RESUMO
The long noncoding RNA (lncRNA) AUXIN-REGULATED PROMOTER LOOP (APOLO) recognizes a subset of target loci across the Arabidopsis thaliana genome by forming RNA-DNA hybrids (R-loops) and modulating local three-dimensional chromatin conformation. Here, we show that APOLO regulates shade avoidance syndrome by dynamically modulating expression of key factors. In response to far-red (FR) light, expression of APOLO anti-correlates with that of its target BRANCHED1 (BRC1), a master regulator of shoot branching in Arabidopsis thaliana. APOLO deregulation results in BRC1 transcriptional repression and an increase in the number of branches. Accumulation of APOLO transcription fine-tunes the formation of a repressive chromatin loop encompassing the BRC1 promoter, which normally occurs only in leaves and in a late response to far-red light treatment in axillary buds. In addition, our data reveal that APOLO participates in leaf hyponasty, in agreement with its previously reported role in the control of auxin homeostasis through direct modulation of auxin synthesis gene YUCCA2, and auxin efflux genes PID and WAG2. We show that direct application of APOLO RNA to leaves results in a rapid increase in auxin signaling that is associated with changes in the plant response to far-red light. Collectively, our data support the view that lncRNAs coordinate shade avoidance syndrome in A. thaliana, and reveal their potential as exogenous bioactive molecules. Deploying exogenous RNAs that modulate plant-environment interactions may therefore become a new tool for sustainable agriculture.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , RNA Longo não Codificante , Arabidopsis/genética , Arabidopsis/metabolismo , RNA Longo não Codificante/genética , RNA Longo não Codificante/metabolismo , Proteínas de Arabidopsis/metabolismo , Ácidos Indolacéticos/metabolismo , Epigênese Genética , Cromatina/metabolismo , Regulação da Expressão Gênica de Plantas , Luz , Fatores de Transcrição/metabolismoRESUMO
Light is an environmental signal that modulates plant defenses against attackers. Recent research has focused on the effects of light on defense hormone signaling; however, the connections between light signaling pathways and the biosynthesis of specialized metabolites involved in plant defense have been relatively unexplored. Here, we show that Arabidopsis BBX29, a protein that belongs to the B-Box transcription factor (TF) family, integrates photomorphogenic signaling with defense responses by promoting flavonoid, sinapate and glucosinolate accumulation in Arabidopsis leaves. AtBBX29 transcript levels were up regulated by light, through photoreceptor signaling pathways. Genetic evidence indicated that AtBBX29 up-regulates MYB12 gene expression, a TF known to induce genes related to flavonoid biosynthesis in a light-dependent manner, and MYB34 and MYB51, which encode TFs involved in the regulation of glucosinolate biosynthesis. Thus, bbx29 knockout mutants displayed low expression levels of key genes of the flavonoid biosynthetic pathway, and the opposite was true in BBX29 overexpression lines. In agreement with the transcriptomic data, bbx29 mutant plants accumulated lower levels of kaempferol glucosides, sinapoyl malate, indol-3-ylmethyl glucosinolate (I3M), 4-methylsulfinylbutyl glucosinolate (4MSOB) and 3-methylthiopropyl glucosinolate (3MSP) in rosette leaves compared to the wild-type, and showed increased susceptibility to the necrotrophic fungus Botrytis cinerea and to the herbivore Spodoptera frugiperda. In contrast, BBX29 overexpressing plants displayed increased resistance to both attackers. In addition, we found that AtBBX29 plays an important role in mediating the effects of ultraviolet-B (UV-B) radiation on plant defense against B. cinerea. Taken together, these results suggest that AtBBX29 orchestrates the accumulation of specific light-induced metabolites and regulates Arabidopsis resistance against pathogens and herbivores.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/genética , Arabidopsis/metabolismo , Glucosinolatos , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Mutação , Flavonoides/farmacologia , Flavonoides/metabolismo , Doenças das Plantas/microbiologia , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Fatores de Transcrição/farmacologiaRESUMO
Plant litter decomposition is a key process for carbon (C) turnover in terrestrial ecosystems. Sunlight has been shown to cause and accelerate C release in semiarid ecosystems, yet the dose-response relationships for these effects have not been evaluated. We conducted a two-phase experiment where plant litter of three species was subjected to a broad range of cumulative solar radiation (CSR) exposures under field conditions. We then evaluated the relationships between CSR exposure and abiotic mass loss, litter quality and the subsequent biotic decomposition and microbial activity in litter. Dose-response relationships demonstrated that CSR exposure was modestly correlated with abiotic mass loss but highly significantly correlated with lignin degradation, saccharification, microbial activity and biotic decay of plant litter across all species. Moreover, a comparison of these dose-response relationships suggested that small reductions in litter lignin due to exposure to sunlight may have large consequences for biotic decay. These results provide strong support for a model that postulates a critical role for lignin photodegradation in the mechanism of photofacilitation and demonstrate that, under natural field conditions, biotic degradation of plant litter is linearly related with the dose of solar radiation received by the material before coming into contact with decomposer microorganisms.
