Diversity of a phosphate transporter gene among species and isolates of arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi (AMF) are a key group of beneficial obligate biotrophs, establishing a mutualistic symbiosis with the roots of most land plants. The molecular markers generally used for their characterization are mainly based on informative regions of nuclear rDNA (SSU-ITS-LSU), although protein-encoding genes have also been proposed. Within functional genes, those encoding for phosphate transporters (PT) are particularly important in AMF, given their primary ability to take up Pi from soil, and to differentially affect plant phosphate nutrition. In this work, we investigated the genetic diversity of PT1 gene sequences and sequences of the taxonomically relevant SSU-ITS-LSU region in two isolates of the species Funneliformis coronatus, three isolates of the species Funneliformis mosseae and two species of the genus Rhizoglomus, originated from geographically distant areas and cultured in vivo. Our results showed that partial PT1 sequences not only successfully differentiated AMF genera and species like ribosomal gene sequences but also highlighted intraspecific diversity among F. mosseae and F. coronatus isolates. The study of functional genes related to the uptake of key mineral nutrients for the assessment of AMF diversity represents a key step in the selection of efficient isolates to be used as inocula in sustainable agriculture

Arbuscular mycorrhizal fungi affect total phenolics content and antioxidant activity in leaves of oak leaf lettuce varieties

Plant secondary metabolites are considered key bioactive compounds for a healthy diet. Arbuscular mycorrhizal fungi (AMF) may interact with host plant metabolism, inducing the accumulation of health-promoting phytochemicals and antioxidant molecules. Lettuce is a largely consumed vegetable, which may interact with AMF to alter its content of secondary metabolites and natural antioxidants molecules, as previously shown in cultivars belonging to var. capitata or var. longifolia. In this study, the effects of red and green leaf Lactuca sativa var. crispa inoculation with different AMF species, Rhizoglomus irregulare and Funneliformis mosseae, were investigated, by assessing the total phenolics and anthocyanins content, and the antioxidant activity of leaf tissue. A significant increase of antioxidant activity and of phenolics were observed in plants of both cultivars inoculated with R. irregulare, compared to non inoculated plants. Likewise, anthocyanins (in red leaf lettuce) were more abundant in inoculated plants than in controls. Altogether, the results indicate that R. irregulare strain showed a stronger ability than F. mosseae in affecting plant metabolism and that mycorrhizal inoculation may be used to enhance concentration of phenolics in leaf type lettuces, provided that a suitable AMF is selected

Gene expression in Rhizoglomus irregulare at two different time points of mycorrhiza establishment in Helianthus annuus roots, as revealed by RNA-seq analysis

Arbuscular mycorrhizal fungi (AMF) play a fundamental role in plant growth and nutrition in natural and agricultural ecosystems. Despite the importance of such symbionts, the different developmental changes occurring during the AMF life cycle have not been fully elucidated at the molecular level. Here, the RNA-seq approach was used to investigate Rhizoglomus irregulare specific and common transcripts at two different time points of mycorrhizal establishment in Helianthus annuus in vivo. Four days after inoculation, transcripts related to cellular remodeling (actin and tubulin), cellular signaling (calmodulin, serine/threonine protein kinase, 14-3-3 protein, and calcium transporting ATPase), lipid metabolism (fatty acid desaturation, steroid hormone, and glycerophospholipid biosynthesis), and biosynthetic processes were detected. In addition to such transcripts, 16 days after inoculation, expressed genes linked to binding and catalytic activities; ion (K+, Ca2+, Fe2+, Zn2+, Mn2+, Pi, ammonia), sugar, and lipid transport; and those involved in vacuolar polyphosphate accumulation were found. Knowledge of transcriptomic changes required for symbiosis establishment and performance is of great importance to understand the functional role of AMF symbionts in food crop nutrition and health, and in plant diversity in natural ecosystems

Mycorrhizal activity and diversity in a long-term organic Mediterranean agroecosystem

