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Glomeromycotina is a lineage of early diverging fungi that establish arbuscular mycorrhizal (AM) symbiosis with land plants. Despite their major ecological role, the genetic basis of their obligate mutualism remains largely unknown, hindering our understanding of their evolution and biology. We compared the genomes of Glomerales (Rhizophagus irregularis, Rhizophagus diaphanus, Rhizophagus cerebriforme) and Diversisporales (Gigaspora rosea) species, together with those of saprotrophic Mucoromycota, to identify gene families and processes associated with these lineages and to understand the molecular underpinning of their symbiotic lifestyle. Genomic features in Glomeromycotina appear to be very similar with a very high content in transposons and protein-coding genes, extensive duplications of protein kinase genes, and loss of genes coding for lignocellulose degradation, thiamin biosynthesis and cytosolic fatty acid synthase. Most symbiosis-related genes in R. irregularis and G. rosea are specific to Glomeromycotina. We also confirmed that the present species have a homokaryotic genome organisation. The high interspecific diversity of Glomeromycotina gene repertoires, affecting all known protein domains, as well as symbiosis-related orphan genes, may explain the known adaptation of Glomeromycotina to a wide range of environmental settings. Our findings contribute to an increasingly detailed portrait of genomic features defining the biology of AM fungi.

The arbuscular mycorrhizal (AM) symbiosis is a beneficial association established between land plants and the members of a subphylum of fungi, the Glomeromycotina. How the two symbiotic partners regulate their association is still enigmatic. Secreted fungal peptides are candidates for regulating this interaction. We searched for fungal peptides with similarities with known plant signalling peptides. We identified CLAVATA (CLV)/EMBRYO SURROUNDING REGION (ESR)-RELATED PROTEIN (CLE) genes in phylogenetically distant AM fungi: four Rhizophagus species and one Gigaspora species. These CLE genes encode a signal peptide for secretion and the conserved CLE C-terminal motif. They seem to be absent in the other fungal clades. Rhizophagus irregularis and Gigaspora rosea CLE genes (RiCLE1 and GrCLE1) are transcriptionally induced in symbiotic vs asymbiotic conditions. Exogenous application of synthetic RiCLE1 peptide on Medicago truncatula affects root architecture, by slowing the apical growth of primary roots and stimulating the formation of lateral roots. In addition, pretreatment of seedlings with RiCLE1 peptide stimulates mycorrhization. Our findings demonstrate for the first time that in addition to plants and nematodes,AMfungi also possess CLE genes. These results pave the way for deciphering new mechanisms by which AM fungi modulate plant cellular responses during the establishment of AM symbiosis.

Background and aims We studied, through exudates employment, the effect of Epichloë (endophytic fungi), both independently and in association with Bromus auleticus (grass), on arbuscular mycorrhizal fungi (AMF) colonization, host and neighbouring plants biomass production and soil changes. Methods Through in vitro and greenhouse experiments, Epichloë endophytes effect on AMF development was evaluated. In vitro studies of exudates effect on Gigaspora rosea and Rhizophagus intraradices were performed using root or endophyte exudates. A 6-month greenhouse experiment was conducted to determine Bromus auleticus endophytic status effect and endophyte exudates role in biomass production, neighbouring plants mycorrhizal colonization and soil properties. Results Endophyte exudates and E+ plant root exudates promoted in vitro AMF development in the pre-infective stage of G. rosea and in carrot root culture mycelium of R. intraradices in a dose-response relationship, while control media and E− plants exudates had no effect. R. intraradices colonization and plant growth was clearly increased by endophytes and their exudates. Conclusions This is the first work evidencing the direct effect of Epichloë endophytes and infected plants root exudates on AMF extramatrical development. While higher levels of AMF colonization were observed in E+ plants, no clear effect was detected in neighbouring plants colonization, plant biomass or soil properties.

The association of arbuscular mycorrhizal (AM) fungi with plant roots is the oldest and ecologically most important symbiotic relationship between higher plants and microorganisms, yet the mechanism by which these fungi detect the presence of a plant host is poorly understood. Previous studies have shown that roots secrete a branching factor (BF) that strongly stimulates branching of hyphae during germination of the spores of AM fungi. In the BF of Lotus, a strigolactone was found to be the active molecule. Strigolactones are known as germination stimulants of the parasitic plants Striga and Orobanche. In this paper, we show that the BF of a monocotyledonous plant, Sorghum, also contains a strigolactone. Strigolactones strongly and rapidly stimulated cell proliferation of the AM fungus Gigaspora rosea at concentrations as low as 10(-13) M. This effect was not found with other sesquiterperne lactones known as germination stimulants of parasitic weeds. Within 1 h of treatment, the density of mitochondria in the fungal cells increased, and their shape and movement changed dramatically. Strigolactones stimulated spore germination of two other phylogenetically distant AM fungi, Glomus intraradices and Gl. claroideum. This was also associated with a rapid increase of mitochondrial density and respiration as shown with Gl. intraradices. We conclude that strigolactones are important rhizospheric plant signals involved in stimulating both the pre-symbiotic growth of AM fungi and the germination of parasitic plants.

