Mechanisms to Mitigate the Trade-Off between Growth and Defense

Stomatal-based immunity differentiation across vascular plant lineages

Some plants are known to actively close their stomata in the presence of foliar pathogens, inhibiting pathogen entry into leaves, leading to 'stoma-based immunity' as the first line of defense. However, the variation in stoma-based innate immunity across the diversity of vascular plants remains unclear. Here, we investigated the stomatal response and guard cell signaling pathway in various seed plant, fern, and lycophyte species when exposed to the bacterial pathogens or pathogen-associated molecular patterns (PAMPs). We observed active stomatal closure in 10 seed plants when exposed to bacteria or PAMPs, whereas none of the nine fern and one lycophyte species exhibited this response. The PAMP flg22-induced reactive oxygen species burst was observed in all species, but the downstream signaling events, including cytosolic Ca2+ accumulation, nitric oxide production, ion fluxes, vacuolar acidification, cytoplasmic pH elevation, vacuolar compartmentation, and disaggregation of the actin cytoskeleton in guard cells, were only observed in seed plants. No such changes were observed in the representatives of ferns and lycophytes. Our findings suggest a major difference in the regulation of stomatal immunity between seed plants and ferns and lycophytes under this study's conditions, unveiling physiological and biophysical mechanisms that may have underpinned the evolutionary adaptation of stomatal responses to pathogen attacks in seed plants.

OsEPSPS Balances Disease Resistance and Plant Growth

The balance between the antagonistic traits, such as plant growth and disease resistance, is crucial for developing elite crop varieties. While the roles of plant hormones in this balance are well established, the regulatory function of secondary metabolites remains largely unexplored. Here, we report that 5-enolpyruvylshikimate-3-phosphate synthase (OsEPSPS), a key enzyme in the shikimate pathway, regulates both plant growth and disease resistance. Silencing the OsEPSPS gene in rice compromises the shikimate pathway but enhances the nicotinate and nicotinamide metabolism, resulting in the accumulations of trigonelline and nicotinamide mononucleotide (NMN). These metabolites boost resistance to rice blast by activating plant immune responses rather than inhibiting the germination and growth of Magnaporthe oryzae. Furthermore, silencing OsEPSPS conferring disease resistance results in less growth in plant. Our findings highlight the pivotal role of OsEPSPS in coordinating plant growth and disease resistance.

Foliar Application of Chlorella Supernatant Protects Turfgrass against Clarireedia jacksonii by Eliciting Induced Resistance and Modulating the Rhizosphere Microbiota

Large-scale culture of the microalga Chlorella produces valuable products. Cultivation also generates tons of supernatant waste that require detoxification and disposal. Recent research has focused on recycling waste supernatant as a plant protectant and biofertilizer, although, to date, most studies have considered its use as a biological control of pathogens infecting dicot plants. By contrast, the current study evaluated whether Chlorella supernatant could protect turfgrass (Agrostis stolonifera), a monocot plant widely used as a turfgrass, against dollar spot disease caused by the fungal pathogen Clarireedia jacksonii (formerly Sclerotinia homoeocarpa) under greenhouse and field conditions. Foliar application of supernatants from Chlorella sp. ABC001 and HS2 cultures reduced the incidence of dollar spot disease in turfgrass under both greenhouse and field conditions without directly inhibiting growth. The effects of supernatant application on the rhizosphere microbiome were investigated using 16S rRNA amplicon sequencing. Application of ABC001 and HS2 supernatants modulated the structure of the rhizosphere microbiome and enriched specific microbial taxa that improved turfgrass health in the presence of C. jacksonii. The application of waste Chlorella supernatant therefore offers an alternative method for protecting monocot plants against fungal pathogens, while also enhancing the composition of soil microbes in the rhizosphere.

The MYB transcription factor TaMYB30 enhances wheat resistance to sharp eyespot disease by scavenging ROS accumulation

Sharp eyespot disease, caused primarily by the necrotrophic fungal pathogen Rhizoctonia cerealis, poses a significant threat to global wheat production. This study reports the functional characterization of an R2R3-MYB transcription factor, TaMYB30, which plays a crucial role in wheat's resistance to R. cerealis. The overexpression of TaMYB30 in transgenic wheat led to enhanced resistance against sharp eyespot disease, whereas its knockdown in wheat notably compromised resistance, indicating that TaMYB30 acts as a positive regulator in wheat's defense against R. cerealis infection. Comparative transcriptomic analysis between transgenic and wild-type wheat following R. cerealis infection revealed that differentially expressed genes were primarily involved in oxidative stress response, peroxidase activity, and glutathione metabolism. Further functional analysis demonstrated that TaMYB30 directly activates the expression of PRX and GST genes. Transgenic wheat with elevated TaMYB30 expression also exhibited significantly enhanced tolerance to oxidative stress compared to wild-type plants. Notably, overexpression of TaMYB30 mitigated hydrogen peroxide (H2O2) accumulation post-infection, suggesting that the resistance conferred by TaMYB30 is likely due to its role in scavenging reactive oxygen species (ROS) accumulation. This research uncovers a novel regulatory function for MYB transcription factors in wheat defense mechanisms and proposes TaMYB30 as a promising candidate for genetic improvement to enhance wheat's resistance to sharp eyespot and oxidative stress.

A rice DELLA protein OsSLR1 positively regulates rice resistance to southern rice black-streaked dwarf virus infection

BACKGROUND

In the course of long-term confrontation with pathogens, plants have developed complex defense mechanisms to protect themselves from various pathogens. Previous studies have reported that the gibberellin (GA) signaling pathway negative regulator SLENDER RICE 1 (SLR1) in rice activates jasmonic acid (JA)-mediated broad-spectrum antiviral immunity, but the exploration regarding whether OsSLR1 exerts effects on alternative antiviral immune pathways remains limited.

RESULTS

Here, we identified that OsSLR1 was significantly induced after virus infection and overexpression of OsSLR1 in rice enhance the resistance of rice to southern rice black-streaked dwarf virus (SRBSDV) in rice. Transcriptome analysis revealed that a total of 2,336 differentially expressed genes (DEGs) were detected upon overexpression of OsSLR1 in rice, including 1,607 upregulated genes and 729 downregulated genes. Gene ontology (GO) enrichment analysis and RT-qPCR analysis revealed that genes related to JA and reactive oxygen species (ROS) were significantly upregulated, while genes associated with abscisic acid (ABA) were significantly downregulated.

CONCLUSIONS

These results suggest that OsSLR1 positively regulates the antiviral immunity of rice by modulating multiple pathways.

WRKY transcription factors: Hubs for regulating plant growth and stress responses

As sessile organisms, plants must directly face various stressors. Therefore, plants have evolved a powerful stress resistance system and can adjust their growth and development strategies appropriately in different stressful environments to adapt to complex and ever-changing conditions. Nevertheless, prioritizing defensive responses can hinder growth; this is a crucial factor for plant survival but is detrimental to crop production. As such, comprehending the impact of adverse environments on plant growth is not only a fundamental scientific inquiry but also imperative for the agricultural industry and for food security. The traditional view that plant growth is hindered during defense due to resource allocation trade-offs is challenged by evidence that plants exhibit both robust growth and defensive capabilities through human intervention. These findings suggest that the growth‒defense trade-off is not only dictated by resource limitations but also influenced by intricate transcriptional regulatory mechanisms. Hence, it is imperative to conduct thorough investigations on the central genes that govern plant resistance and growth in unfavorable environments. Recent studies have consistently highlighted the importance of WRKY transcription factors in orchestrating stress responses and plant-specific growth and development, underscoring the pivotal role of WRKYs in modulating plant growth under stressful conditions. Here, we review recent advances in understanding the dual roles of WRKYs in the regulation of plant stress resistance and growth across diverse stress environments. This information will be crucial for elucidating the intricate interplay between plant stress response and growth and may aid in identifying gene loci that could be utilized in future breeding programs to develop crops with enhanced stress resistance and productivity.

Antagonistic systemin receptors integrate the activation and attenuation of systemic wound signaling in tomato

Pattern recognition receptor (PRR)-mediated perception of damage-associated molecular patterns (DAMPs) triggers the first line of inducible defenses in both plants and animals. Compared with animals, plants are sessile and regularly encounter physical damage by biotic and abiotic factors. A longstanding problem concerns how plants achieve a balance between wound defense response and normal growth, avoiding overcommitment to catastrophic defense. Here, we report that two antagonistic systemin receptors, SYR1 and SYR2, of the wound peptide hormone systemin in tomato act in a ligand-concentration-dependent manner to regulate immune homeostasis. Whereas SYR1 acts as a high-affinity receptor to initiate systemin signaling, SYR2 functions as a low-affinity receptor to attenuate systemin signaling. The expression of systemin and SYR2, but not SYR1, is upregulated upon SYR1 activation. Our findings provide a mechanistic explanation for how plants appropriately respond to tissue damage based on PRR-mediated perception of DAMP concentrations and have implications for uncoupling defense-growth trade-offs.

