Dual requirement of the LjSym4 gene for mycorrhizal development in epidermal and cortical cells of Lotus japonicus roots

• The LjSym4 mutation leads to Lotus japonicus plants that are defective in arbuscular mycorrhiza (AM) development. • Two alleles of LjSym4 with different phenotypic strength are compared here. The development of AM was assessed by considering five parameters related to fungal structures present in root segments from wild-type and mutant plants. The distribution of intercellular hyphae was determined using semithin sections from resin-embedded roots. Cellular interactions were investigated ultrastructurally, whereas cell wall components from the host plant were identified using immunogold labeling. • In roots of Ljsym4-1 mutant, fungal hyphae were mostly restricted to the intercellular spaces of the cortex, indicating a block to infection by mutant cortical cells, which resulted in a very low number of arbuscules. • This observation suggests the presence of an additional, genetically defined 'checkpoint' for mycorrhizal development, located at the wall of cortical cells. The LjSym4 gene is therefore required for infection of both epidermal and cortical cells by AM fungi.

The future has roots in the past: the ideas and scientists that shaped mycorrhizal research

Contents Summary 982 I. Introduction 982 II. The portraits of our ancestors: a gallery of ideas from more than 100 years of mycorrhizal research 983 III. Mycorrhizal fungi in the 'omics' era: first puzzle, how to name mycorrhizal fungi 985 IV. Signalling: a central question of our time? 987 V. The colonization process: how cellular studies predicted future 'omics' data 989 VI. The genetics underlying colonization events 991 VII. Concluding thoughts: chance and needs in mycorrhizal symbioses 992 Acknowledgements 992 References 992 SUMMARY: Our knowledge of mycorrhizas dates back to at least 150 years ago, when the plant pathologists A. B. Frank and G. Gibelli described the surprisingly morphology of forest tree roots surrounded by a fungal mantle. Compared with this history, our molecular study of mycorrhizas remains a young science. To trace the history of mycorrhizal research, from its roots in the distant past, to the present and the future, this review outlines a few topics that were already central in the 19^th century and were seminal in revealing the biological meaning of mycorrhizal associations. These include investigations of nutrient exchange between partners, plant responses to mycorrhizal fungi, and the identity and evolution of mycorrhizal symbionts as just a few examples of how the most recent molecular studies of mycorrhizal biology sprouted from the roots of past research. In addition to clarifying the ecological role of mycorrhizas, some of the recent results have changed the perception of the relevance of mycorrhizas in the scientific community, and in the whole of society. Looking to past knowledge while foreseeing strategies for the next steps can help us catch a glimpse of the future of mycorrhizal research.

Pre-Penetration Apparatus Formation During AM Infection is Associated With a Specific Transcriptome Response in Epidermal Cells

Arbuscular mycorrhizal (AM) associations have strikingly constant structural and functional features, irrespectively of the organisms involved. This suggests the existence of common genetic and molecular determinants. one of the most important characteristics of AMs is the coating of intracellular hyphae by a proliferation of the plant plasma membrane, which always segregates the fungus in an apoplastic interface. This process of intracellular accommodation causes a dramatic reorganization in the host cell cytoplasm, which reaches its peak with the development of the so-called prepenetration apparatus (PPA), a specialised aggregation of organelles described in epidermal cells and predicting fungal development within the cell lumen. We have recently correlated PPA development with the significant regulation of 15 Medicago truncatula genes. Among these, a nodulin-like and an expansin-like sequence are good candidates as molecular markers of epidermal cell responses to AM contact. our results also suggest a novel role for the kinase DMI3 in enhancing the upregulation of these two genes and downregulating defence-related genes such as the Avr9/Cf-9 rapidly elicited protein 264. We here comment on these recent findings and their possible outcomes.

Understanding crop colonization of oilseed rape crops by the cabbage stem flea beetle (Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae))

BACKGROUND

Development of accurate pest monitoring systems is essential for the establishment of integrated pest management strategies. Information about the pest behavior during the colonization process, as well as the sex and reproductive status of the colonizing population often are lacking and hinder their development. The cabbage stem flea beetle (CSFB, Psylliodes chrysocephala) can cause the complete destruction of oilseed rape crops (OSR, Brassica napus). In the present study, the colonization process of OSR fields by the CSFB was studied.

RESULTS

More individuals were caught on the outward facing side of the traps than the side of the trap facing towards the crop at the field border and catches were higher on the trapping units at the center of the field than at its border, suggesting that more beetles were entering than leaving the crop. Catches were higher on lower traps placed near to the crop than on those positioned further from the ground and also were higher during the day than late afternoon and night. The sex-ratio of individuals caught was skewed towards males and sexual maturity was acquired for females during the experiment. Integration of sampling data with local meteorological data showed that the catches correlated mostly with air temperature and relative humidity.

