Investigating function of effector candidates in the interaction between Piriformospora indica and plants

Abstract

Piriformospora indica, a mutualistic root-colonizing basidiomycete, promotes biomass formation and plant health in a wide range of host plants. The fungus colonizes plant roots without causing any visible disease symptoms and thus represents a genetically accessible model to study the molecular basis of processes associated with fungal accommodation and the establishment of root symbioses.Structural and functional analysis of PIIN29 showed that it fullfils the definition of a fungal effector candidate, and possesses E3 ubiquitin ligase activity in vitro. The transcription level of PIIN29 is induced during Arabidopsis root colonized by P. indica as shown by real time PCR in different conditions. Heterologous expression of mature version of PIIN29 (without its native signal peptide) driven by CaMV35S promoter in Arabidopsis (PIIN29OE) results in higher colonization rates of P. indica and pathogen of B. cinerea compared with wild type Col-0. Moreover, PIIN29OE inhibits the production of ROS in response to both flg22 and chitin, decreased transcription of defense genes such as AtWRKY22, and abolished callose deposition elicited by flg22. To investigate the cytology of P. indica during symbiosis, the result of TEM represented that P. indica differentiates biotrophic hyphal bodies penetrated into barley root cytoplasm.Based on in silico analysis, 17 SSPs containing the conserved C-terminal motif RSIDELD are involved in interested effector candidates. Using agroinfiltration, we identify the subcellular localization of PIIN_06837 as plasma membrane. In addition, we reveal that four effectors, PIIN_05098/05851/09689/07519, induce cell death in N. tabacum leaves through T3SS media infiltration.The results of this work can be used as base for the characterization of further P. indica secreted proteins.