Genomic, transcriptomic and metabolomic analyses of Amorphophallus albus provides insights into the evolution and resistance to southern blight pathogen

Introduction

Amorphophallus albus, a perennial herb in the Araceae family, is a valuable cash crop known for its high production of konjac glucomannan and high disease resistance.

Methods

In this study, we present a high-quality, chromosome-scale genome assembly of A. albus using a combination of PacBio HiFi sequencing, DNBSEQ short-read sequencing, and Hi-C technology. To elucidate the molecular mechanisms underlying southern blight resistance, we performed an integrated analysis of transcriptomic and metabolomic profiles across three infection stages of A. albus.

Results and discussion

Here, we assembled and annotated the complete genome of A. albus, providing a chromosome-level assembly with a total genome size of 5.94 Gb and a contig N50 of 5.61 Mb. The A. albus genome comprised 19,908 gene families, including 467 unique families.The slightly larger genome size of A. albus compared to A. konjac may have been affected by a recent whole-genome duplication event. Transcriptional and metabolic analyses revealed significant enrichment of differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) involved in phenylpropanoid biosynthesis, plant hormone signal transduction, phenylalanine metabolism, and the biosynthesis of phenylalanine, tyrosine, and tryptophan. These findings not only advance the understanding of genetic and evolutionary characteristics of A. albus but also provide a foundation for future research on the resistance mechanisms of konjac against southern blight disease.

Rooted in Communication: Exploring Auxin-Salicylic Acid Nexus in Root Growth and Development

Plant hormones are pivotal in orchestrating diverse aspects of growth and developmental processes. Among various phytohormones, auxin and salicylic acid (SA) stand out as important regulators, often exerting opposing effects on overall plant growth. Essentially, research has indicated that auxin and SA-mediated pathways exhibit mutual antagonism during pathogen challenge. Additionally, in recent years, significant advancements have been made in uncovering the molecular intricacies that govern the action and interplay between these two phytohormones during various essential growth-related processes. In this discussion, we briefly delve into the genetic and molecular mechanisms involved in auxin and SA antagonism. We then analyse in detail how this dialogue impacts critical aspects of root development, with an emphasis on the transcriptional and protein regulatory networks. Finally, we propose the potential of exploring their interaction in various other aspects of below ground root growth processes. Understanding this relationship could provide valuable insights for optimizing and enhancing crop growth and yields.

Messenger RNA Surveillance: Current Understanding, Regulatory Mechanisms, and Future Implications

Nonsense-mediated mRNA decay (NMD) is an evolutionarily conserved surveillance mechanism in eukaryotes primarily deployed to ensure RNA quality control by eliminating aberrant transcripts and also involved in modulating the expression of several physiological transcripts. NMD, the mRNA surveillance pathway, is a major form of gene regulation in eukaryotes. NMD serves as one of the most significant quality control mechanisms as it primarily scans the newly synthesized transcripts and differentiates the aberrant and non-aberrant transcripts. The synthesis of truncated proteins is restricted, which would otherwise lead to cellular dysfunctions. The up-frameshift factors (UPFs) play a central role in executing the NMD event, largely by recognizing and recruiting multiple protein factors that result in the decay of non-physiological mRNAs. NMD exhibits astounding variability in its ability across eukaryotes in an array of pathological and physiological contexts. The detailed understanding of NMD and the underlying molecular mechanisms remains blurred. This review outlines our current understanding of NMD, in regulating multifaceted cellular events during development and disease. It also attempts to identify unanswered questions that deserve further investigation.

Reprogrammed Plant Metabolism During Viral Infections: Mechanisms, Pathways and Implications

Plant viruses pose a significant threat to global agriculture, leading to substantial crop losses that jeopardise food security and disrupt ecosystem stability. These viral infections often reprogramme plant metabolism, compromising key pathways critical for growth and defence. For instance, infections by cucumber mosaic virus alter amino acid and secondary metabolite biosynthesis, including flavonoid and phenylpropanoid pathways, thereby weakening plant defences. Similarly, tomato bushy stunt virus disrupts lipid metabolism by altering the synthesis and accumulation of sterols and phospholipids, which are essential for viral replication and compromise membrane integrity. Recent advancements in gene-editing technologies, such as CRISPR/Cas9, and metabolomics offer innovative strategies to mitigate these impacts. Precise genetic modifications can restore or optimise disrupted metabolic pathways, enhancing crop resilience to viral infections. Metabolomics further aids in identifying metabolic biomarkers linked to viral resistance, guiding breeding programmes aimed at developing virus-resistant plants. By reducing the susceptibility of crops to viral infections, these approaches hold significant potential to reduce dependence on chemical pesticides, increase crop yields and promote sustainable agricultural practices. Future research should focus on expanding our understanding of virus-host interactions at the molecular level while exploring the long-term ecological impacts of viral infections. Interdisciplinary approaches integrating multi-omics technologies and sustainable management strategies will be critical in addressing the challenges posed by plant viruses and ensuring global agricultural stability.

Non-adapted bacterial infection suppresses plant reproduction

Environmental stressors, including pathogens, substantially affect the growth of host plants. However, how non-adapted bacteria influence nonhost plants has not been reported. Here, we reveal that infection of Arabidopsis flowers by Xanthomonas oryzae pv. oryzae PXO99A, a bacterial pathogen causing rice blight disease, suppresses ovule initiation and reduces seed number without causing visible disease symptoms. TleB, secreted by the type VI secretion system (T6SS), interacts with plant E3 ligase PUB14 and disrupts the function of the PUB14-BZR1 module, leading to decreased ovule initiation and seed yield. On the other site, PUB14 concurrently promotes TleB's degradation. Our findings indicate that bacterial infections in nonhost plants directly repress offspring production. The regulatory mechanism by effectors PUB14-BZR1 is widely present, suggesting that plants may balance reproduction and defense and produce fewer offspring to conserve resources, thus enabling them to remain in a standby mode prepared for enhanced resistance.

Harnessing Genetic Resistance in Maize and Integrated Rust Management Strategies to Combat Southern Corn Rust

Southern corn rust (SCR) caused by Puccinia polysora Underw. has recently emerged as a focal point of study because of its extensive distribution, significant damage, and high prevalence in maize growing areas such as the United States, Canada, and China. P. polysora is an obligate biotrophic fungal pathogen that cannot be cultured in vitro or genetically modified, thus complicating the study of the molecular bases of its pathogenicity. High temperatures and humid environmental conditions favor SCR development. In severe cases, SCR may inhibit photosynthesis and cause early desiccation of maize, a decrease in kernel weight, and yield loss. Consequently, an expedited and accurate detection approach for SCR is essential for plant protection and disease management. Significant progress has been made in elucidating the pathogenic mechanisms of P. polysora, identifying resistance genes and developing SCR-resistant cultivars. A detailed understanding of the molecular interactions between maize and P. polysora will facilitate the development of novel and effective approaches for controlling SCR. This review gives a concise overview of the biological characteristics and symptoms of SCR, its life cycle, the molecular basis of interactions between maize and P. polysora, the genetic resistance of maize to SCR, the network of maize resistance to P. polysora infection, SCR management, and future perspectives.

Reduced seed viability in exchange for transgenerational plant protection in an endophyte-symbiotic grass: does the defensive mutualism concept pass the fitness test?

BACKGROUND AND AIMS

Epichloë endophytes are vertically transmitted via grass seeds and chemically defend their hosts against herbivory. Endophyte-conferred plant defence via alkaloid biosynthesis might occur independently of costs for host plant growth. However, fitness consequences of endophyte-conferred defence and transgenerational effects on herbivore resistance of progeny plants are rarely studied. The aim of this study was to test whether severe defoliation in mother plants affects their seed production, seed germination rate and the endophyte-conferred resistance of progeny plants.

