Cell-surface receptors play a central role in plant defence by enabling the perception of microbial signatures upon initial contact, activating immune responses and protecting the plant against invasion. In solanaceous plants such as tomato, potato, pepper and their wild relatives, these receptors include pattern-recognition receptors (PRRs) that contribute to recognition of bacteria, fungi and oomycetes. PRR detection of conserved microbe-associated molecular patterns (MAMPs) initiates downstream defence responses that can include the formation of reactive oxygen species, the initiation of MAPK cascades, and the upregulation of defence genes, collectively known as pattern-triggered immunity (PTI). Additional immune receptors at the cell surface detect secreted pathogen virulence proteins and can provide race-specific resistance in the Solanaceae, contributing to a layered defence network that balances broad-spectrum recognition with pathogen-specific immune responses. This review highlights cell-surface immune receptors in the Solanaceae, including PRRs and additional extracellular surveillance proteins that recognize phytopathogens and phytoparasites. We focus on the overall diversity of receptors among solanaceous species, the role of co-receptors in receptor complexes, and downstream signalling networks activated upon MAMP perception. Additionally, we discuss the challenges of inter- and intraspecies receptor compatibility as a limiting step in genetic engineering approaches using solanaceous PRRs for broad-spectrum disease management.

Since its initial detection in Indiana and Illinois in 2015, tar spot of maize, caused by Phyllachora maydis, has rapidly emerged as a significant constraint to maize (Zea mays) production in the continental United States. Over the past decade, this pathogen has caused recurrent disease epidemics throughout maize-growing regions across the United States and Canada, causing substantial yield losses. Notably, in 2024, tar spot was responsible for an estimated economic yield loss of $1.37 billion to U.S. farmers. Despite its agronomic impact to U.S. agriculture, no definitive sources of genetic resistance to P. maydis have been identified in maize germplasm, underscoring a critical need to elucidate the molecular and genetic basis of disease resistance. Accordingly, recent studies have begun to investigate the genetic, molecular, and cellular mechanisms underlying P. maydis virulence and host colonization, with the long-term goal of developing durable resistance strategies. In this review, we synthesize the latest advances in our understanding of host-pathogen interactions within the maize-P. maydis pathosystem, with a focused emphasis on the genetic, molecular, and cellular dynamics that shape these interactions. Building on these insights, we outline key knowledge gaps and propose future research priorities aimed at accelerating the development of durable resistance and effective disease management strategies. Given the significant agricultural impact of P. maydis, coupled with its continued geographical expansion, we propose that this fungal pathogen poses an emerging threat to global maize production and emphasize the necessity for sustained research efforts to improve host resistance and disease management strategies. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2026.

Plants grown in spaceflight exhibit differences in physiology and morphology compared to those grown on Earth. While changes in gravity are a major environmental change, other space-related stressors make it difficult to identify the microgravity-specific responses. These knowledge gaps can be filled by ground-based microgravity simulators that randomize the perceived gravity vector, but these approaches have primarily been limited to smaller plants and seedlings. This study reports a set of meter-scale 2D clinostats that support the growth of plants beyond the seedling stage. Tomato plants were grown in five sequential trials under upright rotating control and clinorotated “simulated microgravity” conditions. We found that simulated microgravity impacted plant growth in each trial, but the response varied by trial. Analysis of environmental co-variates across trials revealed that temperature significantly contributed to variation in plant growth. Further, our results show that moderate heat stress can promote plant growth under simulated microgravity. Thus, this work demonstrates the potential of meter-scale clinostats to uncover interactions between the environmental and simulated microgravity, which alter plant growth.

