Harnessing the Rhizosphere of the Halophyte Grass Aeluropus littoralis for Halophilic Plant-Growth-Promoting Fungi and Evaluation of Their Biostimulant Activities

Hydroponic systems have gained interest and are increasingly used in hot and dry desert areas. Numbers of benefits are offered by hydroponic systems such as the ability to save water, enhance nutrients use efficiency, easy environmental control, and prevention of soil-borne diseases. However, the high consumption of chemical fertilizers for nutrient solution and the sensitivity of closed hydroponic systems to salinity are issues that need solutions. Thus, the main goal of our research activities is to isolate plant growth promoting fungi in order to develop sustainable hydroponic systems. We are working on isolating and testing the possibility to incorporate the cell-free filtrate (CFF) of plant growth promoting fungi (PGPF) in the composition of the nutrient solution. In this work, we isolated six strains of PGPF from the rhizosphere of the halophyte grass Aeluropus littoralis. Phylogenetic analyses of DNA sequences amplified by ITS1 and ITS4 primers identified the isolated fungi as: Byssochlamys spectabilis, Chaetomium globosum, Cephalotheca foveolata, Penicillium melinii, Alternaria tenuissima, and Nigrospora chinensis. The promoting of vigor in tobacco seedlings was used as criteria to evaluate the biostimulant activity of these fungi by adding either their mycelia (DE: direct effect) or their cell-free filtrates (CFF: indirect effect) to the plant-growth media. The best significant growth stimulation was obtained with plants treated by B. spectabilis. However, only the CFFs of Byssochlamys spectabilis (A5.1) and Penicillium melinii (A8) when added at a dilution factor of 1/50 to half-strength nutritive solution (0.5NS) resulted in significant improvement of all assessed growth parameters. Indeed, the A5.1CFF and A8CFF in 0.5NS induced a significant better increase in the biomass production when compared to NS or 0.5NS alone. All fungi produced indole acetic acid in the CFFs, which could be one of the key factors explaining their biostimulant activities. Furthermore, six genes involved in nitrogen-metabolism (NR1 and NRT1), auxin biosynthesis (Tryp1 and YUCCA6-like), and brassinosteroid biosynthesis (DET2 and DWF4) were shown to be induced in roots or leaves following treatment of plants with the all CFFs. This work opens up a prospect to study in deep the biostimulant activity of PGPFs and their applications to decrease the requirement of chemical fertilizers in the hydroponic growing systems.

Initial description of the Genome of Aeluropus littoralis, a halophile grass

Background: The use of wild plant species or their halophytic relatives has been considered in plant breeding programs to improve salt and drought tolerance in crop plants. Aeluropus littoralis serves as halophyte model for identification and isolation of novel stress adaptation genes. This species is described as perennial monocot grass. A. littoralis grows in damp or arid areas, often salt-impregnated places and waste land in cultivated areas. A. littoralis can survive where the water salinity is periodically high and tolerate high salt concentrations in the soil up to 1100 mM sodium chloride. Therefore, it serves as valuable genetic resource to understand molecular mechanisms of stress-responses in monocots. The knowledge can potentially be used for improving tolerance to abiotic stresses in economically important crops. Several morphological, anatomical, ecological, and physiological traits of A. littoralis have been investigated so far and also the transfer of stress related genes to other species resulted in enhanced stress resistance. After watering with salt water the grass is able to excrete salt via its salt glands. Meanwhile, a number of ESTs (expressed sequence tag), genes and promoters induced by the salt and drought stresses were isolated, sequenced and annotated at a molecular level.Results: Here we describe the genome sequence and structure of A. littoralis analyzed by whole genome sequencing and histological analysis. The chromosome number was determined to be 20 (2n = 2X = 20), absence of B chromsomes shown, and the genome size calculated to be 354 Megabasepairs.Conclusions: This genomic information provided here, will support the functional investigation and application of novel genes improving salt stress resistance in crop plants.

