Cationic Calcium Channels Activated by Cyclic Nucleotides in Plants: A Systematic Review Using the PRISMA Method

The primary objective of this review is to analyze primary research published over the past six years concerning cyclic nucleotide-gated calcium channels (CNGC) in plants. The aim is to structure this information to identify and organize existing knowledge regarding their tertiary and quaternary structures, as well as the activation mechanisms of CNGC. Studies on plant CNGC published between January 2018 and May 2025 were included, while research focused on animals, bacteria, or ions other than calcium was excluded. Articles were retrieved from Scopus, Web of Science, and PubMed databases through searches conducted between June 2024 and May 2025, as well as from additional personal sources. A total of 111 articles met the inclusion criteria. These were categorized into seven groups: phylogenetic analysis and classification of plant CNGC monomers, gene expression regulation, structural composition of monomers and tetramers, channel activation, selectivity mechanisms, cellular localization, and the plant species and structural types in which they are found. The findings revealed that CNGC can be activated by individual mechanisms or by the interplay of multiple pathways. However, uncertainties remain regarding certain activation processes. A lack of experimental studies specifically aimed at elucidating their crystallographic structure was evident, which limits a comprehensive understanding of these channels and represents one of the main constraints of the available evidence. This limitation highlights the need for further research to fully elucidate both the activation mechanisms and structural characteristics of CNGC. Despite these constraints, the findings indicate that CNGC play a pivotal role in plant physiology.