Two Medicago truncatula Half-ABC Transporters Are Essential for Arbuscule Development in Arbuscular Mycorrhizal Symbiosis

Abstract

In the symbiotic association of plants and arbuscular mycorrhizal (AM) fungi, the fungal symbiont resides in the root cortical cells where it delivers mineral nutrients to its plant host through branched hyphae called arbuscules. Here, we report a Medicago truncatula mutant, stunted arbuscule (str), in which arbuscule development is impaired and AM symbiosis fails. In contrast with legume symbiosis mutants reported previously, str shows a wild-type nodulation phenotype. STR was identified by positional cloning and encodes a half-size ATP binding cassette (ABC) transporter of a subfamily (ABCG) whose roles in plants are largely unknown. STR is a representative of a novel clade in the ABCG subfamily, and its orthologs are highly conserved throughout the vascular plants but absent from Arabidopsis thaliana. The STR clade is unusual in that it lacks the taxon-specific diversification that is typical of the ABCG gene family. This distinct phylogenetic profile enabled the identification of a second AM symbiosis-induced half-transporter, STR2. Silencing of STR2 by RNA interference results in a stunted arbuscule phenotype identical to that of str. STR and STR2 are coexpressed constitutively in the vascular tissue, and expression is induced in cortical cells containing arbuscules. STR heterodimerizes with STR2, and the resulting transporter is located in the peri-arbuscular membrane where its activity is required for arbuscule development and consequently a functional AM symbiosis.

A petunia ABC protein controls strigolactone-dependent symbiotic signalling and branching

“…Samples were stored at 280 uC until analysis. P. hybrida root exudates and extracts were prepared and analysed by ultra performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) as previously described for Arabidopsis 22 . Orobanchol was provided by K. Yoneyama.…”

The Petunia GRAS Transcription Factor ATA/RAM1 Regulates Symbiotic Gene Expression and Fungal Morphogenesis in Arbuscular Mycorrhiza

“…Their mutation results in defective symbiosis, which is often associated with incomplete development and/or premature senescence of the fungal arbuscules. This is the case for PT4 (Maeda et al, 2006;Javot et al, 2007), STR and STR2 (Zhang et al, 2010;Gutjahr et al, 2012), subtilase (Takeda et al, 2009), and RAM2 . The fact that all these genes fail to be induced in ram1 mutants (Fig.…”

“…To assess the role of the petunia RAM1 in AM-related gene induction, we chose a panel of AM-related marker genes, including ATA/RAM1 itself, the VAPYRIN gene that is required for intracellular accommodation of AM fungi (Feddermann et al, 2010;Pumplin et al, 2010;Murray et al, 2011), the two mycorrhizal phosphate transporters PT4 and PT5 (Wegmüller et al, 2008;Breuillin et al, 2010), the closest petunia homologs of the G-type ABC transporter genes STUNTED ARBUSCULE (STR) and STR2 of M. truncatula (Zhang et al, 2010), a glycerol-3-P acyltransferase that is closely related to the AM-specific RAM2 gene in M. truncatula , and two AM markers with unknown function, a subtilase and BCP (Breuillin et al, 2010). To achieve comparable colonization levels in all genotypes (the wild type and the three ram1 alleles), the plants were inoculated with nurse plants.…”

“…Comparison between transcriptomic studies in dicots (such as M. truncatula, L. japonicus, petunia, and Solanum lycopersicum) and in the monocot model system rice have revealed a conserved set of AM-induced genes (Breuillin et al, 2010). However, only few of them have been functionally elucidated, among them phosphate and ammonium transporters (Maeda et al, 2006;Javot et al, 2007;Guether et al, 2009b), proteases (Takeda et al, 2009;Rech et al, 2013), ATP-binding cassette (ABC) transporters (Zhang et al, 2010;Gutjahr et al, 2012;Kretzschmar et al, 2012), and transcription factors (TFs) such as CYCLOPS (Singh et al, 2014), REQUIRED FOR ARBUSCULAR MYCORRHIZA1 (RAM1; Gobbato et al, 2012), and REQUIRED FOR ARBUSCULE DEVELOPMENT1 (RAD1; Xue et al, 2015).…”

Arbuscular Mycorrhizal Symbiosis Requires a Phosphate Transceptor in the Gigaspora margarita Fungal Symbiont

“…The first-strand cDNA synthesis, RT-PCR, and real-time RT-PCR were performed as reported previously ( Zhang et al, 2010), and the actin gene of G. margarita was used as the internal standard. Real-time qRT-PCR analysis of the selected genes possibly involved in the phosphorus-sensing network was further performed to validate the data derived from the RNA-seq experiment ( Salvioli et al, 2016).…”