Cytosolic and Nucleosolic Calcium-Regulated Molecular Networks in Response to Long-Term Treatment with Abscisic Acid and Methyl Jasmonate in Arabidopsis thaliana .

Calcium acts as a universal secondary messenger that transfers developmental cues and stress signals for gene expression and adaptive growth. A prior study showed that abiotic stresses induce mutually independent cytosolic Ca 2+ ([Ca 2+ ] cyt ) and nucleosolic Ca 2+ ([Ca 2+ ] nuc ) increases in Arabidopsis thaliana root cells. However, gene expression networks deciphering [Ca 2+ ] cyt and [Ca 2+ ] nuc signalling pathways remain elusive. Here, using transgenic A. thaliana to selectively impair abscisic acid (ABA)- or methyl jasmonate (MeJA)-induced [Ca 2+ ] cyt and [Ca 2+ ] nuc increases, we identified [Ca 2+ ] cyt - and [Ca 2+ ] nuc -regulated ABA- or MeJA-responsive genes with a genome oligo-array. Gene co-expression network analysis revealed four Ca 2+ signal-decoding genes, CAM1 , CIPK8 , GAD1 , and CPN20 , as hub genes co-expressed with Ca 2+ -regulated hormone-responsive genes and hormone signalling genes. Luciferase complementation imaging assays showed interactions among CAM1, CIPK8, and GAD1; they also showed interactions with several proteins encoded by Ca 2+ -regulated hormone-responsive genes. Furthermore, CAM1 and CIPK8 were required for MeJA-induced stomatal closure; they were associated with ABA-inhibited seed germination. Quantitative reverse transcription polymerase chain reaction analysis showed the unique expression pattern of [Ca 2+ ]-regulated hormone-responsive genes in cam1 , cipk8 , and gad1 . This comprehensive understanding of distinct Ca 2+ and hormonal signalling will allow the application of approaches to uncover novel molecular foundations for responses to developmental and stress signals in plants.