Variation in leaf complexity modulates light capture and is a target for crop enhancement. Soybean (Glycine max) typically has compound leaves with three leaflets each, but a spontaneous mutation, designated lf2, possesses seven leaflets, offering a means to dissect the molecular mechanisms specifying leaflet number and assess its potential for soybean improvement. However, the developmental and genetic bases of the lf2 mutation remain unknown. Here, we characterize the seven-leaflet phenotype at morphological and developmental levels and identify the mutation responsible for the phenotypic changes. Microscopic examination of leaf emergence sites revealed that the seven-leaflet phenotype arises through a two-step process: five leaflets form initially, followed by secondary leaflet initiation at the margins of the central leaflet. Genetic mapping delineated lf2 to an approximately 2.5 Mb region at the start of chromosome 11. Fortuitously, integration of pedigree analysis with comparative analysis of genomic sequences from the region pinpointed a 2-bp deletion in the coding sequence of a gene, homologous to the Arabidopsis KNAT7 encoding a KNOTTED1-LIKE HOMEOBOX 2 transcription factor, as the sole candidate for Lf2. The deletion is predicted to result in disruption of the putative DNA-binding homeodomain. Expression of the wild-type allele of the candidate gene in the seven-leaflet lf2 mutant restored the three-leaflet phenotype, validating its candidacy. Partial disruption of the wild-type allele through CRISPR-Cas9 editing induced extra leaflet formation. This study advances our understanding of leaflet formation and underscores the potential of targeted modifications at the Lf2 locus as a strategy to achieve diverse soybean plant architecture.

To combat soilborne pathogens, roots activate pattern-triggered immunity (PTI) through pattern-recognition receptors (PRRs) that recognise microbe-associated molecular patterns (MAMPs). Root PTI pathways can differ from their above-ground counterparts and have been well-characterised in the model plant Arabidopsis thaliana but are not well-defined in crops. Gene repurposing coupled with differences in root tissues and root architecture in tomato species (Solanum lycopersicum and S. pimpinellifolium) led us to hypothesise that signalling pathways of Solanaceous-specific PRRs diverge from canonical pathways. The objective of this study was to characterise PTI signalling pathways and responses (ROS, MAPK, gene expression, and growth inhibition) in roots of wild and domesticated tomatoes downstream of three immune receptors: the well-conserved SlFLS2 and the Solanaeceous-specific FLS3 and CORE. We find that Solanum root PTI responses are concentrated in early differentiating root regions compared to late differentiating regions or whole roots, and that FLS3 and CORE signalling pathways are overlapping but distinct from each other and from FLS2. Although the early differentiating root region had strong PTI responses across Solanum cultivars and species, different genetic backgrounds varied in their response dynamics. Our results underscore the complexity of PTI signalling across species and highlight the developmental-stage specificity of tomato root immunity.

Living systems process a broad range of internal and external stimuli, respond to environmental constraints, and adapt to various conditions through tight coordination between signaling networks and cellular mechanics. Among these, calcium signaling and cytoskeletal regulation form an essential interplay that spans multiple scales of biological organization-from ion-protein interactions to intercellular communication and tissue-level behaviors. Calcium ions (Ca2+) act as universal messengers, integrating a wide range of cellular signaling inputs to modulate a broad range of cellular structures and functions through the spatiotemporal dynamics of their concentration changes. Ca2+ signals follow conserved principles, despite their diverse roles, that define regulatory "Rules of Life" (RoLs)-generalized mechanisms that operate across biological contexts. This review focuses on how Ca2+ regulates and is regulated by cytoskeletal dynamics, with a particular emphasis on computational modeling for predictive simulations. As key examples, we highlight three specific RoLs: (1) Ca2+ dynamics facilitate cytoskeletal reorganization following stress and damage, (2) Ca2+ regulates actin dynamics to control synapse processes supporting both synapse formation and exocytosis, and (3) reciprocal coupling of spatiotemporal Ca2+ signaling and cellular dynamics defines distinct cellular roles in emergent multicellular behavior. Finally, we outline future directions toward developing multimodal computational simulations for identifying new RoLs, integrating them into multi-scale computational frameworks, and applications in bioengineering, pharmacology, and regenerative medicine.