Assuntos
Ecossistema , Exposição à Radiação , Lignina/metabolismo , Fotólise , Folhas de Planta/metabolismo , Plantas/metabolismoRESUMO
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.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , Fitocromo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Regulação da Expressão Gênica de Plantas , Hormônios , Luz , Fitocromo/metabolismo , Fitocromo B/metabolismoRESUMO
Photodegradation of aboveground senescent plant material (plant litter) due to exposure to solar radiation has been identified as a dominant control on carbon (C) loss in semi-arid ecosystems [1], upturning traditional models of C cycling based only on available moisture and litter quality. In addition to the photochemical mineralization of organic matter [1, 2], sunlight alters the chemistry of cell walls in plant litter [3, 4], making them more susceptible to subsequent biotic degradation [5-7]. Nevertheless, the interactive effects of sunlight exposure, climate seasonality, and biotic decomposition on C turnover remain unresolved in terrestrial ecosystems. We show here that exposure to sunlight accelerated litter decomposition in a Patagonian woodland with a marked dry summer season. Controls on initial decomposition varied seasonally from direct photochemical mineralization in the dry summer to biotic degradation in the wet winter. By manipulating sunlight received by plant litter using spectral filters that attenuated ultraviolet and short-wave visible light, we demonstrate that direct photodegradation and its legacy, associated with increased microbial access to labile carbohydrates, are responsible for the acceleration of aboveground C turnover in this Mediterranean-type climate. Across plant species and over a 2-year period, litter exposed to the full solar spectrum decomposed twice as fast as litter that received attenuated sunlight. Changes in vegetation cover or biodiversity due to projected increased drought and dry season length [8] will likely exacerbate C losses from aboveground litter due to sunlight exposure, negatively impacting the C balance in ecosystems that are particularly vulnerable to global change [9].
Assuntos
Bactérias/metabolismo , Carbono/deficiência , Ecossistema , Folhas de Planta/metabolismo , Plantas/metabolismo , Estações do Ano , Luz Solar , Florestas , Folhas de Planta/microbiologia , Folhas de Planta/efeitos da radiação , Plantas/microbiologia , Plantas/efeitos da radiaçãoRESUMO
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 pathogens3,4, 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 yield8,9, 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.
Assuntos
Arabidopsis/genética , Regulação da Expressão Gênica de Plantas , Luz , Imunidade Vegetal/genética , Transdução de Sinais , Arabidopsis/enzimologia , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/imunologia , Fitocromo B/metabolismo , Regulação para CimaRESUMO
The growth-defense trade-off in plant biology has gained enormous traction in the last two decades, highlighting the importance of understanding how plants deal with two of the greatest challenges for their survival and reproduction. It has been well established that in response to competition signals perceived by informational photoreceptors, shade-intolerant plants typically activate the shade-avoidance syndrome (SAS). In turn, in response to signals of biotic attack, plants activate a suite of defense responses, many of which are directed to minimize the loss of plant tissue to the attacking agent (broadly defined, the defense syndrome, DS). We argue that components of the SAS, including increased elongation, apical dominance, reduced leaf mass per area (LMA), and allocation to roots, are in direct conflict with configurational changes that plants require to maximize defense. We hypothesize that these configurational trade-offs provide a functional explanation for the suppression of components of the DS in response to competition cues. Based on this premise, we discuss recent advances in the understanding of the mechanisms by which informational photoreceptors, by interacting with jasmonic acid (JA) signaling, help the plant to make intelligent allocation and developmental decisions that optimize its configuration in complex biotic contexts.