In organic agriculture, soil fertility and productivity rely on biological processes carried out by soil microbes, which represent the key elements of agroecosystem functioning. Arbuscular mycorrhizal fungi (AMF), fundamental microorganisms for soil fertility, plant nutrition and health, may play an important role in organic agriculture by compensating for the reduced use of fertilizers and pesticides. Though, AMF activity and diversity following conversion from conventional to organic farming are poorly investigated. Here we studied AMF abundance, diversity and activity in short- and long-term organically and conventionally managed Mediterranean arable agroecosystems. Our results show that both AMF population activity, as assessed by the mycorrhizal inoculum potential (MIP) assay, the percentage of colonized root length of the field crop (maize) and glomalin-related soil protein (GRSP) content were higher in organically managed fields and increased with time since transition to organic farming. Here, we showed an increase of GRSP content in arable organic systems and a strong correlation with soil MIP values. The analysis of AMF spores showed differences among communities of the three microagroecosystems in terms of species richness and composition as suggested by a multivariate analysis. All our data indicate that AMF respond positively to the transition to organic farming by a progressive enhancement of their activity that seems independent from the species richness of the AMF communities. Our study contributes to the understanding of the effects of agricultural managements on AMF, which represent a promising tool for the implementation of sustainable agriculture

First evidence for a major cover crop effect on arbuscular mycorrhizal fungi and organic maize growth

Arbuscular mycorrhizal fungi are increasingly used in organic cropping systems to increase yields. Although cover crops are largely used in organic farming, there is little knowledge on the impact of cover crops on native mycorrhizal fungi. Here, we studied the effect of cover crop diversity on mycorrhizal colonization in subsequent organic maize cultivars differing in the level of genetic diversity. Experiments were conducted from 2010 to 2012 in a Mediterranean environment. First Indian mustard (Brassica juncea L. Czern.), hairy vetch (Vicia villosa Roth), a mix of seven cover crop species (Mix), and natural vegetation (Control) were cultivated as winter cover crops. Then, an organically and a conventionally bred maize hybrid and three organically bred composite cross populations were cultivated. Mycorrhizal propagule dynamics were measured. Results at juvenile stage show a higher mycorrhizal colonization in maize plants grown after hairy vetch, of 35.0 %, and Mix cover crops, of 29.4 %, compared to Indian mustard, of 20.9 %, and Control, of 21.3 %. The potential of soil mycorrhization decreased of 56.5 % following Indian mustard, higher than that of other cover crops, of 34.1–47.3 %. This finding could be explained by the release of isothiocyanates in soils. Moreover, maize shoot biomass, nitrogen, and phosphorus content across all maize genotypes at juvenile stage increased with mycorrhizal colonization. These findings provide the first evidence of the greater role played by cover crop identity in the enhancement of early mycorrhizal colonization of the subsequent crop and of soil mycorrhizal activity

Impact of nitrogen fertilization and soil tillage on arbuscular mycorrhizal fungal communities in a Mediterranean agroecosystem

The impact of nitrogen (N) fertilization and tillage on arbuscular mycorrhizal fungi (AMF) was studied in a Mediterranean arable system by combining molecular, biochemical and morphological analyses of field soil and of soil and roots from trap plants grown in microcosm. Canonical correspondence analysis (CCA) of PCR–DGGE banding patterns evidenced that AMF communities in the field are affected by N-fertilization and tillage. N-fertilization was also the main factor shaping AMF communities in Medicago sativa trap plant soil and roots. The overall sporulation pattern of the different AMF species showed a predominant effect of tillage on AMF communities, as shown by CCA analysis. Funneliformis mosseae was the predominant species sporulating in tilled soils, while Glomus viscosum and Glomus intraradices prevailed in no-tilled soils. Field glomalin-related soil protein content was reduced by tillage practices. Our multimodal approach, providing data on two main production factors affecting soil AMF communities, may help implementing effective agricultural management strategies able to support the beneficial relationship between crops and native AMF symbionts