Gravity is a pervasive cue that directs the growth and development of living systems on Earth and in space environments. However, little is understood about how gravity shapes living systems. This study reports a set of large-scale 2D clinostats that support the growth of plants beyond the seedling stage. Using these clinostats, five replicate experiments containing two tomato cultivars were grown under upright control and simulated microgravity conditions. We showed a variable response to simulated microgravity that was impacted by replicate experiment, but not cultivar. This variable response showed an increase in shoot and root traits under simulated microgravity in some replicate experiments and a reduction in shoot and root traits under simulated microgravity in other replicate experiments. We additionally report a cultivar-specific change in stem vascular anatomy in response to simulated microgravity, which was not impacted by replicate experiment. This work demonstrates the potential to promote plant growth under simulated microgravity and reports a novel modulation of vascular anatomy in response to simulated microgravity. ### Competing Interest Statement The authors have declared no competing interest. * ANOVA : analysis of variance dap : days after planting FOL : Fusarium oxysporum f. sp. Lycopersici H7996 : Hawaii7996 ISS : International Space Station MM : MoneyMaker PCA : Principal Component Analysis PC : Principal Component PDB : potato dextrose broth RPM : revolutions per minute TBA : tert-butyl alcohol National Aeronautics and Space Administration, 19099981

Cytosolic Ca2+ signatures with specific spatiotemporal patterns play crucial roles in plant responses to biotic and abiotic stresses. Perception of microbe- or damage-associated molecular patterns (MAMPs or DAMPs) initiates signaling cascades that represent the first layer of plant defense against pathogens known as pattern-triggered immunity (PTI). During PTI, MAMP/DAMP-induced cytosolic Ca2+ fluxes serve as essential messengers in the initiation and transmission of defense signals at the cellular, whole organ, and systemic levels. However, the specific patterns of these Ca2+ signatures in response to different pathogen cues, and the mechanisms that encode them, remain largely unexplored. In this study, we quantitatively assessed Ca2+ signatures at the single-cell level as well as the local traveling Ca2+ waves induced by global treatment of Arabidopsis cotyledons with MAMPs or DAMPs. We demonstrated that MAMPs induced distinct local spatiotemporal Ca2+ responses in epidermal pavement cells, with Ca2+ traveling waves consistently initiated from a subset of cells and spreading in an approximately radial pattern. These local traveling waves propagated at a slow but constant speed of approximately 1 micron/s and spread to a limited number of neighboring cells. In contrast, wound-induced traveling waves displayed a diffusion-like decay pattern that moved rapidly away from the wounded cell but with diminishing speed over time and distance. Mathematical modeling supported a calcium-induced calcium release mechanism that could recapitulate the constant wave speed induced by MAMPs. These findings contribute to a deeper understanding of plant defense-related Ca2+ signaling mechanisms as well as how defense responses are spatially restricted within tissues. ### Competing Interest Statement The authors have declared no competing interest.

Cytosolic calcium ion (Ca 2+ ) signatures with specific spatiotemporal patterns play crucial roles in plant responses to biotic and abiotic stresses. The perception of microbe- or damage-associated molecular patterns (MAMPs or DAMPs, respectively) initiates cytosolic Ca 2+ fluxes that are essential for the induction and spread of pattern-triggered immunity, the first line of plant defense against pathogens, at the cellular, organ, and systemic levels. Here, we quantitatively assessed Ca 2+ signatures at the single-cell level, as well as the local traveling Ca 2+ waves induced by uniform MAMP or DAMP treatment of Arabidopsis thaliana cotyledons. MAMPs and DAMPs induced distinct local spatiotemporal Ca 2+ responses in epidermal pavement cells, with traveling waves of Ca 2+ consistently initiated from a randomly distributed subset of cells and spreading in an approximately radial pattern. These local traveling waves propagated at a slow but constant speed of ~1 micrometer per second and spread to a limited number of neighboring cells. In contrast, wound-induced traveling waves of Ca 2+ , which are propagated by the diffusion of molecules that activate Ca 2+ channels, displayed a diffusion-like decay pattern that moved rapidly away from the wounded cell but with diminishing speed over time and distance. Mathematical modeling supported a Ca 2+ -induced Ca 2+ release mechanism that recapitulated the constant wave speed induced by MAMPs. These findings contribute to a deeper understanding of plant defense–related Ca 2+ signaling mechanisms, as well as how defense responses are spatially restricted in tissues.