METHODS

In a field study, we tested the effects of defoliation and endophyte symbiosis (Epichloë uncinata) on host plant (Festuca pratensis) performance, loline alkaloid concentrations in leaves and seeds, seed biomass and seed germination rates. In a subsequent greenhouse study, we challenged the progeny of the plants from the field study to aphid herbivory and tested whether defoliation of mother plants affects endophyte-conferred resistance against aphids in progeny plants.

KEY RESULTS

Defoliation of the mother plants resulted in a reduction of alkaloid concentrations in leaves and elevated the alkaloid concentrations in seeds when compared with non-defoliated endophyte-symbiotic plants. Viability and germination rate of seeds of defoliated endophyte-symbiotic plants were significantly lower compared with those of non-defoliated endophyte-symbiotic plants and endophyte-free (defoliated and non-defoliated) plants. During 6 weeks of growth, seedlings of defoliated endophyte-symbiotic mother plants had elevated alkaloid concentrations, which was negatively correlated with aphid performance.

CONCLUSIONS

Endophyte-conferred investment in higher alkaloid levels in seeds, elicited by defoliation, provided protection from herbivores in progenies during the first weeks of plant establishment. Better protection of seeds via high alkaloid concentrations was negatively correlated with seed germination, indicating a trade-off between protection and viability.

Exploring the complex information processes underlying plant behavior

Newly discovered plant behaviors, linked to historical observations, contemporary technologies, and emerging knowledge of signaling mechanisms, argue that plants utilize complex information processing systems. Plants are goal-oriented in an evolutionary and physiological sense; they demonstrate agency and learning. While most studies on plant plasticity, learning, and memory deal with the responsiveness of individual plants to resource availability and biotic stresses, adaptive information is often perceived from and coordinated with neighboring plants, while competition occurs for limited resources. Based on existing knowledge, technologies, and sustainability principles, climate-smart agricultural practices are now being adopted to enhance crop resilience and productivity. A deeper understanding of the dynamics of plant behavior offers a rich palette of potential amelioration strategies for improving the productivity and health of natural and agricultural ecosystems.

Mixed DAMP/MAMP oligosaccharides promote both growth and defense against fungal pathogens of cucumber

Plants recognize a variety of environmental molecules, thereby triggering appropriate responses to biotic or abiotic stresses. Substances containing microbes-associated molecular patterns (MAMPs) and damage-associated molecular patterns (DAMPs) are representative inducers of pathogen resistance and damage repair, thus treatment of healthy plants with such substances can pre-activate plant immunity and cell repair functions. In this study, the effects of DAMP/MAMP oligosaccharides mixture (Oligo-Mix) derived from plant cell wall (cello-oligosaccharide and xylo-oligosaccharide), and fungal cell wall (chitin-oligosaccharide) were examined in cucumber. Treatment of cucumber with Oligo-Mix promoted root germination and plant growth, along with increased chlorophyll contents in the leaves. Oligo-Mix treatment also induced typical defense responses such as MAP kinase activation and callose deposition in leaves. Pretreatment of Oligo-Mix enhanced disease resistance of cucumber leaves against pathogenic fungi Podosphaera xanthii (powdery mildew) and Colletotrichum orbiculare (anthracnose). Oligo-Mix treatment increased the induction of hypersensitive cell death around the infection site of pathogens, which inhibited further infection and the conidial formation of pathogens on the cucumber leaves. RNA-seq analysis revealed that Oligo-Mix treatment upregulated genes associated with plant structural reinforcement, responses to abiotic stresses and plant defense. These results suggested that Oligo-Mix has beneficial effects on growth and disease resistance in cucumber, making it a promising biostimulant for agricultural application.

A frameshift mutation in JAZ10 resolves the growth versus defense dilemma in rice

CRISPR-Cas9 genome editing systems have revolutionized plant gene functional studies by enabling the targeted introduction of insertion-deletions (INDELs) via the nonhomologous end-joining (NHEJ) pathway. Frameshift-inducing INDELs can introduce a premature termination codon and, in other instances, can lead to the appearance of new proteins. Here, we found that mutations in the rice jasmonate (JA) signaling gene OsJAZ10 by CRISPR-Cas9-based genome editing did not affect canonical JA signaling. However, a type of mutant with an INDEL that yielded a novel frameshift protein named FJ10 (Frameshift mutation of JAZ10), exhibited enhanced rice growth and increased resistance to brown planthopper attacks. Overexpression of FJ10 in wild-type plants phenocopies OsJAZ10 frameshift mutants. Further characterization revealed that FJ10 interacts with Slender Rice 1 (OsSLR1) and F-box/Kelch 16 (OsFBK16). These interactions disrupt the function of OsSLR1 in suppressing gibberellin-mediated growth and the function of OsFBK16 in repressing lignin-mediated defense responses, respectively. Field experiments with FJ10-expressing plants demonstrate that this protein uncouples the growth-defense tradeoff, opening broad avenues to obtain cultivars with enhanced yield without compromised defenses.

OsPUB75-OsHDA716 mediates deactivation and degradation of OsbZIP46 to negatively regulate drought tolerance in rice

Histone deacetylases (HDACs) play crucial roles in plant stress responses via modification of histone as well as nonhistone proteins; however, how HDAC-mediated deacetylation of nonhistone substrates affects protein functions remains elusive. Here, we report that the reduced potassium dependency3/histone deacetylase1-type histone deacetylase OsHDA716 and plant U-box E3 ubiquitin ligase OsPUB75 form a complex to regulate rice drought response via deactivation and degradation of basic leucine zipper (bZIP) transcription factor OsbZIP46 in rice (Oryza sativa). OsHDA716 decreases abscisic acid (ABA)-induced drought tolerance, and mechanistic investigations showed that OsHDA716 interacts with and deacetylates OsbZIP46, a key regulator in ABA signaling and drought response, thus inhibiting its transcriptional activity. Furthermore, OsHDA716 recruits OsPUB75 to facilitate ubiquitination and degradation of deacetylated OsbZIP46. Therefore, the OsPUB75-OsHDA716 complex exerts double restrictions on the transcriptional activity and protein stability of OsbZIP46, leading to repression of downstream drought-responsive gene expression and consequently resulting in reduced drought tolerance. Conversely, OsbZIP46 acts as an upstream repressor to repress OsHDA716 expression, and therefore OsHDA716 and OsbZIP46 form an antagonistic pair to reciprocally inhibit each other. Genetic evidence showed that OsHDA716 works with OsbZIP46 in a common pathway to antagonistically regulate rice drought response, revealing that plants can fine-tune stress responses by the complex interplay between chromatin regulators and transcription factors. Our findings unveil an acetylation-dependent regulatory mechanism governing protein functions and shed light on the precise coordination of activity and stability of key transcription factors through a combination of different posttranslational modifications.

SYNTAXIN OF PLANTS 132 underpins secretion of cargoes associated with salicylic acid signaling and pathogen defense

Secretory trafficking in plant cells is facilitated by SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins that drive membrane fusion of cargo-containing vesicles. In Arabidopsis, SYNTAXIN OF PLANTS 132 (SYP132) is an evolutionarily ancient SNARE that functions with syntaxins SYP121 and SYP122 at the plasma membrane. Whereas SYP121 and SYP122 mediate overlapping secretory pathways, albeit with differences in their importance in plant-environment interactions, the SNARE SYP132 is absolutely essential for plant development and survival. SYP132 promotes endocytic traffic of the plasma membrane H+-ATPase AHA1 and aquaporin PIP2;1, and it coordinates plant growth and bacterial pathogen immunity through PATHOGENESIS-RELATED1 (PR1) secretion. Yet, little else is known about SYP132 cargoes. Here, we used advanced quantitative tandem mass tagging (TMT)-MS combined with immunoblot assays to track native secreted cargo proteins in the leaf apoplast. We found that SYP132 supports a basal level of secretion in Arabidopsis leaves, and its overexpression influences salicylic acid and jasmonic acid defense-related cargoes including PR1, PR2, and PR5 proteins. Impairing SYP132 function also suppressed defense-related secretory traffic when challenged with the bacterial pathogen Pseudomonas syringae. Thus, we conclude that, in addition to its role in hormone-related H+-ATPase cycling, SYP132 influences basal plant immunity.

