Up-regulation of genes involved in N-acetylglucosamine uptake and metabolism suggests a recycling mode of chitin in intraradical mycelium of arbuscular mycorrhizal fungi

Abstract

Arbuscular mycorrhizal (AM) fungi colonize roots and form two kinds of mycelium, intraradical mycelium (IRM) and extraradical mycelium (ERM). Arbuscules are characteristic IRM structures that highly branch within host cells in order to mediate resource exchange between the symbionts. They are ephemeral structures and at the end of their life span, arbuscular branches collapse from the tip, fungal cytoplasm withdraws, and the whole arbuscule shrinks into fungal clumps. The exoskeleton of an arbuscule contains structured chitin, which is a polymer of N-acetylglucosamine (GlcNAc), whereas a collapsed arbuscule does not. The molecular mechanisms underlying the turnover of chitin in AM fungi remain unknown. Here, a GlcNAc transporter, RiNGT, was identified from the AM fungus Rhizophagus irregularis. Yeast mutants defective in endogenous GlcNAc uptake and expressing RiNGT took up (14)C-GlcNAc, and the optimum uptake was at acidic pH values (pH 4.0-4.5). The transcript levels of RiNGT in IRM in mycorrhizal Lotus japonicus roots were over 1000 times higher than those in ERM. GlcNAc-6-phosphate deacetylase (DAC1) and glucosamine-6-phosphate isomerase (NAG1) genes, which are related to the GlcNAc catabolism pathway, were also induced in IRM. Altogether, data suggest the existence of an enhanced recycling mode of GlcNAc in IRM of AM fungi.

Regulation of Hyphal Growth and N-Acetylglucosamine Catabolism by Two Transcription Factors in Candida albicans

“…of chitin in intraradical mycelium of arbuscular mycorrhizal fungi (Kobae et al 2015). GlcNAc signaling is also important for a broad range of organisms beyond the fungal kingdom, as it regulates virulence functions in bacteria and inflammasome activation in mammalian cells Wolf et al 2016).…”

Genetic Diversity and Association Characters of Bacteria Isolated from Arbuscular Mycorrhizal Fungal Spore Walls

“…In this study, we found that 74% of the bacteria associated with the spore walls of AMF had chitinolytic activity. Chitinolytic activity of bacteria also enhances AMF and plant root recognition [ 48 ] by stimulating the spores to produce more signaling molecules. In a recent study, Genre et al [ 49 ] reported that short-chain chitin oligomers produced by Gigaspora margarita triggered AM-related signaling pathway by inducing the nuclear Ca 2+ spiking in Medicago truncatula roots.…”

Arbuscular mycorrhiza and soil organic nitrogen: network of players and interactions

“…Specialized or more generic transmembrane transporters facilitate uptake of N-acetylglucosamine (a chitin monomer) to eukaryotic cells [3,107]. Interestingly, genes responsible for N-acetylglucosamine transport across membrane and its further metabolism have also been described from AM fungus Rhizophagus irregularis [75], yet they have only been documented to be active in the intraradical mycelium, possibly recycling organic N from collapsing arbuscules. Regardless of the possible role of N-acetylglucosamine (or other soluble products of chitinolysis) in N nutrition of various microorganisms, chitin oligomers and their derivatives (such as lipo-chitooligosaccharides) also serve as signals to recognize pathogens or symbionts in the plant and microbial worlds [5,93,108].…”