Assuntos
Proteínas de Arabidopsis/metabolismo , Proteínas Cromossômicas não Histona/metabolismo , Ciclopentanos/metabolismo , Oxilipinas/metabolismo , Fotorreceptores de Plantas/metabolismo , Fitocromo/metabolismo , Viridiplantae , Desenvolvimento Vegetal/fisiologia , Doenças das Plantas/imunologia , Imunidade Vegetal/fisiologia , Folhas de Planta/metabolismo , Proteínas de Plantas/metabolismo , Raízes de Plantas/metabolismo , Transdução de Sinais , Viridiplantae/crescimento & desenvolvimento , Viridiplantae/imunologia , Viridiplantae/metabolismoRESUMO
Plants use photoreceptor proteins to detect the proximity of other plants and to activate adaptive responses. Of these photoreceptors, phytochrome B (phyB), which is sensitive to changes in the red (R) to far-red (FR) ratio of sunlight, is the one that has been studied in greatest detail. The molecular connections between the proximity signal (low R:FR) and a model physiological response (increased elongation growth) have now been mapped in considerable detail in Arabidopsis seedlings. We briefly review our current understanding of these connections and discuss recent progress in establishing the roles of other photoreceptors in regulating growth-related pathways in response to competition cues. We also consider processes other than elongation that are controlled by photoreceptors and contribute to plant fitness under variable light conditions, including photoresponses that optimize the utilization of soil resources. In examining recent advances in the field, we highlight emerging roles of phyB as a major modulator of hormones related to plant immunity, in particular salicylic acid and jasmonic acid (JA). Recent attempts to manipulate connections between light signals and defence in Arabidopsis suggest that it might be possible to improve crop health at high planting densities by targeting links between phyB and JA signalling.
Assuntos
Fenômenos Ecológicos e Ambientais , Luz , Fitocromo/metabolismo , Desenvolvimento Vegetal/efeitos da radiação , Transdução de SinaisRESUMO
Under conditions that involve a high risk of competition for light among neighbouring plants, shade-intolerant species often display increased shoot elongation and greater susceptibility to pathogens and herbivores. The functional links between morphological and defence responses to crowding are not well understood. In Arabidopsis, the protein JAZ10 is thought to play a key role connecting the inactivation of the photoreceptor phytochrome B (phyB), which takes place under competition for light, with the repression of jasmonate-mediated plant defences. Here, we show that a null mutation of the JAZ10 gene in Arabidopsis did not affect plant growth nor did it suppress the shade-avoidance responses elicited by phyB inactivation. However, the jaz10 mutation restored many of the defence traits that are missing in the phyB mutant, including the ability to express robust responses to jasmonate and to accumulate indolic glucosinolates. Furthermore, the jaz10phyB double mutant showed a significantly increased resistance to the pathogenic fungus Botrytis cinerea compared with the phyB parental line. Our results demonstrate that, by inactivating JAZ10, it is possible to partially uncouple shade avoidance from defence suppression in Arabidopsis. These findings may provide clues to improve plant resistance to pathogens in crops that are planted at high density.
