Characterization of pathogen effectors and host endogenous peptide elicitors in the rice-magnaporthe oryzae interaction

The arms race is going on forever between plants and pathogens. Along their everlasting co-evolutionary path, plants have developed multilayered surveillance systems and defense lines, whereas pathogens have acquired vast capabilities of evading perception and breaking defense lines. In the interaction of Magnaporthe oryzae and rice, M. oryzae delivers a phalanx of effectors that could enter rice cells and subvert rice defenses, and rice cells deploy an array of surveillance receptors that could sense pathogen attack and initiate defense responses against M. oryzae . This study aims to shed some new light on the rice-M. oryzae interaction from both the pathogen and the host perspectives.;Rice, like Arabidopsis, harbors a family of defense-related genes encoding plant elicitor peptides (Peps). On one hand, M. oryzae induced the expression of the OsPep1-encoding precursor gene OsPROPEP1 via the ethylene (ET) and jasmonate (JA) pathways. On the other hand, synthetic OsPep1 elicited defense response in rice and thereby enhanced resistance against M. oryzae. Furthermore, rice transgenic lines overexpressing OsPROPEP1 showed constant defense gene expression and increased resistance to M. oryzae. All these findings indicate that Pep signaling as an amplifier of plant defense is an integral part of rice innate immunity against M. oryzae.;A family of one-finger zinc finger proteins was identified as pathogen effectors from the secretome of M. oryzae isolate 70-15. Rice leaf sheath live-cell imaging showed that zinc finger effectors were first accumulated in the biotrophic interfacial complex (BIC) and then translocated into rice cells during M. oryzae infection. The underlying mechanism for translocation was likely associated with two host-targeting motifs L/IPXP and L/IXAR, as demonstrated by the analysis of the localizations of BAXand GFP-tagged fusion proteins. Yeast two-hybrid screening of a blast-induced rice cDNA library revealed that the rice nucleus-localized protein HIRA was one of the interactors of this family of zinc finger effectors. The interaction between zinc finger effectors and HIRA was in the nucleus of the rice cell, as shown by bimolecular fluorescence complementation (BIFC). In addition, this interaction was also confirmed by a GST pull-down assay. Zinc finger effectors are in nature DNAbinding proteins, as unveiled by systematic evolution of ligands by exponential enrichment (SELEX). Moreover, zinc finger effectors inhibited BAX-induced programmed cell death (PCD) when transiently expressed in Nicotiana benthamiana. And rice transgenic lines overexpressing zinc finger effectors exhibited lowered defense gene expression and increased susceptibility to M. oryzae. A plausible model has been proposed to elucidate how zinc-finger effectors suppress rice immunity by recruiting HIRA for chromatin remodeling.