Plants under stress may divert resources from growth and development to defence, leading to reduced yields for crops. These shifts in allocation are controlled by poorly known and complex signalling pathways involving phosphorylation and are often initiated by an influx of intracellular calcium, the primary currency of plant information processing. Particularly of interest is the initiation of immune response. Fast response to infection enables an effective immune response. But how are plants able to decode calcium signals to initiate an appropriate immune response? Amazing work published last spring by a team of @QueensUBio researchers including NSERC-PDF Dr. Melissa Bredow, NSERC-PGS Katherine Dunning, and Honours thesis students Alexandra Johnson Dingee, Danalyn Holmes, Alysha Thomson, Danielle Ciren, and Cailun Tanney, together with Dr. Jacqueline Monaghan and collaborators Dr. Kyle Bender, Dr. Marco Trujillo, and Dr. Steven Huber, opens the door to new possibilities on the subject.
Calcium-dependent protein kinases (CPKs) are proteins that act as signalling hubs within cells, with individual CPKs tuned to specific calcium concentration sensitivities. CPK28 regulates immune homeostasis and reproductive stage transitions in multiple plant species. The authors found that phosphorylation on a single CPK28 residue, Ser318, initiates a conformational change allowing for CPK28 activity at low calcium concentrations, enabling a quick immune response when required. This phosphorylation and conformational change is required for immune signalling, thus preventing an unintended and energy costly immune response in the absence of pathogens. Intriguingly, Ser318 phosphorylation was not required for CPK28’s additional function in developmental signalling indicating phosphorylation-dependent pathway specificity.
CPK28’s phosphorylation-dependent dual functionality underscores the complexity of plant signalling networks. Further investigation revealed the conserved function of Ser318 phosphorylation in one of the world’s most agriculturally important crops, rice. Furthermore, the authors remarkably found that ablation of Ser318 resulted in enhanced pathogen resistance without reducing growth – a highly sought agricultural trait. Overall, the work outlined in their paper may lead to the development of disease resistant and high yielding crops, contributing to the safeguarding of global food security. Read the article in PNAS.
