Recalculating growth and defense strategies under competition: key roles of photoreceptors and jasmonates

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.

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.

The growth promotion in endophyte symbiotic plants does not penalise the resistance to herbivores and bacterial microbiota

A trade-off between growth and defence against biotic stresses is common in plants. Fungal endophytes of the genus Epichloë may relieve this trade-off in their host grasses since they can simultaneously induce plant growth and produce antiherbivore alkaloids that circumvent the need for host defence. The Epichloë ability to decouple the growth-defence trade-off was evaluated by subjecting ryegrass with and without Epichloë endophytes to an exogenous treatment with gibberellin (GA) followed by a challenge with Rhopalosiphum padi aphids. In agreement with the endophyte-mediated trade-off decoupling hypothesis, the GA-derived promotion of plant growth increased the susceptibility to aphids in endophyte-free plants but did not affect the insect resistance in endophyte-symbiotic plants. In line with the unaltered insect resistance, the GA treatment did not reduce the concentration of Epichloë-derived alkaloids. The Epichloë mycelial biomass was transiently increased by the GA treatment but at the expense of hyphal integrity. The response of the phyllosphere bacterial microbiota to both GA treatment and Epichloë was also evaluated. Only Epichloë, and not the GA treatment, altered the composition of the phyllosphere microbiota and the abundance of certain bacterial taxa. Our findings clearly demonstrate that Epichloë does indeed relieve the plant growth-defence trade-off.

Environmental Control of Hypocotyl Elongation

The hypocotyl is the embryonic stem connecting the primary root to the cotyledons. Hypocotyl length varies tremendously depending on the conditions. This developmental plasticity and the simplicity of the organ explain its success as a model for growth regulation. Light and temperature are prominent growth-controlling cues, using shared signaling elements. Mechanisms controlling hypocotyl elongation in etiolated seedlings reaching the light differ from those in photoautotrophic seedlings. However, many common growth regulators intervene in both situations. Multiple photoreceptors including phytochromes, which also respond to temperature, control the activity of several transcription factors, thereby eliciting rapid transcriptional reprogramming. Hypocotyl growth often depends on sensing in green tissues and interorgan communication comprising auxin. Hypocotyl auxin, in conjunction with other hormones, determines epidermal cell elongation. Plants facing cues with opposite effects on growth control hypocotyl elongation through intricate mechanisms. We discuss the status of the field and end by highlighting open questions.

Associational Effects of Desmodium Intercropping on Maize Resistance and Secondary Metabolism

Intercropping is drawing increasing attention as a strategy to increase crop yields and manage pest pressure, however the mechanisms of associational resistance in diversified cropping systems remain controversial. We conducted a controlled experiment to assess the impact of co-planting with silverleaf Desmodium (Desmodium uncinatum) on maize secondary metabolism and resistance to herbivory by the spotted stemborer (Chilo partellus). Maize plants were grown either in the same pot with a Desmodium plant or adjacent to it in a separate pot. Our findings indicate that co-planting with Desmodium influences maize secondary metabolism and herbivore resistance through both above and below-ground mechanisms. Maize growing in the same pot with a Desmodium neighbor was less attractive for oviposition by spotted stemborer adults. However, maize exposed only to above-ground Desmodium cues generally showed increased susceptibility to spotted stemborer herbivory (through both increased oviposition and larval consumption). VOC emissions and tissue secondary metabolite titers were also altered in maize plants exposed to Desmodium cues, with stronger effects being observed when maize and Desmodium shared the same pot. Specifically, benzoxazinoids were strongly suppressed in maize roots by direct contact with a Desmodium neighbor while headspace emissions of short-chain aldehydes and alkylbenzenes were increased. These results imply that direct root contact or soil-borne cues play an important role in mediating associational effects on plant resistance in this system.

Continuous mowing differentially affects floral defenses in the noxious and invasive weed Solanum elaeagnifolium in its native range

In weeds, disturbance has been found to affect life history traits and mediate trophic interactions. In urban landscapes, mowing is an important disturbance, and we previously showed that continuous mowing leads to enhanced fitness and defense traits in Solanum elaeagnifolium, Silverleaf Nightshade (SLN). However, most studies have been focused on foliar defenses, ignoring floral defenses. In this study we examined whether continuous mowing affected floral defenses in SLN using mowed and unmowed populations in South Texas, their native range. We found flowers of mowed SLN plants larger but lighter than unmowed plants. Additionally, flowers on plants that were mowed frequently were both heavier and larger. Mowed plants had higher spine density and consequently unmowed flowers had higher herbivore damage. Additionally, early instar Manduca sexta fed on mowed flower-based artificial diets showed no difference in mass than the control and unmowed; however, later instars caterpillars on unmowed diets gained significantly more mass than the mowed treatment and control. Mowed plants had higher spine density which may shed light on why unmowed flowers experienced higher herbivore damage. We found caterpillars fed on high mowing frequency diets were heavier than those on low mowing frequency diets. Collectively, we show that mowing compromises floral traits and enhances plant defenses against herbivores and should be accounted for in management.

Functions of Phytochrome Interacting Factors (PIFs) in Adapting Plants to Biotic and Abiotic Stresses

Plants possess the remarkable ability to sense detrimental environmental stimuli and launch sophisticated signal cascades that culminate in tailored responses to facilitate their survival, and transcription factors (TFs) are closely involved in these processes. Phytochrome interacting factors (PIFs) are among these TFs and belong to the basic helix-loop-helix family. PIFs are initially identified and have now been well established as core regulators of phytochrome-associated pathways in response to the light signal in plants. However, a growing body of evidence has unraveled that PIFs also play a crucial role in adapting plants to various biological and environmental pressures. In this review, we summarize and highlight that PIFs function as a signal hub that integrates multiple environmental cues, including abiotic (i.e., drought, temperature, and salinity) and biotic stresses to optimize plant growth and development. PIFs not only function as transcription factors to reprogram the expression of related genes, but also interact with various factors to adapt plants to harsh environments. This review will contribute to understanding the multifaceted functions of PIFs in response to different stress conditions, which will shed light on efforts to further dissect the novel functions of PIFs, especially in adaption to detrimental environments for a better survival of plants.

Effects of far-red light on the behaviour and reproduction of the zoophytophagous predator Macrolophus pygmaeus and its interaction with a whitefly herbivore

Plants can detect neighbouring plants through a reduction in the ratio between red and far-red light (R:FR). This provides a signal of plant-plant competition and induces rapid plant growth while inhibiting defence against biotic stress, two interlinked responses designated as the shade avoidance syndrome (SAS). Consequently, the SAS can influence plant-herbivore interactions that could cascade to higher trophic levels. However, little is known about how the expression of the SAS can influence tritrophic interactions. We investigated whether changes in R:FR affect the emission of herbivore-induced plant volatiles (HIPVs), and whether these changes influence the attraction of the zoophytophagous predator Macrolophus pygmaeus. We also studied how the expression of the SAS and subsequent inhibition of plant defences affects the reproduction of M. pygmaeus in both the presence and absence of the greenhouse whitefly (WF) (Trialeurodes vaporariorum) as arthropod prey. The results show that changes in R:FR have little effect on HIPV emissions and predator attraction. However, a reduction in R:FR leads to increased reproduction of both the predator and the WFs. We discuss that shade avoidance responses can increase the population development of M. pygmaeus through a combination of reduced plant defences and increased herbivore densities.

