CRT1 is a nuclear-translocated MORC endonuclease that participates in multiple levels of plant immunity

Abstract

Arabidopsis thaliana CRT1 (compromised for recognition of Turnip Crinkle Virus) was previously shown to be required for effector-triggered immunity. Sequence analyses previously revealed that CRT1 contains the ATPase and S5 domains characteristic of Microchidia (MORC) proteins; these proteins are associated with DNA modification and repair. Here we show that CRT1 and its closest homologue, CRH1, are also required for pathogen-associated molecular pattern (PAMP)-triggered immunity, basal resistance, nonhost resistance and systemic acquired resistance. Consistent with its role in PAMP-triggered immunity, CRT1 interacted with the PAMP recognition receptor FLS2. Subcellular fractionation and transmission electron microscopy detected a subpopulation of CRT1 in the nucleus, whose levels increased following PAMP treatment or infection with an avirulent pathogen. These results, combined with the demonstration that CRT1 binds DNA, exhibits endonuclease activity, and affects tolerance to the DNA-damaging agent mitomycin C, argue that this prototypic eukaryotic member of the MORC superfamily has important nuclear functions during immune response activation.

Transcriptional gene silencing by Arabidopsis microrchidia homologues involves the formation of heteromers

“…AtMORC6 has been identified in four independent forward genetic screens (24)(25)(26)31) as required for gene silencing and maintenance of heterochromatin integrity. AtMORC1 is also required for gene silencing (26), although it was originally described as a master regulator in plant disease resistance signaling (30)(31)(32)(33).…”

The Compromised Recognition of Turnip Crinkle Virus1 Subfamily of Microrchidia ATPases Regulates Disease Resistance in Barley to Biotrophic and Necrotrophic Pathogens

“…Genome analysis of Arabidopsis revealed that MORC1 (formerly named CRT1 in Kang et al, 2008Kang et al, , 2010Kang et al, , 2012 has two close (.70% sequence similarity on amino acid [aa] level) and four distant (,50% aa similarity) homologs. A double knockout mutant, morc1-2 morc2-1, lacking MORC1 and its closest homolog MORC2 also displayed compromised ETI to avirulent Pseudomonas syringae, suppressed basal resistance, systemic acquired resistance, and/or PTI to TCV and virulent P. syringae and compromised nonhost resistance to Phytophthora infestans (Kang et al, 2012). Arabidopsis MORC1 physically interacts with at least eleven R proteins belonging to three different structural classes (Martin et al, 2003), including HRT, the R protein involved in recognition of TCV.…”

RNA silencing components mediate resistance signaling against turnip crinkle virus

“…16,17 Most Arabidopsis ecotypes lack the R gene HRT and are therefore susceptible to TCV. 12,[18][19][20][21][22][23][24][25][26][27][28] Only Di-17, a resistant line isolated from the Dijon (Di) ecotype contains HRT, and is resistant to TCV. Following TCV infection, Di-17 plants develop HR, induce defense gene expression such as pathogenesis related (PR)-1, and accumulate salicylic acid (SA).…”

“…12,18,[21][22][23][24] In contrast, plants lacking the dominant gene HRT do not develop HR after TCV infection, and allow systemic spread of the virus that is associated with a crinkled leaf and drooping bolt appearance. 12,[18][19][20][21][22][23][24][25][26][27][28] Resistance to TCV is dependent upon the SA pathway 18,19 as well as blue-light photoreceptors. [21][22][23] Among various components of the SA pathway that regulate HRTmediated resistance to TCV, enhanced disease susceptibility (EDS) 1, which interacts with HRT, is required for potentiation of CP-triggered HR.…”

“…24 HRT also interacts with several other proteins including CRT1 (Compromised for Recognition of TCV). [25][26][27] Unlike EDS1, CRT1 is not associated with HRT activation, rather is required for HRT stability. 28 The activation of HRT does not require silencing suppressor function of CP.…”