The molecular framework balancing growth and defense in response to plant elicitor peptide-induced signals in Arabidopsis

Elevated stress signaling compromises plant growth by suppressing proliferative and formative division in the meristem. Plant elicitor peptide, an endogenous danger signal triggered by biotic and abiotic stresses in Arabidopsis (Arabidopsis thaliana), suppresses proliferative division, alters xylem vessel organization, and disrupts cell-to-cell symplastic connections in roots. To gain insight into the dynamic molecular framework that modulates root development under elevated danger signals, we performed a time-course RNA-sequencing analysis of the root meristem after synthetic PEP1 treatment. Our analyses revealed that SALT TOLERANCE ZINC FINGER (STZ) and its homologs are a potential nexus between the stress response and proliferative cell cycle regulation. Through functional, phenotypic, and transcriptomic analyses, we observed that STZ differentially controls the cell cycle, cell differentiation, and stress response genes in various tissue layers of the root meristem. Moreover, we determined the STZ expression level critical for enabling the growth-defense tradeoff. These findings provide valuable information about the dynamic gene expression changes that occur upon perceiving danger signals in the root meristem and potential engineering strategies to generate stress-resilient plants.

Chemical-sensitized MITOGEN-ACTIVATED PROTEIN KINASE 4 provides insights into its functions in plant growth and immunity

Two mitogen-activated protein kinase (MAPK) cascades with MPK4 and MPK3/MPK6 as the bottommost kinases are key to plant growth/development and immune signaling. Disruption of the MPK4 cascade leads to severe dwarfism and autoimmunity, complicating the study of MPK4 in plant growth/development and immunity. In this study, we successfully rescued the Arabidopsis (Arabidopsis thaliana) mpk4 mutant using a chemical-sensitized MPK4 variant, MPK4YG, creating a conditional activity-null mpk4 mutant named MPK4SR (genotype: PMPK4:MPK4YG mpk4) that could be used to examine the functions of MPK4 in plant growth/development and immunity. We discovered that the duration of the loss of MPK4 activity is important to plant immune responses. Short-term loss of MPK4 activity did not impact flg22-induced ROS burst or resistance against Pseudomonas syringae (Pst). Enhanced Pst resistance was only observed in the MPK4SR plants with stunted growth following prolonged inhibition of MPK4 activity. Transcriptome analyses in plants with short-term loss of MPK4 activity revealed a vital role of MPK4 in regulating several housekeeping processes, including mitosis, transcription initiation, and cell wall macromolecule catabolism. Furthermore, the constitutive weak activation of MPK4GA in the MPK4CA plants (genotype: PMPK4:MPK4GA mpk4) led to early flowering and premature senescence, which was associated with its compromised resistance against Pst. These findings suggest that MPK4 plays important roles in plant growth and development and in maintaining the delicate balance between growth/development and immune adaptation in plants.

Arbuscular mycorrhizal symbiosis reshapes the drought adaptation strategies of a dominant sand-fixation shrub species in northern China

Drylands are home to over 38 % of the world's population and are among the areas most sensitive to climate change and human activity. Most xerophytes rely on arbuscular mycorrhizal fungi (AMF) for improved drought tolerance. Although research has focused on crops and economically significant plants, the response of sand-fixation shrubs to AMF under drought conditions remains underexplored. This study aims to investigate how AMF affects the drought adaptation strategies of the sand-fixation shrub Artemisia ordosica. A culture system for A. ordosica and the main symbiotic partner Funneliformis mosseae was established, and phenotypic, metabolomic, and transcriptomic analyses were conducted to assess physiological changes induced by arbuscular mycorrhizal symbiosis (AMS) under varying drought stress conditions. AMS influenced A. ordosica's metabolic pathways and its drought adaptation strategies, promoted the redistribution of sugars and flavonoids, and shaped different metabolic patterns of seedlings and adult A. ordosica. AMS had an important shaping ability in the accumulation of proline at A. ordosica seedlings, but had a significant influence on the accumulation of sugars of A. ordosica at the adult growth stage. AMS enhanced the ability of the host to adapt to extreme drought by modulating metabolites at the adult growth stage of A. ordosica. AMS also facilitated an accumulation of key metabolites under well-watered conditions but also intensified interactions with pathogens, leading to a trade-off between drought adaptation and immune capacity under extreme drought of A. ordosica during the adult growth stage. This study uses metabolome and transcriptome methods to explore AMS effects on A. ordosica's drought adaptation strategies, revealing a significant trade-off between drought adaptation and immune capacity. The findings highlight AMS's role in modifying the drought adaptation strategies of A. ordosica in desert ecosystems, and enhance our understanding of key species for sand fixation and ecological restoration, and maintain ecological security.

Citrus psyllid management by collective involvement of plant resistance, natural enemies and entomopathogenic fungi

Crops face constant threats from insect pests, which can lead to sudden disasters and global famine. One of the most dangerous pests is the Asian citrus psyllid (ACP), which poses a significant threat to citrus plantations worldwide. Effective and adaptive management strategies to combat ACP are always in demand. Plant resistance (PR) is a key element in pest management, playing crucial roles such as deterring pests through antifeedant and repellant properties, while also attracting natural enemies of these pests. One effective and innovative approach is the use of entomopathogenic fungi (EPF) to reduce pest populations. Additionally, other natural enemies play an important role in controlling certain insect pests. Given the significance of PR, EPF, and natural arthropod enemies (NAE), this review highlights the benefits of these strategies against ACP, drawing on successful examples from recent research. Furthermore, we discuss how EPF can be effectively utilized in citrus orchards, proposing strategies to ensure its efficient use and safeguard food security in the future.

Natural SNP Variation in GbOSM1 Promotor Enhances Verticillium Wilt Resistance in Cotton

Osmotin is classified as the pathogenesis-related protein 5 group. However, its molecular mechanism involved in plant disease resistance remains largely unknown. Here, a Verticillium wilt (VW) resistance-related osmotin gene is identified in Gossypium barbadense (Gb), GbOSM1. GbOSM1 is preferentially expressed in the roots of disease-resistant G. barbadense acc. Hai7124 and highly induced by Verticillium dahliae (Vd). Silencing GbOSM1 reduces the VW resistance of Hai7124, while overexpression of GbOSM1 in disease-susceptible G. hirsutum improves tolerance. GbOSM1 predominantly localizes in tonoplasts, while it relocates to the apoplast upon exposure to osmotic stress or Vd infection. GbOSM1 confers VW resistance by hydrolyzing cell wall polysaccharides of Vd and activating plant immune pathways. Natural variation contributes to a differential CCAAT/CCGAT elements in the OSM1 promoter in cotton accessions. All G. hirsutum (Gh) exhibit the CCAAT haplotype, while there are two haplotypes of CCAAT/CCGAT in G. barbadense, with higher expression and stronger VW resistance in CCGAT haplotype. A NFYA5 transcription factor binds to the CCAAT element of GhOSM1 promoter and inhibits its transcription. Silencing GhNFYA5 results in higher GhOSM1 expression and enhances VW resistance. These results broaden the insights into the functional mechanisms of osmotin and provide an effective strategy to breed VW-resistant cotton.

miR472 Deficiency Enhances Arabidopsis thaliana Defense Without Reducing Seed Production

After having co-existed in plant genomes for at least 200 million years, the products of microRNA (miRNA) and nucleotide-binding leucine-rich repeat protein (NLR) genes formed a regulatory relationship in the common ancestor of modern gymnosperms and angiosperms. From then on, DNA polymorphisms occurring at miRNA target sequences within NLR transcripts must have been compensated by mutations in the corresponding mature miRNA sequence. The potential evolutionary advantage of such regulation remains largely unknown and might be related to two nonexclusive scenarios: (i) miRNA-dependent regulation of NLR levels might prevent defense mis-activation with negative effects on plant growth and reproduction or (ii) reduction of active miRNA levels in response to pathogen-derived molecules (pathogen-associated molecular patterns [PAMPs] and silencing suppressors) might rapidly release otherwise silent NLR transcripts for rapid translation and thereby enhance defense. Here, we used Arabidopsis thaliana plants deficient for miR472 function to study the impact of releasing its NLR targets on plant growth and reproduction and on defense against the fungal pathogen Plectosphaerella cucumerina. We show that miR472 regulation has a dual role, participating both in the tight regulation of plant defense and growth. MIM472 lines, with reduced active miR472, are more resistant to pathogens and, correlatively, have reduced relative growth compared with wild-type plants, although the end of their reproductive phase is delayed, exhibiting higher adult biomass and similar seed yield as the wild-type. Our study highlights how negative consequences of defense activation might be compensated by changes in phenology and that miR472 reduction is an integral part of plant defense responses. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

A trade-off between investment in molecular defense repertoires and growth in plants

Given the negative fitness effects that pathogens impose on their hosts, the benefits of resistance should be universal. However, there is marked variation across plant species in the number of nucleotide-binding leucine-rich repeat receptors, which form a cornerstone of defense. The growth-defense trade-off hypothesis predicts costs associated with defense investment to generate variation in these traits. Our analysis comparing features of the intracellular immune-receptor repertoires with trait data of 187 species shows that in wild plants, the size of the molecular defense repertoire correlates negatively with growth. By contrast, we do not find evidence for a growth-defense trade-off in agricultural plants. Our cross-species approach highlights the central role of defense investment in shaping ecological trait variation and its sensitivity to domestication.

