The Regulation of Invasive Cell-to-Cell Movement during Tissue Colonisation by the Rice Blast Fungus
W. SAKULKOO (1), G. Littlejohn (1), M. Oses-Ruiz (1), N. Talbot (1) (1) Biosciences, University of Exeter, United Kingdom

The rice blast fungus Magnaporthe oryzae and plant viruses exploit plasmodesmata (PD) for their movement into neighbouring host cells and for spreading infectious materials, such as effectors, ahead of the infection front. Although molecular mechanisms used by viruses for spreading through PD have been extensively studied, little is known regarding the means by which pathogenic fungi use PD to move from cell-to-cell, or even if this is the actual route of movement. Here, we applied chemical genetics and live-cell imaging to investigate the regulation of intercellular spread of M. oryzae invasive hyphae (IH) and plant responses inside successively invaded rice cells. Using aniline blue staining, callose deposition at PD was clearly observed in compatible interactions, suggesting that IH may be able to overcome PD-associated defence. We generated an analogue-sensitive pmk1AS mutant containing a point mutation in the gatekeeper residue, causing the kinase to be selectively susceptible to an inhibitor, 1NA-PP1. Inhibition of Pmk1 kinase activity after host surface penetration resulted in restricted fungal growth in the first invaded cells and the activation of host defense responses. Morphogenesis of IH constriction crossing plant cell walls appeared to be reminiscent of appressorial penetration, requiring Pmk1-dependent septin assembly, but not Cdc42 GTPase or ROS siganling. Therefore, the Pmk1 MAPK is important for cell-to-cell movement by M. oryzae IH and for suppression of host immunity. Analysis of Pmk1-dependent gene expression is underway.

Abstract Number: P7-205
Session Type: Poster