Influence of phylogenetic diversity of plant communities on tri-trophic interactions

Phylogenetic diversity of plant communities can influence the interaction between plants, herbivores, and their natural enemies. Plant communities with phylogenetically distant species tend to present a wide variety of functional traits and ecological niches, which in turn can influence competitive interactions among plants as well as food and habitat quality for herbivores and their natural enemies. To assess some different mechanisms by which phylogenetic diversity of plant communities can influence herbivores and their natural enemies, we established 12 experimental plots of tropical trees with two treatments: high and low phylogenetic diversity. We measured plant growth and anti-herbivore defenses, herbivore foliar damage, and predator activity in seven species that were present in both treatments. We found significant differences in the expression of plant traits as a function of species identity and their life history, but also depending on the phylogenetic context in which they grew. Pioneer species had higher growth and produced more phenolics in plots with high phylogenetic diversity versus plants in plots with low phylogenetic diversity. Accordingly, herbivore damage in these species was greater in plots with low phylogenetic diversity. Finally, predator activity on caterpillar clay models placed on plants was greater within the low phylogenetic diversity treatment, but only for non-myrmecophytic species. These results suggest that plant phylogenetic diversity can influence the expression of growth and defensive traits and further modify the interaction between plants, herbivores, and their natural enemies. However, such effects depend on plant life history and the presence of mutualistic interaction with ants.

Tomato deploys defence and growth simultaneously to resist bacterial wilt disease

Plant disease limits crop production, and host genetic resistance is a major means of control. Plant pathogenic Ralstonia causes bacterial wilt disease and is best controlled with resistant varieties. Tomato wilt resistance is multigenic, yet the mechanisms of resistance remain largely unknown. We combined metaRNAseq analysis and functional experiments to identify core Ralstonia-responsive genes and the corresponding biological mechanisms in wilt-resistant and wilt-susceptible tomatoes. While trade-offs between growth and defence are common in plants, wilt-resistant plants activated both defence responses and growth processes. Measurements of innate immunity and growth, including reactive oxygen species production and root system growth, respectively, validated that resistant plants executed defence-related processes at the same time they increased root growth. In contrast, in wilt-susceptible plants roots senesced and root surface area declined following Ralstonia inoculation. Wilt-resistant plants repressed genes predicted to negatively regulate water stress tolerance, while susceptible plants repressed genes predicted to promote water stress tolerance. Our results suggest that wilt-resistant plants can simultaneously promote growth and defence by investing in resources that act in both processes. Infected susceptible plants activate defences, but fail to grow and so succumb to Ralstonia, likely because they cannot tolerate the water stress induced by vascular wilt.

Transcriptomic and genetic approaches reveal that low-light-induced disease susceptibility is related to cellular oxidative stress in tomato

The impact of low light intensities on plant disease outbreaks represents a major challenge for global crop security, as it frequently results in significant yield losses. However, the underlying mechanisms of the effect of low light on plant defense are still poorly understood. Here, using an RNA-seq approach, we found that the susceptibility of tomato to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) under low light was associated with the oxidation-reduction process. Low light conditions exacerbated Pst DC3000-induced reactive oxygen species (ROS) accumulation and protein oxidation. Analysis of gene expression and enzyme activity of ascorbate peroxidase 2 (APX2) and other antioxidant enzymes revealed that these defense responses were significantly induced by Pst DC3000 inoculation under normal light, whereas these genes and their associated enzyme activities were not responsive to pathogen inoculation under low light. Additionally, the reduced ascorbate to dehydroascorbate (AsA/DHA) ratio was lower under low light compared with normal light conditions upon Pst DC3000 inoculation. Furthermore, the apx2 mutants generated by a CRISPR-Cas9 gene-editing approach were more susceptible to Pst DC3000 under low light conditions. Notably, this increased susceptibility could be significantly reduced by exogenous AsA treatment. Collectively, our findings suggest that low-light-induced disease susceptibility is associated with increased cellular oxidative stress in tomato plants. This study sheds light on the intricate relationship between light conditions, oxidative stress, and plant defense responses, and may pave the way for improved crop protection strategies in low light environments.

Multiple pals gene modules control a balance between immunity and development in Caenorhabditis elegans

The immune system continually battles against pathogen-induced pressures, which often leads to the evolutionary expansion of immune gene families in a species-specific manner. For example, the pals gene family expanded to 39 members in the Caenorhabditis elegans genome, in comparison to a single mammalian pals ortholog. Our previous studies have revealed that two members of this family, pals-22 and pals-25, act as antagonistic paralogs to control the Intracellular Pathogen Response (IPR). The IPR is a protective transcriptional response, which is activated upon infection by two molecularly distinct natural intracellular pathogens of C. elegans-the Orsay virus and the fungus Nematocida parisii from the microsporidia phylum. In this study, we identify a previously uncharacterized member of the pals family, pals-17, as a newly described negative regulator of the IPR. pals-17 mutants show constitutive upregulation of IPR gene expression, increased immunity against intracellular pathogens, as well as impaired development and reproduction. We also find that two other previously uncharacterized pals genes, pals-20 and pals-16, are positive regulators of the IPR, acting downstream of pals-17. These positive regulators reverse the effects caused by the loss of pals-17 on IPR gene expression, immunity, and development. We show that the negative IPR regulator protein PALS-17 and the positive IPR regulator protein PALS-20 colocalize inside and at the apical side of intestinal epithelial cells, which are the sites of infection for IPR-inducing pathogens. In summary, our study demonstrates that several pals genes from the expanded pals gene family act as ON/OFF switch modules to regulate a balance between organismal development and immunity against natural intracellular pathogens in C. elegans.

Attackers gain the upper hand over plants in the face of rapid global change

Interactions among organisms in natural ecosystems are the foundational underpinnings of nearly all ecological studies. It has never been more important to increase our awareness of how these interactions are altered by human activity, threatening biodiversity and disrupting ecosystem functioning. Much of the historic focus of species conservation has been the preservation of endangered and endemic species at risk from hunting, over-exploitation, and habitat destruction. However, there is increasing evidence that differences between plants and their attacking organisms in the speed and direction of physiological, demographic, and genetic (adaptation) responses to global change are having devastating consequences, resulting in large-scale losses of dominant or abundant plant species, particularly in forest ecosystems. From the elimination in the wild of the American chestnut to the extensive regional damage caused by insect outbreaks in temperate forest ecosystems, these losses of dominant species change the ecological landscape and functioning, and represent important threats to biodiversity at all scales. Introductions due to human activity, range shifts due to climate change, and their combination are the principal drivers behind these profound ecosystem changes. In this Review, we argue that there is an urgent need to increase our recognition and hone our predictive power for how these imbalances may occur. Moreover, we should seek to minimize the consequences of these imbalances in order to ensure the preservation of the structure, function and biodiversity of entire ecosystems, not just rare or highly endangered species.