• We investigated structural and functional diversity in arbuscular mycorrhizal (AM) symbioses involving three plant species and three AM fungi and measured contributions of the fungi to P uptake using compartmented pots and 33 P. The plant/fungus combinations varied in growth and P responses. Flax (Linum usitatissimum) responded positively to all fungi, and medic (Medicago truncatula) to Glomus caledonium and G. intraradices, but not Gigaspora rosea. Tomato (Lycopersicon esculentum) showed no positive responses. • Hyphal growth in soil was very low for Gi. rosea and high for both Glomus spp. Hyphal lengths in root + hyphal compartment (RHC) and hyphal compartment (HC) were similar for G. intraradices, but much higher in HC for G. caledonium. • Specific activities of 33 P in plants and soil indicated that fungal P uptake made substantial contributions to five plant/fungus combinations and significant contributions to a further two. G. intraradices delivered close to 100% of the P in all three plants. G. caledonium and Gi. rosea delivered less P. The amount was not related to colonisation or to growth or P responses. • We conclude that: AM colonisation can result in complete inactivation of the direct P uptake pathway via root hairs and epidermis; calculations of AM contributions to P uptake from total plant P will often be highly inaccurate; and lack of plant responsiveness does not mean that an AM fungus makes no contribution to P uptake.

High-quality seedlings are one of the key factors in achieving high yield and precocity of blueberries. The inoculation of arbuscular mycorrhizal fungi (AMF) can enhance the development of seedlings in the nursery, ensuring more vigorous seedlings in a shorter time. This study evaluated the effect of inoculation of arbuscular mycorrhizal fungi on the development of ‘PowderBlue’blueberryseedlings. The treatments were arranged in a 4 x 2 factorial scheme, in which the first factor was the arbuscular mycorrhizal fungi Gigaspora rosea, Glomus clarum, G. rosea + G. clarum, and a control level without mycorrhizae, while the second factor consisted of usingindole-3-butyric acid(IBA) and a control level without IBA. Semi-hardwood cuttings were planted in pots containing sterilized soil and kept in a greenhouse for 660 days. The percentage of rooted cuttings, plant height, root system length, shoot dry mass, root dry mass, total dry mass, peroxidase (POD) and superoxide dismutase (SOD) enzyme activities, SPAD index, mycorrhizal efficiency and dependence, number of spores, and soil basal respiration were evaluated. Plants inoculated with G. clarum without IBA and inoculated with G. rosea with IBA showed higher dry matter and SOD and POD enzyme activities, but the use of IBA had a negative effect on the fungus. The inoculation of blueberry cuttings with G. clarummay help seedlingdevelopment, thus improving biometric and biochemical parameters. Furthermore, the plant regulator IBAwas essential in establishing the symbiosis between blueberry and the AMF G. rosea. RESUMO: Um dos fatores primordiais para alcançar alta produtividade e precocidade de mirtileiros é o emprego de mudas de alta qualidade. A inoculação de fungos micorrízicos arbusculares (FMA) pode potencializar o desenvolvimento de plântulas no viveiro, garantindo mudas mais vigorosas e em menor espaço de tempo. O estudo objetivou avaliar o efeito da inoculação de fungos micorrízicosarbusculares no desenvolvimento de mudas de mirtileiro cv. Powderblue. Os tratamentos utilizados foram arranjados em um esquema fatorial 4 x 2, sendo o primeiro fator os diferentes fungos micorrízicos arbusculares G. rosea, G. clarum, G. rosea + G. clarum e um nível controle sem micorrizas, o segundo fator foi com uso de AIB e um nível controle sem AIB. Estacas semi-lenhosas foram plantadas em vasos contendo solo esterilizado, mantidos em casa de vegetação durante 660 dias. A porcentagem de estacas enraizadas, altura de plantas, comprimento de sistema radicular, e massa seca de parte aérea, sistema radicular e planta toda, atividade das enzimas peroxidase e superóxido dismutase, índice SPAD, eficiência e dependência micorrízica, número de esporos e respiração basal do solo foram avaliadas. Plantas inoculadas com G. clarum sem AIB e inoculadas com G. rosea com AIB apresentaram maior matéria seca e atividade das enzimas SOD e POD, em contrapartida, o uso de AIB teve efeito negativo sobre esse fungo. A inoculação de estacas de mirtilo com G. clarum pode auxiliar no desenvolvimento das mudas, melhorando assim, parâmetros biométricos e bioquímicos, além disso, o regulador vegetal AIB demonstra-se essencial no estabelecimento da simbiose entre o mirtileiro e o FMA G. rosea.

