Accumulation of phosphoinositides in distinct regions of the periarbuscular membrane

Abstract

Summary Phosphoinositides and phosphatidic acid are small anionic lipids that comprise a minor proportion of total membrane lipids in eukaryotic cells but influence a broad range of cellular processes including endomembrane trafficking, signaling, exocytosis and endocytosis. To investigate the spatial distribution of phosphoinositides during arbuscular mycorrhizal symbiosis, we generated fluorescent reporters of PI(4,5)P2 and PI4P, as well as phosphatidic acid and diacylglycerol and used them to monitor lipid distribution on the cytoplasmic side of membrane bilayers in colonized cortical cells. The PI4P reporter accumulated strongly on the periarbuscular membrane (PAM) and transiently labeled Golgi bodies, while the PA reporter showed differential labeling of endomembranes and the PAM. Surprisingly, the PI(4,5)P2 reporter accumulated in small, discrete regions of the PAM on the arbuscule trunks, frequently in two regions on opposing sides of the hypha. A mutant reporter with reduced PI(4,5)P2 binding capacity did not show these accumulations. The PI(4,5)P2‐rich regions were detected at all phases of arbuscule development following branching, co‐localized with membrane marker proteins potentially indicating high membrane bilayer content, and were associated with an alteration in morphology of the hypha. A possible analogy to the biotrophic interfacial membrane complex formed in rice infected with Magnaporthe orzyae is discussed.

A nuclear‐targeted effector of Rhizophagus irregularis interferes with histone 2B mono‐ubiquitination to promote arbuscular mycorrhization

“…However, despite multiple efforts we were not able to obtain an antibody that was specific enough to reliably detect RiNLE1 in situ . Therefore, we used an alternative approach by expressing a GFP‐tagged RiNLE1 (no endogenous signal peptide) construct containing a plant signal peptide sequence from MtBCP1 to target it to the apoplast (Ivanov & Harrison, 2019) under the control of the constitutive Lotus japonicus Ubiquitin 1 promotor ( LjUB1p::BCPsp‐GFP‐RiNLE1 ) in Nicotiana leaves. The MtBCP1 signal peptide was chosen because the endogenous signal peptide of RiNLE1 is not well processed in plants, causing an accumulation of recombinant protein in the endoplasmic reticulum (Fig.…”

Functions of Anionic Lipids in Plants

“…Both PI4P and PA are found in the PAM to similar extent than the PM. However, in the trunk part of hyphal branches, discrete regions where PI(4,5)P2, PI4P and PA reporters co-accumulate can be observed (44). This accumulation could correspond to an accumulation of membranes before formation of small bulges.…”

“…During the endosymbiotic association of roots with arbuscular mycorrhizal (AM) fungi in M. truncatulla, the fungus develops intracellular branched hyphae called arbuscules (44). In response, the root cortical cells form a new membrane in continuity with the PM called periarbuscular membrane (PAM) (31).…”

“…By analogy to tip growing cells, anionic lipids might regulate this particular case of polarized secretion. So far, only the pattern of localization of PI4P, PI(4,5)P2 and PA were documented during AM interaction (44) (Figure 3). Both PI4P and PA are found in the PAM to similar extent than the PM.…”

Reprogramming sphingolipid glycosylation is required for endosymbiont persistence in Medicago truncatula

“…Rhizobia and arbuscular mycorrhizal (AM) fungi enter plant cells through host-initiated asymmetric protrusions in the plasma membrane [10][11][12] that grow by means of targeted vesicle secretion and membrane fusion. 13,14 Although these symbioses culminate in vastly different morphological structures, they share a symbiosis-dedicated secretory pathway that drives the rapid growth of membrane around the endosymbiont, [15][16][17] the surface area of which increases 10-to 20-fold that of the plasma membrane and requires a massive amount of lipid synthesis. However, the molecular function of membrane lipids relative to the growth and maturation of the endosymbiotic compartment is unknown.…”