Abstract
Enhanced disease susceptibility1 (EDS1) and phytoalexin deficient4 (PAD4) are well-known regulators of both basal and resistance (R) protein-mediated plant defense. We identified two EDS1-like (GmEDS1a/GmEDS1b) proteins and one PAD4-like (GmPAD4) protein that are required for resistance signaling in soybean (Glycine max). Consistent with their significant structural conservation to Arabidopsis (Arabidopsis thaliana) counterparts, constitutive expression of GmEDS1 or GmPAD4 complemented the pathogen resistance defects of Arabidopsis eds1 and pad4 mutants, respectively. Interestingly, however, the GmEDS1 and GmPAD4 did not complement pathogen-inducible salicylic acid accumulation in the eds1/pad4 mutants. Furthermore, the GmEDS1a/GmEDS1b proteins were unable to complement the turnip crinkle virus coat protein-mediated activation of the Arabidopsis R protein Hypersensitive reaction to Turnip crinkle virus (HRT), even though both interacted with HRT. Silencing GmEDS1a/GmEDS1b or GmPAD4 reduced basal and pathogen-inducible salicylic acid accumulation and enhanced soybean susceptibility to virulent pathogens. The GmEDS1a/GmEDS1b and GmPAD4 genes were also required for Resistance to Pseudomonas syringae pv glycinea2 (Rpg2)-mediated resistance to Pseudomonas syringae. Notably, the GmEDS1a/GmEDS1b proteins interacted with the cognate bacterial effector AvrA1 and were required for its virulence function in rpg2 plants. Together, these results show that despite significant structural similarities, conserved defense signaling components from diverse plants can differ in their functionalities. In addition, we demonstrate a role for GmEDS1 in regulating the virulence function of a bacterial effector.
Highlights
Enhanced disease susceptibility1 (EDS1) and phytoalexin deficient4 (PAD4) are well-known regulators of both basal and resistance (R) protein-mediated plant defense
The predicted catalytic triad residues and the nucleophilic elbow of the GmEDS1 proteins lie within the region that is highly similar to the LP domain of AtEDS1
Western-blot analysis of total protein extracts from infected plants showed that systemic tissues of SEDS1a/EDS1b and SPAD4 plants contained more soybean mosaic virus (SMV) at 4 dpi compared with V plants (Supplemental Fig. S7A), and the silenced plants showed more severe SMVassociated disease symptoms at 10 dpi (Supplemental Fig. S7B). These results suggest that GmEDS1a/ GmEDS1b and GmPAD4 contribute to basal resistance to virulent bacterial, oomycete, and viral pathogens in soybean
Summary
Enhanced disease susceptibility (EDS1) and phytoalexin deficient (PAD4) are well-known regulators of both basal and resistance (R) protein-mediated plant defense. We identified two EDS1-like (GmEDS1a/GmEDS1b) proteins and one PAD4-like (GmPAD4) protein that are required for resistance signaling in soybean (Glycine max). The GmEDS1a/GmEDS1b proteins interacted with the cognate bacterial effector AvrA1 and were required for its virulence function in rpg plants. Together, these results show that despite significant structural similarities, conserved defense signaling components from diverse plants can differ in their functionalities. Resistance (R) protein-mediated or effector-triggered immunity (ETI) is one of the several different types of defense mechanisms induced in response to pathogen infection in plants. EDS1 interacts with suppressor of rps4-RLD1 (SRFR1), a tetratricopeptide repeat domain containing a negative regulator of ETI derived from TIR-NB-LRR proteins (Kim et al, 2009; Kwon et al, 2009)
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