Distinct phosphoinositides define the biotrophic interface of plant-microbe interactions

Connecting the plant cytoskeleton to the cell surface via the phosphoinositides

Plants have developed fine-tuned cellular mechanisms to respond to a variety of intracellular and extracellular signals. These responses often necessitate the rearrangement of the plant cytoskeleton to modulate cell shape and/or to guide vesicle trafficking. At the cell periphery, both actin filaments and microtubules associate with the plasma membrane that acts as an integrator of the intrinsic and extrinsic environments. At this membrane, acidic phospholipids such as phosphatidic acid, and phosphoinositides contribute to the selection of peripheral proteins and thereby regulate the organization and dynamic of the actin and microtubules. After recognition of the importance of phosphatidic acid on cytoskeleton dynamics and rearrangement, it became apparent that the other lipids might play a specific role in shaping the cytoskeleton. This review focuses on the emerging role of the phosphatidylinositol 4,5-bisphosphate for the regulation of the peripherical cytoskeleton during cellular processes such as cytokinesis, polar growth, biotic and abiotic responses.

Keep in contact: multiple roles of endoplasmic reticulum-membrane contact sites and the organelle interaction network in plants

Functional regulation and structural maintenance of the different organelles in plants contribute directly to plant development, reproduction and stress responses. To ensure these activities take place effectively, cells have evolved an interconnected network amongst various subcellular compartments, regulating rapid signal transduction and the exchange of biomaterial. Many proteins that regulate membrane connections have recently been identified in plants, and this is the first step in elucidating both the mechanism and function of these connections. Amongst all organelles, the endoplasmic reticulum is the key structure, which likely links most of the different subcellular compartments through membrane contact sites (MCS) and the ER-PM contact sites (EPCS) have been the most intensely studied in plants. However, the molecular composition and function of plant MCS are being found to be different from other eukaryotic systems. In this article, we will summarise the most recent advances in this field and discuss the mechanism and biological relevance of these essential links in plants.

Engineering crop Phytophthora resistance by targeting pathogen-derived PI3P for enhanced catabolism

Phytophthora pathogens lead to numerous economically damaging plant diseases worldwide, including potato late blight caused by P. infestans and soybean root rot caused by P. sojae. Our previous work showed that Phytophthora pathogens may generate abundant phosphatidylinositol 3-phosphate (PI3P) to promote infection via direct association with RxLR effectors. Here, we designed a disease control strategy for metabolizing pathogen-derived PI3P by expressing secreted Arabidopsis thaliana phosphatidylinositol-4-phosphate 5-kinase 1 (AtPIP5K1), which can phosphorylate PI3P to PI(3,4)P₂. We fused AtPIP5K1 with the soybean PR1a signal peptide (SP-PIP5K1) to enable its secretion into the plant apoplast. Transgenic soybean and potato plants expressing SP-PIP5K1 showed substantially enhanced resistance to various P. sojae and P. infestans isolates, respectively. SP-PIP5K1 significantly reduced PI3P accumulation during P. sojae and soybean interaction. Knockout or inhibition of PI3 kinases (PI3Ks) in P. sojae compromised the resistance mediated by SP-PIP5K1, indicating that SP-PIP5K1 action requires a supply of pathogen-derived PI3P. Furthermore, we revealed that SP-PIP5K1 can interfere with the action of P. sojae mediated by the RxLR effector Avr1k. This novel disease control strategy has the potential to confer durable broad-spectrum Phytophthora resistance in plants through a clear mechanism in which catabolism of PI3P interferes with RxLR effector actions.

The Phytophthora sojae effector PsFYVE1 modulates immunity-related gene expression by targeting host RZ-1A protein

Oomycete pathogens secrete numerous effectors to manipulate plant immunity and promote infection. However, relatively few effector types have been well characterized. In this study, members of an FYVE domain-containing protein family that are highly expanded in oomycetes were systematically identified, and one secreted protein, PsFYVE1, was selected for further study. PsFYVE1 enhanced Phytophthora capsici infection in Nicotiana benthamiana and was necessary for Phytophthora sojae virulence. The FYVE domain of PsFYVE1 had PI3P-binding activity that depended on four conserved amino acid residues. Furthermore, PsFYVE1 targeted RNA-binding proteins RZ-1A/1B/1C in N. benthamiana and soybean (Glycine max), and silencing of NbRZ-1A/1B/1C genes attenuated plant immunity. NbRZ-1A was associated with the spliceosome complex that included three important components, glycine-rich RNA-binding protein 7 (NbGRP7), glycine-rich RNA-binding protein 8 (NbGRP8), and a specific component of the U1 small nuclear ribonucleoprotein complex (NbU1-70K). Notably, PsFYVE1 disrupted NbRZ-1A-NbGRP7 interaction. RNA-seq and subsequent experimental analysis demonstrated that PsFYVE1 and NbRZ-1A not only modulated pre-mRNA alternative splicing (AS) of the necrotic spotted lesions 1 (NbNSL1) gene, but also co-regulated transcription of hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferase (NbHCT), ethylene insensitive 2 (NbEIN2), and sucrose synthase 4 (NbSUS4) genes, which participate in plant immunity. Collectively, these findings indicate that the FYVE domain-containing protein family includes potential uncharacterized effector types and also highlight that plant pathogen effectors can regulate plant immunity-related genes at both AS and transcription levels to promote disease.