Beatriz Estrada

Arbuscular mycorrhizal fungi native from a Mediterranean saline area enhance maize tolerance to salinity through improved ion homeostasis

Soil salinity restricts plant growth and productivity. Na(+) represents the major ion causing toxicity because it competes with K(+) for binding sites at the plasma membrane. Inoculation with arbuscular mycorrhizal fungi (AMF) can alleviate salt stress in the host plant through several mechanisms. These may include ion selection during the fungal uptake of nutrients from the soil or during transfer to the host plant. AM benefits could be enhanced when native AMF isolates are used. Thus, we investigated whether native AMF isolated from an area with problems of salinity and desertification can help maize plants to overcome the negative effects of salinity stress better than non-AM plants or plants inoculated with non-native AMF. Results showed that plants inoculated with two out the three native AMF had the highest shoot dry biomass at all salinity levels. Plants inoculated with the three native AMF showed significant increase of K(+) and reduced Na(+) accumulation as compared to non-mycorrhizal plants, concomitantly with higher K(+) /Na(+) ratios in their tissues. For the first time, these effects have been correlated with regulation of ZmAKT2, ZmSOS1 and ZmSKOR genes expression in the roots of maize, contributing to K(+) and Na(+) homeostasis in plants colonized by native AMF.

Native arbuscular mycorrhizal fungi isolated from a saline habitat improved maize antioxidant systems and plant tolerance to salinity

High soil salinity is a serious problem for crop production because most of the cultivated plants are salt sensitive, which is also the case for the globally important crop plant maize. Salinity stress leads to secondary oxidative stress in plants and a correlation between antioxidant capacity and salt tolerance has been demonstrated in several plant species. The plant antioxidant capacity may be enhanced by arbuscular mycorrhizal fungi (AMF) and it has been proposed that AM symbiosis is more effective with native than with collection AMF species. Thus, we investigated whether native AMF isolated from a dry and saline environment can help maize plants to overcome salt stress better than AMF from a culture collection and whether protection against oxidative stress is involved in such an effect. Maize plants inoculated with three native AMF showed higher efficiency of photosystem II and stomatal conductance, which surely decreased photorespiration and ROS production. Indeed, the accumulation of hydrogen peroxide, the oxidative damage to lipids and the membrane electrolyte leakage in these AM plants were significantly lower than in non-mycorrhizal plants or in plants inoculated with the collection AMF. The activation of antioxidant enzymes such as superoxide dismutase or catalase also accounted for these effects.

A native Glomus intraradices strain from a Mediterranean saline area exhibits salt tolerance and enhanced symbiotic efficiency with maize plants under salt stress conditions

AimsArbuscular mycorrhizal (AM) fungi have been shown to occur naturally in saline environments and it has been suggested that differences in fungal behaviour and efficiency can be due to the origin and adaptation of the AM fungus. These findings invite to look out for AM fungal species isolated in saline environments and compare their salt-tolerance mechanisms with those of species living in non-saline areas.MethodsA fungal strain of G. intraradices (Gi CdG) isolated from a region with serious problems of salinity and affected by desertification, has been compared with a collection strain of the same species, used as a model fungus. An in vitro experiment tested the ability of both AM fungi to grow under increasing salinity and an in vivo experiment compared their symbiotic efficiency with maize plants grown under salt stress conditions.ResultsThe isolate Gi CdG developed better under saline conditions and induced considerably the expression of GintBIP, Gint14-3-3 and GintAQP1 genes, while it showed a lower induction of GintSOD1 gene than the collection G. intraradices strain. The isolate Gi CdG also stimulated the growth of maize plants under two levels of salinity more than the collection strain. The higher symbiotic efficiency of Gi CdG was corroborated by the enhanced efficiency of photosystem II and stomatal conductance and the lower electrolyte leakage exhibited by maize plants under the different conditions assayed.ConclusionsThe higher tolerance to salinity and symbiotic efficiency exhibited by strain Gi CdG as compared to the collection G. intraradices strain may be due to a fungal adaptation to saline environments. Such adaptation may be related to the significant up-regulation of genes encoding chaperones or genes encoding aquaporins. The present study remarks that AM fungi isolated from areas affected by salinity can be a powerful tool to enhance the tolerance of crops to saline stress conditions.

