Non-host plants: Are they mycorrhizal networks players?

Phosphatases: Decoding the Role of Mycorrhizal Fungi in Plant Disease Resistance

Mycorrhizal fungi, a category of fungi that form symbiotic relationships with plant roots, can participate in the induction of plant disease resistance by secreting phosphatase enzymes. While extensive research exists on the mechanisms by which mycorrhizal fungi induce resistance, the specific contributions of phosphatases to these processes require further elucidation. This article reviews the spectrum of mycorrhizal fungi-induced resistance mechanisms and synthesizes a current understanding of how phosphatases mediate these effects, such as the induction of defense structures in plants, the negative regulation of plant immune responses, and the limitation of pathogen invasion and spread. It explores the role of phosphatases in the resistance induced by mycorrhizal fungi and provides prospective future research directions in this field.

Arbuscular Mycorrhizal Fungi as Biostimulant and Biocontrol Agents: A Review

Arbuscular mycorrhizal fungi (AMF) are soil microorganisms living in symbiosis with most terrestrial plants. They are known to improve plant tolerance to numerous abiotic and biotic stresses through the systemic induction of resistance mechanisms. With the aim of developing more sustainable agriculture, reducing the use of chemical inputs is becoming a major concern. After providing an overview on AMF history, phylogeny, development cycle and symbiosis benefits, the current review aims to explore the potential of AMF as biostimulants and/or biocontrol agents. Nowadays, AMF inoculums are already increasingly used as biostimulants, improving mineral nutrient plant acquisition. However, their role as a promising tool in the biocontrol market, as an alternative to chemical phytosanitary products, is underexplored and underdiscussed. Thus, in the current review, we will address the mechanisms of mycorrhized plant resistance to biotic stresses induced by AMF, and highlight the various factors in favor of inoculum application, but also the challenges that remain to be overcome.

Facilitative and competitive interactions between mycorrhizal and nonmycorrhizal plants in an extremely phosphorus-impoverished environment: role of ectomycorrhizal fungi and native oomycete pathogens in shaping species coexistence

Nonmycorrhizal cluster root-forming species enhance the phosphorus (P) acquisition of mycorrhizal neighbours in P-impoverished megadiverse systems. However, whether mycorrhizal plants facilitate the defence of nonmycorrhizal plants against soil-borne pathogens, in return and via their symbiosis, remains unknown. We characterised growth and defence-related compounds in Banksia menziesii (nonmycorrhizal) and Eucalyptus todtiana (ectomycorrhizal, ECM) seedlings grown either in monoculture or mixture in a multifactorial glasshouse experiment involving ECM fungi and native oomycete pathogens. Roots of B. menziesii had higher levels of phytohormones (salicylic and jasmonic acids, jasmonoyl-isoleucine and 12-oxo-phytodienoic acid) than E. todtiana which further activated a salicylic acid-mediated defence response in roots of B. menziesii, but only in the presence of ECM fungi. We also found that B. menziesii induced a shift in the defence strategy of E. todtiana, from defence-related secondary metabolites (phenolic and flavonoid) towards induced phytohormone response pathways. We conclude that ECM fungi play a vital role in the interactions between mycorrhizal and nonmycorrhizal plants in a severely P-impoverished environment, by introducing a competitive component within the facilitation interaction between the two plant species with contrasting nutrient-acquisition strategies. This study sheds light on the interplay between beneficial and detrimental soil microbes that shape plant-plant interaction in severely nutrient-impoverished ecosystems.

An efficient in vitro organogenesis protocol for the endangered relic tree species Bretschneidera sinensis and genetic fidelity assessment using DNA markers

