Membrane steroid-binding protein 1 induced by a diffusible fungal signal is critical for mycorrhization in Medicago truncatula.
Arbuscular mycorrhiza (AM) is a mutualistic biotrophic association that requires a complex exchange of signals between plant and fungus to allow accommodation of the mycosymbiont in the root cortex. Signal exchange happens even before physical contact, activating the plant symbiotic program. We investigated very early transcriptional responses in Medicago truncatula to inoculation with Glomus intraradices and identified four genes induced by diffusible AM fungal signals before contact. Three of them were previously shown to be mycorrhiza induced at later stages of the symbiosis, while MtMSBP1, encoding a membrane-bound steroid-binding protein, is a novel mycorrhizal marker. Expression analyses in plants defective in the symbiotic receptor kinase DMI2 allowed discrimination of two different signaling cascades involved in the perception of the diffusible signals. Thus, while some of the genes are activated in a DMI2-dependent manner, the induction of one of them encoding a proteinase inhibitor is DMI2-independent. Downregulation of MtMSBP1 by RNAi led to an aberrant mycorrhizal phenotype with thick and septated appressoria, decrease number of arbuscules and distorted arbuscule morphology. This provides genetic evidence that MtMSBP1 is critical for mycorrhiza development. We hypothesize that MtMSBP1 plays a role in sterol homeostasis in the root.
Kuhn
Hannah
H
Botanical Institute, University of Karlsruhe and Karlsruhe Institute of Technology, Plant-Microbe Interactions Group, Hertzstrasse 16, D-76187, Karlsruhe, Germany.
Küster
Helge
H
Requena
Natalia
N
D000595:Amino Acid Sequence; D015415:Biomarkers / Q000378:metabolism; D004058:Diffusion; D004721:Endoplasmic Reticulum / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D017343:Genes, Plant; D055137:Glomeromycota / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D025301:Hyphae / Q000378:metabolism; D046913:Medicago truncatula / Q000166:cytology / Q000235:genetics / Q000382:microbiology*; D008969:Molecular Sequence Data; D038821:Mycorrhizae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D036226:Seedlings / Q000382:microbiology; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism; D013559:Symbiosis / Q000235:genetics
D015415:Biomarkers; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins