Growth-defense tradeoffs in plants: a balancing act to optimize fitness

Rapid introgression of the clubroot resistance gene CRa into cabbage skeleton inbred lines through marker assisted selection

Clubroot, caused by Plasmodiophora brassicae, is a globally pervasive soil-borne disease that poses a significant challenge primarily in cruciferous crops. However, the scarcity of resistant materials and the intricate genetic mechanisms within cabbage present major obstacles to clubroot resistance (CR) breeding. In our previous research, we developed an Ogura CMS cabbage variety, "17CR3", which harbors the CRa gene, crucial for CR. The fertility of this variety can be restored through crossing with an Ogura cytoplasmic male sterile (CMS) restore line. In the current investigation, offspring from fertile hybrids were utilized as donor parents in backcrossing with five cabbage inbred lines, with the goal of introducing the CRa gene into elite cabbage cultivars possessing superior agronomic traits. Following five years of continuous field selection combined with molecular marker-assisted selection (MAS), we successfully developed BC4 individuals exhibiting excellent agronomic traits and diverse genetic backgrounds. Whole-genome resequencing revealed a mere 54,213 SNP differences between the genetic makeup of BC4 individuals and their recurrent parents. The results of inoculation identification demonstrated a high degree of co-segregation between the CRa-specific marker KBrH129J18 and resistance to Plasmodiophora brassicae in both inoculated resistant seedlings and cabbage plants harboring CRa across three distinct regions of China. Additionally, results from Semi-Quantitative RT-PCR experiments revealed minimal to no expression of CRa in the majority of susceptible individuals, underscoring the pivotal role of CRa in conferring CR. Moreover, BC3 individuals resulting from the cross between "SK308" and "18CR3", which carried CRa, exhibited resistance to clubroot under the natural conditions of disease-prone fields in Wulong, China. In summary, through a combination of traditional breeding methods and MAS, we successfully bred five cabbage inbred lines carrying the CRa gene from diverse genetic backgrounds, thereby establishing a robust foundation for their integration into breeding programs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01532-2.

An Insect Effector Mimics Its Host Immune Regulator to Undermine Plant Immunity

Plants activate defense machinery when infested by herbivorous insects but avoid such costs in the absence of herbivory. However, the key signaling pathway regulators underlying such flexibility and the mechanisms that insects exploit these components to disarm plant defense systems remain elusive. Here, it is reported that immune repressor 14-3-3e in rice Oryza sativa (OsGF14e) regulates immune homeostasis. Infestation with brown planthopper (BPH) Nilaparvata lugens decreased OsGF14e expression; however, the level of downregulation is limited both by the short duration and the specific feeding location. OsGF14e interacts with Enhanced Disease Resistance 1-like (OsEDR1l), a Raf-like MAP kinase kinase kinase (MAPKKK), and repressed jasmonic acid, jasmonic acid-isoleucine, and H2O2 accumulation by enhancing OsEDR1l abundance and signaling ability. OsGF14e and OsEDR1l overexpression renders rice susceptible to BPH, whereas their knockout increases plant resistance but compromises rice growth and grain yield. Intriguingly, BPH 14-3-3e protein (Nl14) that shares high sequence homology and structural similarity with OsGF14e is identified from BPH saliva and egg-associated secretions. Mediated through BPH feeding and oviposition, Nl14, similar to OsGF14e, interacts with OsEDR1l and triggers the OsEDR1l signaling, thereby suppressing plant defenses and facilitating BPH infestation. Apparently, structural and functional mimicry makes it possible for this newly discovered BPH effector to exploit rice OsGF14e-EDR1l immune suppression module. The results reveal a novel mechanism deployed by herbivorous insects, in a manner similar to certain pathogen effectors, to evade host plant defenses by mimicking host immune regulators.

Growth-tolerance tradeoffs shape the survival outcomes and ecophysiological strategies of Atlantic Forest species in the rehabilitation of mining-impacted sites

The initial performance of seedlings of tree species from different functional groups, regarding the growth-defense tradeoff, might determine its long-term success during the rehabilitation of mining areas. We monitored the field performance of six native tree species of the Atlantic Forest in the Fundão dam tailing that has been under rehabilitation for 35 months. Additionally, we explored the morphophysiological traits driving the superior performance of three species. The study examined the survival strategies of pioneer species (Anadenanthera colubrina, Bixa orellana, Peltophorum dubium) and secondary species (Cedrela fissilis, Handroanthus impetiginosus, Handroanthus serratifolius), as well as the photosynthetic, nutritional, and antioxidant metabolism of the successful species. Most species accumulated excessive Fe in their leaves, except for the pioneer species A. colubrina and P. dubium. However, the nutritional status of the plants, concerning leaf nutrient concentration, was adequate for their growth in the waste. The species A. colubrina, C. fissilis, and H. serratifolius exhibited poor physiological performance, primarily due to substrate compaction and excessive foliar metal concentrations. The successful performance of P. dubium was attributed to avoidance mechanisms, allowing a cost-effective growth-defense tradeoff, thus maintaining photosynthetic efficiency at the expense of energy investment in antioxidant protection. The excess Fe allocation in the photosynthetic tissues of B. orellana was linked to a greater investment in antioxidant metabolism, which was related to the protection of the photosynthetic machinery. The Fe hyperaccumulation in H. impetiginosus led to increased oxidative damage, which was mitigated by investments in tolerance mechanisms, including photosynthetic adjustments (stomatal limitation, non-photochemical energy dissipation), as well as the activation of the enzymatic antioxidant system. The persistence and success of the Atlantic Forest tree species were not related to their ecological successional classification. Instead, it was the different mechanisms of tolerance and avoidance that allowed both pioneer and secondary species to thrive in the impacted area.

Unveiling the role of microRNAs in nonhost resistance to Sclerotinia sclerotiorum: Rice-specific microRNAs attack the pathogen via cross-kingdom RNAi

The development of rapeseed with high resistance against the pathogen Sclerotinia sclerotiorum is impeded by the lack of effective resistance resources within host species. Unraveling the molecular basis of nonhost resistance (NHR) holds substantial value for resistance improvement in crops. In the present study, small RNA sequencing and transcriptome sequencing were carried out between rice (a nonhost species of S. sclerotiorum) and rapeseed during infection, revealing the involvement of rice miRNAs on translation-related processes in both rice and the pathogen. Specifically, rice-specific miRNAs with potential capability for cross-kingdom RNAi against S. sclerotiorum were explored, of which Os-miR169y was selected as a representative case to elucidate its role in resistance to S. sclerotiorum. The silence of Os-miR169y decreased the resistance level of rice to S. sclerotiorum, and heterologous expression of Os-miR169y in Arabidopsis and rapeseed significantly enhanced the host resistance. The dual-luciferase reporter assay indicates that Os-miR169y targets S. sclerotiorum 60S ribosomal protein L19 (SsRPL19). Overexpressing Os-miR169y (OEss-miR169y) and RNAi of SsRPL19 (RNAiss-RPL19) in S. sclerotiorum significantly impaired the growth and pathogenicity of the pathogen, while overexpressing SsRPL19 exhibited a contrast effect. Yeast-two-hybridization revealed an interlinking role of SsRPL19 with multiple large and small ribosomal subunits, indicating its important role in translation. Proteome sequencing detected a decreased amount of proteins in transformants OEss-miR169y and RNAiss-RPL19 and significant suppression on key metabolic pathways such as carbon and nitrogen metabolisms. Collectively, this study suggests that rice can secrete specific miRNAs to suppress genes essential for S. sclerotiorum, such as Os-miR169y, which targets and suppresses SsRPL19 and thus impairs protein synthesis in the pathogen. This study sheds light on the intrinsic mechanisms of rice NHR against S. sclerotiorum, and further demonstrates the potential of using nonhost-specific "pathogen-attacking" miRNAs in improving resistance in host species.

Strawberry plant growth enhancement: Effects of artificial light and methyl jasmonate-salicylic acid treatments on physiology and metabolism

Strawberries, known for their antioxidant properties, exhibit changes in physiology and metabolite profiles based on cultivation techniques. In Indonesia, strawberries are typically grown in highland regions, but climate change has necessitated adjustments in cultivation practices to enhance production and quality. This study investigates the adaptation of strawberry plants in lowland environments using light-emitting diodes (LEDs) and the exogenous application of methyl jasmonate (MeJA) and methyl salicylic acid (MeSA). A randomized block design was used with two factors: LED light types and MeJA-MeSA treatments. While the treatments did not significantly affect shoot growth (initially 1.5-2 cm, increasing 3-5 times by day 3), chlorophyll content, or fruit sugar levels, notable effects were observed in leaf glucose accumulation. The control group showed a fivefold increase (0.55 μg ml-1), while LED-hormone treatments resulted in a 27-64 % lower increase (0.20-0.40 μg ml-1). Fructose levels followed a similar pattern, and malic acid content was highest in the MeJA treatment (5.76 mg ml-1), with MeSA treatments also enhancing malic acid (5.91 mg ml-1). The secondary metabolite analysis, conducted using GC-MS and LC-MS, identified key defense-related compounds, including terpenoids, saturated fats, alkaloids, and amino acid derivatives, which play a role in the plant's defense mechanisms. These findings highlight the potential of LED lighting and hormone applications to modulate strawberry physiology and suggest further research into their role in plant stress responses.

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.

Proteomic insight into growth and defense strategies under low ultraviolet-B acclimation in the cyanobacterium Nostoc sphaeroides

Prioritizing defense over growth often occurs under ultraviolet (UV)-B radiation while several studies showed its growth-promoting effects on photosynthetic organisms, how they overcome the growth-defense trade-off is unclear. This study deciphered the acclimation responses of the cyanobacterium Nostoc sphaeroides to low UV-B radiation (0.08 W m-2) using quantitative proteomic, physiological and biochemical analyses. We identified 628 significantly altered proteins, among which energy production and conversion related proteins dominated. The UV-B-acclimated cells exhibited a significant increase in the abundance of the phycoerythrin and chlorophyll synthesis related enzymes, along with enhanced linear and cyclic electron transport rates, which further led to a rise in light-induced NADPH generation (27 %) and ATP content (67 %). The enhanced photosynthetic energy supply could fuel both growth and defense in Nostoc sphaeroides. The UV-B-acclimated cells showed enhanced photosynthetic carbon fixation, as evidenced by an increase in extracellular carbonic anhydrase activity (142 %), ribulose-1,5-bisphosphate carboxylase/oxygenase activity (87 %) and the pH compensation point, compared to non-UV-B-acclimated cells. Low UV-B also induced ribosome heterogeneity, as indicated by significant changes in the abundance of core ribosomal proteins, RNA modification related enzymes, and ribosome biogenesis and translation related accessory factors. Additionally, low UV-B activated multiple defense strategies, such as significant upregulation of mycosporine-like amino acid synthesis, RecA-dependent DNA repair pathways and the glutathione redox system. Our findings suggested that growth and defense were balanced by enhancing the photosynthetic energy supply under low UV-B acclimation in the cyanobacterium Nostoc sphaeroides, which provides novel insight into mechanisms for overcoming growth-defense trade-offs.

OPDA signaling channels resource (e-) allocation from the photosynthetic electron transfer chain to plastid cysteine biosynthesis in defense activation

A primary precursor of jasmonates, 12-oxo-phytodienoic acid (OPDA), is an autonomous hormone signal that activates and fine-tunes plant defense responses, as well as growth and development. However, the architecture of its signaling circuits remains largely elusive. Here we describe that OPDA signaling drives photosynthetic reductant powers toward sulfur assimilation in the chloroplasts, incorporating sulfide into cysteine. Under stressed states, OPDA-accumulated in the chloroplasts-binds and promotes cyclophilin 20-3, an OPDA receptor, to transfer electrons from thioredoxin F2, an electron carrier in the photosynthesis reaction, to serine acetyltransferase 1 (SAT1). The charge carrier (H+, e-) then splits dimeric SAT1 trimers in half to signal the recruitment of dimeric O-acetylserine(thiol)lyase B, forming a hetero-oligomeric cysteine synthase complex (CSC). CSC formation and its metabolic products (especially glutathione) then coordinate redox-resolved retrograde signaling from the chloroplasts to the nucleus in adjusting expression of OPDA-responsive genes such as GLUTAREDOXIN 480 and CYTOCHROME P450, and triggering defense responses against various ecological constraints such as salinity and excess oxidants, as well as mechanical wounding. We thus conclude that OPDA signaling regulates a unique metabolic switch in channeling light input into outputs that fuel/shape a multitude of physiological processes, optimizing plant growth fitness and survival capacity under a range of environmental stress cues.

OsWRKY26 negatively regulates bacterial blight resistance by suppressing OsXa39 expression

Plants are susceptible to infection by various pathogens with high epidemic potential. Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial blight in rice, one of the most significant diseases in both temperate and tropical regions. In this study, we report the identification and characterization of OsWRKY26, a sucrose-inducible transcription factor, that plays a role in the plant defense responses following Xoo infection. We found that mutant plants with defective OsWRKY26 showed enhanced defense response specifically to Xoo, indicating that this transcription factor acts as a negative defense regulator. In contrast, mutant plants did not exhibit higher resistance compared to wild-type (WT) plants when infected with the rice blast fungal pathogen Magnaporthe oryzae. Transcriptomic analysis of mutant and WT plants revealed that several pathogen resistance genes were upregulated in mutants. Of these, we selected OsXa39 for further analysis. Transient expression experiments in rice protoplasts showed that OsWRKY26 repressed the expression of a Luciferase reporter gene driven by the OsXa39 promoter. Chromatin immunoprecipitation analysis revealed that OsWRKY26 binds directly to the promoter region of OsXa39. These findings suggest that OsWRKY26 negatively regulates the defense response during Xoo infection by repressing OsXa39 as well as other pathogen-related genes such as OsXa47, OsBBR1, OsRSR1, OsPR1a, OsPR1-11, OsPR2, and OsPR4c.

The blue-light receptor CRY1 serves as a switch to balance photosynthesis and plant defense

Plant stomata open in response to blue light, allowing gas exchange and water transpiration. However, open stomata are potential entry points for pathogens. Whether plants can sense pathogens and mount defense responses upon stomatal opening and how blue-light cues are integrated to balance growth-defense trade-offs are poorly characterized. We show that the Arabidopsis blue-light photoreceptor CRYPTOCHROME 1 (CRY1) mediates various aspects of immunity, including pathogen-triggered stomatal closure as well as activation of plant immunity through a typical light-responsive protein LATE UPREGULATED IN RESPONSE TO HYALOPERONOSPORA PARASITICA (LURP1). LURP1 undergoes N-terminal palmitoylation in the presence of bacterial flagellin, prompting a change in subcellular localization from the cytoplasm to plasma membrane, where it enhances the activity of the receptor FLAGELLIN SENSING 2 (FLS2) to mediate plant defense. Collectively, these findings reveal that blue light regulates stomatal defense and highlight the dual functions of CRY1 in photosynthesis and immunity.

The long noncoding RNA ALEX1 confers a functional phase state of ARF3 to enhance rice resistance to bacterial pathogens

Rice bacterial blight is a devastating disease worldwide, causing significant yield losses. Understanding how plants defend against microbial infection is critical for sustainable crop production. In this study, we show that ALEX1, a previously identified pathogen-induced long noncoding RNA, localizes to the nucleus and directly binds AUXIN RESPONSE FACTOR 3 (ARF3). We showed that ARF3 forms the condensates in the nucleus via its intrinsically disordered middle region (MR), and that these ARF3 condensates display solid-like properties. We further revealed that ALEX1 directly binds the MR of ARF3 to regulate ARF3 condensate dynamics and promote ARF3 homodimerization. The dispersed, dimeric form of ARF3, referred to as its functional phase state, enhances its ability to transcriptionally repress the expression of downstream target genes such as JAZ13, thereby modulating the jasmonic acid signaling pathway and enhancing pathogen resistance in rice. Collectively, this study reveals the role of a long noncoding RNA in regulating protein condensation and complex assembly, thus contributing to plant pathogen resistance.

Glutathione accelerates the cell cycle and cellular reprogramming in plant regeneration

The plasticity of plant cells underlies their wide capacity to regenerate, with increasing evidence in plants and animals implicating cell-cycle dynamics in cellular reprogramming. To investigate the cell cycle during cellular reprogramming, we developed a comprehensive set of cell-cycle-phase markers in the Arabidopsis root. Using single-cell RNA sequencing profiles and live imaging during regeneration, we found that a subset of cells near an ablation injury dramatically increases division rate by truncating G1 phase. Cells in G1 undergo a transient nuclear peak of glutathione (GSH) prior to coordinated entry into S phase, followed by rapid divisions and cellular reprogramming. A symplastic block of the ground tissue impairs regeneration, which is rescued by exogenous GSH. We propose a model in which GSH from the outer tissues is released upon injury, licensing an exit from G1 near the wound to induce rapid cell division and reprogramming.

Transposon-triggered epigenetic chromatin dynamics modulate EFR-related pathogen response

Infectious diseases drive wild plant evolution and impact crop yield. Plants, like animals, sense biotic threats through pattern recognition receptors (PRRs). Overly robust immune responses can harm plants; thus, understanding the tuning of defense response mechanisms is crucial for developing pathogen-resistant crops. In this study, we found that an inverted-repeat transposon (EFR-associated IR, Ea-IR) located between the loci encoding PRRs ELONGATION FACTOR-TU RECEPTOR (EFR) and myosin XI-k (XI-k) in Arabidopsis affects chromatin organization, promoting the formation of a repressive chromatin loop. Upon pathogen infection, chromatin changes around EFR and XI-k correlate with increased EFR transcription. Pathogen-induced chromatin opening causes RNA polymerase II readthrough, producing a longer, Ea-IR-containing XI-k transcript, processed by Dicer-like enzymes into small RNAs, which reset chromatin to a repressive state attenuating the immune response after infection. Arabidopsis accessions lacking Ea-IR have higher basal EFR levels and resistance to pathogens. We show a scenario in which a transposon, chromatin organization and gene expression interact to fine-tune immune responses, during both the course of infection and the course of evolution.

Genome-wide association study of metabolic traits in the giant duckweed Spirodela polyrhiza

The exceptionally high growth rate and high flavonoid content make the giant duckweed Spirodela polyrhiza (L.) Schleid. (Arales: Lemnaceae Martinov) an ideal organism for food production and metabolic engineering. To facilitate this, identification of the genetic basis underlying growth and metabolic traits is essential. Here, we analysed growth and content of 42 metabolites in 137 S. polyrhiza genotypes and characterized the genetics underpinning these traits using a genome-wide association (GWA) approach. We found that biomass positively correlated with the content of many free amino acids, including L-glutamine, L-tryptophan, and L-serine, but negatively correlated with specialized metabolites, such as flavonoids. GWA analysis showed that several candidate genes involved in processes such as photosynthesis, protein degradation, and organ development were jointly associated with multiple metabolic traits. The results suggest the above genes are suitable targets for simultaneous optimization of duckweed growth and metabolite levels. This study provides insights into the metabolic diversity of S. polyrhiza and its underlying genetic architecture, paving the way for industrial applications of this plant via targeted breeding or genetic engineering.

Effect of elevated ammonium on biotic and abiotic stress defense responses and expression of related genes in cucumber (Cucumis sativus L.) plants

Ammonium (NH4+) enhances plant defense mechanisms but can be phytotoxic as the sole nitrogen source. To investigate the impact of a balanced NH4+ and NO3- ratio on plant defense parameters without adverse effects, cucumber plants (Cucumis sativus L.) were grown under control (14 mM NO3- + 2 mM NH4+) and elevated level of NH4+ (eNH4+, 8 mM NO3-+ 8 mM NH4+). Plants subjected to eNH4+ showed significantly increased shoot and root biomass by about 41% and 47%, respectively. Among the antioxidant enzymes studied, ascorbate peroxidase (EC 1.11.1.11) activity was increased up to 3.3 fold in eNH4+ compared with control plants, which was associated with enhanced resistance to paraquat. Upregulation of PATHOGENESIS RELATED PROTEIN 4 (PR4) and LIPOXYGENASE 1 (LOX1), accompanied by increased concentrations of salicylic acid and nitric oxide, conferred more excellent resistance of eNH4+ plants to powdery mildew infection. However, the expression levels of ACC OXIDASE 1 (ACO1) and RESPIRATORY BURST OXIDASE HOMOLOGS B (RBOHB) were lower in eNH4+ plants, which was consistent with decreased NADPH oxidase activity and lower leaf H2O2 levels. The biosynthesis of phenolics was enhanced, whereas the activities of polymerizing enzymes and lignin deposition were reduced by half in eNH4+ plants. Besides, a significant effect on plant biomass under salt or drought stress has not been observed between control and eNH4+ plants. These results showed that different defense pathways are distinctively affected by eNH4+ treatment, and the NH4+ to NO3- ratio may play a role in fine-tuning the plant defense response.

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.

A type II secreted subtilase from commensal rhizobacteria cleaves immune elicitor peptides and suppresses flg22-induced immune activation

Plant roots grow in association with a community of microorganisms collectively known as the rhizosphere microbiome. Immune activation in response to elicitors like the flagellin-derived epitope flg22 restricts bacteria on plant roots but also inhibits plant growth. Some commensal root-associated bacteria are capable of suppressing the plant immune response to elicitors. In this study, we investigated the ability of 165 root-associated bacteria to suppress flg22-induced immune activation and growth restriction. We demonstrate that a type II secreted subtilase, which we term immunosuppressive subtilase A (IssA), from Dyella japonica strain MF79 cleaves the immune elicitor peptide flg22 and suppresses immune activation. IssA homologs are found in other plant-associated commensals, with particularly high conservation in the order Xanthomonadales. This represents a novel mechanism by which commensal microbes modulate flg22-induced immunity in the rhizosphere microbiome.

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.

A canonical protein complex controls immune homeostasis and multipathogen resistance

The calcium (Ca2+) sensor ROD1 (RESISTANCE OF RICE TO DISEASES1) is a master regulator of immunity in rice. By screening suppressors of rod1 mutants, we show that ROD1 governs immune homeostasis by surveilling the activation of a canonical immune pathway. Mutations in OsTIR (TIR-only protein), OsEDS1 (enhanced disease susceptibility 1), OsPAD4 (phytoalexin deficient 4), and OsADR1 (activated disease resistance 1) all abolish enhanced disease resistance of rod1 plants. OsTIR catalyzes the production of second messengers 2'-(5″-phosphoribosyl)-5'-adenosine monophosphate (pRib-AMP) and diphosphate (pRib-ADP), which trigger formation of an OsEDS1-OsPAD4-OsADR1 (EPA) immune complex. ROD1 interacts with OsTIR and inhibits its enzymatic activity, whereas mutation of ROD1 leads to constitutive activation of the EPA complex. Thus, we unveil an immune network that fine-tunes immune homeostasis and multipathogen resistance in rice.

