Structural Basis for Interactions of thePhytophthora sojaeRxLR Effector Avh5 with Phosphatidylinositol 3-Phosphate and for Host Cell Entry

Abstract

Oomycetes, such as Phytophthora sojae, are plant pathogens that employ protein effectors that enter host cells to facilitate infection. Plants may overcome infection by recognizing pathogen effectors via intracellular receptors (R proteins) that form part of their defense system. Entry of some effector proteins into plant cells is mediated by conserved RxLR motifs in the effectors and phosphoinositides (PIPs) resident in the host plasma membrane such as phosphatidylinositol 3-phosphate (PtdIns(3)P). Recent reports differ regarding the regions on RxLR effector proteins involved in PIP recognition. To clarify these differences, I have structurally and functionally characterized the P. sojae effector, avirulence homolog-5 (Avh5).

The phospholipid code: a key component of dying cell recognition, tumor progression and host–microbe interactions

“…Furthermore, another effector protein from the same species, Avh5, was found to enter soybean root and human lung epithelial cells via PI(3)P binding, with both the RXLR motif as well as a lysine-rich region shown to be required for cell entry. 82 Likewise, fungal-derived effectors AvrL567 (Melampsora lini), Avr2 (Fusarium oxysporum f. sp. lycopersici) and AvrLm6 (Leptosphaeria maculans) containing the RXLR motif were also shown to bind PI(3)P and facilitate protein entry into soybean root cells.…”

Microbe-Independent Entry of Oomycete RxLR Effectors and Fungal RxLR-Like Effectors Into Plant and Animal Cells Is Specific and Reproducible

“…Furthermore, in recent work ( Fig. 2; Sun et al, 2013) we have introduced the use of propidium iodide to identify cells which may have died and hence may take up protein nonspecifically.…”

“…Two classes of experiments have provided information that these effectors do not require the microbe for entry. The first are plant transient expression experiments, by bombardment or agroinfiltration, in which the effector in question is secreted from the plant and then must re-enter to trigger a measured response (usually cell death in the presence of a cognate R gene) (Dou et al, 2008;Rafiqi et al, 2010;Gu et al, 2011;Anderson et al, 2012;Sun et al, 2013). The second is to expose root tips or leaf tissue to purified effectors and then, to measure entry microscopically using antibodies, or by the presence of a chemical or protein fluorescent label attached to the effector (Dou et al, 2008;Plett et al, 2011;Wawra et al, 2012).…”

“…Similar experiments have also identified fungal effectors that appear to enter plant cells in the absence of the microbe, via RxLR-like motifs ([R, K, H]×[L, M, I, F, W, Y]); with no dEER-like motifs) Gu et al, 2011;Plett et al, 2011). The demonstration that those oomycete and fungal effectors can bind host cell surface phosphatidyinositol-3-phosphate (PI-3-P) via the RxLR motifs, and that PI-3-P binding is required for entry has provided a mechanistic basis for RxLR-dependent entry Sun et al, 2013). A surprising finding to emerge from these studies was that many of these oomycete and fungal effectors could enter not only plant cells but also human lung epithelial cells Sun et al, 2013).…”

“…The demonstration that those oomycete and fungal effectors can bind host cell surface phosphatidyinositol-3-phosphate (PI-3-P) via the RxLR motifs, and that PI-3-P binding is required for entry has provided a mechanistic basis for RxLR-dependent entry Sun et al, 2013). A surprising finding to emerge from these studies was that many of these oomycete and fungal effectors could enter not only plant cells but also human lung epithelial cells Sun et al, 2013).…”