Bacterial effector targeting of a plant iron sensor facilitates iron acquisition and pathogen colonization

Abstract

Acquisition of nutrients from different species is necessary for pathogen colonization. Iron is an essential mineral nutrient for nearly all organisms, but little is known about how pathogens manipulate plant hosts to acquire iron. Here we report that AvrRps4, an effector protein delivered by Pseudomonas syringae bacteria to plants, interacts with and targets the plant iron sensor protein BRUTUS (BTS) to facilitate iron uptake and pathogen proliferation in Arabidopsis thaliana. Infection of rps4 and eds1 by P. syringae pv. tomato (Pst) DC3000 expressing AvrRps4 resulted in iron accumulation, especially in the plant apoplast. AvrRps4 alleviates BTS-mediated degradation of bHLH115 and ILR3(IAA-Leucine resistant 3), two iron regulatory proteins. In addition, BTS is important for accumulating immune proteins EDS1 at both the transcriptional and protein levels upon Pst (avrRps4) infections. Our findings suggest that AvrRps4 targets BTS to facilitate iron accumulation and BTS contributes to RPS4/EDS1-mediated immune responses.

Perception of structurally distinct effectors by the integrated WRKY domain of a plant immune receptor

“…S7), suggesting that AvrRps4 could target multiple WRKY domains to promote virulence. In addition to WRKY TFs, a recent publication suggests AvrRps4 can interact with BTS domains to affect pathogen colonization (51). Understanding whether these functions are related requires further investigation.…”

Natural variation in Arabidopsis ISR1 affects iron localization and induced systemic resistance

“…Iron plays a dual role in plant immunity: low iron availability can restrict pathogen growth whereas excess iron can contribute to generation of reactive oxygen species (Liu et al, 2007;Segond et al, 2009;Aznar et al, 2014;Ye et al, 2014;Aznar and Dellagi, 2015;Xing et al, 2021).…”

“…Iron plays a dual role in plant immunity: low iron availability can restrict pathogen growth whereas excess iron can contribute to generation of reactive oxygen species (Liu et al, 2007; Segond et al, 2009; Aznar et al, 2014; Ye et al, 2014; Aznar and Dellagi, 2015; Xing et al, 2021). Because isr1 mutants do not display a phenotype on iron-deficient medium, it is unlikely that ISR1 is essential for plant viability under iron limitation.…”

“…Iron accumulation and ROS are observed at the sites of fungal infection by Blumeria graminis and Colletotrichum graminicola (Liu et al, 2007; Ye et al, 2014) and iron-deficient maize and Arabidopsis are significantly more susceptible to pathogen infection (Aznar et al, 2014; Ye et al, 2014). At the same time, iron chelation is a widely used virulence mechanism by bacterial pathogens (Segond et al, 2009; Kieu et al, 2012; Aznar and Dellagi, 2015; Xing et al, 2021). Collectively these data implicate precise regulation of iron availability as critical to the outcome of plant-microbe interactions, indicating that there is tension between the role of iron in defense and a pathogen’s need for iron to survive.…”

The receptor kinase SRF3 coordinates iron-level and flagellin dependent defense and growth responses in plants

“…Transcriptional signatures of Pseudomonas simiae WCS417 and long-term iron deficiency in leaves display an overlap of about 20%, among these genes, the transcription factor MYB DOMAIN PROTEIN 72 (MYB72) plays a role at the interface of both signaling pathways [11][12][13] . Recently, a protein effector from the foliar pathogen Pseudomonas syringae was shown to disable a key iron homeostasis regulator, the E3 ligase BRUTUS (BTS), to increase apoplastic iron content and promote colonization 14 . Finally, the presence of the microbial siderophore, deferrioxamine (DFO), affects the transcriptional landscape of iron homeostasis and immunity genes, suggesting a role for siderophores in mediating nutritional immunity 10 .…”