Effectors from Wheat Rust Fungi Suppress Multiple Plant Defense Responses

Abstract

Fungi that cause cereal rust diseases (genus Puccinia) are important pathogens of wheat globally. Upon infection, the fungus secretes a number of effector proteins. Although a large repository of putative effectors has been predicted using bioinformatic pipelines, the lack of available high-throughput effector screening systems has limited functional studies on these proteins. In this study, we mined the available transcriptomes of Puccinia graminis and P. striiformis to look for potential effectors that suppress host hypersensitive response (HR). Twenty small (<300 amino acids), secreted proteins, with no predicted functions were selected for the HR suppression assay using Nicotiana benthamiana, in which each of the proteins were transiently expressed and evaluated for their ability to suppress HR caused by four cytotoxic effector-R gene combinations (Cp/Rx, ATR13/RPP13, Rpt2/RPS-2, and GPA/RBP-1) and one mutated R gene-Pto(Y207D). Nine out of twenty proteins, designated Shr1 to Shr9 (suppressors of hypersensitive response), were found to suppress HR in N. benthamiana. These effectors varied in the effector-R gene defenses they suppressed, indicating these pathogens can interfere with a variety of host defense pathways. In addition to HR suppression, effector Shr7 also suppressed PAMP-triggered immune response triggered by flg22. Finally, delivery of Shr7 through Pseudomonas fluorescens EtHAn suppressed nonspecific HR induced by Pseudomonas syringae DC3000 in wheat, confirming its activity in a homologous system. Overall, this study provides the first evidence for the presence of effectors in Puccinia species suppressing multiple plant defense responses.

A novel fungal effector from Puccinia graminis suppressing RNA silencing and plant defense responses

“…a). Interestingly, both PgtSR1 alleles were also able to partially suppress cell death induced by four other effector‐R gene combinations described previously (Ramachandran et al ., ): ATR13 / RPP13 , GPA / RBP‐1 , Avr Rpt2 / RPS‐2 and Cp / Rx (Fig. a).…”

Divergent and convergent modes of interaction between wheat and Puccinia graminis f. sp. tritici isolates revealed by the comparative gene co-expression network and genome analyses

“…Like other biotrophic plant pathogens, Pgt infects susceptible host plants by engaging in a complex interaction that involves multiple proteins from both the fungus and plant. Effector proteins secreted by the fungus interact directly with host plant factors and function to alter plant cellular defenses, architecture, and metabolism, ultimately leading to a compatible plant-pathogen interaction [4–8]. Recognition of effector proteins by plant host resistance genes forms the basis of effector-triggered immunity and drives fast evolution of effector complement in the pathogen populations [9, 10].…”

Non-host Resistance: DNA Damage Is Associated with SA Signaling for Induction of PR Genes and Contributes to the Growth Suppression of a Pea Pathogen on Pea Endocarp Tissue

“…Multiple regulatory substances are released from fungal spores following inoculation on their respective host tissues. Of current interest are the proteins that exit the fungal cell via their SignalP sequences (Ramachandran et al, 2016). The functional properties of defense proteins (described above) can range from those that specialize in digesting the cell wall barriers to those that are metabolic enzymes or proteins with unknown function.…”