Beneficial microorganisms: Regulating growth and defense for plant welfare

Beneficial microorganisms (BMs) promote plant growth and enhance stress resistance. This review summarizes how BMs induce growth promotion by improving nutrient uptake, producing growth-promoting hormones and stimulating root development. How BMs enhance disease resistance and help protect plants from abiotic stresses has also been explored. Growth-defense trade-offs are known to affect the ability of plants to survive under unfavourable conditions. This review discusses studies demonstrating that BMs regulate growth-defense trade-offs through microbe-associated molecular patterns and multiple pathways, including the leucine-rich repeat receptor-like kinase pathway, abscisic acid signalling pathway and specific transcriptional factor regulation. This multifaceted relationship underscores the significance of BMs in sustainable agriculture. Finally, the need for integration of artificial intelligence to revolutionize biofertilizer research has been highlighted. This review also elucidates the cutting-edge advancements and potential of plant-microbe synergistic microbial agents.

Foliar implications of polystyrene nanoplastics on leafy vegetables and its ecological consequences

The rise of airborne micro-nanoplastics (MNPs) pollution poses a significant threat to agroecological systems. Despite this issue, there is a critical gap in our understanding of their specific effects on various leafy vegetable species. To address this, we conducted a controlled experiment applying Polystyrene Nanoplastics (PS-NPs) on four leafy vegetables: Brassica rapa var. chinensis, B. rapa var. parachinensis, Amaranthus viridis, and Allium tuberosum. Our results showed that PS-NPs tend to accumulate within the epidermal layers and cuticles of these vegetables, particularly around stomatal apertures. More PS-NPs were found on the adaxial and abaxial side of leaves, compared to the cross-section. The abundance of PS-NPs accumulations varied significantly among the studied species due to differences in leaf structure. Notably, leaves with trichomes trapped more PS-NPs particles. These accumulation significantly reduced chlorophyll content and photosynthetic rates, altering the growth and nutritional quality of the vegetables. Our findings reveal the ecological effects of PS-NPs on the nutrient content, phenotype, physiology, growth and biomass metrics of common leafy vegetables. This highlights the potential for PS-NPs accumulation in edible plant tissues, raising concerns about food security and human health.

The MdIAA29-MdARF4 complex plays an important role in balancing plant height with salt and drought stress responses

Breeding dwarf apple (Malus domestica) varieties is a recent trend in agriculture because such varieties are easy to maintain and have high yields; however, dwarf apple trees generally have poor stress tolerance. Balancing apple plant height and stress response has been an important breeding goal. In this study, aux/indole-3-acetic acid 29 gene in apple (MdIAA29) overexpression lines (#1, #2, and #3) had reduced plant height by 39%, 31%, and 35%, respectively, suitable for close planting applications. Surprisingly, the dwarf MdIAA29-overexpressing lines also showed increased plant tolerance to salt and drought stresses. Further analysis showed that MdIAA29 inhibited the regulation of auxin response factor 4 (ARF4) on Gretchen Hagen 3.9 (GH3.9) gene and 9-cis-epoxycarotenoid dioxygenase 3 (NCED3) gene in apple and changed the contents of auxin and abscisic acid in different tissues, thus achieving a balance between plant height and stress tolerance. In addition, we also found that MdIAA7 enhanced the inhibitory effect of MdIAA29 on MdARF4. In brief, the MdIAA29-MdARF4 complex significantly impacts the height of apple plants and their ability to respond to salt and drought stress.

Crop antiviral defense: Past and future perspective

Viral pathogens not only threaten the health and life of humans and animals but also cause enormous crop yield losses and contribute to global food insecurity. To defend against viral pathogens, plants have evolved an intricate immune system to perceive and cope with such attacks. Although most of the fundamental studies were carried out in model plants, more recent research in crops has provided new insights into the antiviral strategies employed by crop plants. We summarize recent advances in understanding the biological roles of cellular receptors, RNA silencing, RNA decay, hormone signaling, autophagy, and ubiquitination in manipulating crop host-mediated antiviral responses. The potential functions of circular RNAs, the rhizosphere microbiome, and the foliar microbiome of crops in plant-virus interactions will be fascinating research directions in the future. These findings will be beneficial for the development of modern crop improvement strategies.

ZmICE1a regulates the defence-storage trade-off in maize endosperm

The endosperm of cereal grains feeds the entire world as a major food supply; however, little is known about its defence response during endosperm development. The Inducer of CBF Expression 1 (ICE1) is a well-known regulator of cold tolerance in plants. ICE1 has a monocot-specific homologue that is preferentially expressed in cereal endosperms but with an unclear regulatory function. Here we characterized the function of monocot-specific ZmICE1a, which is expressed in the entire endosperm, with a predominant expression in its peripheral regions, including the aleurone layer, subaleurone layer and basal endosperm transfer layer in maize (Zea mays). Loss of function of ZmICE1a reduced starch content and kernel weight. RNA sequencing and CUT&Tag-seq analyses revealed that ZmICE1a positively regulates genes in starch synthesis while negatively regulating genes in aleurone layer-specific defence and the synthesis of indole-3-acetic acid and jasmonic acid (JA). Exogenous indole-3-acetic acid and JA both induce the expression of numerous defence genes, which show distinct spatial-specific expression in the basal endosperm transfer layer and subaleurone layer, respectively. Moreover, we dissected a JA-ZmJAZ9-ZmICE1a-MPI signalling axis involved in JA-mediated defence regulation. Overall, our study revealed ZmICE1a as a key regulator of endosperm defence response and a coordinator of the defence-storage trade-off in endosperm development.

Herbivore kairomones affect germination speed, seedling growth, and herbivory

Seeds and seedlings are particularly vulnerable to herbivory. Unlike mature plants, which can wait until herbivory is experienced to induce defense, seeds and seedlings face mortality if they wait. Slug mucus functions as a kairomone, a non-attack-related substance emitted by consumers that is detected by a prey species (in this case, plants). While snail mucus has been shown to induce defense in seedlings, it is not widely confirmed whether slugs have the same effect and whether seeds can also detect and react to such herbivore cues. We investigated how exposure to Arion subfuscus mucus affected growth and defense in Brassica nigra seeds and seedlings. Seeds exposed to slug mucus germinated 5% faster than control (water only) seeds, but the resulting seedlings weighed 16% less than control seedlings. To test whether this difference results from herbivore-exposed plants allocating energy from growth to defense, we conducted choice bioassays assessing slug preference for control seedlings versus seedlings that were either (A) exposed to mucus only as a seed; or (B) exposed to mucus as a seed and seedling. While slugs did not differentiate between control seedlings and ones exposed to herbivore cues only as a seed, they ate 88% less biomass of seedlings exposed to mucus as both seeds and seedlings. These results suggest that slug mucus induces changes in plant traits related to defense and growth/competitive ability. Future research should determine the chemical mechanisms of this induced defense.

Microbiota responses to mutations affecting NO homeostasis in Arabidopsis thaliana

Interactions between plants and microorganisms are pivotal for plant growth and productivity. Several plant molecular mechanisms that shape these microbial communities have been identified. However, the importance of nitric oxide (NO) produced by plants for the associated microbiota remains elusive. Using Arabidopsis thaliana isogenic mutants overproducing NO (nox1, NO overexpression) or down-producing NO (i.e. nia1nia2 impaired in the expression of both nitrate reductases NR1/NIA1 and NR2/NIA2; the 35s::GSNOR1 line overexpressing nitrosoglutathione reductase (GSNOR) and 35s::AHB1 line overexpressing haemoglobin 1 (AHB1)), we investigated how altered NO homeostasis affects microbial communities in the rhizosphere and in the roots, soil microbial activity and soil metabolites. We show that the rhizosphere microbiome was affected by the mutant genotypes, with the nox1 and nia1nia2 mutants causing opposite shifts in bacterial and fungal communities compared with the wild-type (WT) Col-0 in the rhizosphere and roots, respectively. These mutants also exhibited distinctive soil metabolite profiles than those from the other genotypes while soil microbial activity did not differ between the mutants and the WT Col-0. Our findings support our hypothesis that changes in NO production by plants can influence the plant microbiome composition with differential effects between fungal and bacterial communities.