Initial Description of the Genome of Aeluropus Littoralis, a Halophile Grass

Background: The use of wild plant species or their halophytic relatives has been considered in plant breeding programs to improve salt and drought tolerance in crop plants. Aeluropus littoralis serves as halophyte model for identification and isolation of novel stress adaptation genes. This species is described as perennial monocot grass. A. littoralis grows in damp or arid areas, often salt-impregnated places and waste land in cultivated areas. A. littoralis can survive where the water salinity is periodically high and tolerate high salt concentrations in the soil up to 1100 mM sodium chloride. Therefore, it serves as valuable genetic resource to understand molecular mechanisms of stress-responses in monocots. The knowledge can potentially be used for improving tolerance to abiotic stresses in economically important crops. Several morphological, anatomical, ecological, and physiological traits of A. littoralis have been investigated so far and also the transfer of stress related genes to other species resulted in enhanced stress resistance. After watering with salt water the grass is able to excrete salt via its salt glands. Meanwhile, a number of ESTs (expressed sequence tag), genes and promoters induced by the salt and drought stresses were isolated, sequenced and annotated at a molecular level. Results: Here we describe the genome sequence and structure of A. littoralis analyzed by whole genome sequencing and histological analysis. The chromosome number was determined to be 20 (2n = 2X = 20), absence of B chromsomes shown, and the genome size calculated to be 354 Megabasepairs.Conclusions: This genomic information provided here, will support the functional investigation and application of novel genes improving salt stress resistance in crop plants.

Ion Content, Antioxidant Enzyme Activity and Transcriptional Response Under Salt Stress and Recovery Condition in the Halophyte Grass Aeluropus Littoralis

Background: The production of reactive oxygen species (ROS) is a common feature of various plant cells in dealing with abiotic stresses. Plants have developed an effective enzymatic and non-enzymatic antioxidant defense systems to scavenge ROS and cope with oxidative stress. Halophyte antioxidant defense mechanisms represent one of the best examples for this trait. Several of salt-responsive promoters and genes originated here during evolution. The present work aimed to investigate a set of physiological, elemental, biochemical and molecular responses involved in tolerance to salt stress in the halophyte grass Aeluropus littoralis. Results: The content of total Chlorophyll (Chl), Chl a and Cars were increased under salinity condition, while the Chl b content was reduced. Sodium ion (Na+) in three time-points of salinity condition (S1, S2 and S3) significantly increased, and reduction was observed in three time-points of recovery condition (R1, R2 and R3). The amount of potassium ions (K+) in leaf and stem was decreased during salt stress, and increased during recovery condition. K+ accumulations in root significantly increased in S2 and S3. Calcium (Ca2+) and magnesium (Mg2+) content significantly declined in leaf, root and stem during stress treatment, whereas it increased significantly during recovery condition in the leaves. The amount of the amino acid proline, associated with drought and salt stress, as well as the activity of ROS related enzyme showed an increase during salt treatment. The APX, POD and SOD maximum activities were reported at S3 in roots while decreased at R. RT-qPCR analysis of antioxidant related genes showed up-regulation at S1 and S3 in root, but the down-regulation was observed in R. The highest transcription levels were observed in CAT and pAPX at S1 in leaf, while the maximum levels were seen in SOD and cAPX at S2.Conclusions: The halophyte mechanisms in A. littoralis, contribute to overcome ROS in oxidative stress. SOD activity was more responsive in S, indicating the importance of SOD in oxidative damage. Increasing proline content may be considered as a stress-induced marker to identify oxidative damage. During the salt stress phase an increase of mRNA abundance from genes encoding enzymes assiciated with atioxidant activities was found. The positive correlation between the transcript level of CAT and CAT activities in leaf indicated the important regulatory function during salt stress for detoxifying ROS. Based on the transcript abundance and activity CAT is proposed as the main H2O2-scavenging enzyme to keep the balance of redox reaction in A. littoralis. The salt stress tolerance is associated with high Na+ absorbtion for osmotic balance and a corresponding reduction in K+, Mg2+, and Ca2+ ions. Further it was found that plants under S3 and R2 had more chlorophyll b content as compared to chlorophyll a that demonstrated optimization of leaf function under high salt condition.

Four new species (Trombidiformes: Eriophyoidea: Eriophyidae) and one new record of Aceria from arid and semi-arid areas in East Iran

During the field study of eriophyoid mites from autochthonous plants in semi-arid and arid environment in East Iran (Birjand, South Khorasan, from 2016 to 2017), four new Aceria species (Trombidiformes: Eriophyoidea: Eriophyidae) were collected. They are Aceria halothamni sp. nov. on Halothamnus auriculus (Moq.) Botsch. (Amaranthaceae), Aceria acanthophylli sp. nov. on Acanthophyllum sordidum Bunge ex Boiss. (Caryophyllaceae), Aceria samoli sp. nov. on Samolus valerandi L. (Primulaceae), Aceria aeluropi sp. nov. on Aeluropus littoralis (Gouan) Parl. (Poaceae). In addition, Aceria atriplicis Wilson & Oldfield, 1966 was also found on Atriplex leucoclada Boiss. (Amaranthaceae), which is a new record for Iran. All these species are illustrated and described herein. They appear to be vagrants and no symptom was observed on their infested plants.