Assuntos
Proteínas de Arabidopsis/metabolismo , Proteínas de Arabidopsis/fisiologia , Arabidopsis/crescimento & desenvolvimento , Proteínas Nucleares/metabolismo , Proteínas Nucleares/fisiologia , Fitocromo B/metabolismo , Imunidade Vegetal , Arabidopsis/genética , Arabidopsis/imunologia , Arabidopsis/fisiologia , Botrytis/fisiologia , Ciclopentanos/metabolismo , Resistência à Doença/efeitos da radiação , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Genes de Plantas , Glucosinolatos/metabolismo , Luz , Mutação/genética , Oxilipinas/metabolismo , Doenças das Plantas/imunologia , Doenças das Plantas/microbiologia , Imunidade Vegetal/efeitos da radiação , Regulação para Cima/genética , Regulação para Cima/efeitos da radiaçãoRESUMO
Under conditions of competition for light, which lead to the inactivation of the photoreceptor phytochrome B (phyB), the growth of shade-intolerant plants is promoted and the accumulation of direct anti-herbivore defenses is down-regulated. Little is known about the effects of phyB on emissions of volatile organic compounds (VOCs), which play a major role as informational cues in indirect defense. We investigated the effects of phyB on direct and indirect defenses in tomato (Solanum lycopersicum) using two complementary approaches to inactivate phyB: illumination with a low red to far-red ratio, simulating competition, and mutation of the two PHYB genes present in the tomato genome. Inactivation of phyB resulted in low levels of constitutive defenses and down-regulation of direct defenses induced by methyl jasmonate (MeJA). Interestingly, phyB inactivation also had large effects on the blends of VOCs induced by MeJA. Moreover, in two-choice bioassays using MeJA-induced plants, the predatory mirid bug Macrolophus pygmaeus preferred VOCs from plants in which phyB was inactivated over VOCs from control plants. These results suggest that, in addition to repressing direct defense, phyB inactivation has consequences for VOC-mediated tritrophic interactions in canopies, presumably attracting predators to less defended plants, where they are likely to find more abundant prey.
Assuntos
Herbivoria , Fitocromo B/metabolismo , Comportamento Predatório , Solanum lycopersicum/metabolismo , Solanum lycopersicum/parasitologia , Compostos Orgânicos Voláteis/metabolismo , Animais , Ciclopentanos/farmacologia , Análise Discriminante , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Análise dos Mínimos Quadrados , Lepidópteros/fisiologia , Solanum lycopersicum/genética , Solanum lycopersicum/imunologia , Oxilipinas/farmacologia , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/fisiologia , Tricomas/ultraestruturaAssuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Proteínas Cromossômicas não Histona/metabolismo , Fitocromo B/metabolismo , Desenvolvimento Vegetal , Folhas de Planta/metabolismo , Arabidopsis/efeitos da radiação , Fenóis/metabolismo , Desenvolvimento Vegetal/efeitos da radiação , Folhas de Planta/efeitos da radiação , Transdução de Sinais/efeitos da radiação , Raios UltravioletaRESUMO
Solar UV-B radiation (280-315 nm) has a significant influence on trophic relationships in natural and managed ecosystems, affecting plant-insect interactions. We explored the effects of ambient UV-B radiation on the levels of herbivory by stink bugs (Nezara viridula and Piezodorus guildinii) in field-grown soybean crops. The experiments included two levels of UV-B radiation (ambient and attenuated UV-B) and four soybean cultivars known to differ in their content of soluble leaf phenolics. Ambient UV-B radiation increased the accumulation of the isoflavonoids daidzin and genistin in the pods of all cultivars. Soybean crops grown under attenuated UV-B had higher numbers of unfilled pods and damaged seeds than crops grown under ambient UV-B radiation. Binary choice experiments with soybean branches demonstrated that stink bugs preferred branches of the attenuated UV-B treatment. We found a positive correlation between percentage of undamaged seeds and the contents of daidzin and genistin in pods. Our results suggest that constitutive and UV-B-induced isoflavonoids increase plant resistance to stink bugs under field conditions.