TOR balances plant growth and cold tolerance by orchestrating amino acid-derived metabolism in tomato

The target of rapamycin (TOR) kinase is a central signaling hub that plays a crucial role in precisely orchestrating plant growth, development, and stress responses. This suggests that TOR is intricately involved in maintaining the balance between plant growth and stress responses. Nevertheless, despite the observed effects, the specific mechanisms through which TOR operates in these processes remain obscure. In this study, we investigated how the tomato (Solanum lycopersicum) TOR (SlTOR) affects plant growth and cold responses. We demonstrated that SlTOR inhibition transcriptionally primes cold stress responses, consequently enhancing tomato cold tolerance. A widely targeted metabolomics analysis revealed the disruption of amino acid metabolism homeostasis under cold stress upon SlTOR inhibition, which led to the accumulation of two important cryoprotective metabolites: salicylic acid (SA) and putrescine (Put). Next, we discovered SlPGH1 (2-PHOSPHO-D-GLYCERATE HYDRO-LYASE 1) as a direct substrate of SlTOR. Inhibiting SlTOR led to increased SlCBF1 (C-REPEAT-BINDING FACTOR 1) expression via SlPGH1, potentially triggering the activation of cold-responsive genes and subsequent metabolic alterations. Our study provides a mechanistic framework that elucidates how SlTOR modulates amino acid-related metabolism to enhance tomato cold tolerance, which sheds light on the complex interplay between growth and stress responses orchestrated by TOR.

Stomata: gatekeepers of uptake and defense signaling by green leaf volatiles in maize

Plants adapt to balance growth-defense tradeoffs in response to both biotic and abiotic stresses. Green leaf volatiles (GLVs) are released after biotic and abiotic stresses and function as damage-associated signals in plants. Although, GLVs enter plants primarily through stomata, the role of stomatal regulation on the kinetics of GLV uptake remains largely unknown. Here, we illustrate the effect of stomatal closure on the timing and magnitude of GLV uptake. We closed stomata by either exposing maize (Zea mays) plants to darkness or applying abscisic acid, a phytohormone that closes the stomata in light. Then, we exposed maize seedlings to (Z)-3-hexen-1-ol and compared its dynamic uptake under different stomatal conditions. Additionally, we used (E)-3-hexen-1-ol, an isomer of (Z)-3-hexen-1-ol not made by maize, to exclude the role of internal GLVs in our assays. We demonstrate that closed stomata effectively prevent GLV entry into exposed plants, even at high concentrations. Furthermore, our findings indicate that reduced GLV uptake impairs GLV-driven induction of biosynthesis of sesquiterpenes, a group of GLV-inducible secondary metabolites, with or without herbivory. These results elucidate how stomata regulate the perception of GLV signals, thereby dramatically changing the plant responses to herbivory, particularly under water stress or dark conditions.

CRISPR/Cas9-mediated knockout of NtMYC2a gene involved in resistance to bacterial wilt in tobacco

MYC2 is a class of bHLH family transcription factors and a major regulatory factor in the JA signaling pathway, and its molecular function in tobacco has not been reported. In this study, CRISPR/Cas9-mediated MYC2 gene NtMYC2a knockout mutants at tobacco was obtained and its agronomic traits, disease resistance, and chemical composition were identified. Comparing with the WT, the leaf width of the KO-NtMYC2a was narrowed, the nornicotine content and mecamylamine content increased significantly and the resistance to Ralstonia solanacearum significantly decreased. The transcriptome sequencing results showed that DEGs related to immunity, signal transduction and growth and development were enriched between KO-NtMYC2a and WT. NtJAR1 and NtCOI1 in KO-NtMYC2a were down-regulated to regulating the JA signaling pathway, result in a significant decrease in tobacco's resistance to R. solanacearum. Our research provides theoretical support for the functional research of MYC2 and the study of the mechanism of tobacco bacterial wilt resistance.

Ozone Priming Enhanced Low Temperature Tolerance of Wheat (Triticum Aestivum L.) based on Physiological, Biochemical and Transcriptional Analyses

Low temperature significantly inhibits plant growth in wheat (Triticum aestivum L.), prompting the exploration of effective strategies to mitigate low temperature stress. Several priming methods enhance low temperature stress tolerance; however, the role of ozone priming remains unclear in wheat. Here we found ozone priming alleviated low temperature stress in wheat. Transcriptome analysis showed that ozone priming positively modulated the 'photosynthesis-antenna proteins' pathway in wheat under low temperature. This was confirmed by the results of ozone-primed plants, which had higher trapped energy flux and electron transport flux per reaction, and less damage to chloroplasts than non-primed plants under low temperature. Ozone priming also mitigated the overstimulation of glutathione metabolism and induced the accumulation of total ascorbic acid and glutathione, as well as maintaining redox homeostasis in wheat under low temperature. Moreover, gene expressions and enzyme activities in glycolysis pathways were upregulated in ozone priming compared with non-priming after the low temperature stress. Furthermore, exogenous antibiotics significantly increased low temperature tolerance, which further proved that the inhibition of ribosome biogenesis by ozone priming was involved in low temperature tolerance in wheat. In conclusion, ozone priming enhanced wheat's low temperature tolerance through promoting light-harvesting capacity, redox homeostasis and carbohydrate metabolism, as well as inhibiting ribosome biogenesis.

Photorespiratory Metabolism and Its Regulatory Links to Plant Defence Against Pathogens

When plants face biotic stress, the induction of defence responses imposes a massive demand for carbon and energy resources, which could decrease the reserves allocated towards growth. These growth-defence trade-offs have important implications for plant fitness and productivity and influence the outcome of plant-pathogen interactions. Biotic stress strongly affects plant cells' primary metabolism, including photosynthesis and respiration, the main source of energy and carbon skeletons for plant growth, development, and defence. Although the nature of photosynthetic limitations imposed by pathogens is variable, infection often increases photorespiratory pressure, generating conditions that promote ribulose-1,5-bisphosphate oxygenation, leading to a metabolic shift from assimilation to photorespiration. Photorespiration, the significant metabolic flux following photosynthesis, protects the photosynthetic apparatus from photoinhibition. However, recent studies reveal that its role is far beyond photoprotection. The intermediates of the photorespiratory cycle regulate photosynthesis, and photorespiration interacts with the metabolic pathways of nitrogen and sulphur, shaping the primary metabolism for stress responses. This work aims to present recent insights into the integration of photorespiration within the network of primary metabolism under biotic stress. It also explores the potential implications of regulating photosynthetic-photorespiratory metabolism for plant defence against bacterial and fungal pathogens.

Silence is not always golden: A closer look at potential environmental and ecotoxicological impacts of large-scale dsRNA application

RNA interference (RNAi) technology has emerged as a pivotal strategy in sustainable pest management, offering a targeted approach that significantly mitigates the environmental and health risks associated with traditional insecticides. Originally implemented through genetically modified organisms (GMOs) to produce specific RNAi constructs, the technology has evolved in response to public and regulatory concerns over GMOs. This evolution has spurred the development of non-transgenic RNAi applications such as spray-induced gene silencing (SIGS), which employs double-stranded RNA (dsRNA) to silence pest genes directly without altering the plant's genetic makeup. Despite its advantages in specificity and reduced ecological footprint, SIGS faces significant obstacles, particularly the instability of dsRNA in field conditions, which limits its practical efficacy. To overcome these limitations, innovative delivery mechanisms have been developed. These include nanotechnology-based systems, minicells, and nanovesicles, which are designed to protect dsRNA from degradation and enhance its delivery to target organisms. While these advancements have improved the stability and application efficiency of dsRNA, comprehensive assessments of their environmental safety and the potential for increased exposure risks to non-target organisms remain incomplete. This comprehensive review aims to elucidate the environmental fate of dsRNA and evaluate the potential risks associated with its widespread application on non-target organisms, encompassing soil microorganisms, beneficial insects, host plants, and mammals. The objective is to establish a more refined framework for RNAi risk assessment within environmental and ecotoxicological contexts, thereby fostering the development of safer, non-transgenic RNAi-based pest control strategies.