Phyllachora maydis is an ascomycete foliar fungal pathogen and the causal agent of tar spot in maize. Although P. maydis is considered an economically important foliar pathogen of maize, our general knowledge of the trophic lifestyle and functional role of effector proteins from this fungal pathogen remains limited. Here, we utilized a genome-informed approach to predict the trophic lifestyle of P. maydis and functionally characterized a subset of candidate effectors from this fungal pathogen. Leveraging the most recent P. maydis genome annotation and the CATAStrophy pipeline, we show that this fungal pathogen encodes a predicted carbohydrate-active enzymes (CAZymes) repertoire consistent with that of biotrophs. To investigate fungal pathogenicity, we selected 18 candidate effector proteins that were previously shown to be expressed during primary disease development. We assessed whether these putative effectors share predicted structural similarity with other characterized fungal effectors and determined whether any suppress plant immune responses. Using AlphaFold2 and Foldseek, we showed that one candidate effector, PM02_g1115, adopts a predicted protein structure similar to that of an effector from Verticillium dahlia. Furthermore, transient expression of candidate effector-fluorescent protein fusions in Nicotiana benthamiana revealed two putative effectors, PM02_g378 and PM02_g2610, accumulated predominantly in the cytosol, and three candidate effectors, PM02_g1115, PM02_g7882, and PM02_g8240, consistently attenuated chitin-mediated reactive oxygen species production. Collectively, the results presented herein provide insights into the predicted trophic lifestyle and putative functions of effectors from P. maydis and will likely stimulate continued research to elucidate the molecular mechanisms used by P. maydis to induce tar spot.

Tar spot, a disease caused by the ascomycete fungal pathogen Phyllachora maydis, is considered one of the most significant yield-limiting diseases of maize (Zea mays) within the United States. P. maydis may also be found in association with other fungi, forming a disease complex that is thought to result in the characteristic fisheye lesions. Understanding how P. maydis colonizes maize leaf cells is essential for developing effective disease control strategies. Here, we used histological approaches to elucidate how P. maydis infects and multiplies within susceptible maize leaves. We collected tar spot-infected maize leaf samples from four different fields in northern Indiana at three different time points during the growing season. Samples were chemically fixed and paraffin-embedded for high-resolution light and scanning electron microscopy. We observed a consistent pattern of disease progression in independent leaf samples collected across different geographical regions. Each stroma contained a central pycnidium that produced asexual spores. Perithecia with sexual spores developed in the stomatal chambers adjacent to the pycnidium, and a cap of spores formed over the stroma. P. maydis reproductive structures formed around but not within the vasculature. We observed P. maydis associated with two additional fungi, one of which is likely a member of the Paraphaeosphaeria genus; the other is an unknown fungi. Our data provide fundamental insights into how this pathogen colonizes and spreads within maize leaves. This knowledge can inform new approaches to managing tar spot, which could help mitigate the significant economic losses caused by this disease.

Plants possess cell-surface recognition receptors that detect molecular patterns from microbial invaders and initiate an immune response. Understanding the conservation of pattern-triggered immunity within different plant organs and across species is crucial to its sustainable and effective use in plant disease management but is currently unclear.We examined the activation and immune response patterns of three pattern recognition receptors (PRRs: SlFLS2, SlFLS3, and SlCORE) in different developmental regions of roots and in leaves of multiple accessions of domesticated and wild tomato (Solanum lycopersicum and S. pimpinellifolium) using biochemical and genetic assays.Roots from different tomato accessions differed in the amplitude and dynamics of their immune response, but all exhibited developmental-specific PTI responses in which the root early differentiation zone was the most sensitive to molecular patterns. PRR signaling pathways also showed distinct but occasionally overlapping responses downstream of each immune receptor in tomato roots.These results reveal that each PRR initiates a unique PTI pathway and suggest that the specificity and complexity of tomato root immunity are tightly linked to the developmental stage, emphasizing the importance of spatial and temporal regulation in PTI.