PS Integrins and Laminins: Key Regulators of Cell Migration during Drosophila Embryogenesis

During embryonic development, there are numerous cases where organ or tissue formation depends upon the migration of primordial cells. In the Drosophila embryo, the visceral mesoderm (vm) acts as a substrate for the migration of several cell populations of epithelial origin, including the endoderm, the trachea and the salivary glands. These migratory processes require both integrins and laminins. The current model is that αPS1βPS (PS1) and/or αPS3βPS (PS3) integrins are required in migrating cells, whereas αPS2βPS (PS2) integrin is required in the vm, where it performs an as yet unidentified function. Here, we show that PS1 integrins are also required for the migration over the vm of cells of mesodermal origin, the caudal visceral mesoderm (CVM). These results support a model in which PS1 might have evolved to acquire the migratory function of integrins, irrespective of the origin of the tissue. This integrin function is highly specific and its specificity resides mainly in the extracellular domain. In addition, we have identified the Laminin α1,2 trimer, as the key extracellular matrix (ECM) component regulating CVM migration. Furthermore, we show that, as it is the case in vertebrates, integrins, and specifically PS2, contributes to CVM movement by participating in the correct assembly of the ECM that serves as tracks for migration.

Importance of native arbuscular mycorrhizal inoculation in the halophyte Asteriscus maritimus for successful establishment and growth under saline conditions

Background and aimsThe biological restoration of saline habitats could be achieved by using halophyte plant species together with adapted arbuscular mycorrhizal fungi (AMF). An interesting plant to be used in restoration of saline environments, Asteriscus maritimus, is highly mycotrophic. The aim of this study was to assess the effectiveness of native and allochthonous AMF to enhance the establishment and growth of the halophyte A. maritimus under saline conditions.MethodsWe studied the symbiotic effectiveness of four AMF strains (three native fungal isolates from a saline soil and one allochthonous, from collection) in A. maritimus subjected to increasing salinity stress. We measured plant physiological parameters by which AMF may ameliorate the detrimental effects of salinity stress.ResultsA. maritimus plants showed a high mycorrhizal dependency, even in absence of salt stress. Plants inoculated with native AMF had higher shoot dry weight, efficiency of photosystem II, stomatal conductance and accumulation of glutathione than those inoculated with the collection AMF at the highest level of salinity. Moreover, at this salt level, only 30xa0% of A. maritimus plants inoculated with the collection AMF survived, while with the three native AMF, the rate of survival was 100xa0%.ConclusionsResults points out the importance of native AMF inoculation in the establishment, survival and growth of A. maritimus plants. Inoculation with these native AMF enhanced A. maritimus salt tolerance by increasing efficiency of photosystem II, stomatal conductance and glutathione content and by reducing oxidative damage. Thus, the use of adequate native AMF inocula could be a critical issue for success in recovering saline degraded areas.

The conserved transmembrane proteoglycan Perdido/Kon-tiki is essential for myofibrillogenesis and sarcomeric structure in Drosophila

ABSTRACT Muscle differentiation requires the assembly of high-order structures called myofibrils, composed of sarcomeres. Even though the molecular organization of sarcomeres is well known, the mechanisms underlying myofibrillogenesis are poorly understood. It has been proposed that integrin-dependent adhesion nucleates myofibrils at the periphery of the muscle cell to sustain sarcomere assembly. Here, we report a role for the gene perdido (perd, also known as kon-tiki, a transmembrane chondroitin proteoglycan) in myofibrillogenesis. Expression of perd RNAi in muscles, prior to adult myogenesis, can induce misorientation and detachment of Drosophila adult abdominal muscles. In comparison to controls, perd-depleted muscles contain fewer myofibrils, which are localized at the cell periphery. These myofibrils are detached from each other and display a defective sarcomeric structure. Our results demonstrate that the extracellular matrix receptor Perd has a specific role in the assembly of myofibrils and in sarcomeric organization. We suggest that Perd acts downstream or in parallel to integrins to enable the connection of nascent myofibrils to the Z-bands. Our work identifies the Drosophila adult abdominal muscles as a model to investigate in vivo the mechanisms behind myofibrillogenesis.

Diversispora clara (Glomeromycetes)— a new species from saline dunes in the Natural Park Cabo de Gata (Spain)

A new species of Diversispora (Glomeromycetes) was found in saline sand dunes of the Natural Park Cabo de Gata (Almeria, Andalucia, Southern Spain) in the rhizosphere of Asteriscus maritimus, a plant species especially adapted to saline environments. The new fungal species forms brilliant white spores that are 79-130 × 75-125 µm and have one wall consisting of three layers. The subtending hyphae are, as typical for many spp., thin-walled, hyaline, and cylindrical (or rarely constricted) and flexible and fragile below the septa separating the spore and hyphal contents. The septa form regularly at the spore bases or, less frequently, in subtending hyphae at short distances from the spore base. Phylogenetic analyses of the ITS and partial 28S ribosomal gene confirm that D. clara forms a monophyletic, independent clade within Diversispora .

