Suppression of a specific branch of mitogen-activated protein kinase (MAPK) signaling by bacterial AvrRpt2-like cysteine proteases: Mechanistic elucidation and application for MAPK studies.

• Applicant: Dr. Justin Lee
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems ; Plant Physiology
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 327033184

Plants recognize conserved structures of pathogens during the infection process and activate defence reactions. One key signalling event is the activation of mitogen-activated protein kinases (MAPKs/MPKs). We recently reported a new function of a well-studied bacterial pathogenesis effector called AvrRpt2, where it blocked the pathogen-induced activation of specific MAPKs (i.e. inhibition of MPK4/MPK11 but not MPK3/MPK6). This novel function of blocking MPK4/MPK11 activation is conserved in homologs from a number of plant-associated and soil bacteria (that includes agronomically important phytopathogens like Ralstonia solanacearum, Erwinia amylovora and Acidovorax citrulli). Additionally, we also have preliminary findings that multiple transcription factors known to be important for stress regulation are destabilized or their expression is blocked by AvrRpt2. We propose that these may be novel virulence functions of AvrRpt2, which seem to be independent of previously known AvrRpt2 targets. In this proposal, we aim to elucidate the molecular mechanism for these processes. Since the cysteine protease activity of AvrRpt2 is essential for these functions, the AvrRpt2 cleaved substrates must be responsible for the observed effects on the MAPKs and transcription factors. Hence, we will use a proteomics-based method (called TAILs) to detect the novo N-termini of cleaved proteins in plants expressing AvrRpt2 and hence identify new in vivo AvrRpt2 substrates. Furthermore, we want to exploit the specific AvrRpt2-mediated interference with MPK4/MPK11 activation to bypass the constraints imposed by the extreme dwarf phenotype and lethality of the mpk4mpk11 double mutant and study signalling unique to these two MAPKs in healthy plants. The knowledge gleaned from the current study will advance the understanding of bacterial infection strategies and allow us to improve pest management schemes against pathogens.

• DFG Programme: Research Grants