Interactive effects of changes in UV radiation and climate on terrestrial ecosystems, biogeochemical cycles, and feedbacks to the climate system

Terrestrial organisms and ecosystems are being exposed to new and rapidly changing combinations of solar UV radiation and other environmental factors because of ongoing changes in stratospheric ozone and climate. In this Quadrennial Assessment, we examine the interactive effects of changes in stratospheric ozone, UV radiation and climate on terrestrial ecosystems and biogeochemical cycles in the context of the Montreal Protocol. We specifically assess effects on terrestrial organisms, agriculture and food supply, biodiversity, ecosystem services and feedbacks to the climate system. Emphasis is placed on the role of extreme climate events in altering the exposure to UV radiation of organisms and ecosystems and the potential effects on biodiversity. We also address the responses of plants to increased temporal variability in solar UV radiation, the interactive effects of UV radiation and other climate change factors (e.g. drought, temperature) on crops, and the role of UV radiation in driving the breakdown of organic matter from dead plant material (i.e. litter) and biocides (pesticides and herbicides). Our assessment indicates that UV radiation and climate interact in various ways to affect the structure and function of terrestrial ecosystems, and that by protecting the ozone layer, the Montreal Protocol continues to play a vital role in maintaining healthy, diverse ecosystems on land that sustain life on Earth. Furthermore, the Montreal Protocol and its Kigali Amendment are mitigating some of the negative environmental consequences of climate change by limiting the emissions of greenhouse gases and protecting the carbon sequestration potential of vegetation and the terrestrial carbon pool.

Mechanical wounding impacts the growth versus defense balance in tomato (Solanum lycopersicum)

Plants have evolved elaborate surveillance systems that allow them to perceive the attack by pests and pathogens and activate the appropriate defenses. Mechanical stimulation, such as mechanical wounding, represents one of the most reliable cues for the perception of potential herbivore aggressors. Here we demonstrate that mechanical wounding disturbs the growth versus defense balance in tomato, a physiological condition where growth reduction arises as a pleiotropic consequence of the activation of defense responses (or vice-versa). We observed that multiple lesions on tomato leaves impairs the formation of several growth-related traits, including shoot elongation, leaf expansion and time for flowering, while concomitantly activating the production of defense responses such as trichome formation and the upregulation of defense-related genes. We also provide genetic evidence that this wound-induced growth repression is possibly a consequence of tomato plants sensing the injuries via jasmonates (JAs), a class of plant hormones known to be master regulators of the plant growth versus defense balance. Besides providing a mechanistic explanation on how the growth and defense balance is shifted when plants are subjected to a specific type of mechanical stimulus, our results may offer a practical explanation for why tomato productivity is so negatively impacted by herbivore attack.

Tuning the Wavelength: Manipulation of Light Signaling to Control Plant Defense

The growth-defense trade-off in plants is a phenomenon whereby plants must balance the allocation of their resources between developmental growth and defense against attack by pests and pathogens. Consequently, there are a series of points where growth signaling can negatively regulate defenses and where defense signaling can inhibit growth. Light perception by various photoreceptors has a major role in the control of growth and thus many points where it can influence defense. Plant pathogens secrete effector proteins to manipulate defense signaling in their hosts. Evidence is emerging that some of these effectors target light signaling pathways. Several effectors from different kingdoms of life have converged on key chloroplast processes to take advantage of regulatory crosstalk. Moreover, plant pathogens also perceive and react to light in complex ways to regulate their own growth, development, and virulence. Recent work has shown that varying light wavelengths may provide a novel way of controlling or preventing disease outbreaks in plants.

Multiple pals gene modules control a balance between immunity and development in Caenorhabditis elegans

The immune system continually battles against pathogen-induced pressures, which often leads to the evolutionary expansion of immune gene families in a species-specific manner. For example, the pals gene family expanded to 39 members in the Caenorhabditis elegans genome, in comparison to a single mammalian pals ortholog. Our previous studies have revealed that two members of this family, pals-22 and pals-25 , act as antagonistic paralogs to control the Intracellular Pathogen Response (IPR). The IPR is a protective transcriptional response, which is activated upon infection by two molecularly distinct natural intracellular pathogens of C. elegans - the Orsay virus and the fungus Nematocida parisii from the microsporidia phylum. In this study, we identify a previously uncharacterized member of the pals family, pals-17 , as a newly described negative regulator of the IPR. pals-17 mutants show constitutive upregulation of IPR gene expression, increased immunity against intracellular pathogens, as well as impaired development and reproduction. We also find that two other previously uncharacterized pals genes, pals-20 and pals-16 , are positive regulators of the IPR, acting downstream of pals-17 . These positive regulators reverse the effects caused by the loss of pals-17 on IPR gene expression, immunity and development. We show that the negative IPR regulator protein PALS-17 and the positive IPR regulator protein PALS-20 colocalize inside intestinal epithelial cells, which are the sites of infection for IPR-inducing pathogens. In summary, our study demonstrates that several pals genes from the expanded pals gene family act as ON/OFF switch modules to regulate a balance between organismal development and immunity against natural intracellular pathogens in C. elegans .

AUTHOR SUMMARY

Immune responses to pathogens induce extensive rewiring of host physiology. In the short term, these changes are generally beneficial as they can promote resistance against infection. However, prolonged activation of immune responses can have serious negative consequences on host health, including impaired organismal development and fitness. Therefore, the balance between activating the immune system and promoting development must be precisely regulated. In this study, we used genetics to identify a gene in the roundworm Caenorhabditis elegans called pals-17 that acts as a repressor of the Intracellular Pathogen Response (IPR), a defense response against viral and microsporidian infections. We also found that pals-17 is required for the normal development of these animals. Furthermore, we identified two other pals genes, pals-20 and pals-16 , as suppressors of pals-17 mutant phenotypes. Finally, we found that PALS-17 and PALS-20 proteins colocalize inside intestinal cells, where viruses and microsporidia invade and replicate in the host. Taken together, our study demonstrates a balance between organismal development and immunity that is regulated by several genetic ON/OFF switch 'modules' in C. elegans .

MYC transcription factors coordinate tryptophan-dependent defence responses and compromise seed yield in Arabidopsis

Robust plant immunity negatively affects other fitness traits, including growth and seed production. Jasmonate (JA) confers broad-spectrum protection against plant consumers by stimulating the degradation of JASMONATE ZIM-DOMAIN (JAZ) proteins, which in turn relieves repression on transcription factors (TFs) coincident with reduced growth and fecundity. The molecular mechanisms underlying JA-mediated decreases in fitness remain largely unknown. To assess the contribution of MYC TFs to growth and reproductive fitness at high levels of defence, we mutated three MYC genes in a JAZ-deficient mutant (jazD) of Arabidopsis thaliana that exhibits strong defence and low seed yield. Genetic epistasis analysis showed that de-repression of MYC TFs in jazD not only conferred strong resistance to insect herbivory but also reduced shoot and root growth, fruit size and seed yield. We also provided evidence that the JAZ-MYC module coordinates the supply of tryptophan with the production of indole glucosinolates and the proliferation of endoplasmic reticulum bodies that metabolise glucosinolates through the action of β-glucosidases. Our results establish MYCs as major regulators of growth- and reproductive-defence trade-offs and further indicate that these factors coordinate tryptophan availability with the production of amino acid-derived defence compounds.

