Functional Identification of Novel Cell Death-inducing Effector Proteins from Magnaporthe oryzae

Abstract

Background Secreted effector proteins play critical roles in plant-fungal interactions. The Magnaporthe oryzae genome encodes a large number of secreted proteins. However, the function of majority of M. oryzae secreted proteins remain to be characterized. We previously identified 851 in planta-expressed M. oryzae genes encoding putative secreted proteins, and characterized five M. oryzae cell death–inducing proteins MoCDIP1 to MoCDIP5. In the present study, we expand our work on identification of novel MoCDIP proteins. Results We performed transient expression assay of 98 more in planta-expressed M. oryzae putative secreted protein genes, and identified eight novel proteins, MoCDIP6 to MoCDIP13, that induced plant cell death. Yeast secretion assay and truncation expression analysis revealed that the signal peptides that led the secretion of proteins to the extracellular space, were required for cell death inducing activity of the novel MoCDIPs except for MoCDIP8. Exogenous treatment of rice seedlings with recombinant MoCDIP6 or MoCDIP7 resulted in enhanced resistance to blast fungus, indicating that the two MoCDIPs trigger cell death and elicit defense responses in rice. Conclusions The newly identified MoCDIP6 to MoCDIP13, together with previously identified MoCDIP1 to MoCDIP5, provide valuable targets for further dissection of the molecular mechanisms underlying the rice-blast fungus interaction. Electronic supplementary material The online version of this article (10.1186/s12284-019-0312-z) contains supplementary material, which is available to authorized users.

Apoplastic Cell Death-Inducing Proteins of Filamentous Plant Pathogens: Roles in Plant-Pathogen Interactions

“…The M. oryzae genome harbors 19 proteins with the CFEM domain (Kou et al, 2017). Two CFEM-containing proteins Wang et al, 2003;Zhang et al, 2004; Billard et al, 1988;Huet and Pernollet, 1989 P. colocasiae † 15-kDa glycoprotein Elicitin ND Induces cell death and SAR in taro leaf Mishra et al, 2009 P. cryptogea † Cryptogein Elicitin ND Induces cell death, SAR and defense of tobacco against P. nicotianae Ricci et al, 1989;Galiana et al, 1997;Mikes et al, 1997;Leborgne-Castel et al, 2008;Coursol et al, 2015;Kulik et al, 2015;Ptáčková et al, 2015;Starý et al, Huet et al, 1994;Kamoun et al, 1997Kamoun et al, , 1998Kanzaki et al, 2003;Huitema et al, 2005;Du et al, 2015 (Continued) Frontiers in Genetics | www.frontiersin.org Mateos et al, 1997;Khatib et al, 2004 P. parasitica † PpNLP/NLP Pp NLP ND Induces cell death; carries a nlp20 pattern recognized by RLP23 which associates with SOBIR1 and BAK1 complex to trigger immune responses Fellbrich et al, 2002;Qutob et al, 2006;Ottmann et al, 2009;Böhm et al, Kamoun et al, 1993;Mouton-Perronnet et al, 1995;Capasso et al, 1999 PPTG_02039, PPTG_14297, PPTG_09966 MoCDIP2 and MoCDIP11 have been identified to induce cell in the non-host N. benthamiana and host rice cells Guo et al, 2019). MoCDIP2 contains a CFEM domain at the N-terminus, and a GPI-anchored site at the C-terminus, whereas MoCDIP11 contains only a CFEM domain at the N-terminus.…”

“…Targeted deletion of the genes encoding these proteins did not impair the virulence of pathogens ( Table 2). One possibility why these apoplastic CDIPs were dispensable for virulence could be due to the functional redundancy with other apoplastic effectors (Yoshino et al, 2012;Guo et al, 2019).…”

“…The M. oryzae genome harbors 19 proteins with the CFEM domain ( Kou et al, 2017 ). Two CFEM-containing proteins MoCDIP2 and MoCDIP11 have been identified to induce cell in the non-host N. benthamiana and host rice cells ( Chen S. et al, 2013 ; Guo et al, 2019 ). MoCDIP2 contains a CFEM domain at the N-terminus, and a GPI-anchored site at the C-terminus, whereas MoCDIP11 contains only a CFEM domain at the N-terminus.…”

“…MoCDIP2 contains a CFEM domain at the N-terminus, and a GPI-anchored site at the C-terminus, whereas MoCDIP11 contains only a CFEM domain at the N-terminus. Transient expression assays in rice protoplasts or N. benthamiana leaves revealed that the signal peptides that led the secretion of proteins, were required for cell death inducing activity of MoCDIP2 and MoCDIP11, indicating that both two effectors function in the apoplast ( Chen S. et al, 2013 ; Guo et al, 2019 ).…”

“…Studies from diverse filamentous pathogens have shown that many oomycete or fungal effector proteins possess the ability to induce cell death in plants (Gijzen and Nürnberger, 2006), including avirulence (AVR) proteins which trigger hypersensitive response (HR) upon recognition by cognate resistance (R) proteins (Kamoun, 2006;Ellis et al, 2009), nuclear-localized Crinkling and Necrosis proteins (CRNs) and nucleo-cytoplasmic RxLR proteins with capacity to induce plant cell death (Torto et al, 2003;Amaro et al, 2017), and extracellular cell death-inducing proteins (CDIPs) that function in the plant apoplast (Guo et al, 2019). The role of AVR proteins, CRN and RxLR effectors involved in the interactions of plants with filamentous pathogens have been reviewed extensively (Ellis et al, 2009;Giraldo and Valent, 2013;Amaro et al, 2017;Lo Presti and Kahmann, 2017).…”