Overlaps in the Transcriptional Profiles ofMedicago truncatulaRoots Inoculated with Two Different Glomus Fungi Provide Insights into the Genetic Program Activated during Arbuscular Mycorrhiza  

Abstract

Arbuscular mycorrhiza (AM) is a widespread symbiotic association between plants and fungal microsymbionts that supports plant development under nutrient-limiting and various stress conditions. In this study, we focused on the overlapping genetic program activated by two commonly studied microsymbionts in addition to identifying AM-related genes. We thus applied 16,086 probe microarrays to profile the transcriptome of the model legume Medicago truncatula during interactions with Glomus mosseae and Glomus intraradices and specified a total of 201 plant genes as significantly coinduced at least 2-fold, with more than 160 being reported as AM induced for the first time. Several hundred genes were additionally up-regulated during a sole interaction, indicating that the plant genetic program activated in AM to some extent depends on the colonizing microsymbiont. Genes induced during both interactions specified AM-related nitrate, ion, and sugar transporters, enzymes involved in secondary metabolism, proteases, and Kunitz-type protease inhibitors. Furthermore, coinduced genes encoded receptor kinases and other components of signal transduction pathways as well as AM-induced transcriptional regulators, thus reflecting changes in signaling. By the use of reporter gene expression, we demonstrated that one member of the AM-induced gene family encoding blue copper binding proteins (MtBcp1) was both specifically and strongly up-regulated in arbusculecontaining regions of mycorrhizal roots. A comparison of the AM expression profiles to those of nitrogen-fixing root nodules suggested only a limited overlap between the genetic programs orchestrating root endosymbioses.

Potential agricultural benefits through biotechnological manipulation of plant fungal associations

“…that received plant monosaccharides from a number of plants including carrots, wheat, and onion [12,21]. During the symbiotic exchange there was coordinated upregulation of plant (Medicago truncatula) and fungal (Glomus mosseae, Glomus intraradices) nutrient transporters [22]. MtPt4, a phosphate transporter, was found only in plant roots during mycorrhizal association [22], this coincided with Figure 1.…”

“…During the symbiotic exchange there was coordinated upregulation of plant (Medicago truncatula) and fungal (Glomus mosseae, Glomus intraradices) nutrient transporters [22]. MtPt4, a phosphate transporter, was found only in plant roots during mycorrhizal association [22], this coincided with Figure 1. Potential plant benefits from symbiotic fungal gene manipulations or plant gene manipulations.…”

“…Red denotes fungal genes, green denotes plant genes. Genes shown are representative of numerous potentially important genes in the different functional groups [10,22,26,30]. the upregulation of the fungal phosphate transporters GmosPT and GvPT during colonization of inner cortical root cells [23].…”

Ascorbate oxidase: The unexpected involvement of a ‘wasteful enzyme’ in the symbioses with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi

“…Localization, in both cases, of the AO protein in the highly specialized structures at the host-symbiont interface, suggests an important role for this enzyme in the general mechanism of symbiosis. The involvement of AO in AM symbiosis is confirmed by the fact that in M. truncatula two genes encoding putative AO proteins are shown to be up-regulated when roots were mycorrhized by two different AM fungi [26]. Higher AO activity could also be detected in roots of Cucumis sativus mycorrhized with Glomus mosseae (R. Balestrini and M.C.…”

The expression of GintPT, the phosphate transporter of Rhizophagus irregularis, depends on the symbiotic status and phosphate availability

“…Baseline range and threshold cycle (Ct) values were automatically calculated using iCycler software. Transcript levels were normalized to the Ct value of GintEF1α (Gonzàlez-Guerrero et al 2010) for the fungal gene and MtTef (Hohnjec et al 2005) for plant gene. Only Ct values leading to a Ct mean with a standard deviation below 0.5 were considered.…”