An RxLR Effector from Phytophthora infestans Prevents Re-localisation of Two Plant NAC Transcription Factors from the Endoplasmic Reticulum to the Nucleus

Abstract

The potato late blight pathogen Phytophthora infestans secretes an array of effector proteins thought to act in its hosts by disarming defences and promoting pathogen colonisation. However, little is known about the host targets of these effectors and how they are manipulated by the pathogen. This work describes the identification of two putative membrane-associated NAC transcription factors (TF) as the host targets of the RxLR effector PITG_03192 (Pi03192). The effector interacts with NAC Targeted by Phytophthora (NTP) 1 and NTP2 at the endoplasmic reticulum (ER) membrane, where these proteins are localised. Transcripts of NTP1 and NTP2 rapidly accumulate following treatment with culture filtrate (CF) from in vitro grown P. infestans, which acts as a mixture of Phytophthora PAMPs and elicitors, but significantly decrease during P. infestans infection, indicating that pathogen activity may prevent their up-regulation. Silencing of NTP1 or NTP2 in the model host plant Nicotiana benthamiana increases susceptibility to P. infestans, whereas silencing of Pi03192 in P. infestans reduces pathogenicity. Transient expression of Pi03192 in planta restores pathogenicity of the Pi03192-silenced line. Moreover, colonisation by the Pi03192-silenced line is significantly enhanced on N. benthamiana plants in which either NTP1 or NTP2 have been silenced. StNTP1 and StNTP2 proteins are released from the ER membrane following treatment with P. infestans CF and accumulate in the nucleus, after which they are rapidly turned over by the 26S proteasome. In contrast, treatment with the defined PAMP flg22 fails to up-regulate NTP1 and NTP2, or promote re-localisation of their protein products to the nucleus, indicating that these events follow perception of a component of CF that appears to be independent of the FLS2/flg22 pathway. Importantly, Pi03192 prevents CF-triggered re-localisation of StNTP1 and StNTP2 from the ER into the nucleus, revealing a novel effector mode-of-action to promote disease progression.

Integration of decoy domains derived from protein targets of pathogen effectors into plant immune receptors is widespread

“…Others have been demonstrated more recently to be involved in resistance, targeted by effectors or guarded by NLRs. NAC transcription factors have, for instance, only very recently been shown to be targeted by an effector of the potato light bight pathogen Pythophthora infestans and to play an important role in resistance to this pathogen (McLellan et al ., 2013). Corresponding NAC domains are integrated in different classes of NLRs from mono‐ and dicotyledonous plants (Table S1).…”

RXLR Effector AVR2 Up-Regulates a Brassinosteroid-Responsive bHLH Transcription Factor to Suppress Immunity

“…Consequently, the expression of BR-responsive genes was examined by qRT-PCR following treatment of wild-type potato cv Desiree with the bacterial flagellinderived PAMP flg22 and with P. infestans culture filtrate (CF), which can be regarded as a cocktail of P. infestans PAMPs (McLellan et al, 2013). As anticipated, in contrast to the PTI marker genes StWRKY7 and StACRE31 (McLellan et al, 2013;Nguyen et al, 2010), the BR marker genes were actively down-regulated following flg22 and CF treatments, as were additional genes, StDWF5 and StSTDH, associated with BR biosynthesis (Fig. 3, A and B).…”

“…infestans strain 88069 expressing tdTomato fluorescent protein (McLellan et al, 2013, Saunders et al, 2012 was grown on rye (Secale cereale) agar supplemented with 20 mg/mL geneticin (Thermo Fisher Scientific Ltd.) as a selective antibiotic. To harvest sporangia, 10-d-old plates were flooded with 5 mL sterile distilled water before scraping with a spreader onto a 70-mM cell strainer placed on a 50-mL falcon tube.…”

Evidence for intragenic recombination and selective sweep in an effector gene of Phytophthora infestans

“…However, this RXLR effector repertoire is likely expanding, contributing to the enormous size of the P. infestans genome (Haas et al., 2009; Raffaele & Kamoun, 2012). Biochemical and virulent functions of some RXLR effectors in P. infestans have been characterized recently (Bozkurt et al., 2011; King et al., 2014; McLellan et al., 2013; Wang et al., 2015; Yang, McLellan, et al., 2016). …”