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.

A Novel Single Base Mutation in OsSPL42 Leads to the Formation of Leaf Lesions in Rice

Rice spotted-leaf mutants serve as valuable resources for studying plant programmed cell death (PCD) and disease resistance mechanisms, making them crucial for research on disease resistance in rice. Map-based cloning was used to identify and clone the spotted-leaf gene OsSPL42. Then, functional complementation and CRISPR/Cas9 techniques were also employed to further validate the function of this gene. By applying leaf clippings for bacterial blight (BB) inoculation, the BB resistance of different rice lines was assessed. The results in this study were as follows: The OsSPL42 behaved as a recessive nuclear gene and was narrowed down to a 111 kb region on chromosome 8. All T0 transgenic rice plants in the complementation experiments exhibited a wild-type phenotype, without any lesion spots on the rice leaves. This suggests that the LOC_Os08g06100 encoding O-methyltransferase is the candidate gene for the mutant spl42. The OsSpl42 is widely expressed and the OsSPL42-GFP protein is mainly localized in the cytoplasm. OsSPL42 overexpression lines are more susceptible to BBs, which indicates that OsSPL42 may act as a negative regulator of rice resistance to BB. In summary, we speculate that OsSPL42 plays an important role in the regulation of pathogen response, providing new insights into plant defense mechanisms.

The Cost of Self-Defense: Browsing Effects in the Rare Plant Species Salix arizonica

Coevolution between plants and their animal predators has led to diverse defensive adaptations. Multiple theories of defense propose that there are resource allocation costs associated with producing chemical defenses. One leading hypothesis, optimal defense theory (ODT), suggests that natural selection will result in the allocation of resources to defenses that optimize the cost-to-benefit ratio between defense and other functional processes. The population decline of the rare subalpine wetland species, Arizona willow (Salix arizonica), has been attributed to various biotic and abiotic factors, with browsing from wild and domestic ungulates as a significant concern for at least three decades. In a field experiment using natural populations, we compare the relationship between phytochemical defense and height in Arizona willows with and without long-term protection from browsing via browse exclosures. Consistent with the predictions of ODT, individuals with physical protection from ungulate browsing for multiple years had significantly lower phenolic glycoside (PG) concentrations and increased plant height compared to unprotected individuals. A similar pattern was found across all individuals, whereby total PG concentration and height were negatively correlated. In a short-term experiment in natural populations, changes in levels of defense were not observed when plants received protection for only one growing season. The contrasting pattern of defense plasticity in response to long-term versus short-term physical protection suggests a differential plastic response in this long-lived species. Delayed reduction in PG concentration may serve as a benefit to avoid mismatches between environmental cues and responses. Our research sheds light on the intricate dynamics between plant-defense strategies, environmental pressures, and evolutionary adaptations in shaping plant-browser interactions.

Virulence regulation in plant-pathogenic bacteria by host-secreted signals

Bacterial pathogens manipulate host signaling pathways and evade host defenses using effector molecules, coordinating their deployment to ensure successful infection. However, host-derived metabolites as signals, and their critical role in regulating bacterial virulence requires further insights. Effective regulation of virulence, which is essential for pathogenic bacteria, involves controlling factors that enable colonization, defense evasion, and tissue damage. This regulation is dynamic, influenced by environmental cues including signals from host plants like exudates. Plant exudates, comprising of diverse compounds released by roots and tissues, serve as rich chemical signals affecting the behavior and virulence of associated bacteria. Plant nutrients act as signaling molecules that are sensed through membrane-localized receptors and intracellular response mechanisms in bacteria. This review explains how different bacteria detect and answer to secreted chemical signals, regulating virulence gene expression. Our main emphasis is exploring the recognition process of host-originated signaling molecules through molecular sensors on cellular membranes and intracellular signaling pathways. This review encompasses insights into how bacterial strains individually coordinate their virulence in response to various distinct host-derived signals that can positively or negatively regulate their virulence. Furthermore, we explained the interruption of plant defense with the perception of host metabolites to dampen pathogen virulence. The intricate interplay between pathogens and plant signals, particularly in how pathogens recognize host metabolic signals to regulate virulence genes, portrays a crucial initial interaction leading to profound influences on infection outcomes. This work will greatly aid researchers in developing new strategies for preventing and treating infections.

SmJAZs-SmbHLH37/SmERF73-SmSAP4 module mediates jasmonic acid signaling to balance biosynthesis of medicinal metabolites and salt tolerance in Salvia miltiorrhiza

Salvia miltiorrhiza holds significant importance in traditional Chinese medicine. Stress-associated proteins (SAP), identified by A20/AN1 zinc finger structural domains, play crucial roles in regulating plant growth, development, resistance to biotic and abiotic stress, and hormone responses. Herein, we conducted a genome-wide identification of the SAP gene family in S. miltiorrhiza. The expression analysis revealed a significant upregulation of SmSAP4 under methyl jasmonate (MeJA) and salt stress. Overexpressing SmSAP4 in S. miltiorrhiza hairy roots increased tanshinones content while decreasing salvianolic acids content, while RNAi-silencing SmSAP4 had the opposite effect. SmSAP4 overexpression in both Arabidopsis thaliana and S. miltiorrhiza hairy roots decreased their salt stress tolerance, accompanied by increased activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and a hindered ability to maintain the Na+ : K+ ratio. Further investigations demonstrated that MeJA alleviated the inhibitory effect of SmJAZ3 on SmSAP4 activation by SmbHLH37 and SmERF73. However, MeJA did not affect the inhibition of SmSAP4 activation by SmJAZ8 through SmbHLH37. In summary, our research reveals that SmSAP4 negatively regulates the accumulation of salvianic acid through the SmJAZs-SmbHLH37/SmERF73-SmSAP4 module and positively impacting the accumulation of tanshinones. Additionally, it functions as a negative regulator under salt stress.

Functional stress responses in Glaucophyta: Evidence of ethylene and abscisic acid functions in Cyanophora paradoxa

Glaucophytes, an enigmatic group of freshwater algae, occupy a pivotal position within the Archaeplastida, providing insights into the early evolutionary history of plastids and their host cells. These algae possess unique plastids, known as cyanelles that retain certain ancestral features, enabling a better understanding of the plastid transition from cyanobacteria. In this study, we investigated the role of ethylene, a potent hormone used by land plants to coordinate stress responses, in the glaucophyte alga Cyanophora paradoxa. We demonstrate that C. paradoxa produces gaseous ethylene when supplied with exogenous 1-aminocyclopropane-1-carboxylic acid (ACC), the ethylene precursor in land plants. In addition, we show that cells produce ethylene natively in response to abiotic stress, and that another plant hormone, abscisic acid (ABA), interferes with ethylene synthesis from exogenously supplied ACC, while positively regulating reactive oxygen species (ROS) accumulation. ROS synthesis also occurred following abiotic stress and ACC treatment, possibly acting as a second messenger in stress responses. A physiological response of C. paradoxa to ACC treatment is growth inhibition. Using transcriptomics, we reveal that ACC treatment induces the upregulation of senescence-associated proteases, consistent with the observation of growth inhibition. This is the first report of hormone usage in a glaucophyte alga, extending our understanding of hormone-mediated stress response coordination into the Glaucophyta, with implications for the evolution of signaling modalities across Archaeplastida.

