Receptor-associated kinases control the lipid provisioning program in plant-fungal symbiosis

Evolution of small molecule-mediated regulation of arbuscular mycorrhiza symbiosis

The arbuscular mycorrhizal (AM) symbiosis formed by most extant land plants with symbiotic fungi evolved 450 Ma. AM promotes plant growth by improving mineral nutrient and water uptake, while the symbiotic fungi obtain carbon in return. A number of plant genes regulating the steps leading to an efficient symbiosis have been identified; however, our understanding of the metabolic processes involved in the symbiosis and how they were wired to symbiosis regulation during plant evolution remains limited. Among them, the exchange of chemical signals, the activation of dedicated biosynthesis pathways and the production of secondary metabolites regulating late stages of the AM symbiosis begin to be well described across several land plant clades. Here, we review our current understanding of these processes and propose future directions to fully grasp the phylogenetic distribution and role played by small molecules during this ancient plant symbiosis. This article is part of the theme issue 'The evolution of plant metabolism'.

Alpine and subalpine plant microbiome mediated plants adapt to the cold environment: A systematic review

With global climate change, ecosystems are affected, some of which are more vulnerable than others, such as alpine ecosystems. Microbes play an important role in environmental change in global ecosystems. Plants and microbes are tightly associated, and symbiotic or commensal microorganisms are crucial for plants to respond to stress, particularly for alpine plants. The current study of alpine and subalpine plant microbiome only stays at the community structure scale, but its ecological function and mechanism to help plants to adapt to the harsh environments have not received enough attention. Therefore, it is essential to systematically understand the structure, functions and mechanisms of the microbial community of alpine and subalpine plants, which will be helpful for the conservation of alpine and subalpine plants using synthetic microbial communities in the future. This review mainly summarizes the research progress of the alpine plant microbiome and its mediating mechanism of plant cold adaptation from the following three perspectives: (1) Microbiome community structure and their unique taxa of alpine and subalpine plants; (2) The role of alpine and subalpine plant microbiome in plant adaptation to cold stress; (3) Mechanisms by which the microbiome of alpine and subalpine plants promotes plant adaptation to low-temperature environments. Finally, we also discussed the future application of high-throughput technologies in the development of microbial communities for alpine and subalpine plants. The existing knowledge could improve our understanding of the important role of microbes in plant adaptation to harsh environments. In addition, perspective further studies on microbes' function confirmation and microbial manipulations in microbiome engineering were also discussed.

Sugars, Lipids and More: New Insights Into Plant Carbon Sources During Plant-Microbe Interactions

Heterotrophic microbes rely on host-derived carbon sources for their growth and survival. Depriving pathogens of plant carbon is therefore a promising strategy for protecting plants from disease and reducing yield losses. Importantly, this carbon starvation-mediated resistance is expected to be more broad-spectrum and durable than race-specific R-gene-mediated resistance. Although sugars are well characterized as major carbon sources for bacteria, emerging evidence suggests that plant-derived lipids are likely to be an essential carbon source for some fungal microbes, particularly biotrophs. Here, we comprehensively discuss the dual roles of carbon sources (mainly sugars and lipids) and their transport processes in immune signalling and microbial nutrition. We summarize recent findings revealing the crucial roles of lipids as susceptibility factors at all stages of pathogen infection. In particular, we discuss the potential pathways by which lipids and other plant carbon sources are delivered to biotrophs, including protein-mediated transport, vesicle trafficking and autophagy. Finally, we highlight knowledge gaps and offer suggestions for clarifying the mechanisms that underlie nutrient uptake by biotrophs, providing guidance for future research on the application of carbon starvation-mediated resistance.

Potential Regulatory Effects of Arbuscular Mycorrhizal Fungi on Lipid Metabolism of Maize in Response to Low-Temperature Stress

The specific mechanisms underlying membrane lipid remodeling and changes in gene expression induced by arbuscular mycorrhizal fungi (AMF) in low-temperature-stressed plants are still unclear. In this study, physiological, transcriptomic, and lipidomic analyses were used to elucidate the physiological mechanisms by which AMF can enhance the adaptation of maize plants to low-temperature stress. The results showed that the relative electrical conductivity and malondialdehyde content of maize leaves were decreased after the inoculation with AMF, indicating that AMF reduced the peroxidation of membrane lipids and maintained the fluidity of the cell membrane. Transcriptomic analysis showed the presence of 702 differentially expressed genes induced by AMF in maize plants exposed to low-temperature stress. Furthermore, lipidomic analysis revealed changes in 10 lipid classes in AMF-inoculated maize plants compared with their noninoculated counterparts under low-temperature stress conditions. Lipid remodeling is an important strategy that arbuscular mycorrhizal plants adopt to cope with low-temperature stress.