Bretschneidera sinensis is a monotypic species of rare and tertiary relic trees mainly distributed in China. B. sinensis is a potentially valuable horticultural plant, which has significant ornamental and research value, and is a crucial tool for the study of phylogeography. The artificial cultivation of B. sinensis is of great scientific value and practical significance. In this study, we developed a direct organogenesis process of B. sinensis using mature zygotic embryos as initial materials. The highest sterile germination induction (54.5%) from the mature zygotic embryo was obtained in a Murashige and Skoog (MS) medium with 2.0 mg·L-1 6-benzylaminopurine (6-BA) and 0.2 mg·L-1 α-naphthaleneacetic acid (NAA). The highest percentage of shoot regeneration (90.37%) was attained using 1.0 mg·L-1 6-BA and 0.01 mg·L-1 NAA in the MS medium. The Woody Plant Medium (WPM) had the greatest adventitious shoot elongation rate of 93.33%. The most optimized rooting rate was 88.89% in a half-strength MS medium containing 2.0 mg·L-1 indole-3-butyric acid (IBA) and 1.0 mg·L-1 NAA. The genetic fidelity of in vitro regenerated plantlets was assessed using inter-simple sequence repeats and random amplified polymorphic DNA molecular markers, confirming the genetic uniformity and stability of regenerated B. sinensis plantlets. Our research presents an effective in vitro propagation system for B. sinensis, laying the groundwork for its germplasm conservation and large-scale production while maintaining high genetic integrity.

Root structure syndromes of four families of monocots in the Middle Urals

The present article tests the following general assumption: plant taxa with different specializations towards mycorrhizal interactions should have different root syndromes. Roots of 61 species common in boreal zone were studied: 16 species of Poaceae, 24 species of Cyperaceae, 14 species of Orchidaceae, and 7 species of Iridaceae. Using a fixed material of 5 individuals of each species, the following was determined: number of orders of branching roots; transverse dimensions of root, stele and cortex; number of primary xylem vessels and exodermis layers; length of root hairs; abundance of mycorrhiza. Species of each family had well-defined syndromes. Roots of Orchidaceae and Iridaceae were thick with a large stele and developed exodermis. Orchidaceae had no branching roots and had long root hairs. In Iridaceae, roots were branched, and root hairs were short. Roots of Poaceae and Cyperaceae were thin with a relatively thin stele. Root hairs were short in Poaceae and long in Cyperaceae. Our finding that root syndromes of four families of monocots differed is a new and unexpected discovery. The high specificity of root syndromes in Cyperaceae, Iridaceae, Poaceae, and Orchidaceae indicates that species of these families use different strategies to obtain water and soil nutrients.

Arbuscular mycorrhizal fungi-indicative blumenol-C-glucosides predict lipid accumulations and fitness in plants grown without competitors

Hydroxy- and carboxyblumenol C-glucosides specifically accumulate in roots and leaves of plants harboring arbuscular mycorrhizal fungi (AMF). To explore blumenol function in AMF relationships, we silenced an early key-gene in blumenol biosynthesis, CCD1 (carotenoid cleavage dioxygenase 1), in the ecological model plant, Nicotiana attenuata, and analyzed whole-plant performance in comparison with control and CCaMK-silenced plants, unable to form AMF associations. Root blumenol accumulations reflected a plant's Darwinian fitness, as estimated by capsule production, and were positively correlated with AMF-specific lipid accumulations in roots, with relationships that changed as plants matured when grown without competitors. When grown with wild-type competitors, transformed plants with decreased photosynthetic capacity or increased carbon flux to roots had blumenol accumulations that predicted plant fitness and genotype trends in AMF-specific lipids, but had similar levels of AMF-specific lipids between competing plants, likely reflecting AMF-networks. We propose that when grown in isolation, blumenol accumulations reflect AMF-specific lipid allocations and plant fitness. When grown with competitors, blumenol accumulations predict fitness outcomes, but not the more complicated AMF-specific lipid accumulations. RNA-seq analysis provided candidates for the final biosynthetic steps of these AMF-indicative blumenol C-glucosides; abrogation of these steps will provide valuable tools for understanding blumenol function in this context-dependent mutualism.

