The Change in Fatty Acids and Sugars Reveals the Association between Trifoliate Orange and Endophytic Fungi

Chemical and physical characteristics of wheat root mucilage influenced by Serendipita indica symbiosis: a comparison among four cultivars

Although there is evidence to suggest that the endophytic fungus Serendipita indica plays a crucial role in enhancing plant tolerance against biotic/abiotic stressors, less is known about the impacts of this symbiosis association on root mucilage chemical composition and its physical functions. The mucilage of inoculated and non-inoculated seedlings of four wheat cultivars (i.e., Roshan, Ghods, Kavir and Pishtaz) were extracted using an aeroponic method. Total solute concentration (TCm), carbon content (Cmucilage), electrical conductivity (EC), pH, fatty acids, surface tension (σm), and viscosity (ηm) of mucilage were measured. Ghods and Kavir had the highest and lowest root colonization percents, respectively. Saturated fatty acids, including palmitic and stearic acids, were dominant over unsaturated fatty acids in wheat root mucilage. However, their compositions were significantly different among wheat cultivars. S. indica colonization, especially for Ghods, increased the TCm, Cmucilage, and palmitic acid. Moreover, root mucilage of S. indica-inoculated Ghods had lower σm and greater ηm. An increased amount of powerful surfactants like palmitic acid in the mucilage of S. indica inoculated treatments led to lower σm and greater ηm. Such studies provide further support for the idea that plant-released mucilage plays a major role in modifying the physical environment of the rhizosphere. This knowledge toward truly understanding the rhizosphere can be potentially used for improving the rhizosphere soil quality and increasing crop growth and yield.

Molecular insights and omics-based understanding of plant-microbe interactions under drought stress

The detrimental effects of adverse environmental conditions are always challenging and remain a major concern for plant development and production worldwide. Plants deal with such constraints by physiological, biochemical, and morphological adaptations as well as acquiring mutual support of beneficial microorganisms. As many stress-responsive traits of plants are influenced by microbial activities, plants have developed a sophisticated interaction with microbes to cope with adverse environmental conditions. The production of numerous bioactive metabolites by rhizospheric, endo-, or epiphytic microorganisms can directly or indirectly alter the root system architecture, foliage production, and defense responses. Although plant-microbe interactions have been shown to improve nutrient uptake and stress resilience in plants, the underlying mechanisms are not fully understood. "Multi-omics" application supported by genomics, transcriptomics, and metabolomics has been quite useful to investigate and understand the biochemical, physiological, and molecular aspects of plant-microbe interactions under drought stress conditions. The present review explores various microbe-mediated mechanisms for drought stress resilience in plants. In addition, plant adaptation to drought stress is discussed, and insights into the latest molecular techniques and approaches available to improve drought-stress resilience are provided.

Use of Piriformospora indica to Promote Growth of Strawberry Daughter Plants

As an endophytic fungus, the growth-promoting effects of Piriformospora indica have been widely confirmed in many of its host plants. In this study, we investigated the influences of P. indica colonization on the growth of the daughter plants of two strawberry cultivars, ‘Benihoppe’ and ‘Sweet Charlie.’ The results showed that the fungus colonization significantly promoted the growth of the daughter plants of both of the two strawberry varieties. Its colonization greatly improved almost all of the growth parameters of the ‘Benihoppe’ daughter plants, including the above-ground fresh weight, above-ground dry weight, root fresh weight, root dry weight, plant height, petiole length, leaf area, number of roots and chlorophyll content. However, the fungus colonization showed significant improving effects on only the above-ground fresh weight, root fresh weight and root dry weight of ‘Sweet Charlie.’ Surprisingly, the average root length of ‘Benihoppe’ and ‘Sweet Charlie’ was suppressed by about 14.3% and 24.6%, respectively, by P. indica. Moreover, after P. indica colonization, the leaf nitrate reductase activity and root activity upregulated by 30.12% and 12.74%, and 21.85% and 21.16%, respectively, for the ‘Benihoppe’ and ‘Sweet Charlie’ daughter plants. Our study indicated that P. indica could promote the growth of strawberry daughter plants by improving rooting, strengthening photosynthetic pigments production and nutrient absorption and accelerating biomass accumulation. The fungus shows great potential to be used in the strawberry industry, especially in the breeding of daughter plants.