Microbe-Friendly Plants Enable Beneficial Interactions with Soil Rhizosphere Bacteria by Lowering Their Defense Responses

The use of plant growth-promoting rhizobacteria presents a promising addition to conventional mineral fertilizer use and an alternative strategy for sustainable agricultural crop production. However, genotypic variations in the plant host may result in variability of the beneficial effects from these plant-microbe interactions. This study examined growth promotion effects of commercial vegetable crop cultivars of tomato, cucumber and broccoli following application with five rhizosphere bacteria. Biochemical assays revealed that the bacterial strains used possess several nutrient acquisition traits that benefit plants, including nitrogen fixation, phosphate solubilization, biofilm formation, and indole-3-acetic acid (IAA) production. However, different host cultivars displayed genotype-specific responses from the inoculations, resulting in significant (p < 0.05) plant growth promotion in some cultivars but insignificant (p > 0.05) or no growth promotion in others. Gene expression profiling in tomato cultivars revealed that these cultivar-specific phenotypes are reflected in differential expressions of defense and nutrient acquisition genes, suggesting that plants can be categorized into "microbe-friendly" cultivars (with little or no defense responses against beneficial microbes) and "microbe-hostile" cultivars (with strong defense responses). These results validate the notion that "microbe-friendly" (positive interaction with rhizosphere microbes) should be considered an important trait in breeding programs when developing new cultivars which could result in improved crop yields.

Transcriptomic and metabolomic reveal OsCOI2 as the jasmonate-receptor master switch in rice root

Jasmonate is an essential phytohormone involved in plant development and stress responses. Its perception occurs through the CORONATINE INSENSITIVE (COI) nuclear receptor allowing to target the Jasmonate-ZIM domain (JAZ) repressors for degradation by the 26S proteasome. Consequently, repressed transcription factors are released and expression of jasmonate responsive genes is induced. In rice, three OsCOI genes have been identified, OsCOI1a and the closely related OsCOI1b homolog, and OsCOI2. While the roles of OsCOI1a and OsCOI1b in plant defense and leaf senescence are well-established, the significance of OsCOI2 in plant development and jasmonate signaling has only emerged recently. To unravel the role of OsCOI2 in regulating jasmonate signaling, we examined the transcriptomic and metabolomic responses of jasmonate-treated rice lines mutated in both the OsCOI1a and OsCOI1b genes or OsCOI2. RNA-seq data highlight OsCOI2 as the primary driver of the extensive transcriptional reprogramming observed after a jasmonate challenge in rice roots. A series of transcription factors exhibiting an OsCOI2-dependent expression were identified, including those involved in root development or stress responses. OsCOI2-dependent expression was also observed for genes involved in specific processes or pathways such as cell-growth and secondary metabolite biosynthesis (phenylpropanoids and diterpene phytoalexins). Although functional redundancy exists between OsCOI1a/b and OsCOI2 in regulating some genes, oscoi2 plants generally exhibit a weaker response compared to oscoi1ab plants. Metabolic data revealed a shift from the primary metabolism to the secondary metabolism primarily governed by OsCOI2. Additionally, differential accumulation of oryzalexins was also observed in oscoi1ab and oscoi2 lines. These findings underscore the pivotal role of OsCOI2 in jasmonate signaling and suggest its involvement in the control of the growth-defense trade-off in rice.

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.

A KNOX Ⅱ transcription factor suppresses the NLR immune receptor BRG8-mediated immunity in rice

Nucleotide-binding site and leucine-rich repeat (NLR) proteins are activated by detecting pathogen effectors, which in turn trigger host defenses and cell death. Although many NLRs have been identified, the mechanisms responsible for NLR-triggered defense responses are still poorly understood. In this study, through a genome-wide association study approach, we identified a novel NLR gene, Blast Resistance Gene 8 (BRG8), which confers resistance to rice blast and bacterial blight diseases. BRG8 overexpression and complementation lines exhibit enhanced resistance to both pathogens. Subcellular localization assays showed that BRG8 is localized in both the cytoplasm and the nucleus. Additional evidence revealed that nuclear-localized BRG8 can enhance rice immunity without a hypersensitive response (HR)-like phenotype. We also demonstrated that the coiled-coil domain of BRG8 not only physically interacts with itself but also interacts with the KNOX Ⅱ protein HOMEOBOX ORYZA SATIVA59 (HOS59). Knockout mutants of HOS59 in the BRG8 background show enhanced resistance to Magnaporthe oryzae strain CH171 and Xoo strain CR4, similar to that of the BRG8 background. By contrast, overexpression of HOS59 in the BRG8 background will compromise the HR-like phenotype and resistance response. Further analysis revealed that HOS59 promotes the degradation of BRG8 via the 26S proteasome pathway. Collectively, our study highlights HOS59 as an NLR immune regulator that fine-tunes BRG8-mediated immune responses against pathogens, providing new insights into NLR associations and functions in plant immunity.

Exploring Novel Genomic Loci and Candidate Genes Associated with Plant Height in Bulgarian Bread Wheat via Multi-Model GWAS

In the context of crop breeding, plant height (PH) plays a pivotal role in determining straw and grain yield. Although extensive research has explored the genetic control of PH in wheat, there remains an opportunity for further advancements by integrating genomics with growth-related phenomics. Our study utilizes the latest genome-wide association scan (GWAS) techniques to unravel the genetic basis of temporal variation in PH across 179 Bulgarian bread wheat accessions, including landraces, tall historical, and semi-dwarf modern varieties. A GWAS was performed with phenotypic data from three growing seasons, the calculated best linear unbiased estimators, and the leveraging genotypic information from the 25K Infinium iSelect array, using three statistical methods (MLM, FarmCPU, and BLINK). Twenty-five quantitative trait loci (QTL) associated with PH were identified across fourteen chromosomes, encompassing 21 environmentally stable quantitative trait nucleotides (QTNs), and four haplotype blocks. Certain loci (17) on chromosomes 1A, 1B, 1D, 2A, 2D, 3A, 3B, 4A, 5B, 5D, and 6A remain unlinked to any known Rht (Reduced height) genes, QTL, or GWAS loci associated with PH, and represent novel regions of potential breeding significance. Notably, these loci exhibit varying effects on PH, contribute significantly to natural variance, and are expressed during seedling to reproductive stages. The haplotype block on chromosome 6A contains five QTN loci associated with reduced height and two loci promoting height. This configuration suggests a substantial impact on natural variation and holds promise for accurate marker-assisted selection. The potentially novel genomic regions harbor putative candidate gene coding for glutamine synthetase, gibberellin 2-oxidase, auxin response factor, ethylene-responsive transcription factor, and nitric oxide synthase; cell cycle-related genes, encoding cyclin, regulator of chromosome condensation (RCC1) protein, katanin p60 ATPase-containing subunit, and expansins; genes implicated in stem mechanical strength and defense mechanisms, as well as gene regulators such as transcription factors and protein kinases. These findings enrich the pool of semi-dwarfing gene resources, providing the potential to further optimize PH, improve lodging resistance, and achieve higher grain yields in bread wheat.

Unveiling the impact of nitrogen deficiency on alkaloid synthesis in konjac corms (Amorphophallus muelleri Blume)

BACKGROUND

Konjac corms are known for their alkaloid content, which possesses pharmacological properties. In the primary cultivation areas of konjac, nitrogen deficiency is a common problem that significantly influences alkaloid synthesis. The impact of nitrogen deficiency on the alkaloids in konjac corms remains unclear, further complicated by the transition from mother to daughter corms during their growth cycle.

