Poster abstracts
Poster number 14 submitted by Reid Gohmann
Niche establishment role of AvrE1 is distinct from immune suppression
Reid Gohmann (Molecular, Cellular, and Developmental Biology Graduate Program), David Mackey (Horticulture and Crop Science; Molecular Genetics)
Abstract:
Phytopathogenic bacteria translocate type III effector proteins (T3Es) directly into the cytoplasm of host cells where they carry out diverse functions to promote virulence. While the ability of T3Es to disrupt host immunity is well established, more recently emerging is their role in establishing a water- and nutrient-rich niche capable of supporting rapid and robust bacterial growth. T3Es of the conserved AvrE-family, including AvrE1 from Pseudomonas syringae pathovar tomato (Pto) and WtsE from Pantoea stewartii subsp. stewartii, induce water-soaking in the extracellular apoplast space of infected leaves[1,2]. AvrE-family effectors accomplish this by forming water- and solute-permeable pores in the host plasma membrane that allow cytoplasmic contents to flow outside the host cell[3]. Additionally, WtsE was shown to induce host metabolism genes[2], and AvrE1 was shown to induce the plant hormone ABA[4], which also promotes water-soaking, indicating that AvrE-family effectors function through multiple synergistic mechanisms to establish a growth-supportive niche.
Our recent work indicates that niche-establishment by AvrE1 is distinct from an immune suppressive role. We show that AvrE1 alone can promote the growth of an effectorless Pto strain, but not to the level of wild-type Pto, which expresses 35 additional T3Es, including many capable of suppressing host immunity. However, in an immune-compromised plant line, the strain with only AvrE1 grows to the level of wild-type Pto in a wild-type host. Consistent with the inability of AvrE1 to suppress immunity, we show that it does not limit the transcription of defense genes or the formation of cell wall fortifications. Follow-up work is focused on the ability of AvrE1 to promote niche establishment by perturbing host physiology, including the synthesis and transport of the plant hormone ABA, and the activation of host primary metabolism, which leads to increased abundance of nutritive compounds.
References:
[1] Ekanayake, G., et al. A method for quantitation of apoplast hydration in Arabidopsis leaves reveals water-soaking activity of effectors of Pseudomonas syringae during biotrophy. Sci Rep 12, 18363 (2022)
[2] Gentzel I. et al. Dynamic nutrient acquisition from a hydrated apoplast supports biotrophic proliferation of a bacterial pathogen of maize. Cell Host Microbe 30(4):502-517.e4. (2022)
[3] Nomura, K., et al. Bacterial pathogens deliver water- and solute-permeable channels to plant cells. Nature 621, 586–591 (2023)
[4] Roussin-Léveillée, C., et al. Evolutionarily conserved bacterial effectors hijack abscisic acid signaling to induce an aqueous environment in the apoplast. Cell Host Microbe 30(4), 489-501 (2022)
Keywords: Plant pathology, Niche establishment, Type III effectors