Calcium signaling in plant immunity

Matthew Jerome Marcec

doi:10.7273/000004414

Secondary messengers are molecules that plants release or produce after sensing any environmental stress and include calcium, Reactive oxygen Species (ROS) and Nitric Oxide (NO). Secondary messengers are quickly sequestered by the plant making the rise in concentration of these molecules and subsequent sequestering excellent signaling mechanisms. When plants recognize biotic stresses (i.e., pathogens), pathogen-associated molecular patterns are perceived by Pattern Recognition Receptors (PRR) that trigger large bursts of calcium that initiates a signal transduction pathway. The rise in cytosolic calcium activates calcium dependent proteins, other secondary messengers such as ROS which leads to alteration of gene expression and hormone signaling to defend against pathogen attacks. Our hypothesis called the “Lock and Key” predicts that the timing, maximum concentration amplitude, and sequestering of one response, calcium, regulates other secondary messenger signals for the correct plant defense to the perception of pathogens. Each secondary messenger response, such as calcium and ROS, must remain unperturbed providing a “key” to unlock the “lock” which is, in the case of plant immunity, resistance to pathogen infections. It also predicts that for each unique environmental response a unique calcium and other secondary messenger response exists. This hypothesis was tested by purposefully perturbing the “key”, amplitude, timing and recovery of calcium through pharmacological calcium channel blockers and observed their effects on ROS responses in response to bacteria flagellin and using ROS scavengers and mutants with no ROS responses effects on calcium responses. These examinations suggest that calcium is the initial secondary messenger response in plant bacterial perception but ROS regulates calcium amplitude and timing. The “lock” is then examined through the discovery of a unique mutant Silent Knight 1 (silk1) that is unable to induce a calcium response to any stress perception. Through phenotype analysis and transcriptomics, silk1 reveals hormone signaling and defense mechanisms are completely absent without a calcium response. These data give us a clearer view of the fundamental mechanisms of immune signaling. This understanding, will aid to produce disease resistant crops and may be able to aid in rapid pathogen detection as well.

Calcium signaling in plant immunity

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