CONCLUSION

This study provides new information about the dispersion of the CSFB in OSR fields during the colonization process, and highlights correlations between local meteorological factors and activity of the CSFB, and represent a new step towards implementing monitoring strategies against this pest. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

When new human-modified habitats favour the expansion of an amphibian pioneer species: Evolutionary history of the natterjack toad (Bufo calamita) in a coal basin

Human activities affect microevolutionary dynamics by inducing environmental changes. In particular, land cover conversion and loss of native habitats decrease genetic diversity and jeopardize the adaptive ability of populations. Nonetheless, new anthropogenic habitats can also promote the successful establishment of emblematic pioneer species. We investigated this issue by examining the population genetic features and evolutionary history of the natterjack toad (Bufo [Epidalea] calamita) in northern France, where populations can be found in native coastal habitats and coalfield habitats shaped by European industrial history, along with an additional set of European populations located outside this focal area. We predicted contrasting patterns of genetic structure, with newly settled coalfield populations departing from migration-drift equilibrium. As expected, coalfield populations showed a mosaic of genetically divergent populations with short-range patterns of gene flow, and native coastal populations indicated an equilibrium state with an isolation-by-distance pattern suggestive of postglacial range expansion. However, coalfield populations exhibited (i) high levels of genetic diversity, (ii) no evidence of local inbreeding or reduced effective population size and (iii) multiple maternal mitochondrial lineages, a genetic footprint depicting independent colonization events. Furthermore, approximate Bayesian computations suggested several evolutionary trajectories from ancient isolation in glacial refugia during the Pleistocene, with biogeographical signatures of recent expansion probably confounded by human-mediated mixing of different lineages. From an evolutionary and conservation perspective, this study highlights the ecological value of industrial areas, provided that ongoing regional gene flow is ensured within the existing lineage boundaries.

Microbial Community Colonization Process Unveiled through eDNA-PFU Technology in Mesocosm Ecosystems

Microbial communities are essential components of aquatic ecosystems and are widely employed for the detection, protection, and restoration of water ecosystems. The polyurethane foam unit (PFU) method, an effective and widely used environmental monitoring technique, has been improved with the eDNA-PFU method, offering efficiency, rapidity, and standardization advantages. This research aimed to explore the colonization process of microbial communities within PFUs using eDNA-PFU technology. To achieve this, we conducted ten-day monitoring and sequencing of microbial communities within PFUs in a stable and controlled artificial aquatic ecosystem, comparing them with water environmental samples (eDNA samples). Results showed 1065 genera in eDNA-PFU and 1059 in eDNA, with eDNA-PFU detecting 99.95% of eDNA-identified species. Additionally, the diversity indices of bacteria and eukaryotes in both methods showed similar trends over time in the colonization process; however, relative abundance differed. We further analyzed the colonization dynamics of microbes in eDNA-PFU and identified four clusters with varying colonization speeds. Notably, we found differences in colonization rates between bacteria and eukaryotes. Furthermore, the Molecular Ecological Networks (MEN) showed that the network in eDNA-PFU was more modular, forming a unique microbial community differentiated from the aquatic environment. In conclusion, this study, using eDNA-PFU, comprehensively explored microbial colonization and interrelationships in a controlled mesocosm system, providing foundational data and reference standards for its application in aquatic ecosystem monitoring and beyond.

Competition in the Periphytic Algal Community during the Colonization Process: Evidence from the World's Largest Water Diversion Project

Periphytic algal colonization is common in aquatic systems, but its interspecific competition remains poorly understood. In order to fill the gap, the process of periphytic algal colonization in the Middle Route of the South to North Water Diversion Project was studied. The results showed that the process was divided into three stages: the initial colonization stage (T1, 3-6 days), community formation stage (T2, 12-18 days) and primary succession stage (T3, 24-27 days). In T1, the dominant species were Diatoma vulgaris (Bory), Navicula phyllepta (Kützing) and Fragilaria amphicephaloides (Lange-Bertalot) belonging to Heterokontophyta; these species boasted wide niche widths (NWs), low niche overlap (NO) and low ecological response rates (ERRs). In T2, the dominant species were Diatoma vulgaris, Cymbella affinis (Kützing), Navicula phyllepta, Fragilaria amphicephaloides, Gogorevia exilis (Kützing), Melosira varians (C.Agardh), Phormidium willei (N.L.Gardner) and Cladophora rivularis (Kuntze). These species displayed wider NWs, lower NO, and lower ERRs than those in T1. In T3, the dominant species were Diatoma vulgaris, Cymbella affinis, Navicula phyllepta, Fragilaria amphicephaloides, Achnanthes exigu (Grunow), etc. Among them, Heterokontophyta such as Diatoma vulgaris and Cymbella affinis had a competitive advantage based on NWs and ERRs. Cyanobacteria like Phormidium willei lost their dominant status due to the narrower NW and the increased NO. It could be concluded the interspecific competition became fiercer and shaped the colonization process; this study will be helpful in understanding the colonization of periphytic algal communities.