Seasonal patterns of rhizosphere microorganisms suggest carbohydrate-degrading and nitrogen-fixing microbes contribute to the attribute of full-year shooting in woody bamboo Cephalostachyum pingbianense

Compared with the ordinary single-season shooting among woody bamboos in Poaceae, the attribute of full-year shooting in Cephalostachyum pingbianense represents a unique shooting type or mechanism. Nevertheless, except for the overall physiological mechanism, the effect of ecological factors, especially soil microorganisms, on this full-year shooting characteristic remains unclear. In this study, 16S rRNA and ITS rRNA genes were sequenced using the Illumina platform. Our aims were to detect the seasonal changes in rhizospheric microbial communities of C. pingbianense and to discover the correlations of soil microbes with soil properties and bamboo shoot productivity. The results showed that seasonal change had no significant effect on bacterial alpha diversity, but significantly affected bacterial and fungal community structures as well as fungal richness. Among all soil properties examined, soil temperature, soil moisture and organic matter were the predominant factors affecting bacterial community diversity and structure. Soil temperature and soil moisture also significantly influenced fungal community structure, while available phosphorus had the greatest effect on fungal diversity. In each season, bacterial genera Acidothermus, Roseiarcus, and Bradyrhizobium, along with fungal genera Saitozyma, Mortierella, Trichoderma, etc., were dominant in bacterial and fungal communities, respectively. Bacterial community functions in four seasons were dominated by chemoheterotrophy, cellulolysis, and nitrogen fixation. Saprotrophic fungi occupied a high proportion in soil samples of all seasons. In addition, correlation analysis revealed that the bamboo shoot productivity was positively correlated with multiple microbial taxa involved in carbon and nitrogen cycles. It is proposed that highly abundant microbes involved in carbohydrate degradation and nitrogen fixation in the rhizosphere soil may contribute to the attribute of producing bamboo shoots all year round in C. pingbianense. This study is among the few cases revealing the connection between bamboo shooting characteristics and soil microorganisms, and provides new physiological and ecological insights into the forest management of woody bamboos.

Elevation and plant species identity jointly shape a diverse arbuscular mycorrhizal fungal community in the High Arctic

Knowledge about the distribution and local diversity patterns of arbuscular mycorrhizal (AM) fungi are limited for extreme environments such as the Arctic, where most studies have focused on spore morphology or root colonization. We here studied the joint effects of plant species identity and elevation on AM fungal distribution and diversity. We sampled roots of 19 plant species in 18 locations in Northeast Greenland, using next generation sequencing to identify AM fungi. We studied the joint effect of plant species, elevation and selected abiotic conditions on AM fungal presence, richness and composition. We identified 29 AM fungal virtual taxa (VT), of which six represent putatively new VT. Arbuscular mycorrhizal fungal presence increased with elevation, and as vegetation cover and the active soil layer decreased. Arbuscular mycorrhizal fungal composition was shaped jointly by elevation and plant species identity. We demonstrate that the Arctic harbours a relatively species-rich and nonrandomly distributed diversity of AM fungi. Given the high diversity and general lack of knowledge exposed herein, we encourage further research into the diversity, drivers and functional role of AM fungi in the Arctic. Such insight is urgently needed for an area with some of the globally highest rates of climate change.

Plant invasions facilitated by suppression of root nutrient acquisition rather than by disruption of mycorrhizal association in the native plant

Invasive species have profound negative impacts on native ranges. Unraveling the mechanisms employed by invasive plant species is crucial to controlling invasions. One important approach that invasive plants use to outcompete native plants is to disrupt mutualistic interactions between native roots and mycorrhizal fungi. However, it remains unclear how differences in the competitive ability of invasive plants affect native plant associations with mycorrhizae. Here, we examined how a native plant, Xanthium strumarium, responds to invasive plants that differed in competitive abilities (i.e., as represented by aboveground plant biomass) by measuring changes in root nitrogen concentration (root nutrient acquisition) and mycorrhizal colonization rate. We found that both root nitrogen concentration and mycorrhizal colonization rate in the native plant were reduced by invasive plants. The change in mycorrhizal colonization rate of the native plant was negatively correlated with both aboveground plant biomass of the invasive plants and the change in aboveground plant biomass of the native plant in monocultures relative to mixed plantings. In contrast, the change in root nitrogen concentration of the native plant was positively correlated with aboveground plant biomass of the invasive plants and the change in aboveground plant biomass of the native plant. When we compared the changes in mycorrhizal colonization rate and root nitrogen concentration in the native plant grown in monocultures with those of native plants grown with invasive plants, we observed a significant tradeoff. Our study shows that invasive plants can suppress native plants by reducing root nutrient acquisition rather than by disrupting symbiotic mycorrhizal associations, a novel finding likely attributable to a low dependence of the native plant on mycorrhizal fungi.