Cell communication lockdown: How plants close plasmodesmata in MAMP immune response

How do plants protect themselves from microbial invaders? One response is the closure of plasmodesmata to stop the spread of microbial effector proteins that help pathogens evade the immune response, protecting neighboring uninfected cells. While the phenomenon of plasmodesmata closure in response of microbe-associated molecular patterns (MAMPs) is well-documented, the underlying signaling and mechanisms need further investigation. Li et al. have determined that in Arabidopsis this process is mediated by Synaptotagmin 1 (Syt1), a transmembrane protein that connects to both the endoplasmic reticulum and the plasma membrane. Upon exposure to flagellin peptide, a MAMP, the levels of plasma membrane phospholipid PI(4,5)P₂ increase. This increase is detected by Syt1, causing it to a form a complex with annexin 4 and initiating calcium signaling, increasing callose deposition within the plasmodesmata. Because the aperture of the plasmodesmata pore is controlled by callose deposition, this MAMP response decreases the pore size and prevents the MAMPs from spreading to nearby cells. This study helps elucidate the underlying mechanisms of plant innate immune responses and could inform future work on local regulation specific to the plasmodesmata and on the heterogeneity of intracellular calcium signaling. (Summary by Elise Krespan) Cell Reports 10.1016/j.celrep.2025.115672