Calcium (Ca2+) is known as a secondary messenger in plant growth, development, and stress perception. Plants generate stress-specific Ca2+ signals (Ca2+ signatures) to translate extracellular signals into cellular responses. Extracellular Adenosine 5’-triphosphate (eATP) is a crucial signalling molecule in plants but poorly understood. Upon abiotic and biotic stresses, ATP is released into the extracellular matrix, where it is referred as eATP, to regulate plant growth and development, salt tolerance, immunity, and the Damage-Associated Molecular Patterns (DAMP) response. Two plasma membrane (PM) eATP receptors DOES NOT RESPOND TO NUCLEOTIDES1 (DORN1/P2K1) and DORN2/P2K2 have been identified in Arabidopsis thaliana in the past decade. The perception of eATP leads to downstream changes of secondary messengers, including cytosolic free calcium ([Ca2+]cyt) increase, reactive oxygen species (ROS) and nitric oxide (NO) production. Subsequently, [Ca2+]cyt regulates production of defence-related hormones (such as jasmonic acid, JA), plant elicitor peptides (PEPs), and indolic glucosinolates (IG). However, the PM calcium channels underpinning eATP-induced [Ca2+]cyt increase remain poorly studied. Here, my PhD project revealed the role of Cyclic Nucleotide-Gated Channels (CNGC) 2, 6 and 19 as putative calcium channels in eATP signalling.

By employing (apo)aequorin as a Ca2+ reporter, CNGC2 was found to be involved in Arabidopsis root’s [Ca2+]cyt responses to both eATP and eADP. Transcriptional analysis showed that the expression of CNGC6 and CNGC19 was upregulated by eATP in a DORN1/P2K1- and CNGC2-dependent manner. The involvement of CNGC6 and CNGC19 in the root’s eATP-induced [Ca2+]cyt increase was then discovered and (for CNGC19) investigated further using GCaMP3 as a [Ca2+]cyt reporter, as a function of phosphate nutrition. Notably, both CNGC2 and CNGC19 were suggested to modulate the root’s transcription of components of eATP-activated defence pathways. As a result, loss-of-function mutants of CNGC19 exhibited increased susceptibility to infection by the parasitic cyst nematode, Heterodera schachtii.