The essential oils of basil are widely used in the cosmetic, pharmaceutical, food, and flavoring industries. Little is known about the potential of arbuscular mycorrhizal (AM) fungi to affect their production in this aromatic plant. The effects of colonization by three AM fungi, Glomus mosseae BEG 12, Gigaspora margarita BEG 34, and Gigaspora rosea BEG 9 on shoot and root biomass, abundance of glandular hairs, and essential oil yield of Ocimum basilicum L. var. Genovese were studied. Plant P content was analyzed in the various treatments and no differences were observed. The AM fungi induced various modifications in the considered parameters, but only Gi. rosea significantly affected all of them in comparison to control plants or the other fungal treatments. It significantly increased biomass, root branching and length, and the total amount of essential oil (especially α-terpineol). Increased oil yield was associated to a significantly larger number of peltate glandular trichomes (main sites of essential oil synthesis) in the basal and central leaf zones. Furthermore, Gi. margarita and Gi. rosea increased the percentage of eugenol and reduced linalool yield. Results showed that different fungi can induce different effects in the same plant and that the essential oil yield can be modulated according to the colonizing AM fungus.

• A survey of 12 plants colonized by six species of arbuscular mycorrhizal fungi was conducted to explore the diversity of Arum and Paris mycorrhizal structures. • Surveyed root material was sectioned both longitudinally and transversely, double-stained and mycorrhizal structures were identified. A detailed time course experiment using four plant, and four fungal species, was used to investigate the sequential development of hyphae, arbuscules, hyphal coils, arbusculate coils and vesicles. • The survey indicated that there was a continuum of mycorrhizal structures ranging from Arum to Paris, depending upon both the host plant and the fungus. The time course showed that total colonization increased, and that the establishment of the various mycorrhizal structures did not appear to change greatly over time. • It was concluded that identification of fungal structures and their subsequent development into morphological types is not easily defined. Visual inspection of root squashes is not always adequate, especially where transverse sections are needed to determine if longitudinal hyphae are inter or intracellular; this is essential to distinguish intermediate types.

Arbuscular mycorrhizal fungi (AMF) are common and important plant symbionts. They have coenocytic hyphae and form multinucleated spores. The nuclear genome of AMF is polymorphic and its organization is not well understood, which makes the development of reliable molecular markers challenging. In stark contrast, their mitochondrial genome (mtDNA) is homogeneous. To assess the intra- and inter-specific mitochondrial variability in closely related Glomus species, we performed 454 sequencing on total genomic DNA of Glomus sp. isolate DAOM-229456 and we compared its mtDNA with two G. irregulare isolates. We found that the mtDNA of Glomus sp. is homogeneous, identical in gene order and, with respect to the sequences of coding regions, almost identical to G. irregulare. However, certain genomic regions vary substantially, due to insertions/deletions of elements such as introns, mitochondrial plasmid-like DNA polymerase genes and mobile open reading frames. We found no evidence of mitochondrial or cytoplasmic plasmids in Glomus species, and mobile ORFs in Glomus are responsible for the formation of four gene hybrids in atp6, atp9, cox2, and nad3, which are most probably the result of horizontal gene transfer and are expressed at the mRNA level. We found evidence for substantial sequence variation in defined regions of mtDNA, even among closely related isolates with otherwise identical coding gene sequences. This variation makes it possible to design reliable intra- and inter-specific markers.

A microarray carrying 5,648 probes of Medicago truncatula root-expressed genes was screened in order to identify those that are specifically regulated by the arbuscular mycorrhizal (AM) fungus Gigaspora rosea, by Pi fertilisation or by the phytohormones abscisic acid and jasmonic acid. Amongst the identified genes, 21% showed a common induction and 31% a common repression between roots fertilised with Pi or inoculated with the AM fungus G. rosea, while there was no obvious overlap in the expression patterns between mycorrhizal and phytohormone-treated roots. Expression patterns were further studied by comparing the results with published data obtained from roots colonised by the AM fungi Glomus mosseae and Glomus intraradices, but only very few genes were identified as being commonly regulated by all three AM fungi. Analysis of Pi concentrations in plants colonised by either of the three AM fungi revealed that this could be due to the higher Pi levels in plants inoculated by G. rosea compared with the other two fungi, explaining that numerous genes are commonly regulated by the interaction with G. rosea and by phosphate. Differential gene expression in roots inoculated with the three AM fungi was further studied by expression analyses of six genes from the phosphate transporter gene family in M. truncatula. While MtPT4 was induced by all three fungi, the other five genes showed different degrees of repression mirroring the functional differences in phosphate nutrition by G. rosea, G. mosseae and G. intraradices.