Arbuscular Mycorrhizal Fungi and Endophytic Fungi Activate Leaf Antioxidant Defense System of Lane Late Navel Orange

Arbuscular mycorrhizal (AM) fungi and endophytic fungi collectively symbiose well with plants and, thus, stimulate plant growth; however, it is not clear whether field inoculation of the fungi enhances the resistance potential of plants, particularly in citrus. In the present study, we inoculated AM fungi (Acaulospora scrobiculata, Diversispora spurca, and D. versiformis) and endophytic fungi (Piriformospora indica) on an eight-year-old lane late navel orange (Citrus sinensis (L.) Osb) trees grafted on Poncirus trifoliata in a field, and we analyzed the response of the leaf antioxidant defense system. Approximately 2 years after inoculation, the root fungal colonization rate and soil hyphal length significantly increased. Fungal inoculation significantly increased the activity of leaf antioxidant enzymes, such as superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase, and the content of non-enzymatic antioxidants, such as reduced ascorbic acid and reduced glutathione. As a result, fungi-inoculated plants maintained lower concentrations of hydrogen peroxide and superoxide anion radicals and lower levels of membrane lipid peroxidation (according to malondialdehyde level) in leaves than uninoculated plants. Among them, inoculation of D. spurca and A. scrobiculata showed relatively higher effects in enhancing the antioxidant defense system than the other fungi. Furthermore, inoculation of D. spurca induced expressions of CsFe-SOD, CsMn-SOD, CsPOD, CsCAT1, and CsPRR7; inoculation of A. scrobiculata and D. versiformis induced expressions of CsCAT1; CsCAT1 and CsPOD were also induced by inoculation of P. indica. All four inoculations almost upregulated expressions of CsFAD6. AM fungi had superior effects than endophytic fungi (e.g., P. indica). According to our findings, inoculation with beneficial fungi, specifically mycorrhizal fungus D. spurca, activated the antioxidant defense system of field citrus trees, thus, having potentially superior resistance in inoculated plants.

Root Endophytic Fungi Regulate Changes in Sugar and Medicinal Compositions of Polygonum cuspidatum

Polygonum cuspidatum Sieb. et Zucc is an important industrial crop because it contains a large amount of medicinal secondary metabolites (such as polydatin, resveratrol, chrysophanol, and emodin). However, it is unclear whether root endophytic fungi increase the content of secondary metabolites in the plant. This study aimed to analyze the effects of Funneliformis mosseae (Fm) and Piriformospora indica (Pi) alone or in combination on plant growth, root morphology, thirteen sugars concentrations, and six secondary metabolites (physcion, chrysophanol, emodin, aloe-emodin, polydatin, and resveratrol) concentrations of P. cuspidatum. After 11 weeks of the fungal inoculation, the roots could be colonized by Fm and Pi single or in combination, along with the higher root colonization frequency of Fm > Pi > Fm + Pi in the descending order. In addition, Fm and Pi improved plant growth performance (plant height, stem diameter, leaf number, and shoot and root biomass) and root morphology (average diameter, maximum diameter, total length, area, and volume) to varying degrees, depending on fungal inoculations, in which Pi displayed a relatively better effect on plant growth. Single Fm and Pi inoculation significantly increased three disaccharides (sucrose, maltose, and trehalose) accumulation, while dual inoculum (Fm + Pi) only elevated sucrose concentrations. Most monosaccharides concentrations, such as D-arabinose, D-galactose, D-sorbitol, D-fructose, glucose, and L-rhamnose were not altered or inhibited by the endophytic fungi, except the increase in L-fucose and inositol. All fungal treatments significantly increased root chrysophanol and resveratrol concentrations, while decreased aloe-emodin concentrations. In addition, single Pi and dual Fm + Pi increased emodin concentrations, and single Fm and dual Fm + Pi elevated physcion and polydatin concentrations. It was concluded that Fm and Pi promoted the growth of P. cuspidatum, and the combination of Fm and Pi was more conducive to the production of some secondary metabolites than single inoculation.

Elucidating the Mechanisms Underlying Enhanced Drought Tolerance in Plants Mediated by Arbuscular Mycorrhizal Fungi

Plants are often subjected to various environmental stresses during their life cycle, among which drought stress is perhaps the most significant abiotic stress limiting plant growth and development. Arbuscular mycorrhizal (AM) fungi, a group of beneficial soil fungi, can enhance the adaptability and tolerance of their host plants to drought stress after infecting plant roots and establishing a symbiotic association with their host plant. Therefore, AM fungi represent an eco-friendly strategy in sustainable agricultural systems. There is still a need, however, to better understand the complex mechanisms underlying AM fungi-mediated enhancement of plant drought tolerance to ensure their effective use. AM fungi establish well-developed, extraradical hyphae on root surfaces, and function in water absorption and the uptake and transfer of nutrients into host cells. Thus, they participate in the physiology of host plants through the function of specific genes encoded in their genome. AM fungi also modulate morphological adaptations and various physiological processes in host plants, that help to mitigate drought-induced injury and enhance drought tolerance. Several AM-specific host genes have been identified and reported to be responsible for conferring enhanced drought tolerance. This review provides an overview of the effect of drought stress on the diversity and activity of AM fungi, the symbiotic relationship that exists between AM fungi and host plants under drought stress conditions, elucidates the morphological, physiological, and molecular mechanisms underlying AM fungi-mediated enhanced drought tolerance in plants, and provides an outlook for future research.