Natural variation in the transcription factor REPLUMLESS contributes to both disease resistance and plant growth in Arabidopsis

When attacked by pathogens, plants need to reallocate energy from growth to defense to fend off the invaders, frequently incurring growth penalties. This phenomenon is known as the growth-defense tradeoff and is orchestrated by a hardwired transcriptional network. Altering key factors involved in this network has the potential to increase disease resistance without growth or yield loss, but the mechanisms underlying such changes require further investigation. By conducting a genome-wide association study (GWAS) of leaves infected by the hemi-biotrophic bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000, we discovered that the Arabidopsis transcription factor REPLUMLESS (RPL) is necessary for bacterial resistance. More importantly, RPL functions in promoting both disease resistance and growth. Transcriptome analysis revealed a cluster of genes in the GRETCHEN HAGEN 3 (GH3) family that were significantly upregulated in rpl mutants, leading to the accumulation of indole-3-acetic acid-aspartic acid (IAA-Asp). Consistent with this observation, transcripts of virulence effector genes were activated by IAA-Asp accumulated in the rpl mutants. We found that RPL protein could directly bind to GH3 promoters and repress their expression. RPL also repressed flavonol synthesis by directly repressing CHI expression and thus activated the auxin transport pathway, which promotes plant growth. Therefore, RPL plays an important role in plant immunity and functions in the auxin pathway to optimize Arabidopsis growth and defense.

Predictability of parental ultraviolet-B environment shapes the growth strategies of clonal Glechoma longituba

Although there is an increasing debate about ecological consequences of environmental predictability for plant phenotype and fitness, the effect of predictability of parental environments on the offspring is still indefinite. To clarify the role of environmental predictability in maternal effects and the growth strategy of clonal offspring, a greenhouse experiment was conducted with Glechoma longituba. The parental ramets were arranged in three ultraviolet-B (UV-B) conditions, representing two predictable environments (regular and enhanced UV-B) and an unpredictable environment (random UV-B), respectively. The offspring environments were the same as their parent or not (without UV-B). At the end of experiment, the growth parameters of offspring were analyzed. The results showed that maternal effects and offspring growth were regulated by environmental predictability. Offspring of unpredictable environmental parents invested more resources in improving defense components rather than in rapid growth. Although offspring of predictable parents combined two processes of defense and growth, there were still some differences in the strategies between the two offspring, and the offspring of regular parent increased the biomass allocation to roots (0.069 g of control vs. 0.092 g of regular), but that of enhanced parent changed the resource allocation of nitrogen in roots and phosphorus in blade. Moreover, when UV-B environments of parent and offspring were matched, it seemed that maternal effects were not adaptive, while the growth inhibition in the predictable environment was weaker than that in unpredictable environment. In the predictable environment, the recovered R/S and the increased defense substances (flavonoid and anthocyanin) contributed to improving offspring fitness. In addition, when UV-B environments of parent and offspring were mismatched, offspring growth was restored or improved to some extent. The offspring performance in mismatched environments was controlled by both transgenerational effect and within-generational plasticity. In summary, the maternal effects affected growth strategies of offspring, and the differences of strategies depended on the predictability of parental UV-B environments, the clone improved chemical defense to cope with unpredictable environments, while the growth and defense could be balanced in predictable environments. The anticipatory maternal effects were likely to improve the UV-B resistance.

Into a dilemma of plants: the antagonism between chemical defenses and growth

Chemical defenses are imperative for plant survival, but their production is often associated with growth restrictions. Here we review the most recent theories to explain this complex dilemma of plants. Plants are a nutritional source for a myriad of pests and pathogens that depend on green tissues to complete their life cycle. Rather than remaining passive victims, plants utilize an arsenal of chemical defenses to fend off biotic attack. While the deployment of such barriers is imperative for survival, the production of these chemical defenses is typically associated with negative impacts on plant growth. Here we discuss the most recent theories which explain this highly dynamic growth versus defense dilemma. Firstly, we discuss the hypothesis that the antagonism between the accumulation of chemical defenses and growth is rooted in the evolutionary history of plants and may be a consequence of terrestrialization. Then, we revise the different paradigms available to explain the growth versus chemical defense antagonism, including recent findings that update these into more comprehensive and plausible theories. Finally, we highlight state-of-the-art strategies that are now allowing the activation of growth and the concomitant production of chemical barriers in plants. Growth versus chemical defense antagonism imposes large ecological and economic costs, including increased crop susceptibility to pests and pathogens. In a world where these plant enemies are the main problem to increase food production, we believe that this review will summarize valuable information for future studies aiming to breed highly defensive plants without the typical accompanying penalties to growth.

Plant defense strategies against attack by multiple herbivores

Plants may effectively tailor defenses by recognizing their attackers and reprogramming their physiology. Although most plants are under attack by a large diversity of herbivores, surprisingly little is known about the physiological capabilities of plants to deal with attack by multiple herbivores. Studies on dual herbivore attack identified that defense against one attacker may cause energetic and physiological constraints to deal with a second attacker. How these constraints shape plant plasticity in defense to their full community of attackers is a major knowledge gap in plant science. Here, we provide a framework for plant defense to multiherbivore attack by defining the repertoire of plastic defense strategies that may allow plants to optimize their defenses against a multitude of stressors.

Shade suppresses wound-induced leaf repositioning through a mechanism involving PHYTOCHROME KINASE SUBSTRATE (PKS) genes

Shaded plants challenged with herbivores or pathogens prioritize growth over defense. However, most experiments have focused on the effect of shading light cues on defense responses. To investigate the potential interaction between shade-avoidance and wounding-induced Jasmonate (JA)-mediated signaling on leaf growth and movement, we used repetitive mechanical wounding of leaf blades to mimic herbivore attacks. Phenotyping experiments with combined treatments on Arabidopsis thaliana rosettes revealed that shade strongly inhibits the wound effect on leaf elevation. By contrast, petiole length is reduced by wounding both in the sun and in the shade. Thus, the relationship between the shade and wounding/JA pathways varies depending on the physiological response, implying that leaf growth and movement can be uncoupled. Using RNA-sequencing, we identified genes with expression patterns matching the hyponastic response (opposite regulation by both stimuli, interaction between treatments with shade dominating the wound signal). Among them were genes from the PKS (Phytochrome Kinase Substrate) family, which was previously studied for its role in phototropism and leaf positioning. Interestingly, we observed reduced shade suppression of the wounding effect in pks2pks4 double mutants while a PKS4 overexpressing line showed constitutively elevated leaves and was less sensitive to wounding. Our results indicate a trait-specific interrelationship between shade and wounding cues on Arabidopsis leaf growth and positioning. Moreover, we identify PKS genes as integrators of external cues in the control of leaf hyponasty further emphasizing the role of these genes in aerial organ positioning.

Plants face different types of stressful situations without the ability to relocate to favorable environments. For example, increasing plant density reduces access to sunlight as plants start to shade each other. Foliar shading represents a stress that many plants cope with by changing their morphology. This includes elongation of stem-like structures and repositioning of leaves to favor access to unfiltered sunlight. Plants also defend themselves against various pathogens including herbivores. Defense mechanisms include the production of deterrent chemical and morphological adaptations such as stunted growth and downwards leaf repositioning. Here we studied the morphological response of plants when simultaneously facing shade and herbivore stress. When facing both stresses petiole growth was intermediate between the shade-enhanced and wound-repressed response. In contrast, the shade cue overrides the wounding cue leading to a similar upwards leaf repositioning in the combined treatments or in the response to shade alone. Using gene expression analyses and genetics we identified two members of the Phytochrome Kinase Substrate family as playing a signal integration role when plants simultaneously faced both stresses. This contributes to our understanding of the mechanisms underlying plant morphological adaptations when facing multiple stresses.

