A Phakopsora pachyrhizi Effector Suppresses PAMP-Triggered Immunity and Interacts with a Soybean Glucan Endo-1,3-β-Glucosidase to Promote Virulence

Abstract

Asian soybean rust, caused by the fungus Phakopsora pachyrhizi, is one of the most important diseases affecting soybean production in tropical areas. During infection, P. pachyrhizi secretes proteins from haustoria that are transferred into plant cells to promote virulence. To date, only one candidate P. pachyrhizi effector protein has been characterized in detail to understand the mechanism by which it suppresses plant defenses to enhance infection. Here, we aimed to extend understanding of the pathogenic mechanisms of P. pachyrhizi based on the discovery of host proteins that interact with the effector candidate Phapa-7431740. We demonstrated that Phapa-7431740 suppresses pathogen-associated molecular pattern triggered immunity (PTI), and it interacts with a soybean glucan endo-1,3- β-glucosidase (GmβGLU), a pathogenesis-related (PR) protein belonging to the PR-2 family. Structural and phylogenetic characterization of PR-2 protein family predicted in the soybean genome and comparison to PR-2 family members in Arabidopsis thaliana and cotton, demonstrated that GmβGLU is a type IV β-1,3-glucanase. Transcriptional profiling during an infection time course showed that the GmβGLU mRNA is highly induced during the initial hours after infection, coinciding with peak of expression of Phapa-7431740. The effector was able to interfere with the activity of GmβGLU in vitro, with a dose-dependent inhibition. Our results suggest that Phapa-7431740 may suppress PTI by interfering with glucan endo-1,3-β-glucosidase activity.

Natural immunity stimulation using ELICE16INDURES® plant conditioner in field culture of soybean

“…PAMPs are compounds with conserved structures [ 8 ], and plant responses triggered by them are called innate or general immunity. PAMP-related defense responses and related biochemical pathways have long been widely studied [ 9 10 11 12 ].…”

WGCNA Identifies a Comprehensive Gene Co-Expression Network Associated with Development in autotetraploid potato tissues

“…Its expression is highly induced several hours after soybean infection with Phakopsora pachyrhizi. Soybean PEPPA-7431740 may trigger immunity by interfering with the activity of -1, 3-β-glucosidase within glucan and inhibiting pathogen-associated molecular patterns [30]. The pesticide GLY-15 has a good antiviral activity against tobacco Mosaic virus in plants.…”

A soybean rust effector protease suppresses host immunity and cleaves a 3-deoxy-7-phosphoheptulonate synthase

“…The identification and characterization of conserved effectors with functions in suppressing or eliciting the plant immune system and the identification of their immune targets is critical to generating durable resistance against SBR. In a recent study, a P. pachyrhizi effector, Phapa-7431740, suppressed PTI and interacted with a soybean glucan endo-1,3-β-glucosidase ( Gm βGLU), a PR protein belonging to the PR-2 family (Bueno et al, 2022). Similarly, Pp EC23 was previously shown to suppress soybean PTI and ETI and physically interact with the soybean transcription factor SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL)12l, a negative immune regulator (Qi et al, 2016) and possible susceptibility gene.…”

“…P. pachyrhizi encodes many secreted proteins (Link et al, 2014; Kunjeti et al, 2016; de Carvalho et al, 2017; Elmore et al, 2020), but only two have been functionally characterized for their roles in P. pachyrhizi virulence (Qi et al, 2016; Bueno et al, 2022). Previously, a large-scale screen to identify putative P. pachyrhizi effectors capable of suppressing or activating plant immunity was conducted by our group, in which we identified a P. pachyrhizi predicted effector protease named Pp EC15 (Qi et al, 2018).…”