,3′-cAMP and 3′,5′-cAMP represent parallel signaling systems in Arabidopsis thaliana, with different enzymatic origins and largely distinct downstream effects. In vitro enzymatic assays show that plant adenylate cyclases (ACs), including AFB5 and HpAC1, produce specifically 3′,5′-cAMP from ATP, whereas the TIR domain of protein L7 also catalyzes the formation of 2′,3′-cAMP from RNA. Comprehensive multiomics analyses reveal that two isomers elicit distinct yet partially overlapping metabolic, proteomic, and transcriptional response: 2′,3′-cAMP activates broad, stress-adaptive gene expression reprogramming, while 3′,5′-cAMP fine-tunes responses related to nutrient status and cellular homeostasis. Our findings establish the existence of dual cAMP signaling systems in plants, each with specialized functions and provide insights into the complex regulatory networks governing plant physiology. 12 19 AAAS application/pdf 1