Kon-tiki enhances PS2 integrin adhesion and localizes its ligand, Thrombospondin, in the myotendinous junction

ABSTRACT Cell–extracellular-matrix adhesion is mediated by cell receptors, mainly integrins and transmembrane proteoglycans, which can functionally interact. How these receptors are regulated and coordinated is largely unknown. We show that the conserved transmembrane Drosophila proteoglycan Kon-tiki (Kon, also known as Perdido) interacts with the αPS2βPS integrin (αPS2 is encoded by inflated and βPS by myospheroid) to mediate muscle–tendon adhesion. kon and inflated double mutant embryos show a synergistic increase in muscle detachment. Furthermore, Kon modulates αPS2βPS signaling at the muscle attachment, since phosphorylated Fak is reduced in kon mutants. This reduction in integrin signaling can be rescued by the expression of a truncated Kon protein containing its transmembrane and extracellular domains, suggesting that these domains are sufficient to mediate this signaling. We show that these domains are sufficient to properly localize the αPS2βPS ligand, Thrombospondin, to the muscle attachment, and to partially rescue Kon-dependent muscle–tendon adhesion. We propose that Kon can engage in a protein complex with αPS2βPS and enhance integrin-mediated signaling and adhesion by recruiting its ligand, which would increase integrin-binding affinity to the extracellular matrix, resulting in the consolidation of the myotendinous junction. Summary: The Drosophila proteoglycan Kon-tiki/Perdido enhances αPS2βPS integrin adhesion and localizes its ligand, Thrombospondin. This would lead to increased integrin adhesion to the ECM, and consolidation of the muscle–tendon junction.

Analysis of the role of Nidogen/entactin in basement membrane assembly and morphogenesis in Drosophila

Basement membranes (BMs) are thin sheet-like specialized extracellular matrices found at the basal surface of epithelia and endothelial tissues. They have been conserved across evolution and are required for proper tissue growth, organization, differentiation and maintenance. The major constituents of BMs are two independent networks of Laminin and Type IV Collagen interlinked by the proteoglycan Perlecan and the glycoprotein Nidogen/entactin (Ndg). The ability of Ndg to bind in vitro Collagen IV and Laminin, both with key functions during embryogenesis, anticipated an essential role for Ndg on morphogenesis linking the Laminin and Collagen IV networks. This was supported by results from in vitro and cultured embryonic tissues experiments. However, the fact that elimination of Ndg in C. elegans and mice did not affect survival, strongly questioned this proposed linking role. Here, we have isolated mutations in the only Ndg gene present in Drosophila. We find that while, similar to C.elegans and mice, Ndg is not essential for overall organogenesis or viability, it is required for appropriate fertility. We also find, alike in mice, tissue-specific requirements of Ndg for proper assembly and maintenance of certain BMs, namely those of the adipose tissue and flight muscles. In addition, we have performed a thorough functional analysis of the different Ndg domains in vivo. Our results support an essential requirement of the G3 domain for Ndg function and unravel a new key role for the Rod domain in regulating Ndg incorporation into BMs. Furthermore, uncoupling of the Laminin and Collagen IV networks is clearly observed in the larval adipose tissue in the absence of Ndg, indeed supporting a linking role. In light of our findings, we propose that BM assembly and/or maintenance is tissue-specific, which could explain the diverse requirements of a ubiquitous conserved BM component like Nidogen. Author Summary Basement membranes (BMs) are thin layers of specialized extracellular matrices present in every tissue of the human body. Its main constituents are two networks of Laminin and Type IV Collagen linked by Nidogen (Ndg) and proteoglycans. They form an organized scaffold that regulates organ morphogenesis and function. Mutations affecting BM components are associated with organ dysfunction and several congenital diseases. Thus, a better comprehension of BM assembly and maintenance will not only help to learn more about organogenesis but also to a better understanding and, hopefully, treatment of these diseases. Here, we have used Drosophila to analyse the role of Ndg in BM formation in vivo. Elimination of Ndg in worms and mice does not affect survival, strongly questioning its proposed linking role, derived from in vitro experiments. Here, we show that in the fly Ndg is dispensable for BM assembly and preservation in many tissues, but absolutely required in others. Furthermore, our functional study of the different Ndg domains challenges the significance of some interactions between BM components derived from in vitro experiments, while confirming others, and reveals a new key requirement for the Rod domain in Ndg function and incorporation into BMs.