Jasmonate Signaling Pathway Modulates Plant Defense, Growth, and Their Trade-Offs

Lipid-derived jasmonates (JAs) play a crucial role in a variety of plant development and defense mechanisms. In recent years, significant progress has been made toward understanding the JA signaling pathway. In this review, we discuss JA biosynthesis, as well as its core signaling pathway, termination mechanisms, and the evolutionary origin of JA signaling. JA regulates not only plant regeneration, reproductive growth, and vegetative growth but also the responses of plants to stresses, including pathogen as well as virus infection, herbivore attack, and abiotic stresses. We also focus on the JA signaling pathway, considering its crosstalk with the gibberellin (GA), auxin, and phytochrome signaling pathways for mediation of the trade-offs between growth and defense. In summary, JA signals regulate multiple outputs of plant defense and growth and act to balance growth and defense in order to adapt to complex environments.

Coordinated resource allocation to plant growth-defense tradeoffs

Plant resource allocation patterns often reveal tradeoffs that favor growth (G) over defense (D), or vice versa. Ecologists most often explain G-D tradeoffs through principles of economic optimality, in which negative trait correlations are attributed to the reconciliation of fitness costs. Recently, researchers in molecular biology have developed 'big data' resources including multi-omic (e.g. transcriptomic, proteomic and metabolomic) studies that describe the cellular processes controlling gene expression in model species. In this synthesis, we bridge ecological theory with discoveries in multi-omics biology to better understand how selection has shaped the mechanisms of G-D tradeoffs. Multi-omic studies reveal strategically coordinated patterns in resource allocation that are enabled by phytohormone crosstalk and transcriptional signal cascades. Coordinated resource allocation justifies the framework of optimality theory, while providing mechanistic insight into the feedbacks and control hubs that calibrate G-D tradeoff commitments. We use the existing literature to describe the coordinated resource allocation hypothesis (CoRAH) that accounts for balanced cellular controls during the expression of G-D tradeoffs, while sustaining stored resource pools to buffer the impacts of future stresses. The integrative mechanisms of the CoRAH unify the supply- and demand-side perspectives of previous G-D tradeoff theories.

Phytochrome B regulates jasmonic acid-mediated defense response against Botrytis cinerea in Arabidopsis

The phytochrome B mediated light signaling integrates with various phytohormone signalings to control plant immune response. However, it is still unclear whether phyB-mediated light signaling has an effect on the biosynthesis of jasmonate during plant defense response against Botrytis cinerea. In this study, we demonstrated that phyB-mediated light signaling has a role in this process. Initially, we confirmed that phyb plants were obviously less resistant to B. cinerea while phyB overexpressing plants showed significantly enhanced resistance. We also found that the expression of numerous JA biosynthesis genes was promoted upon treatment with red or white light when compared to that of darkness, and that this promotion is dependent on phyB. Consistent with the gene expression results, phyb plants accumulated reduced pool of JA-Ile, indicating that phyB-mediated light signaling indeed increased JA biosynthesis. Further genetic analysis showed that light-mediated JAZ9 degradation and phyB-enhanced resistance were dependent on the receptor COI1, and that pif1/3/4/5 (pifq) can largely rescue the severe symptom of phyb. Taken together, our study demonstrates that phyB may participate in plant defense against B. cinerea through the modulation of the biosynthesis of JA.

Comparative transcriptomic and proteomic profiling reveals molecular models of light signal regulation of shade tolerance in bowl lotus (Nelumbo nucifera)

Bowl lotus is categorized as a heliophyte, and shaded environments can severely retard its development and blossoming. We conducted a comparative omics study of light response difference between two cultivars, 'HongYunDieYing' (shade tolerant) and 'YingYing' (shade intolerant), to understand the mechanisms behind the shade tolerance response. The results indicated that 'HongYunDieYing' had a faster light signal response than that in 'YingYing'. Furthermore, 214 proteins in 'HongYunDieYing' and 171 proteins in 'YingYing' were differentially expressed at both the transcriptional and protein levels. These correlated members were mainly involved in photosynthesis, metabolism, secondary metabolites, ribosome, and protein biosynthesis. However, glycolysis/gluconeogenesis, carbon metabolism, fatty acid metabolism, glutathione metabolism, and hormone signaling, were unique to 'HongYunDieYing'. The molecular model of light signal regulation of shade tolerance was constructed: the upstream light signal transduction related gene (cryptochrome 1, phytohormone B, phytochrome-interacting factor 3/5, ELONGATED HYPOCOTYL 5, and SUPPRESSOR OF PHYA-1) played a decisive role in regulating shade tolerance traits. Some transcription factors (MYBs, bHLHs and WRKYs) and hormone signaling (auxin, gibberellin and ethylene) were involved in mediating light signaling to regulate downstream biological events. These regulators and biological processes synergistically regulated the shade tolerance of lotus. SIGNIFICANCE: Lotus requires sufficient sunlight for growth and development, and shaded environments will severely retard lotus growth and blossoming. At present, there are few reports on the systematic identification and characterization of light signal response-related regulators in lotus. This study focuses on the comparative analysis two bowl lotus cultivars with the different shade tolerance traits at transcriptome and proteome levels to uncover the novel insight of the light signal-related biological network and potential candidates involved in the mechanism. The results provide a theoretical basis for the bowl lotus breeding and the expansion of its applications.

Mechanisms of far-red light-mediated dampening of defense against Botrytis cinerea in tomato leaves

Plants detect neighboring competitors through a decrease in the ratio between red and far-red light (R:FR). This decreased R:FR is perceived by phytochrome photoreceptors and triggers shade avoidance responses such as shoot elongation and upward leaf movement (hyponasty). In addition to promoting elongation growth, low R:FR perception enhances plant susceptibility to pathogens: the growth-defense tradeoff. Although increased susceptibility in low R:FR has been studied for over a decade, the associated timing of molecular events is still unknown. Here, we studied the chronology of FR-induced susceptibility events in tomato (Solanum lycopersicum) plants pre-exposed to either white light (WL) or WL supplemented with FR light (WL+FR) prior to inoculation with the necrotrophic fungus Botrytis cinerea (B.c.). We monitored the leaf transcriptional changes over a 30-h time course upon infection and followed up with functional studies to identify mechanisms. We found that FR-induced susceptibility in tomato is linked to a general dampening of B.c.-responsive gene expression, and a delay in both pathogen recognition and jasmonic acid-mediated defense gene expression. In addition, we found that the supplemental FR-induced ethylene emissions affected plant immune responses under the WL+FR condition. This study improves our understanding of the growth-immunity tradeoff, while simultaneously providing leads to improve tomato resistance against pathogens in dense cropping systems.

Plant Communication

Communication occurs when a sender emits a cue perceived by a receiver that changes the receiver's behavior. Plants perceive information regarding light, water, other nutrients, touch, herbivores, pathogens, mycorrhizae, and nitrogen-fixing bacteria. Plants also emit cues perceived by other plants, beneficial microbes, herbivores, enemies of herbivores, pollinators, and seed dispersers. Individuals responding to light cues experienced increased fitness. Evidence for benefits of responding to cues involving herbivores and pathogens is more limited. The benefits of emitting cues are also less clear, particularly for plant–plant communication. Reliance on multiple or dosage-dependent cues can reduce inappropriate responses, and plants often remember past cues. Plants have multiple needs and prioritize conflicting cues such that the risk of abiotic stress is treated as greater than that of shading, which is in turn treated as greater than that of consumption. Plants can distinguish self from nonself and kin from strangers. They can identify the species of competitor or consumer and respond appropriately. Cues involving mutualists often contain highly specific information.