Assuntos
Genisteína/metabolismo , Glycine max/efeitos da radiação , Herbivoria , Heterópteros , Isoflavonas/metabolismo , Animais , Frutas/metabolismo , Glycine max/metabolismo , Raios UltravioletaRESUMO
Shade-intolerant plants respond to low red : far-red (R : FR) ratios, which signal the proximity of potential competitors, by down-regulating immune responses. Here we investigated the mechanisms underlying this immune suppression in Arabidopsis. We used genetic, transcriptomic and metabolomic approaches to examine the functional connections between R : FR ratio and Arabidopsis resistance to the fungus Botrytis cinerea. Low R : FR ratios reduced the concentration of indol-3-ylmethyl glucosinolate (I3M) (an indolic glucosinolate, iGS) and camalexin in plants inoculated with B. cinerea, and attenuated the I3M response triggered by jasmonate elicitation. These effects on metabolite abundance correlated with reduced expression of iGS and camalexin biosynthetic genes. Furthermore, the effect of low R : FR increasing Arabidopsis susceptibility to B. cinerea was not present in mutants deficient in the biosynthesis of camalexin (pad3) or metabolism of iGS (pen2). Finally, in a mutant deficient in the JASMONATE ZIM DOMAIN-10 (JAZ10) protein, which does not respond to low R : FR with increased susceptibility to B. cinerea, supplemental FR failed to down-regulate iGS production. These results indicate that suppression of Arabidopsis immunity against B. cinerea by low R : FR ratios is mediated by reduced levels of Trp-derived defenses, and provide further evidence for a functional role of JAZ10 in the link between phytochrome and jasmonate signaling.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/imunologia , Glucosinolatos/metabolismo , Indóis/metabolismo , Proteínas Nucleares/metabolismo , Fitocromo/metabolismo , Doenças das Plantas/imunologia , Tiazóis/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/genética , Vias Biossintéticas , Botrytis/fisiologia , Ciclopentanos/metabolismo , Suscetibilidade a Doenças , Regulação da Expressão Gênica de Plantas , Glucosinolatos/química , Ácidos Indolacéticos/metabolismo , Indóis/química , Mutação , Proteínas Nucleares/genética , Oxilipinas/metabolismo , Doenças das Plantas/microbiologia , Imunidade Vegetal , Folhas de Planta/genética , Folhas de Planta/imunologia , Folhas de Planta/metabolismo , Folhas de Planta/efeitos da radiação , Transdução de Sinais , Tiazóis/químicaRESUMO
How plants balance resource allocation between growth and defense under conditions of competitive stress is a key question in plant biology. Low red : far-red (R : FR) ratios, which signal a high risk of competition in plant canopies, repress jasmonate-induced defense responses. The mechanism of this repression is not well understood. We addressed this problem in Arabidopsis by investigating the role of DELLA and JASMONATE ZIM domain (JAZ) proteins. We showed that a quintuple della mutant and a phyB mutant were insensitive to jasmonate for several physiological readouts. Inactivation of the photoreceptor phyB by low R : FR ratios rapidly reduced DELLA protein abundance, and the inhibitory effect of FR on jasmonate signaling was missing in the gai-1 mutant, which encodes a stable version of the GAI DELLA protein. We also demonstrated that low R : FR ratios and the phyB mutation stabilized the protein JAZ10. Furthermore, we demonstrated that JAZ10 was required for the inhibitory effect of low R : FR on jasmonate responses, and that the jaz10 mutation restored jasmonate sensitivity to the phyB mutant. We conclude that, under conditions of competition for light, plants redirect resource allocation from defense to rapid elongation by promoting DELLA degradation and enhancing JAZ10 stability.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Regulação da Expressão Gênica de Plantas , Proteínas Nucleares/metabolismo , Fitocromo B/metabolismo , Reguladores de Crescimento de Plantas/metabolismo , Arabidopsis/genética , Arabidopsis/imunologia , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/genética , Ciclopentanos/metabolismo , Giberelinas/metabolismo , Luz , Mutação , Proteínas Nucleares/genética , Oxilipinas/metabolismo , Fitocromo B/genética , Estabilidade Proteica , Proteólise , Plântula , Transdução de SinaisRESUMO
Plant fitness is often defined by the combined effects of herbivory and competition, and plants must strike a delicate balance between their ability to capture limiting resources and defend against herbivore attack. Many plants use indirect defenses, such as volatile compounds and extra floral nectaries (EFN), to attract canopy arthropods that are natural enemies of herbivorous organisms. While recent evidence suggests that upon perception of low red to far-red (R:FR) ratios, which signal the proximity of competitors, plants down-regulate resource allocation to direct chemical defenses, it is unknown if a similar phytochrome-mediated response occurs for indirect defenses. We evaluated the interactive effects of R:FR ratio and simulated herbivory on nectar production by EFNs of passion fruit (Passiflora edulis f. flavicarpa). The activity of petiolar EFNs dramatically increased in response to simulated herbivory and hormonal treatment with methyl jasmonate (MeJA). Low R:FR ratios, which induced a classic "shade-avoidance" repertoire of increased stem elongation in P. edulis, strongly suppressed the EFN response triggered by simulated herbivory or MeJA application. Strikingly, the EFN response to wounding and light quality was localized to the branches that received the treatments. In vines like P. edulis, a local response would allow the plants to precisely adjust their light harvesting and defense phenotypes to the local conditions encountered by individual branches when foraging for resources in patchy canopies. Consistent with the emerging paradigm that phytochrome regulation of jasmonate signaling is a central modulator of adaptive phenotypic plasticity, our results demonstrate that light quality is a strong regulator of indirect defenses.
