MST50 is involved in multiple MAP kinase signaling pathways in Magnaporthe oryzae

Abstract

Appressorium formation plays a critical role in Magnaporthe oryzae. Mst50 is an adapter protein of the Mst11-Mst7-Pmk1 cascade that is essential for appressorium formation. To further characterize its functions, affinity purification was used to identify Mst50-interacting proteins (MIPs) in this study. Two of the MIPs are Mst11 and Mst7 that are known to interact with Mst50 for Pmk1 activation. Surprisingly, two other MIPs are Mck1 and Mkk2 that are the upstream kinases of the Mps1 pathway. Domain deletion analysis showed that the sterile alpha-motif of Mst50 but not the Ras-association domain was important for its interaction with Mck1 and responses to cell wall and oxidative stresses. The mst50 mutant was reduced in Mps1 activation under stress conditions. MIP11 encodes a RACK1 protein that also interacted with Mck1. Deletion of MIP11 resulted in defects in cell wall integrity, Mps1 phosphorylation and plant infection. Furthermore, Mst50 interacted with histidine kinase Hik1, and the mst50 mutant was reduced in Osm1 phosphorylation. These results indicated that Mst50 is involved in all three MAPK pathways in M. oryzae although its functions differ in each pathway. Several MIPs are conserved hypothetical proteins and may be involved in responses to various signals and crosstalk among signaling pathways.

Regulatory network of genes associated with stimuli sensing, signal transduction and physiological transformation of appressorium inMagnaporthe oryzae

“…Recent interaction analysis of Mst50 protein revealed that the sterile alpha domain exclusively interacts with an upstream protein kinase Mck1 associated with the MPS1 pathway under cell wall and cell membrane-directed oxidative stress (Li et al 2017a). More so, the Mst50-Histidine kinase (Hik1) interaction promotes the phosphorylation of Osm1 under similar oxidative stress conditions (Li et al 2017a). This confirms the existence of pathway crosstalk among the components of MAPK signalling cascade during fungal development and stress response.…”

Magnaporthe oryzae SMO1encodes a Ras GTPase-activating protein required for spore morphology, appressorium function and rice blast disease

“…Ras-association domain was not important for response to oxidative stress (Li et al 2017). M.oryzae Ras2 is therefore essential for cellular viability, and a key mediator between both the Pmk1 MAPK and cAMP signalling cascades (Qi et al 2015;Zhou et al 2014).…”

“…Affinity purification was used to identify a series of Mst50-interacting proteins (MIPs) as well as upstream kinases of the Mps1 pathway, and also the histidine kinase Hik1 (Li et al 2017). These interactions suggest a role for Mst50 in three different signalling pathways.…”

Expression of HopAI interferes with MAP kinase signalling in Magnaporthe oryzae

“…The M. oryzae strains Guy11, 70-15, Ku80 (Villalba et al, 2008), KV103 (Khang et al, 2010) and HopAI and HopI1 transformants generated in this study (Table 1) were routinely cultured on OTA plates or CM agar plates at 258C as described (Xu and Hamer, 1996;Zhao et al, 2005;Park et al, 2006). For assaying sensitivity to hyperosmotic stress, colony growth was assayed on CM plates with 1 M sorbitol (Dixon et al, 1999;Li et al, 2017). Vegetative hyphae harvested from 2-day-old liquid CM cultures were used for the preparation of protoplasts and isolation of genomic DNA, RNA and proteins as described (Nishimura et al, 2003;Zhao et al, 2005;Park et al, 2006).…”