Seed-borne fungal endophytes constrain reproductive success of host plants under ozone pollution

Tropospheric ozone is among the global change factors that pose a threat to plants and microorganisms. Symbiotic microorganisms can assist plants to cope with stress, but their role in the tolerance of plants to ozone is poorly understood. Here, we subjected endophyte-symbiotic and non-symbiotic plants of Lolium multiflorum, an annual species widely distributed in temperate grasslands, to high and low (i.e., charcoal-filtered air) ozone levels at vegetative and reproductive phases. Exposure to high ozone reduced leaf photochemical efficiency and greenness in both symbiotic and non-symbiotic plants. However, ozone-induced oxidative damage at biochemical level (i.e., lipid peroxidation) was mostly detected in symbiotic plants. Ozone exposure at the vegetative phase did not affect the reproductive investment in seeds, indicating full recovery from stress. Ozone exposure at the reproductive phase reduced biomass and seed production only in symbiotic plants indicating a symbiont-associated cost. At low ozone, endophyte-symbiotic plants showed a steeper slope in the relationship between seed number and seed weight (i.e., a number-weight trade-off) compared to non-symbiotic plants. However, when plants were treated at the reproductive phase, ozone increased the imbalance between seed number and seed weight in both endophyte-symbiotic and non-symbiotic plants. Plants with endophytes at the reproductive stage produced fewer seeds, which were not compensated by increased seed weight. Thus, fungal mycelium growing within ovaries or ozone-induced antioxidant systems may result in costs that finally depress the fitness of plants. Despite ozone pollution could destabilize plant-endophyte mutualisms and render them dysfunctional, other endophyte-mediated benefits (e.g., resistance to herbivory, tolerance to drought) could over-compensate these losses and explain the high incidence of the symbiosis in nature.

Regulation of Flowering Time: When and Where?

In seasonal flowering, plants need to monitor environmental variables. A combination of photoreceptors and the circadian clock initiate signals that regulate a network of genes in the leaf vascular system which communicates through mobile FLOWERING LOCUS T (FT) proteins, with the shoot apical meristem (SAM). At the SAM, a second network of genes is turned on specifically in certain cell domains, established by a second mobile protein, TERMINAL FLOWER 1 (TFL1), to ensure that flowering signals are translated into floral meristems at the flanks of the SAM but without compromising the nature of the SAM itself. Here, we provide an update on recent findings about the integration of light signals upstream of FT and tissue-specific events that occur in the SAM to balance flower production with SAM endurance.

New Insights on the Regulation of Glucosinolate Biosynthesis via COP1 and DELLA Proteins in Arabidopsis Thaliana

The biosynthesis of defensive secondary metabolites, such as glucosinolates (GSLs), is a costly process, which requires nutrients, ATP, and reduction equivalents, and, therefore, needs well-orchestrated machinery while coordinating defense and growth. We discovered that the key repressor of light signaling, the CONSTITUTIVE PHOTOMORPHOGENIC 1/SUPPRESSOR OF PHYTOCHROME A-105 (COP1/SPA) complex, is a crucial component of GSL biosynthesis regulation. Various mutants in this COP1/SPA complex exhibited a strongly reduced level of GSL and a low expression of jasmonate (JA)-dependent genes. Furthermore, cop1, which is known to accumulate DELLA proteins in the dark, shows reduced gibberellin (GA) and JA signaling, thereby phenocopying other DELLA-accumulating mutants. This phenotype can be complemented by a dominant gain-of-function allele of MYC3 and by crossing with a mutant having low DELLA protein levels. Hence, SPA1 interacts with DELLA proteins in a yeast two-hybrid screen, whereas high levels of DELLA inhibit MYC function and suppress JA signaling. DELLA accumulation leads to reduced synthesis of GSL and inhibited growth. Thus, the COP1/SPA-mediated degradation of DELLA not only affects growth but also regulates the biosynthesis of GSLs.

Fungal endophytes can eliminate the plant growth-defence trade-off

A trade-off between growth and defence functions is commonly observed in plants. We propose that the association of plants with Epichloë fungal endophytes may eliminate this trade-off. This would be a consequence of the double role of these endophytes in host plants: the stimulation of plant growth hormones (e.g. gibberellins) and the fungal production of antiherbivore alkaloids. We put forward a model that integrates this dual effect of endophytes on plant growth and defence and test its predictions by means of meta-analysis of published literature. Our results support the notion that the enhanced plant resistance promoted by endophytes does not compromise plant growth. The limits and ecological benefits of this endophyte-mediated lack of plant growth-defence trade-off are discussed.

Distinctive in-planta acclimation responses to basal growth and acute heat stress were induced in Arabidopsis by cattle manure biochar

In-planta mechanisms of biochar (BC)-mediated improved growth were evaluated by examining oxidative stress, metabolic, and hormonal changes of Arabidopsis wild-type plants under basal or acute heat stress (-HS/ + HS) conditions with or without BC (+ BC/-BC). The oxidative stress was evaluated by using Arabidopsis expressing redox-sensitive green fluorescent protein in the plastids (pla-roGFP2). Fresh biomass and inflorescence height were greater in + BC(‒HS) plants than in the -BC(‒HS) plants, despite similar leaf nutrient levels, photosystem II (PSII) maximal efficiencies and similar oxidative poise. Endogenous levels of jasmonic and abscisic acids were higher in the + BC(‒HS) treatment, suggesting their role in growth improvement. HS in ‒BC plants caused reductions in inflorescence height and PSII maximum quantum yield, as well as significant oxidative stress symptoms manifested by increased lipid peroxidation, greater chloroplast redox poise (oxidized form of roGFP), increased expression of DNAJ heat shock proteins and Zn-finger genes, and reduced expression of glutathione-S-transferase gene in addition to higher abscisic acid and salicylic acid levels. Oxidative stress symptoms were significantly reduced by BC. Results suggest that growth improvements by BC occurring under basal and HS conditions are induced by acclimation mechanisms to 'microstresses' associated with basal growth and to oxidative stress of HS, respectively.

LEDs Make It Resilient: Effects on Plant Growth and Defense

Light spectral composition influences plant growth and metabolism, and has important consequences for interactions with plant-feeding arthropods and their natural enemies. In greenhouse horticulture, light spectral composition can be precisely manipulated by light-emitting diodes (LEDs), and LEDs are already used to optimize crop production and quality. However, because light quality also modulates plant secondary metabolism and defense, it is important to understand the underlying mechanisms in the context of the growth-defense trade-off. We review the effects of the spectral composition of supplemental light currently used, or potentially used, in greenhouse horticulture on the mechanisms underlying plant growth and defense. This information is important for exploring opportunities to optimize crop performance and pest management, and thus for developing resilient crop-production systems.

