Delineating plant responses to the 3',5'- and 2',3'-cAMP isomers

Much like in animals, both the 3',5'- and the 2,'3'-cAMP isomers are present in plants. The former is the enzymatic product of adenylate cyclases (ACs), the latter is an RNA degradation product. While there is increasing evidence that both isomers can elicit or modulate a broad range of physiological responses, the question of the specificity of responses to isomers has remained, at least partially, unresolved. To delineate isomer-specific responses in Arabidopsis thaliana, we applied a comparative proteomics approach. Our results demonstrate that exposure to 200 nM of either isomer can elicit similar changes in the proteome, supporting the existence of isomer-insensitive targets predominantly involved in RNA processing and metabolism. The 3',5'-specific proteins are enriched in categories such as protein transport and the establishment of protein localization, consistent with the recognised roles of ACs and 3',5'-cAMP in the cytosolic microenvironment. Several RNA-processing components are selectively regulated by the 2',3'-isomer, including proteins that play a critical role in spliceosome stability. At the physiological level, both isomers equally mitigate H₂O₂-induced net K⁺ efflux and Ca²⁺ influx in roots. However, when examining isomer specificity in well-characterized downstream targets, the Cyclic Nucleotide-Gated Channels 2 and 18 (CNGC2 and CNGC18), we noted strict selectivity for 3',5'-cAMP and this would imply that in vivo gating requires catalytically active of ACs.