FIGURE 4.

ILKs integrate Ca²⁺- and receptor-mediated signaling in the plant immune response. (A) Nodes represent proteins and edges represent experimentally verified interactions (solid line). The arrangement of nodes is based on the classical a tiered organization of signal transduction cascades; postulated plant integrin-like receptors and plasma membrane receptors are placed in the upper tier, followed by transporters, ILKs, Ca²⁺-regulated proteins, and phospho-site interacting 14-3-3 proteins. The network was constructed using the information in the Biogrid database and visualized using Cytoscape 3.2.1. (B) Proposed model of ILKs’ roles in signal transduction; the arrows show the known (continuous lines) or postulated (broken lines) direction of signal transduction. Plant or pathogen-derived signals reach the plant cell and activate several signal-processing pathways. (1) Plant Integrin-like receptors sense shifts in the composition and mechanical tension of the cell wall and plasma membrane; ILKs are possible transducers of signals from these receptors, through modulation of transporter activity. (2) Membrane receptor-like kinases (RLKs) bind specific ligands to recruit and activate cytosolic proteins (RLCKs); downstream MAP kinase module transmits the signal to effector proteins located in diverse cellular compartments. (3) Rapid calcium fluxes triggered by stimuli, increase Ca²⁺ concentration in the cytosol and activate Ca²⁺ sensors. ILKs bridge ion- and receptor-mediated signaling pathways. ILKs participate in pathways activated by PAMP and DAMP receptors, and their activity may be modulated by Ca²⁺ sensors (such as calmodulins). Concerted activation of these pathways results in immediate physiological changes, including the depolarization of the PM, turgor pressure, and induction of the transcriptome program. The plant response to pathogen attack encompasses both the activation of the immune system (defense program), as well as appropriate modifications in the plant growth. Continuous lines represent events for which experimental evidence exists, while broken lines depict proposed pathways.