Shade Avoidance: Expanding the Color and Hormone Palette

Major strides have been made over the past decade in elucidating the mechanisms that mediate shade-avoidance responses. The canonical PHYTOCHROME INTERACTING FACTOR (PIF)-auxin pathway that begins with inactivation of phytochrome B (phyB) by a low red:far-red (R:FR) ratio, and that leads to increased elongation, has been thoroughly characterized in arabidopsis (Arabidopsisthaliana) seedlings. Nevertheless, studies in other life stages and plant species have demonstrated the role of other wavelengths, photoreceptors, and hormones in the orchestration of shade-avoidance responses. We highlight recent developments that illustrate how canopy light cues regulate signaling through auxin, gibberellins (GAs), jasmonic acid (JA), salicylic acid (SA), abscisic acid (ABA), and strigolactones (SLs) to modulate key aspects of plant growth, metabolism, and defense.

Herbivore-induced defenses are not under phylogenetic constraints in the genus Quercus (oak): Phylogenetic patterns of growth, defense, and storage

The evolution of plant defenses is often constrained by phylogeny. Many of the differences between competing plant defense theories hinge upon the differences in the location of meristem damage (apical versus auxiliary) and the amount of tissue removed. We analyzed the growth and defense responses of 12 Quercus (oak) species from a well-resolved molecular phylogeny using phylogenetically independent contrasts. Access to light is paramount for forest-dwelling tree species, such as many members of the genus Quercus. We therefore predicted a greater investment in defense when apical meristem tissue was removed. We also predicted a greater investment in defense when large amounts of tissue were removed and a greater investment in growth when less tissues were removed. We conducted five simulated herbivory treatments including a control with no damage and alterations of the location of meristem damage (apical versus auxiliary shoots) and intensity (25% versus 75% tissue removal). We measured growth, defense, and nutrient re-allocation traits in response to simulated herbivory. Phylomorphospace models were used to demonstrate the phylogenetic nature of trade-offs between characteristics of growth, chemical defenses, and nutrient re-allocation. We found that growth-defense trade-offs in control treatments were under phylogenetic constraints, but phylogenetic constraints and growth-defense trade-offs were not common in the simulated herbivory treatments. Growth-defense constraints exist within the Quercus genus, although there are adaptations to herbivory that vary among species.

Social networking in crop plants: Wired and wireless cross-plant communications

The plant-associated microbial community (microbiome) has an important role in plant-plant communications. Plants decipher their complex habitat situations by sensing the environmental stimuli and molecular patterns and associated with microbes, herbivores and dangers. Perception of these cues generates inter/intracellular signals that induce modifications of plant metabolism and physiology. Signals can also be transferred between plants via different mechanisms, which we classify as wired- and wireless communications. Wired communications involve direct signal transfers between plants mediated by mycorrhizal hyphae and parasitic plant stems. Wireless communications involve plant volatile emissions and root exudates elicited by microbes/insects, which enable inter-plant signalling without physical contact. These producer-plant signals induce microbiome adaptation in receiver plants via facilitative or competitive mechanisms. Receiver plants eavesdrop to anticipate responses to improve fitness against stresses. An emerging body of information in plant-plant communication can be leveraged to improve integrated crop management under field conditions.

Plant Defense Responses to Biotic Stress and Its Interplay With Fluctuating Dark/Light Conditions

Plants are subjected to a plethora of environmental cues that cause extreme losses to crop productivity. Due to fluctuating environmental conditions, plants encounter difficulties in attaining full genetic potential for growth and reproduction. One such environmental condition is the recurrent attack on plants by herbivores and microbial pathogens. To surmount such attacks, plants have developed a complex array of defense mechanisms. The defense mechanism can be either preformed, where toxic secondary metabolites are stored; or can be inducible, where defense is activated upon detection of an attack. Plants sense biotic stress conditions, activate the regulatory or transcriptional machinery, and eventually generate an appropriate response. Plant defense against pathogen attack is well understood, but the interplay and impact of different signals to generate defense responses against biotic stress still remain elusive. The impact of light and dark signals on biotic stress response is one such area to comprehend. Light and dark alterations not only regulate defense mechanisms impacting plant development and biochemistry but also bestow resistance against invading pathogens. The interaction between plant defense and dark/light environment activates a signaling cascade. This signaling cascade acts as a connecting link between perception of biotic stress, dark/light environment, and generation of an appropriate physiological or biochemical response. The present review highlights molecular responses arising from dark/light fluctuations vis-à-vis elicitation of defense mechanisms in plants.

Control of Plant Growth and Defense by Photoreceptors: From Mechanisms to Opportunities in Agriculture

Plants detect and respond to the proximity of competitors using light signals perceived by photoreceptor proteins. A low ratio of red to far-red radiation (R:FR ratio) is a key signal of competition that is sensed by the photoreceptor phytochrome B (phyB). Low R:FR ratios increase the synthesis of growth-related hormones, including auxin and gibberellins, promoting stem elongation and other shade-avoidance responses. Other photoreceptors that help plants to optimize their developmental configuration and resource allocation patterns in the canopy include blue light photoreceptors, such as cryptochromes and phototropins, and UV receptors, such as UVR8. All photoreceptors act by directly or indirectly controlling the activity of two major regulatory nodes for growth and development: the COP1/SPA ubiquitin E3 ligase complex and the PIF transcription factors. phyB is also an important modulator of hormonal pathways that regulate plant defense against herbivores and pathogens, including the jasmonic acid signaling pathway. In this Perspective, we discuss recent advances on the studies of the mechanisms that link photoreceptors with growth and defense. Understanding these mechanisms is important to provide a functional platform for breeding programs aimed at improving plant productivity, stress tolerance, and crop health in species of agronomic interest, and to manipulate the light environments in protected agriculture.

Deciphering OPDA Signaling Components in the Momilactone-Producing Moss Calohypnum plumiforme

Jasmonic acid (JA) and its biologically active form jasmonoyl-L-isoleucine (JA-Ile) regulate defense responses to various environmental stresses and developmental processes in plants. JA and JA-Ile are synthesized from α-linolenic acids derived from membrane lipids via 12-oxo-phytodienoic acid (OPDA). In the presence of JA-Ile, the COI1 receptor physically interacts with JAZ repressors, leading to their degradation, resulting in the transcription of JA-responsive genes by MYC transcription factors. Although the biosynthesis of JA-Ile is conserved in vascular plants, it is not recognized by COI1 in bryophytes and is not biologically active. In the liverwort Marchantia polymorpha, dinor-OPDA (dn-OPDA), a homolog of OPDA with two fewer carbons, and its isomer dn-iso-OPDA accumulate after wounding and are recognized by COI1 to activate downstream signaling. The moss Calohypnum plumiforme produces the antimicrobial-specialized metabolites, momilactones. It has been reported that JA and JA-Ile are not detected in C. plumiforme and that OPDA, but not JA, can induce momilactone accumulation and the expression of these biosynthetic genes, suggesting that OPDA or its derivative is a biologically active molecule in C. plumiforme that induces chemical defense. In the present study, we investigated the biological functions of OPDA and its derivatives in C. plumiforme. Searching for the components potentially involving oxylipin signaling from transcriptomic and genomic data revealed that two COI1, three JAZ, and two MYC genes were present. Quantification analyses revealed that OPDA and its isomer iso-OPDA accumulated in larger amounts than dn-OPDA and dn-iso-OPDA after wounding. Moreover, exogenously applied OPDA, dn-OPDA, or dn-iso-OPDA induced the transcription of JAZ genes. These results imply that OPDA, dn-OPDA, and/or their isomers potentially act as biologically active molecules to induce the signaling downstream of COI1-JAZ. Furthermore, co-immunoprecipitation analysis showed the physical interaction between JAZs and MYCs, indicating the functional conservation of JAZs in C. plumiforme with other plants. These results suggest that COI1-JAZ-MYC mediated signaling is conserved and functional in C. plumiforme.