RESULTS

This study examined 21 alkaloids, including eight indole alkaloids, five isoquinoline alkaloids, and eight other types of alkaloids, along with the associated gene expressions throughout the development of Amorphophallus muelleri Blume under varying nitrogen levels. Nitrogen deficiency significantly reduced corm diameter and fresh weight and delayed the transformation process. Under low nitrogen conditions, the content of indole alkaloids and the expression of genes involved in their biosynthesis, such as tryptophan synthase (TRP) and tryptophan decarboxylase (TDC), exhibited a substantial increase in daughter corms, with fold changes of 61.99 and 19.31, respectively. Conversely, in the mother corm, TDC expression was markedly reduced, showing only 0.04 times the expression level observed under 10 N treatment. The patterns of isoquinoline alkaloid accumulation in corms subjected to nitrogen deficiency were notably distinct from those observed for indole alkaloids. The accumulation of isoquinoline alkaloids was significantly higher in mother corms, with expression levels of aspartate aminotransferase (GOT), chorismate mutase (CM), tyrosine aminotransferase (TAT), and pyruvate decarboxylase (PD) being 4.30, 2.89, 921.18, and 191.40 times greater, respectively. Conversely, in daughter corms, the expression levels of GOT and CM in the 0 N treatment were markedly lower (0.01 and 0.83, respectively) compared to the 10 N treatment.

CONCLUSIONS

The study suggests that under nitrogen deficiency, daughter corms preferentially convert chorismate into tryptophan to synthesize indole alkaloids, while mother corms convert it into tyrosine, boosting the production of isoquinoline alkaloids. This research provides valuable insights into the mechanisms of alkaloid biosynthesis in A. muelleri and can aid in developing nitrogen fertilization strategies and in the extraction and utilization of alkaloids.

Altering cold-regulated gene expression decouples the salicylic acid-growth trade-off in Arabidopsis

In Arabidopsis (Arabidopsis thaliana), overproduction of salicylic acid (SA) increases disease resistance and abiotic stress tolerance but penalizes growth. This growth-defense trade-off has hindered the adoption of SA-based disease management strategies in agriculture. However, investigation of how SA inhibits plant growth has been challenging because many SA-hyperaccumulating Arabidopsis mutants have developmental defects due to the pleiotropic effects of the underlying genes. Here, we heterologously expressed a bacterial SA synthase gene in Arabidopsis and observed that elevated SA levels decreased plant growth and reduced the expression of cold-regulated (COR) genes in a dose-dependent manner. Growth suppression was exacerbated at below-ambient temperatures. Severing the SA-responsiveness of individual COR genes was sufficient to overcome the growth inhibition caused by elevated SA at ambient and below-ambient temperatures while preserving disease- and abiotic-stress-related benefits. Our results show the potential of decoupling SA-mediated growth and defense trade-offs for improving crop productivity.

Transcriptome-wide N6-methyladenosine profiling reveals growth-defense trade-offs in the response of rice to brown planthopper (Nilaparvata lugens) infestation

BACKGROUND

N6-Methyladenosine (m6A) is a common messenger RNA (mRNA) modification that affects various physiological processes in stress responses. However, the role of m6A modifications in plants responses to herbivore stress remains unclear.

RESULTS

Here, we found that an infestation of brown planthopper (Nilaparvata lugens) female adults enhanced the resistance of rice to N. lugens. The m6A methylome analysis of N. lugens-infested and uninfested rice samples was performed to explore the interaction between rice and N. lugens. The m6A methylation mainly occurred in genes that were actively expressed in rice following N. lugens infestation, while an analysis of the whole-genomic mRNA distribution of m6A showed that N. lugens infestation caused an overall decrease in the number of m6A methylation sites across the chromosomes. The m6A methylation of genes involved in the m6A modification machinery and several defense-related phytohormones (jasmonic acid and salicylic acid) pathways was increased in N. lugens-infested rice compared to that in uninfested rice. In contrast, m6A modification levels of growth-related phytohormone (auxin and gibberellin) biosynthesis-related genes were significantly attenuated during N. lugens infestation, accompanied by the down-regulated expression of these transcripts, indicating that rice growth was restricted during N. lugens attack to rapidly optimize resource allocation for plant defense. Integrative analysis of the differential patterns of m6A methylation and the corresponding transcripts showed a positive correlation between m6A methylation and transcriptional regulation.

CONCLUSION

The m6A modification is an important strategy for regulating the expression of genes involved in rice defense and growth during rice-N. lugens interactions. These findings provide new ideas for formulating strategies to control herbivorous pests. © 2024 Society of Chemical Industry.

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.

A telomere-to-telomere Eucalyptus regnans genome: unveiling haplotype variance in structure and genes within one of the world's tallest trees

BACKGROUND

Eucalyptus regnans (Mountain Ash) is an Australian native giant tree species which form forests that are among the highest known carbon-dense biomasses in the world. To enhance genomic studies in this ecologically important species, we assembled a high-quality, mostly telomere-to-telomere complete, chromosome-level, haplotype-resolved reference genome. We sampled a single tree, the Centurion, which is currently a contender for the world's tallest flowering plant.

RESULTS

Using long-read sequencing data (PacBio HiFi, Oxford Nanopore ultra-long reads) and chromosome conformation capture data (Hi-C), we assembled the most contiguous and complete Eucalyptus reference genome to date. For each haplotype, we observed contig N50s exceeding 36 Mbp, scaffold N50s exceeding 43 Mbp, and genome BUSCO completeness exceeding 99%. The assembled genome revealed extensive structural variations between the two haplotypes, consisting mostly of insertions, deletions, duplications and translocations. Analysis of gene content revealed haplotype-specific genes, which were enriched in functional categories related to transcription, energy production and conservation. Additionally, many genes reside within structurally rearranged regions, particularly duplications, suggesting that haplotype-specific variation may contribute to environmental adaptation in the species.

CONCLUSIONS

Our study provides a foundation for future research into E. regnans environmental adaptation, and the high-quality genome will be a powerful resource for conservation of carbon-dense giant tree forests.

RNA silencing is a key regulatory mechanism in the biocontrol fungus Clonostachys rosea-wheat interactions

BACKGROUND

Small RNA (sRNAs)- mediated RNA silencing is emerging as a key player in host-microbe interactions. However, its role in fungus-plant interactions relevant to biocontrol of plant diseases is yet to be explored. This study aimed to investigate Dicer (DCL)-mediated endogenous and cross-kingdom gene expression regulation in the biocontrol fungus Clonostachys rosea and wheat roots during interactions.

RESULTS

C. rosea Δdcl2 strain exhibited significantly higher root colonization than the WT, whereas no significant differences were observed for Δdcl1 strains. Dual RNA-seq revealed the upregulation of CAZymes, membrane transporters, and effector coding genes in C. rosea, whereas wheat roots responded with the upregulation of stress-related genes and the downregulation of growth-related genes. The expression of many of these genes was downregulated in wheat during the interaction with DCL deletion strains, underscoring the influence of fungal DCL genes on wheat defense response. sRNA sequencing identified 18 wheat miRNAs responsive to C. rosea, and three were predicted to target the C. rosea polyketide synthase gene pks29. Two of these miRNAs (mir_17532_x1 and mir_12061_x13) were observed to enter C. rosea from wheat roots with fluorescence analyses and to downregulate the expression of pks29, showing plausible cross-kingdom RNA silencing of the C. rosea gene by wheat miRNAs.

CONCLUSIONS

We provide insights into the mechanisms underlying the interaction between biocontrol fungi and plant roots. Moreover, the study sheds light on the role of sRNA-mediated gene expression regulation in C. rosea-wheat interactions and provides preliminary evidence of cross-kingdom RNA silencing between plants and biocontrol fungi.