Cellular responses to biotic stress frequently involve signaling pathways that are conserved across eukaryotes. These pathways include the cytoskeleton, a proteinaceous network that senses external cues at the cell surface and signals to interior cellular components. During biotic stress, dynamic cytoskeletal rearrangements serve as a platform from which early immune-associated processes are organized and activated. Bacterial pathogens of plants and animals use proteins called type III effectors (T3Es) to interfere with host immune signaling, thereby promoting virulence. We previously found that RipU, a T3E from the soilborne phytobacterial pathogen Ralstonia solanacearum, co-localizes with the plant cytoskeleton. Here, we show that RipU from R. solanacearum K60 (RipUK60) associated with and altered the organization of both the actin and microtubule cytoskeleton. We found that pharmacological disruption of the tomato (Solanum lycopersicum) cytoskeleton promoted R. solanacearum K60 colonization. Importantly, tomato plants inoculated with R. solanacearum K60 lacking RipUK60 (ΔripUK60) had reduced wilting symptoms and significantly reduced root colonization when compared to plants inoculated with wild-type R. solanacearum K60. Collectively, our data suggest that R. solanacearum K60 uses the type III effector RipUK60 to remodel cytoskeletal organization, thereby promoting pathogen virulence.

ABSTRACT Tar spot, a disease caused by the ascomycete fungal pathogen Phyllachora maydis , is considered one of the most significant yield-limiting diseases of maize ( Zea mays L.) within the United States. P. maydis may also be found in association with other fungi, forming a disease complex with characteristic fish eye lesions. Understanding how P. maydis colonizes maize leaf cells is essential for developing effective disease control strategies. Here, we used histological approaches to elucidate how P. maydis infects and multiplies within susceptible maize leaves. We collected tar spot-infected maize leaf samples from four different fields in northern Indiana at three different time points during the growing season. Samples were chemically fixed and paraffin-embedded for high-resolution light and scanning electron microscopy. We observed a consistent pattern of disease progression in independent leaf samples collected across different geographical regions. Each stromata contained a central pycnidium that produced asexual spores. Perithecia with sexual spores developed in the stomatal chambers adjacent to the pycnidia, and a cap of spores formed over the stromata. P. maydis reproductive structures formed around but not within the vasculature. In our samples containing fish eye lesions, P. maydis is associated with two additional fungi, one of which is likely a member of the Paraphaeospheria genus; the other is an unknown fungi. Our data provide fundamental insights into how this pathogen colonizes and spreads within maize leaves. This knowledge can inform new approaches to managing tar spot, which could help mitigate the significant economic losses caused by this disease.

A major challenge in global crop production is mitigating yield loss due to plant diseases. One of the best means of disease control is plant resistance, but the identification of genes that promote resistance has been limited by the subjective quantification of disease, which is typically scored by the human eye. We hypothesized that image-based, non-destructive quantification of disease phenotypes would enable the rapid identification of new disease resistance loci. We tested this using the interaction between tomato and Ralstonia solanacearum , a soilborne pathogen that causes bacterial wilt disease. We acquired over 40,000 time-series images of disease progression in a tomato recombinant inbred line population, and developed an image analysis pipeline providing a suite of ten traits to quantify wilt disease based on plant shape and size. Quantitative trait loci (QTL) analyses using image-based phenotyping identified QTL that were both unique and shared compared with those identified by human assessment of wilting. When shared loci were identified, image-based phenotyping could detect some QTL several days earlier than human assessment. Thus, expanding the phenotypic space of disease with image-based, non- destructive phenotyping allowed both earlier detection and identified new genetic components of resistance.

Plant diseases caused by soilborne pathogens are a major limiting factor in crop production. Bacterial wilt dis-ease, caused by soilborne bacteria in the Ralstonia solanacearum Species Complex (Ralstonia), results in significant crop loss throughout the world. Ralstonia invades root systems and colonizes plant xylem, changing plant physiology and ultimately causing plant wilting in susceptible varieties. Elucidating how Ralstonia invades and colonizes plants is central to developing strategies for crop protection. Here we review Ralstonia pathogenesis from root detection and attachment, early root colonization, xylem invasion and subsequent wilting. We focus primarily on studies in tomato from the last 5-10 years. Recent work has identified elegant mechanisms Ralstonia uses to adapt to the plant xylem, and has discovered new genes that function in Ralstonia fitness in planta. A picture is emerging of an amazingly versatile pathogen that uses multiple strategies to make its surrounding environment more hospitable and can adapt to new environments.