Identification of histone deacetylase genes in Dendrobium officinale and their expression profiles under phytohormone and abiotic stress treatments

The deacetylation of core histones controlled by the action of histone deacetylases (HDACs) plays an important role in the epigenetic regulation of plant gene transcription. However, no systematic analysis of HDAC genes in Dendrobium officinale, a medicinal orchid, has been performed. In the current study, a total of 14 histone deacetylases in D. officinale were identified and characterized using bioinformatics-based methods. These genes were classified into RPD3/HDA1, SIR2, and HD2 subfamilies. Most DoHDAC genes in the same subfamily shared similar structures, and their encoded proteins contained similar motifs, suggesting that the HDAC family members are highly conserved and might have similar functions. Different cis-acting elements in promoters were related to abiotic stresses and exogenous plant hormones. A transient expression assay in onion epidermal cells by Agrobacterium-mediated transformation indicated that all of the detected histone deacetylases such as DoHDA7, DoHDA9, DoHDA10, DoHDT3, DoHDT4, DoSRT1 and DoSRT2, were localized in the nucleus. A tissue-specific analysis based on RNA-seq suggested that DoHDAC genes play a role in growth and development in D. officinale. The expression profiles of selected DoHDAC genes under abiotic stresses and plant hormone treatments were analyzed by qRT-PCR. DoHDA3, DoHDA8, DoHDA10 and DoHDT4 were modulated by multiple abiotic stresses and phytohormones, indicating that these genes were involved in abiotic stress response and phytohormone signaling pathways. These results provide valuable information for molecular studies to further elucidate the function of DoHDAC genes.

Breaking Bad News: Dynamic Molecular Mechanisms of Wound Response in Plants

Recognition and repair of damaged tissue are an integral part of life. The failure of cells and tissues to appropriately respond to damage can lead to severe dysfunction and disease. Therefore, it is essential that we understand the molecular pathways of wound recognition and response. In this review, we aim to provide a broad overview of the molecular mechanisms underlying the fate of damaged cells and damage recognition in plants. Damaged cells release the so-called damage associated molecular patterns to warn the surrounding tissue. Local signaling through calcium (Ca2+), reactive oxygen species (ROS), and hormones, such as jasmonic acid, activates defense gene expression and local reinforcement of cell walls to seal off the wound and prevent evaporation and pathogen colonization. Depending on the severity of damage, Ca2+, ROS, and electrical signals can also spread throughout the plant to elicit a systemic defense response. Special emphasis is placed on the spatiotemporal dimension in order to obtain a mechanistic understanding of wound signaling in plants.

Environmental effects of stratospheric ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2019

This assessment, by the United Nations Environment Programme (UNEP) Environmental Effects Assessment Panel (EEAP), one of three Panels informing the Parties to the Montreal Protocol, provides an update, since our previous extensive assessment (Photochem. Photobiol. Sci., 2019, 18, 595-828), of recent findings of current and projected interactive environmental effects of ultraviolet (UV) radiation, stratospheric ozone, and climate change. These effects include those on human health, air quality, terrestrial and aquatic ecosystems, biogeochemical cycles, and materials used in construction and other services. The present update evaluates further evidence of the consequences of human activity on climate change that are altering the exposure of organisms and ecosystems to UV radiation. This in turn reveals the interactive effects of many climate change factors with UV radiation that have implications for the atmosphere, feedbacks, contaminant fate and transport, organismal responses, and many outdoor materials including plastics, wood, and fabrics. The universal ratification of the Montreal Protocol, signed by 197 countries, has led to the regulation and phase-out of chemicals that deplete the stratospheric ozone layer. Although this treaty has had unprecedented success in protecting the ozone layer, and hence all life on Earth from damaging UV radiation, it is also making a substantial contribution to reducing climate warming because many of the chemicals under this treaty are greenhouse gases.

JA-Ile-macrolactone 5b Induces Tea Plant (Camellia sinensis) Resistance to Both Herbivore Ectropis obliqua and Pathogen Colletotrichum camelliae

Jasmonates (JAs), the group of lipid-derived hormones, were found to control the defense responses in a myriad of plants. Meaningfully, the macrolactones of 12-hydroxy jasmonate isoleucine (12OH-JA-Ile) were reported to induce the defensive response of wild tobacco. However, little to nothing has been known about the elicitation effect of JA-Ile-macrolactones on woody plants to harmful organisms, let alone its underlying mechanisms. Here, we first optimized the synthetic routine using mild toxic reagent isobutyl chloroformate instead of ethyl chloroformate for conjugation, and we used acetonitrile (MeCN) instead of ethyl alcohol for the better dissolution of p-toluenesulfonic acid (p-TsOH) to gain JA-Ile-macrolactones. JA-Ile-macrolactone 5b-treated tea plants significantly inhibited the larvae weight gain of Ectropis obliqua larvae and the lesions caused by Colletotrichum camelliae. Furthermore, the expression level of CsOPR3 was significantly upregulated in 5b-treated leaves. Meanwhile, 5b reduced the accumulation of eriodictyol 7-O-glucuronide (EDG) in tea plants, which was confirmed to promote the growth rate of E. obliqua larvae by artificial diet assay. In conclusion, our study proved that the exogenous application of 5b could induce the tea plant resistance both to herbivore E. obliqua and pathogen C. camelliae, and EDG was identified as one of the secondary metabolites that could influence the growth rate of E. obliqua, but it did not directly influence the infection of C. camelliae in vitro. Further research should be carried out to clarify the mechanism through which 5b induces tea plant resistance to C. camelliae.

A light-dependent molecular link between competition cues and defence responses in plants

Growth responses to competition¹ and defence responses to the attack of consumer organisms² are two classic examples of adaptive phenotypic plasticity in plants. However, the mechanistic and functional links between these responses are not well understood. Jasmonates, a family of lipid-derived signals, are potent growth inhibitors and central regulators of plant immunity to herbivores and pathogens^3,4, with both roles being evolutionarily conserved from bryophytes⁵ to angiosperms⁶. When shade-intolerant plants perceive the proximity of competitors using the photoreceptor phytochrome B, they activate the shade-avoidance syndrome and downregulate jasmonate responses⁷. Despite the central implications of this light-mediated change in the growth/defence balance for plant adaptation and crop yield^8,9, the mechanisms by which photoreceptors relay light cues to the jasmonate signalling pathway remain poorly understood¹⁰. Here, we identify a sulfotransferase (ST2a) that is strongly upregulated by plant proximity perceived by phytochrome B via the phytochrome B-phytochrome interacting factor signalling module. By catalysing the formation of a sulfated jasmonate derivative, ST2a acts to reduce the pool of precursors of active forms of jasmonates and represents a direct molecular link between photoreceptors and hormone signalling in plants. The metabolic step defined by this enzyme provides a molecular mechanism for prioritizing shade avoidance over defence under intense plant competition.