Regulatory balance between ear rot resistance and grain yield and their breeding applications in maize and other crops

BACKGROUND

Fungi are prevalent pathogens that cause substantial yield losses of major crops. Ear rot (ER), which is primarily induced by Fusarium or Aspergillus species, poses a significant challenge to maize production worldwide. ER resistance is regulated by several small effect quantitative trait loci (QTLs). To date, only a few ER-related genes have been identified that impede molecular breeding efforts to breed ER-resistant maize varieties.

AIM OF REVIEW

Our aim here is to explore the research progress and mine genic resources related to ER resistance, and to propose a regulatory model elucidating the ER-resistant mechanism in maize as well as a trade-off model illustrating how crops balance fungal resistance and grain yield. Key Scientific Concepts of Review: This review presents a comprehensive bibliometric analysis of the research history and current trends in the genetic and molecular regulation underlying ER resistance in maize. Moreover, we analyzed and discovered the genic resources by identifying 162 environmentally stable loci (ESLs) from various independent forward genetics studies as well as 1391 conservatively differentially expressed genes (DEGs) that respond to Fusarium or Aspergillus infection through multi-omics data analysis. Additionally, this review discusses the syntenies found among maize ER, wheat Fusariumhead blight (FHB), and rice Bakanaedisease (RBD) resistance-related loci, along with the significant overlap between fungal resistance loci and reported yield-related loci, thus providing valuable insights into the regulatory mechanisms underlying the trade-offs between yield and defense in crops.

BW312 Hordeum vulgare semi-dwarf mutant exhibits a shifted metabolic profile towards pathogen resistance

INTRODUCTION

Plant hormonal mutants, which do not produce or are insensitive to hormones, are often affected in their growth and development, but other metabolic rearrangements might be involved. A trade-off between growth and stress response is necessary for the plant survival.

OBJECTIVES

Here, we explore the metabolic profile and the pathogen resistance of a brassinosteroid-insensitive Hordeum vulgare L. semi-dwarf mutant, BW312.

METHODS

We investigate BW312 metabolism through a chemical enrichment analysis, confirming a shifted metabolic profile towards pathogen resistance. The effective pathogen resistance of the mutant was tested in presence of Pyrenophora teres and Fusarium graminearum.

RESULTS

Four compound families were increased in the mutant (pyrrolidines, basic amino acids, alkaloids, monounsaturated fatty acids), while two compound families were decreased (pyrrolidinones, anthocyanins). Dipeptides were also altered (increased and decreased). BW312 displayed a better resistance to Pyrenophora teres in the earliest stage of infection with a 21.5% decrease of the lesion length 10 days after infection. BW312 also exhibited a reduced lesion length (43.3%) and a reduced browning of the lesions (55.5%) when exposed to Fusarium graminearum at the seedling stage.

CONCLUSION

The observed metabolomic shift strongly suggests that the BW312 semi-dwarf mutant is in a primed state, resulting in a standby state of alertness to pathogens.

Different multicellular trichome types coordinate herbivore mechanosensing and defense in tomato

Herbivore-induced wounding can elicit a defense response in plants. However, whether plants possess a surveillance system capable of detecting herbivore threats and initiating preparatory defenses before wounding occurs remains unclear. In this study, we reveal that tomato (Solanum lycopersicum) trichomes can detect and respond to the mechanical stimuli generated by herbivores. Mechanical stimuli are preferentially perceived by long trichomes, and this mechanosensation is transduced via intra-trichome communication. This communication presumably involves calcium waves, and the transduced signals activate the jasmonic acid (JA) signaling pathway in short glandular trichomes, resulting in the upregulation of the Woolly (Wo)-SlMYC1 regulatory module for terpene biosynthesis. This induced defense mechanism provides plants with an early warning system against the threat of herbivore invasion. Our findings represent a perspective on the role of multicellular trichomes in plant defense and the underlying intra-trichome communication.

Single nucleotide polymorphisms in SEPALLATA 2 underlie fruit length variation in cucurbits

Complete disruption of critical genes is generally accompanied by severe growth and developmental defects, which dramatically hinder its utilization in crop breeding. Identifying subtle changes, such as single-nucleotide polymorphisms (SNPs), in critical genes that specifically modulate a favorable trait is a prerequisite to fulfill breeding potential. Here, we found 2 SNPs in the E-class floral organ identity gene cucumber (Cucumis sativus) SEPALLATA2 (CsSEP2) that specifically regulate fruit length. Haplotype (HAP) 1 (8G2667A) and HAP2 (8G2667T) exist in natural populations, whereas HAP3 (8A2667T) is induced by ethyl methanesulfonate mutagenesis. Phenotypic characterization of 4 near-isogenic lines and a mutant line showed that HAP2 fruits are significantly longer than those of HAP1, and those of HAP3 are 37.8% longer than HAP2 fruit. The increasing fruit length in HAP1-3 was caused by a decreasing inhibitory effect on CRABS CLAW (CsCRC) transcription (a reported positive regulator of fruit length), resulting in enhanced cell expansion. Moreover, a 7638G/A-SNP in melon (Cucumis melo) CmSEP2 modulates fruit length in a natural melon population via the conserved SEP2-CRC module. Our findings provide a strategy for utilizing essential regulators with pleiotropic effects during crop breeding.

Tree growth rate-mediated trade-off between drought resistance and recovery in the Northern Hemisphere

The frequency and severity of drought events have increased with climate warming. This poses a significant threat to tree growth and survival worldwide. However, the underlying mechanism of tree growth responses to drought across diverse geographic regions and species remains inconclusive. Here, we used 2808 tree ring width chronologies of 32 species from 1951 to 2020 to examine the relationships between growth rates and resistance and recovery of trees in response to drought in the Northern Hemisphere. We found that trees with fast growth rates exhibited lower drought resistance but higher drought recovery compared to those with slow growth rates, which was further corroborated by the trade-off between resistance and recovery in response to variations in leaf photosynthetic traits. The difference in growth rates also well explained the large variability in the drought resistance and recovery for different geographic regions, as well as for species from different clades and successional stages. Our study provides a conclusive and uniform perspective that tree growth rate regulates drought resistance and recovery, shedding light on the diverse strategies employed by tree species in response to drought stress in the Northern Hemisphere.

A role of epigenetic mechanisms in regulating female reproductive responses to temperature in a pest beetle

Many species are threatened by climate change and must rapidly respond to survive in changing environments. Epigenetic modifications, such as DNA methylation, can facilitate plastic responses by regulating gene expression in response to environmental cues. Understanding epigenetic responses is therefore essential for predicting species' ability to rapidly adapt in the context of global environmental change. Here, we investigated the functional significance of different methylation-associated cellular processes on temperature-dependent life history in seed beetles, Callosobruchus maculatus Fabricius 1775 (Coleoptera: Bruchidae). We assessed changes under thermal stress in (1) DNA methyltransferase (Dnmt1 and Dnmt2) expression levels, (2) genome-wide methylation and (3) reproductive performance, with (2) and (3) following treatment with 3-aminobenzamide (3AB) and zebularine (Zeb) over two generations. These drugs are well-documented to alter DNA methylation across the tree of life. We found that Dnmt1 and Dnmt2 were expressed throughout the body in males and females, but were highly expressed in females compared with males and exhibited temperature dependence. However, whole-genome methylation did not significantly vary with temperature, and only marginally or inconclusively with drug treatment. Both 3AB and Zeb led to profound temperature-dependent shifts in female reproductive life history trade-off allocation, often increasing fitness compared with control beetles. Mismatch between magnitude of treatment effects on DNA methylation versus life history effects suggest potential of 3AB and Zeb to alter reproductive trade-offs via changes in DNA repair and recycling processes, rather than or in addition to (subtle) changes in DNA methylation. Together, our results suggest that epigenetic mechanisms relating to Dnmt expression, DNA repair and recycling pathways, and possibly DNA methylation, are strongly implicated in modulating insect life history trade-offs in response to temperature change.

