No abstract

In plants, a variety of stimuli trigger long-range calcium signals that travel rapidly along the vasculature to distal tissues via poorly understood mechanisms. Here, we use quantitative imaging and analysis to demonstrate that traveling calcium waves are mediated by diffusion and bulk flow of amino acid chemical messengers. We propose that wounding triggers release of amino acids that diffuse locally through the apoplast, activating the calcium-permeable channel GLUTAMATE RECEPTOR-LIKE 3.3 as they pass. Over long distances through the vasculature, the wound-triggered dynamics of a fluorescent tracer show that calcium waves are likely driven by bulk flow of a channel-activating chemical. We observed that multiple stimuli trigger calcium waves with similar dynamics, but calcium waves alone cannot initiate all systemic defense responses, suggesting that mobile chemical messengers are a core component of complex systemic signaling in plants.

No abstract

The plant immune system relies on the perception of molecules that signal the presence of a microbe threat. This triggers signal transduction that mediates a range of cellular responses via a collection of molecular machinery including receptors, small molecules, and enzymes. One response to pathogen perception is the restriction of cell-to-cell communication by plasmodesmal closure. We previously found that while chitin and flg22 trigger specialized immune signaling cascades in the plasmodesmal plasma membrane, both execute plasmodesmal closure via callose synthesis at the plasmodesmata. This indicates the signaling pathways ultimately converge at or upstream of callose synthesis. To establish the hierarchy of signaling at plasmodesmata and characterize points of convergence in microbe elicitor-triggered signaling, we profiled the dependence of plasmodesmal responses triggered by different elicitors on a range of plasmodesmal signaling machinery. We identified that, like chitin, flg22 signals via RBOHD to induce plasmodesmal closure. Further, we found that PDLP1, PDLP5 and CALS1 are common to microbe- and SA-triggered responses, identifying PDLPs as a candidate signaling nexus. To understand how PDLPs relay a signal to CALS1, we screened for PDLP5 interactors and found NHL3, which is also required for chitin-, flg22- and SA-triggered plasmodesmal responses and PDLP-mediated activation of callose synthesis. We conclude that a PDLP-NHL3 complex acts as an integrating node of plasmodesmal signaling cascades, transmitting multiple immune signals to activate CALS1 and plasmodesmata closure.