Breaking barriers: improving time and space resolution of arbuscular mycorrhizal symbiosis with single-cell sequencing approaches

The cell and molecular bases of arbuscular mycorrhizal (AM) symbiosis, a crucial plant-fungal interaction for nutrient acquisition, have been extensively investigated by coupling traditional RNA sequencing techniques of roots sampled in bulk, with methods to capture subsets of cells such as laser microdissection. These approaches have revealed central regulators of this complex relationship, yet the requisite level of detail to effectively untangle the intricacies of temporal and spatial development remains elusive.The recent adoption of single-cell RNA sequencing (scRNA-seq) techniques in plant research is revolutionizing our ability to dissect the intricate transcriptional profiles of plant-microbe interactions, offering unparalleled insights into the diversity and dynamics of individual cells during symbiosis. The isolation of plant cells is particularly challenging due to the presence of cell walls, leading plant researchers to widely adopt nuclei isolation methods. Despite the increased resolution that single-cell analyses offer, it also comes at the cost of spatial perspective, hence, it is necessary the integration of these approaches with spatial transcriptomics to obtain a comprehensive overview.To date, few single-cell studies on plant-microbe interactions have been published, most of which provide high-resolution cell atlases that will become crucial for fully deciphering symbiotic interactions and addressing future questions. In AM symbiosis research, key processes such as the mutual recognition of partners during arbuscule development within cortical cells, or arbuscule senescence and degeneration, remain poorly understood, and these advancements are expected to shed light on these processes and contribute to a deeper understanding of this plant-fungal interaction.

Walking on a tightrope: cell wall-associated kinases act as sensors and regulators of immunity and symbiosis

This article is a Commentary on Zhang et al. (2024), 242: 2180–2194.

Genome-Wide Identification and Evolutionary Analysis of Receptor-like Kinase Family Genes Provides Insights into Anthracnose Resistance of Dioscorea alata

Dioscorea alata, commonly known as "greater yam", is a vital crop in tropical and subtropical regions of the world, yet it faces significant threats from anthracnose disease, mainly caused by Colletotrichum gloeosporioides. However, exploring disease resistance genes in this species has been challenging due to the difficulty of genetic mapping resulting from the loss of the flowering trait in many varieties. The receptor-like kinase (RLK) gene family represents essential immune receptors in plants. In this study, genomic analysis revealed 467 RLK genes in D. alata. The identified RLKs were distributed unevenly across chromosomes, likely due to tandem duplication events. However, a considerable number of ancient whole-genome or segmental duplications dating back over 100 million years contributed to the diversity of RLK genes. Phylogenetic analysis unveiled at least 356 ancient RLK lineages in the common ancestor of Dioscoreaceae, which differentially inherited and expanded to form the current RLK profiles of D. alata and its relatives. The analysis of cis-regulatory elements indicated the involvement of RLK genes in diverse stress responses. Transcriptome analysis identified RLKs that were up-regulated in response to C. gloeosporioides infection, suggesting their potential role in resisting anthracnose disease. These findings provide novel insights into the evolution of RLK genes in D. alata and their potential contribution to disease resistance.

A receptor required for chitin perception facilitates arbuscular mycorrhizal associations and distinguishes root symbiosis from immunity

Plants establish symbiotic associations with arbuscular mycorrhizal fungi (AMF) to facilitate nutrient uptake, particularly in nutrient-limited conditions. This partnership is rooted in the plant's ability to recognize fungal signaling molecules, such as chitooligosaccharides (chitin) and lipo-chitooligosaccharides. In the legume Medicago truncatula, chitooligosaccharides trigger both symbiotic and immune responses via the same lysin-motif-receptor-like kinases (LysM-RLKs), notably CERK1 and LYR4. The nature of plant-fungal engagement is opposite according to the outcomes of immunity or symbiosis signaling, and as such, discrimination is necessary, which is challenged by the dual roles of CERK1/LYR4 in both processes. Here, we describe a LysM-RLK, LYK8, that is functionally redundant with CERK1 for mycorrhizal colonization but is not involved in chitooligosaccharides-induced immunity. Genetic mutation of both LYK8 and CERK1 blocks chitooligosaccharides-triggered symbiosis signaling, as well as mycorrhizal colonization, but shows no further impact on immunity signaling triggered by chitooligosaccharides, compared with the mutation of CERK1 alone. LYK8 interacts with CERK1 and forms a receptor complex that appears essential for chitooligosaccharides activation of symbiosis signaling, with the lyk8/cerk1 double mutant recapitulating the impact of mutations in the symbiosis signaling pathway. We conclude that this novel receptor complex allows chitooligosaccharides activation specifically of symbiosis signaling and helps the plant to differentiate between activation of these opposing signaling processes.