Arabidopsis MORC1 and MED9 Interact to Regulate Defense Gene Expression and Plant Fitness

Arabidopsis MORC1 (Microrchidia) is required for multiple levels of immunity. We identified 14 MORC1-interacting proteins (MIPs) via yeast two-hybrid screening, eight of which have confirmed or putative nuclear-associated functions. While a few MIP mutants displayed altered bacterial resistance, MIP13 was unusual. The MIP13 mutant was susceptible to Pseudomonas syringae, but when combined with morc1/2, it regained wild-type resistance; notably, morc1/2 is susceptible to the same pathogen. MIP13 encodes MED9, a mediator complex component that interfaces with RNA polymerase II and transcription factors. Expression analysis of defense genes PR1, PR2, and PR5 in response to avirulent P. syringae revealed that morc1/2 med9 expressed these genes in a slow but sustained manner, unlike its lower-order mutants. This expression pattern may explain the restored resistance and suggests that the interplay of MORC1/2 and MED9 might be important in curbing defense responses to maintain fitness. Indeed, repeated challenges with avirulent P. syringae triggered significant growth inhibition in morc1/2 med9, indicating that MED9 and MORC1 may play an important role in balancing defense and growth. Furthermore, the in planta interaction of MED9 and MORC1 occurred 24 h, not 6 h, postinfection, suggesting that the interaction functions late in the defense signaling. Our study reveals a complex interplay between MORC1 and MED9 in maintaining an optimal balance between defense and growth in Arabidopsis.

The NRC0 gene cluster of sensor and helper NLR immune receptors is functionally conserved across asterid plants

Nucleotide-binding domain and leucine-rich repeat-containing receptor (NLR) proteins can form complex receptor networks to confer innate immunity. An NLR-REQUIRED FOR CELL DEATH (NRC) is a phylogenetically related node that functions downstream of a massively expanded network of disease resistance proteins that protect against multiple plant pathogens. In this study, we used phylogenomic methods to reconstruct the macroevolution of the NRC family. One of the NRCs, termed NRC0, is the only family member shared across asterid plants, leading us to investigate its evolutionary history and genetic organization. In several asterid species, NRC0 is genetically clustered with other NLRs that are phylogenetically related to NRC-dependent disease resistance genes. This prompted us to hypothesize that the ancestral state of the NRC network is an NLR helper-sensor gene cluster that was present early during asterid evolution. We provide support for this hypothesis by demonstrating that NRC0 is essential for the hypersensitive cell death that is induced by its genetically linked sensor NLR partners in 4 divergent asterid species: tomato (Solanum lycopersicum), wild sweet potato (Ipomoea trifida), coffee (Coffea canephora), and carrot (Daucus carota). In addition, activation of a sensor NLR leads to higher-order complex formation of its genetically linked NRC0, similar to other NRCs. Our findings map out contrasting evolutionary dynamics in the macroevolution of the NRC network over the last 125 million years, from a functionally conserved NLR gene cluster to a massive genetically dispersed network.

Cross-family transfer of the Arabidopsis cell-surface immune receptor LORE to tomato confers sensing of 3-hydroxylated fatty acids and enhanced disease resistance

Plant pathogens pose a high risk of yield losses and threaten food security. Technological and scientific advances have improved our understanding of the molecular processes underlying host-pathogen interactions, which paves the way for new strategies in crop disease management beyond the limits of conventional breeding. Cross-family transfer of immune receptor genes is one such strategy that takes advantage of common plant immune signalling pathways to improve disease resistance in crops. Sensing of microbe- or host damage-associated molecular patterns (MAMPs/DAMPs) by plasma membrane-resident pattern recognition receptors (PRR) activates pattern-triggered immunity (PTI) and restricts the spread of a broad spectrum of pathogens in the host plant. In the model plant Arabidopsis thaliana, the S-domain receptor-like kinase LIPOOLIGOSACCHARIDE-SPECIFIC REDUCED ELICITATION (AtLORE, SD1-29) functions as a PRR, which senses medium-chain-length 3-hydroxylated fatty acids (mc-3-OH-FAs), such as 3-OH-C10:0, and 3-hydroxyalkanoates (HAAs) of microbial origin to activate PTI. In this study, we show that ectopic expression of the Brassicaceae-specific PRR AtLORE in the solanaceous crop species Solanum lycopersicum leads to the gain of 3-OH-C10:0 immune sensing without altering plant development. AtLORE-transgenic tomato shows enhanced resistance against Pseudomonas syringae pv. tomato DC3000 and Alternaria solani NL03003. Applying 3-OH-C10:0 to the soil before infection induces resistance against the oomycete pathogen Phytophthora infestans Pi100 and further enhances resistance to A. solani NL03003. Our study proposes a potential application of AtLORE-transgenic crop plants and mc-3-OH-FAs as resistance-inducing biostimulants in disease management.

Transcriptional and hormonal profiling uncovers the interactions between plant developmental stages and RNA virus infection

Arabidopsis thaliana is more susceptible to certain viruses during its later developmental stages. The differential responses and the mechanisms behind this development-dependent susceptibility to infection are still not fully understood. Here we explored the outcome of a viral infection at different host developmental stages by studying the response of A. thaliana to infection with turnip mosaic virus at three developmental stages: juvenile vegetative, bolting, and mature flowering plants. We found that infected plants at later stages downregulate cell wall biosynthetic genes and that this downregulation may be one factor facilitating viral spread and systemic infection. We also found that, despite being more susceptible to infection, infected mature flowering plants were more fertile (i.e. produce more viable seeds) than juvenile vegetative and bolting infected plants; that is, plants infected at the reproductive stage have greater fitness than plants infected at earlier developmental stages. Moreover, treatment of mature plants with salicylic acid increased resistance to infection at the cost of significantly reducing fertility. Together, these observations support a negative trade-off between viral susceptibility and plant fertility. Our findings point towards a development-dependent tolerance to infection.

Are miRNAs applicable for balancing crop growth and defense trade-off?

Securing agricultural supplies for the increasing population without negative impacts on environment demands new crop varieties with higher yields, better quality, and stronger stress resilience. But breeding such super crop varieties is restrained by growth-defense (G-D) trade-off. MicroRNAs (miRNAs) are versatile regulators of plant growth and immune responses, with several being demonstrated to simultaneously regulate crop growth and defense against biotic stresses and to balance G-D trade-off. Increasing evidence also links miRNAs to the metabolism and signaling of phytohormones, another type of master regulator of plant growth and defense. Here, we synthesize the reported functions of miRNAs in crop growth, development, and responses to bio-stressors, summarize the regulatory scenarios of miRNAs based on their relationship with target(s), and discuss how miRNAs, particularly those involved in crosstalk with phytohormones, can be applied in balancing G-D trade-off in crops. We also propose several open questions to be addressed for adopting miRNAs in balancing crop G-D trade-off.

From trade-off to synergy: microbial insights into enhancing plant growth and immunity

The reduction in crop yield caused by pathogens and pests presents a significant challenge to global food security. Genetic engineering, which aims to bolster plant defence mechanisms, emerges as a cost-effective solution for disease control. However, this approach often incurs a growth penalty, known as the growth-defence trade-off. The precise molecular mechanisms governing this phenomenon are still not completely understood, but they generally fall under two main hypotheses: a "passive" redistribution of metabolic resources, or an "active" regulatory choice to optimize plant fitness. Despite the knowledge gaps, considerable practical endeavours are in the process of disentangling growth from defence. The plant microbiome, encompassing both above- and below-ground components, plays a pivotal role in fostering plant growth and resilience to stresses. There is increasing evidence which indicates that plants maintain intimate associations with diverse, specifically selected microbial communities. Meta-analyses have unveiled well-coordinated, two-way communications between plant shoots and roots, showcasing the capacity of plants to actively manage their microbiota for balancing growth with immunity, especially in response to pathogen incursions. This review centers on successes in making use of specific root-associated microbes to mitigate the growth-defence trade-off, emphasizing pivotal advancements in unravelling the mechanisms behind plant growth and defence. These findings illuminate promising avenues for future research and practical applications.