Background Environmental stress due to climate or pathogens is a major threat to modern agriculture. Plant genetic resistance to these stresses is one way to develop more resilient crops, but accurately quantifying plant phenotypic responses can be challenging. Here we develop and test a set of metrics to quantify plant wilting, which can occur in response to abiotic stress such as heat or drought, or in response to biotic stress caused by pathogenic microbes. These metrics can be useful in genomic studies to identify genes and genomic regions underlying plant resistance to a given stress. Results We use two datasets: one of tomatoes inoculated with Ralstonia solanacearum , a soilborne pathogen that causes bacterial wilt disease, and another of soybeans exposed to water stress. For both tomato and soybean, the metrics predict the visual wilting score provided by human experts. Specific to the tomato dataset, we demonstrate that our metrics can capture the genetic difference of bacterium wilt resistance among resistant and susceptible tomato genotypes. In soybean, we show that our metrics can capture the effect of water stress. Conclusion Our proposed RGB image-based wilting metrics can be useful for identifying plant wilting caused by diverse stresses in different plant species.

The root cap is a small tissue located at the tip of the root with critical functions for root growth. Present in nearly all vascular plants, the root cap protects the root meristem, influences soil penetration, and perceives and transmits environmental signals that are critical for root branching patterns. To perform these functions, the root cap must remain relatively stable in size and must integrate endogenous developmental pathways with environmental signals, yet the mechanism is not clear. We previously showed that low pH conditions altered root cap development, and these changes are mediated by the NIN LIKE PROTEIN 7 (NLP7) transcription factor, a master regulator of nitrate signaling. Here we show that in Arabidopsis NLP7 integrates nitrate signaling with auxin pathways to regulate root cap development. We found that low nitrate conditions promote aberrant release of root cap cells. Nitrate deficiency impacts auxin pathways in the last layer of the root cap, and this is mediated in part by NLP7. Mutations in NLP7 abolish the auxin minimum in the last layer of the root cap and alter root cap expression of the auxin carriers PIN-LIKES 3 (PILS3) and PIN-FORMED 7 (PIN7) as well as transcription factors that regulate PIN expression. Together, our data reveal NLP7 as a link between endogenous auxin pathways and nitrate signaling in the root cap.

The Ralstonia solanacearum species complex is a group of globally important plant pathogens. Bacteria in this very large and genetically diverse group all colonize the xylem elements of angiosperm plants and cause high-impact wilting diseases of many crops. Because they threaten economic and food security, several R. solanacearum species complex subgroups are strictly regulated as quarantine pests. Biologically meaningful and consistent nomenclature is essential for organisms that have major economic and regulatory importance, such as plant-pathogenic Ralstonia. There are currently three species of Ralstonia wilt pathogens: R. pseudosolanacearum (corresponding to two phylogenetic groups that are described in the literature as phylotypes I and III), R. solanacearum (phylotypes IIA, IIB, and IIC), and R. syzygii (phylotype IV, containing three subspecies: subsp. syzygii, subsp. celebensis, and subsp. indonesiensis). A recent paper proposed reclassifying phylotype I as a new species named “ Ralstonia nicotianae.” The purpose of this commentary is to register our objection to the taxon “ Ralstonia nicotianae.” [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

High-throughput phenotyping platforms for growth chamber and greenhouse-grown plants enable nondestructive, automated measurements of plant traits including shape, aboveground architecture, length, and biomass over time. However, to establish these platforms, many of these methods require expensive equipment or phenotyping expertise. Here we present a relatively inexpensive and simple phenotyping method for imaging hundreds of small- to medium-sized growth chamber or greenhouse-grown plants with a digital camera. Using this method, we image hundreds of tomato plants in 1 day.