Assuntos
Herbivoria , Luz , Passiflora/efeitos da radiação , Néctar de Plantas/biossíntese , Acetatos/farmacologia , Animais , Formigas/fisiologia , Comportamento Animal , Ciclopentanos/farmacologia , Regulação para Baixo , Oxilipinas/farmacologia , Passiflora/efeitos dos fármacos , Passiflora/fisiologia , Desenvolvimento Vegetal/efeitos dos fármacos , Desenvolvimento Vegetal/efeitos da radiação , Néctar de Plantas/fisiologia , Transdução de SinaisRESUMO
Ultraviolet-B radiation (UV-B: 280-315 nm) has damaging effects on cellular components and macromolecules. In plants, natural levels of UV-B can reduce leaf area expansion and growth, which can lead to reduced productivity and yield. UV-B can also have important effects on herbivorous insects. Owing to the successful implementation of the Montreal Protocol, current models predict that clear-sky levels of UV-B radiation will decline during this century in response to ozone recovery. However, because of climate change and changes in land use practices, future trends in UV doses are difficult to predict. In the experiments reported here, we used an exclusion approach to study the effects of solar UV-B radiation on soybean crops, which are extensively grown in many areas of the world that may be affected by future variations in UV-B radiation. In a first experiment, performed under normal management practices (which included chemical pest control), we found that natural levels of UV-B radiation reduced soybean yield. In a second experiment, where no pesticides were applied, we found that solar UV-B significantly reduced insect herbivory and, surprisingly, caused a concomitant increase in crop yield. Our data support the idea that UV-B effects on agroecosystems are the result of complex interactions involving multiple trophic levels. A better understanding of the mechanisms that mediate the anti-herbivore effect of UV-B radiation may be used to design crop varieties with improved adaptation to the cropping systems that are likely to prevail in the coming decades in response to agricultural intensification.