CLAVATA3 Signaling Buffers Arabidopsis Shoot Apical Meristem Activity in Response to Photoperiod

Land plants grow throughout their life cycle via the continuous activity of stem cell reservoirs contained within their apical meristems. The shoot apical meristem (SAM) of Arabidopsis and other land plants responds to a variety of environmental cues, yet little is known about the response of meristems to seasonal changes in day length, or photoperiod. Here, the vegetative and reproductive growth of Arabidopsis wild-type and clavata3 (clv3) plants in different photoperiod conditions was analyzed. It was found that SAM size in wild-type Arabidopsis plants grown in long-day (LD) conditions gradually increased from embryonic to reproductive development. clv3 plants produced significantly more leaves as well as larger inflorescence meristems and more floral buds than wild-type plants in LD and short-day (SD) conditions, demonstrating that CLV3 signaling limits vegetative and inflorescence meristem activity in both photoperiods. The clv3 phenotypes were more severe in SDs, indicating a greater requirement for CLV3 restriction of SAM function when the days are short. In contrast, clv3 floral meristem size and carpel number were unchanged between LD and SD conditions, which shows that the photoperiod does not affect the regulation of floral meristem activity through the CLV3 pathway. This study reveals that CLV3 signaling specifically restricts vegetative and inflorescence meristem activity in both LD and SD photoperiods but plays a more prominent role during short days.

Comparison of Growth and Metabolomic Profiles of Two Afforestation Cypress Species Cupressus chengiana and Platycladus orientalis Grown at Minjiang Valley in Southwest China

In recent years, afforestation has been conducted in China's hot and dry valleys. However, there is still a paucity of knowledge regarding the performance of tree species in these semi-arid regions, particularly with regard to interspecies differences. The present study compares the growth and metabolome characteristics of two widely used cypress species, namely Cupressus chengiana and Platycladus orientalis, grown at two sites with distinct climate conditions in the hot and dry Minjiang Valley in southwestern China. The findings indicate that C. chengiana trees exhibit superior growth rates compared to P. orientalis trees at both study sites. In comparison to P. orientalis trees, C. chengiana trees demonstrated a greater tendency to close their stomata in order to prevent water loss at the hotter and drier site, Llianghekou (LHK). Additionally, C. chengiana trees exhibited significantly lower hydrogen peroxide levels than P. orientalis trees, either due to lower production and/or higher scavenging of reactive oxygen species. C. chengiana trees accumulated soluble sugars as well as sugar derivatives, particularly those involved in sucrose and galactose metabolisms under stressful conditions. The species-specific differences were also reflected in metabolites involved in the tricarboxylic acid cycle, nitrogen, and secondary metabolisms. The metabolome profiles of the two species appeared to be influenced by the prevailing climatic conditions. It appeared that the trees at the drier and hotter site, LHK, were capable of efficient nitrogen uptake from the soil despite the low soil nitrogen concentration. This study is the first to compare the growth performance and metabolic profiles of two widely used tree species with high resistance to adverse conditions. In addition to the species-specific differences and adaptations to different sites, the present study also provides insights into potential management strategies to alleviate abiotic stress, particularly with regard to nitrogen nutrients, in the context of climate change.

Over-accumulation of chloroplast-nucleus located WHIRLY1 in barley leads to a decrease in growth and an enhanced stress resistance

WHIRLY1 is a chloroplast-nucleus located DNA/RNA-binding protein with functions in development and stress tolerance. By overexpression of HvWHIRLY1 in barley, one line with a 10-fold and two lines with a 50-fold accumulation of the protein were obtained. In these lines, the relative abundance of the nuclear form exceeded that of the chloroplast form. Growth of the plants was shown to be compromised in a WHIRLY1 abundance-dependent manner. Over-accumulation of WHIRLY1 in chloroplasts had neither an evident impact on nucleoid morphology nor on the composition of the photosynthetic apparatus. Nevertheless, oeW1 plants were found to be compromised in the light reactions of photosynthesis as well as in carbon fixation. The reduction in growth and photosynthesis was shown to be accompanied by a decrease in the levels of cytokinins and an increase in the level of jasmonic acid. Gene expression analyses revealed that in nonstress conditions the oeW1 plants had enhanced levels of pathogen response (PR) gene expression indicating activation of constitutive defense. During growth in continuous light of high irradiance PR gene expression increased indicating that under stress conditions oeW1 are capable to further enhance defense.

Isocitrate lyase promotes Puccinia striiformis f. sp. tritici susceptibility in wheat (Triticum aestivum) by suppressing accumulation of glyoxylate cycle intermediates

Plant fungal parasites manipulate host metabolism to support their own survival. Among the many central metabolic pathways altered during infection, the glyoxylate cycle is frequently upregulated in both fungi and their host plants. Here, we examined the response of the glyoxylate cycle in bread wheat (Triticum aestivum) to infection by the obligate biotrophic fungal pathogen Puccinia striiformis f. sp. tritici (Pst). Gene expression analysis revealed that wheat genes encoding the two unique enzymes of the glyoxylate cycle, isocitrate lyase (TaICL) and malate synthase, diverged in their expression between susceptible and resistant Pst interactions. Focusing on TaICL, we determined that the TaICL B homoeolog is specifically upregulated during early stages of a successful Pst infection. Furthermore, disruption of the B homoeolog alone was sufficient to significantly perturb Pst disease progression. Indeed, Pst infection of the TaICL-B disruption mutant (TaICL-BY400*) was inhibited early during initial penetration, with the TaICL-BY400* line also accumulating high levels of malic acid, citric acid, and aconitic acid. Exogenous application of malic acid or aconitic acid also suppressed Pst infection, with trans-aconitic acid treatment having the most pronounced effect by decreasing fungal biomass 15-fold. Thus, enhanced TaICL-B expression during Pst infection may lower accumulation of malic acid and aconitic acid to promote Pst proliferation. As exogenous application of aconitic acid and malic acid has previously been shown to inhibit other critical pests and pathogens, we propose TaICL as a potential target for disruption in resistance breeding that could have wide-reaching protective benefits for wheat and beyond.

Companion basil plants prime the tomato wound response through volatile signaling in a mixed planting system

KEY MESSAGE

Volatile compounds released from basil prime the tomato wound response by promoting jasmonic acid, mitogen-activated protein kinase, and reactive oxygen species signaling. Within mixed planting systems, companion plants can promote growth or enhance stress responses in target plants. However, the mechanisms underlying these effects remain poorly understood. To gain insight into the molecular nature of the effects of companion plants, we investigated the effects of basil plants (Ocimum basilicum var. minimum) on the wound response in tomato plants (Solanum lycopersicum cv. 'Micro-Tom') within a mixed planting system under environmentally controlled chamber. The results showed that the expression of Pin2, which specifically responds to mechanical wounding, was induced more rapidly and more strongly in the leaves of tomato plants cultivated with companion basil plants. This wound response priming effect was replicated through the exposure of tomato plants to an essential oil (EO) prepared from basil leaves. Tomato leaves pre-exposed to basil EO showed enhanced expression of genes related to jasmonic acid, mitogen-activated protein kinase (MAPK), and reactive oxygen species (ROS) signaling after wounding stress. Basil EO also enhanced ROS accumulation in wounded tomato leaves. The wound response priming effect of basil EO was confirmed in wounded Arabidopsis plants. Loss-of-function analysis of target genes revealed that MAPK genes play pivotal roles in controlling the observed priming effects. Spodoptera litura larvae-fed tomato leaves pre-exposed to basil EO showed reduced growth compared with larvae-fed control leaves. Thus, mixed planting with basil may enhance defense priming in both tomato and Arabidopsis plants through the activation of volatile signaling.

Agave Wilt Susceptibility by Reduction of Free Hexoses in Root Tissue of Agave tequilana Weber var. azul Commercial Plants in the Fructan Accumulation Process

Agave tequilana stems store fructan polymers, the main carbon source for tequila production. This crop takes six or more years for industrial maturity. In conducive conditions, agave wilt disease increases the incidence of dead plants after the fourth year. Plant susceptibility induced for limited photosynthates for defense is recognized in many crops and is known as "sink-induced loss of resistance". To establish whether A. tequilana is more prone to agave wilt as it ages, because the reduction of water-soluble carbohydrates in roots, as a consequence of greater assembly of highly polymerized fructans, were quantified roots sucrose, fructose, and glucose, as well as fructans in stems of agave plants of different ages. The damage induced by inoculation with Fusarium solani or F. oxysporum in the roots or xylem bundles, respectively, was recorded. As the agave plant accumulated fructans in the stem as the main sink, the amount of these hexoses diminished in the roots of older plants, and root rot severity increased when plants were inoculated with F. solani, as evidence of more susceptibility. This knowledge could help to structure disease management that reduces the dispersion of agave wilt, dead plants, and economic losses at the end of agave's long crop cycle.

