Functional Characterization of a Magnesium Transporter of Root Endophytic Fungus Piriformospora indica

Magnesium (Mg) is a crucial macronutrient required for the regular growth of plants. Here we report the identification, isolation and functional characterization of Mg-transporter PiMgT1 in root endophytic fungus Piriformospora indica. We also report the role of P. indica in the improvement of the Mg nutrition of the plant particularly under Mg deficiency condition. Protein BLAST (BLASTp) for conserved domains analysis showed that PiMgT1 belong to CorA like protein family of bacteria. We have also observed the presence of conserved ‘GMN’ signature sequence which suggests that PiMgT1 belongs to Mg transporter family. Phylogenetic analysis revealed that PiMgT1 clustered among fungal CorA family members nearer to basidiomycetes. Functionality of PiMgT1 was confirmed by complementation of a yeast magnesium transporter mutant CM66. We have observed that PiMgT1 restored the growth of mutant and showed comparable growth with that of WT. We found statistically significant (p < 0.05) two fold increase in the total intracellular Mg content of mutant complemented with PiMgT1 as compared to the mutant. These observations suggest that PiMgT1 is actively involved in Mg uptake by the fungus and may be helping in the nutritional status of the host plant

The beneficial fungus Piriformospora indica confers benefits to plants under low-phosphate stress conditions

P. indica, a root endophytic fungus, lives in beneficial relationship with plants and protects them from biotic and abiotic stresses. Despite its positive impact on the host, little is known about the genes involved in stress tolerance. In Arabidopsis, a whole cascade of genes participates in abiot-ic stress tolerance responses, starting from stress perception to transcriptional activation of downstream target genes. Inorganic phosphate (Pi) limitation is one of the major abiotic stresses for plants used in agriculture. P. indica is known to improve the nutritional status of the plant by transporting soluble Pi to the host. I identified target genes of P. indica under low Pi (LP) stress conditions in Arabidopsis roots. Understanding the function of the genes and their gene products is of critical importance for the development of transgenic strategies and to improve low Pi stress tolerance in crops. Furthermore, WRKY6 functions as a repressor of several Pi-related processes in LP-exposed Arabidopsis roots, among them are Pi transporter and metabolism genes. Besides stimulation of the Pi metabolism in the wrky6 mutant under LP conditions, P. indica also in-duced root growth development and this effect was stronger in the wrky6 background than in the WT. Using this system, I showed that the three unrelated factors “presence of P. indica”, “Pi lim-itation” and “absence of WRKY6” promote Pi metabolism and root development in Arabidopsis. I identified genes, which participate in establishing the benefits for the plant.Der Wurzelendophyt P. indica lebt in wechselseitigen Beziehungen mit Pflanzen und schützt diese vor biotischen und abiotischen Belastungen. Trotz seines positiven Einflusses ist sehr wenig über die Gene, die in die Stresstoleranz involviert sind, bekannt. Für Arabidopsis ist eine Reihe an Genen bekannt, die in die abiotische Stressantwort involviert sind, beginnend mit der Stresserkennung bis hin zur transkriptionelen Aktivierung nachgeschalteter Gene. Einer der größten abiotioschen Umweltfaktoren bei Nutzpflanzen ist der Mangel an anorganischem Phosphat (Pi) im Boden. Durch den Transport von verfügbarem Pi verbessert P. indica den Nährstoffhaushalt der Pflanze. Ich habe Zielgene von P. indica identifiziert, die unter Pi-Mangel in Arabidopsis-Wurzeln reguliert werden. Es wird wichtig sein, die Funktionen dieser Gene und deren Produkte zu verstehen, um die Stresstoleranz von Nutzpflanzen bei geringer Phosphatverfügbarkeit biotechnologisch zu erhöhen. Weiterhin konnte ich zeigen, dass WRKY6 als wichtiger Repressor verschiedener Pi-regulierter Prozesse in Wurzeln von Arabidopsis Pflanzen fungiert, die unter Pi-Mangel leiden. Darzu gehören Gene für Pi-Transporter und Metabolismus. Neben der Stimulation des Pi-Metabolismus fördert P. indica auch das Wurzelwachstum und die Wurzelentwicklung in der wrky6 Mutante unter Pi-limitierenden Bedingungen, wobei der stimulierende Effekt des Pilze bei der Mutante größer ist als beim Wildtyp. Mit Hilfe diese Modellsystems konnte ich zeigen, dass die drei nicht in Beziehung zueinander stehenden Faktoren „Anwesenheit von P. indica“, „Pi-Mangel“ und „Fehlen von WRKY6“ die Phosphataufnahme und das Wurzelwachstum fördern. Ich habe Gene identifiziert, die an dieser vorteilhaften Entwicklung der Wurzel beteidigt sind

Microarray analyses during early and later stages of the Arabidopsis/Piriformospora indica interaction

Colonization of the roots of different plant species by Piriformospora indica results in better plant performance and biotic and abiotic stress tolerance. An increase of the biomass and seed yield is other beneficial effect of P. indica for the host plants. The interaction of P. indica with Arabidopsis thaliana roots is a unique model system to study symbiotic relationships. We describe a co-cultivation system which allows us to investigate the effects of fungal exudates on the root transcriptome before and after the establishment of a physical contact, and during early phases of root colonization. We present a detailed protocol which facilitates easy reproduction of the results (NCBI GEO accession number GSE58771) published by Vahabi et al. (2015) in BMC Plant Biology [1]

Piriformospora indica Reprograms Gene Expression in Arabidopsis Phosphate Metabolism Mutants But Does Not Compensate for Phosphate Limitation

Piriformospora indica is an endophytic fungus of Sebacinaceae which colonizes the roots of many plant species and confers benefits to the hosts. We demonstrate that approximately 75% of the genes, which respond to P. indica in Arabidopsis roots, differ among seedlings grown on normal phosphate (Pi) or Pi limitation conditions, and among wild-type and the wrky6 mutant impaired in the regulation of the Pi metabolism. Mapman analyses suggest that the fungus activates different signaling, transport, metabolic and developmental programs in the roots of wild-type and wrky6 seedlings under normal and low Pi conditions. Under low Pi, P. indica promotes growth and Pi uptake of wild-type seedlings, and the stimulatory effects are identical for mutants impaired in the PHOSPHATE TRANSPORTERS1;1, -1;2 and -1;4. The data suggest that the fungus does not stimulate Pi uptake, but adapts the expression profiles to Pi limitation in Pi metabolism mutants

Additional file 1: Table S1. of WRKY6 restricts Piriformospora indica-stimulated and phosphate-induced root development in Arabidopsis

Genes which are up-regulated more than 2-fold in wrky6 + P. indica in LP (log2 value ≥ 1 or ≤ −1). (XLS 200 kb

Additional file 2: Table S2. of WRKY6 restricts Piriformospora indica-stimulated and phosphate-induced root development in Arabidopsis

Genes which were regulated more than 2-fold (log2 value ≥ 1) in response to Pi limitation, P. indica and mutation of WRKY6. Table S3. Primers used in this study. Table S4. Microarray validation with Real-time PCR. (PDF 563 kb