Assuntos
Glycine max/efeitos da radiação , Insetos/fisiologia , Raios Ultravioleta , Animais , Antioxidantes/metabolismo , Ascorbato Peroxidases/metabolismo , Biomassa , Catalase/metabolismo , Clorofila/metabolismo , Produtos Agrícolas , Herbivoria , Folhas de Planta/química , Energia Solar , Glycine max/crescimento & desenvolvimento , Luz SolarAssuntos
Arabidopsis/imunologia , Imunidade Vegetal , Luz Solar , Animais , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Resistência à Doença , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Herbivoria , Insetos , Fotossíntese , Fitocromo B/genética , Fitocromo B/metabolismo , Doenças das Plantas/imunologia , Doenças das Plantas/microbiologia , Doenças das Plantas/parasitologia , Folhas de Planta/metabolismo , Folhas de Planta/efeitos da radiação , Pseudomonas syringae/patogenicidade , Receptores de Superfície Celular/genética , Receptores de Superfície Celular/metabolismoRESUMO
Light is emerging as a central regulator of plant immune responses against herbivores and pathogens. Solar UV-B radiation plays an important role as a positive modulator of plant defense. However, since UV-B photons can interact with a wide spectrum of molecular targets in plant tissues, the mechanisms that mediate their effects on plant defense have remained elusive. Here, we show that ecologically meaningful doses of UV-B radiation increase Arabidopsis resistance to the necrotrophic fungus Botrytis cinerea and that this effect is mediated by the photoreceptor UVR8. The UV-B effect on plant resistance was conserved in mutants impaired in jasmonate (JA) signaling (jar1-1 and P35S:JAZ10.4) or metabolism of tryptophan-derived defense compounds (pen2-1, pad3-1, pen2 pad3), suggesting that neither regulation of the JA pathway nor changes in levels of indolic glucosinolates (iGS) or camalexin are involved in this response. UV-B radiation, acting through UVR8, increased the levels of flavonoids and sinapates in leaf tissue. The UV-B effect on pathogen resistance was still detectable in tt4-1, a mutant deficient in chalcone synthase and therefore impaired in the synthesis of flavonoids, but was absent in fah1-7, a mutant deficient in ferulic acid 5-hydroxylase, which is essential for sinapate biosynthesis. Collectively, these results indicate that UVR8 plays an important role in mediating the effects of UV-B radiation on pathogen resistance by controlling the expression of the sinapate biosynthetic pathway.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/imunologia , Arabidopsis/microbiologia , Botrytis/fisiologia , Proteínas Cromossômicas não Histona/metabolismo , Ácidos Cumáricos/metabolismo , Raios Ultravioleta , Arabidopsis/genética , Arabidopsis/efeitos da radiação , Botrytis/efeitos dos fármacos , Botrytis/efeitos da radiação , Ácidos Cumáricos/química , Ciclopentanos/farmacologia , Resistência à Doença/efeitos dos fármacos , Resistência à Doença/imunologia , Resistência à Doença/efeitos da radiação , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Glucosinolatos/metabolismo , Indóis/metabolismo , Mutação/genética , Oxilipinas/farmacologia , Fenóis/metabolismo , Doenças das Plantas/imunologia , Doenças das Plantas/microbiologia , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genética , Transdução de Sinais/efeitos da radiação , Tiazóis/metabolismoRESUMO
Light is an important modulator of plant immune responses. Here, we show that inactivation of the photoreceptor phytochrome B (phyB) by a low red/far-red ratio (R:FR), which is a signal of competition in plant canopies, down-regulates the expression of defense markers induced by the necrotrophic fungus Botrytis cinerea, including the genes that encode the transcription factor ETHYLENE RESPONSE FACTOR1 (ERF1) and the plant defensin PLANT DEFENSIN1.2 (PDF1.2). This effect of low R:FR correlated with a reduced sensitivity to jasmonate (JA), thus resembling the antagonistic effects of salicylic acid (SA) on JA responses. Low R:FR failed to depress PDF1.2 mRNA levels in a transgenic line in which PDF1.2 transcription was up-regulated by constitutive expression of ERF1 in a coronatine insensitive1 (coi1) mutant background (35S::ERF1/coi1). These results suggest that the low R:FR effect, in contrast to the SA effect, requires a functional SCFCOI1-JASMONATE ZIM-DOMAIN (JAZ) JA receptor module. Furthermore, the effect of low R:FR depressing the JA response was conserved in mutants impaired in SA signaling (sid2-1 and npr1-1). Plant exposure to low R:FR ratios and the phyB mutation markedly increased plant susceptibility to B. cinerea; the effect of low R:FR was (1) independent of the activation of the shade-avoidance syndrome, (2) conserved in the sid2-1 and npr1-1 mutants, and (3) absent in two RNA interference lines disrupted for the expression of the JAZ10 gene. Collectively, our results suggest that low R:FR ratios depress Arabidopsis (Arabidopsis thaliana) immune responses against necrotrophic microorganisms via a SA-independent mechanism that requires the JAZ10 transcriptional repressor and that this effect may increase plant susceptibility to fungal infection in dense canopies.