The cotton MYB33 gene is a hub gene regulating the trade-off between plant growth and defense in Verticillium dahliae infection

INTRODUCTION

Sessile plants engage in trade-offs between growth and defense capacity in response to fluctuating environmental cues. MYB is an important transcription factor that plays many important roles in controlling plant growth and defense. However, the mechanism behind how it keeps a balance between these two physiological processes is still largely unknown.

OBJECTIVES

Our work focuses on the dissection of the molecular mechanism by which GhMYB33 regulates plant growth and defense.

METHODS

The CRISPR/Cas9 technique was used to generate mutants for deciphering GhMYB33 functions. Yeast two-hybrid, luciferase complementary imaging, and co-immunoprecipitation assays were used to prove that proteins interact with each other. We used the electrophoretic mobility shift assay, yeast one-hybrid, and luciferase activity assays to analyze GhMYB33 acting as a promoter. A β-glucuronidase fusion reporter and 5' RNA ligase mediated amplification of cDNA ends analysis showed that ghr-miR319c directedly cleaved the GhMYB33 mRNA.

RESULTS

Overexpressing miR319c-resistant GhMYB33 (rGhMYB33) promoted plant growth, accompanied by a significant decline in resistance against Verticillium dahliae. Conversely, its knockout mutant, ghmyb33, demonstrated growth restriction and concomitant augmentation of V. dahliae resistance. GhMYB33 was found to couple with the DELLA protein GhGAI1 and bind to the specific cis-elements of GhSPL9 and GhDFR1 promoters, thereby modulating internode elongation and plant resistance in V. dahliae infection. The ghr-miR319c was discovered to target and suppress GhMYB33 expression. The overexpression of ghr-miR319c led to enhanced plant resistance and a simultaneous reduction in plant height.

CONCLUSION

Our findings demonstrate that GhMYB33 encodes a hub protein and controls the expression of GhSPL9 and GhDFR1, implicating a pivotal role for the miR319c-MYB33 module to regulate the trade-offs between plant growth and defense.

A Solanum lycopersicum polyamine oxidase contributes to the control of plant growth, xylem differentiation, and drought stress tolerance

Polyamines are involved in several plant physiological processes. In Arabidopsis thaliana, five FAD-dependent polyamine oxidases (AtPAO1 to AtPAO5) contribute to polyamine homeostasis. AtPAO5 catalyzes the back-conversion of thermospermine (T-Spm) to spermidine and plays a role in plant development, xylem differentiation, and abiotic stress tolerance. In the present study, to verify whether T-Spm metabolism can be exploited as a new route to improve stress tolerance in crops and to investigate the underlying mechanisms, tomato (Solanum lycopersicum) AtPAO5 homologs were identified (SlPAO2, SlPAO3, and SlPAO4) and CRISPR/Cas9-mediated loss-of-function slpao3 mutants were obtained. Morphological, molecular, and physiological analyses showed that slpao3 mutants display increased T-Spm levels and exhibit changes in growth parameters, number and size of xylem elements, and expression levels of auxin- and gibberellin-related genes compared to wild-type plants. The slpao3 mutants are also characterized by improved tolerance to drought stress, which can be attributed to a diminished xylem hydraulic conductivity that limits water loss, as well as to a reduced vulnerability to embolism. Altogether, this study evidences conservation, though with some significant variations, of the T-Spm-mediated regulatory mechanisms controlling plant growth and differentiation across different plant species and highlights the T-Spm role in improving stress tolerance while not constraining growth.

Attenuated total reflection Fourier-transform infrared spectroscopy for the prediction of hormone concentrations in plants

Plant hormones are important in the control of physiological and developmental processes including seed germination, senescence, flowering, stomatal aperture, and ultimately the overall growth and yield of plants. Many currently available methods to quantify such growth regulators quickly and accurately require extensive sample purification using complex analytic techniques. Herein we used ultra-performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS) to create and validate the prediction of hormone concentrations made using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectral profiles of both freeze-dried ground leaf tissue and extracted xylem sap of Japanese knotweed (Reynoutria japonica) plants grown under different environmental conditions. In addition to these predictions made with partial least squares regression, further analysis of spectral data was performed using chemometric techniques, including principal component analysis, linear discriminant analysis, and support vector machines (SVM). Plants grown in different environments had sufficiently different biochemical profiles, including plant hormonal compounds, to allow successful differentiation by ATR-FTIR spectroscopy coupled with SVM. ATR-FTIR spectral biomarkers highlighted a range of biomolecules responsible for the differing spectral signatures between growth environments, such as triacylglycerol, proteins and amino acids, tannins, pectin, polysaccharides such as starch and cellulose, DNA and RNA. Using partial least squares regression, we show the potential for accurate prediction of plant hormone concentrations from ATR-FTIR spectral profiles, calibrated with hormonal data quantified by UHPLC-HRMS. The application of ATR-FTIR spectroscopy and chemometrics offers accurate prediction of hormone concentrations in plant samples, with advantages over existing approaches.

Abolishing ARF8A activity promotes disease resistance in tomato

Auxin response factors (ARFs) are a family of transcription factors that regulate auxin-dependent developmental processes. Class A ARFs function as activators of auxin-responsive gene expression in the presence of auxin, while acting as transcriptional repressors in its absence. Despite extensive research on the functions of ARF transcription factors in plant growth and development, the extent, and mechanisms of their involvement in plant resistance, remain unknown. We have previously reported that mutations in the tomato AUXIN RESPONSE FACTOR8 (ARF8) genes SlARF8A and SlARF8B result in the decoupling of fruit development from pollination and fertilization, leading to partial or full parthenocarpy and increased yield under extreme temperatures. Here, we report that fine-tuning of SlARF8 activity results in increased resistance to fungal and bacterial pathogens. This resistance is mostly preserved under fluctuating temperatures. Thus, fine-tuning SlARF8 activity may be a potent strategy for increasing overall growth and yield.

Plant cell wall-mediated disease resistance: Current understanding and future perspectives

Beyond their function as structural barriers, plant cell walls are essential elements for the adaptation of plants to environmental conditions. Cell walls are dynamic structures whose composition and integrity can be altered in response to environmental challenges and developmental cues. These wall changes are perceived by plant sensors/receptors to trigger adaptative responses during development and upon stress perception. Plant cell wall damage caused by pathogen infection, wounding, or other stresses leads to the release of wall molecules, such as carbohydrates (glycans), that function as damage-associated molecular patterns (DAMPs). DAMPs are perceived by the extracellular ectodomains (ECDs) of pattern recognition receptors (PRRs) to activate pattern-triggered immunity (PTI) and disease resistance. Similarly, glycans released from the walls and extracellular layers of microorganisms interacting with plants are recognized as microbe-associated molecular patterns (MAMPs) by specific ECD-PRRs triggering PTI responses. The number of oligosaccharides DAMPs/MAMPs identified that are perceived by plants has increased in recent years. However, the structural mechanisms underlying glycan recognition by plant PRRs remain limited. Currently, this knowledge is mainly focused on receptors of the LysM-PRR family, which are involved in the perception of various molecules, such as chitooligosaccharides from fungi and lipo-chitooligosaccharides (i.e., Nod/MYC factors from bacteria and mycorrhiza, respectively) that trigger differential physiological responses. Nevertheless, additional families of plant PRRs have recently been implicated in oligosaccharide/polysaccharide recognition. These include receptor kinases (RKs) with leucine-rich repeat and Malectin domains in their ECDs (LRR-MAL RKs), Catharanthus roseus RECEPTOR-LIKE KINASE 1-LIKE group (CrRLK1L) with Malectin-like domains in their ECDs, as well as wall-associated kinases, lectin-RKs, and LRR-extensins. The characterization of structural basis of glycans recognition by these new plant receptors will shed light on their similarities with those of mammalians involved in glycan perception. The gained knowledge holds the potential to facilitate the development of sustainable, glycan-based crop protection solutions.

Revisiting growth-defence trade-offs and breeding strategies in crops

Plants have evolved a multi-layered immune system to fight off pathogens. However, immune activation is costly and is often associated with growth and development penalty. In crops, yield is the main breeding target and is usually affected by high disease resistance. Therefore, proper balance between growth and defence is critical for achieving efficient crop improvement. This review highlights recent advances in attempts designed to alleviate the trade-offs between growth and disease resistance in crops mediated by resistance (R) genes, susceptibility (S) genes and pleiotropic genes. We also provide an update on strategies for optimizing the growth-defence trade-offs to breed future crops with desirable disease resistance and high yield.