RESUMO
B-Box-containing zinc finger transcription factors (BBX) are involved in light-mediated growth, affecting processes such as hypocotyl elongation in Arabidopsis thaliana. However, the molecular and hormonal framework that regulates plant growth through BBX proteins is incomplete. Here, we demonstrate that BBX21 inhibits the hypocotyl elongation through the brassinosteroid (BR) pathway. BBX21 reduces the sensitivity to 24-epiBL, a synthetic active BR, principally at very-low concentrations in simulated shade. The biosynthesis profile of BRs showed that two active BR -brassinolide (BL) and 28-homobrassinolide (28-homoBL)- and 8 of 11 intermediates can be repressed by BBX21 under white light (WL) or simulated shade. Furthermore, BBX21 represses the expression of CYTOCHROME P450 90B1 (DWF4/CYP90B1), BRASSINOSTEROID-6-OXIDASE 1 (BR6OX1, CYP85A1) and BR6OX2 (CYP85A2) genes involved in the BR biosynthesis in WL while specifically promoting DWF4 and PHYB ACTIVATION TAGGED SUPPRESSOR 1 (CYP2B1/BAS1) expression in WL supplemented with far-red (WL+FR), a treatment that simulates shade. In addition, BBX21 represses BR signalling genes such as PACLOBUTRAZOL RESISTANCE1 (PRE1), PRE3 and ARABIDOPSIS MYB-LIKE 2 (MYBL2), and auxin-related and expansin genes, such as INDOLE-3-ACETIC ACID INDUCIBLE 1 (IAA1), IAA4 and EXPANSIN 11 (EXP11) in short-term shade. By a genetic approach we found that BBX21 acts genetically upstream of BRASSINAZOLE-RESISTANT 1 (BZR1) for the promotion of DWF4 and BAS1 gene expression in shade. We propose that BBX21 integrates the BR homeostasis and shade-light signalling allowing the fine-tuning of hypocotyl elongation in Arabidopsis.
RESUMO
Plants detect competitors in shaded environments by perceiving a reduction in photosynthetically active radiation (PAR) and the reduction between the red and far-red light (R:FR) ratio and blue photons. These light signals are detected by phytochromes and cryptochromes, which trigger shade avoidance responses such as shoot and petiole elongation and lead to increased susceptibility to pathogen attack. We studied morphological, anatomical, and photosynthesis differences in potato plants (Solanum tuberosum var. Spunta) exposed to sunlight or simulated shade in a greenhouse. We found that simulated shade strongly induced stem and internode elongation with a higher production of free auxin in stems and a lower production of tubers. The mesophyll thickness of the upper leaves of plants grown in simulated shade was lower, but the epidermis was wider compared with the leaves of plants cultivated in sunlight. In addition, the photosynthesis rate was lower in the upper leaves exposed to nonsaturated irradiances and higher in the basal leaves at saturated irradiances compared with control plants. RNA-seq analysis showed that 146 and 155 genes were up- and downregulated by shade, respectively. By quantitative reverse transcription polymerase chain reaction, we confirmed that FLOWERING LOCUS T (FT), WRKY-like, and PAR1b were induced, while FLAVONOL 4-SULFOTRANSFERASE was repressed under shade. In shaded plants, leaves and tubers were more susceptible to the necrotrophic fungus Botrytis cinerea attack. Overall, our work demonstrates configurational changes between growth and defense decisions in potato plants cultivated in simulated shade.
Assuntos
Solanum tuberosum , Solanum tuberosum/genética , Transcriptoma , Luz , Luz Solar , Folhas de Planta/genéticaRESUMO
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
The B-box (BBX) proteins are zinc-finger transcription factors with a key role in growth and developmental regulatory networks mediated by light. AtBBX21 overexpressing (BBX21-OE) potato (Solanum tuberosum) plants, cultivated in optimal water conditions, have a higher photosynthesis rate and stomatal conductance without penalty in water use efficiency (WUE) and with a higher tuber yield. In this work, we cultivated potato plants in two water regimes: 100 and 35% field capacity of water restriction that imposed leaf water potentials between -0.3 and -1.2 MPa for vegetative and tuber growth during 14 or 28 days, respectively. We found that 42-day-old plants of BBX21-OE were more tolerant to water restriction with higher levels of chlorophylls and tuber yield than wild-type spunta (WT) plants. In addition, the BBX21-OE lines showed higher photosynthesis rates and WUE under water restriction during the morning. Mechanistically, we found that BBX21-OE lines were more tolerant to moderated drought by enhancing mesophyll conductance (gm ) and maximum capacity of electron transport (Jmax ), and by reducing abscisic acid (ABA) sensitivity in plant tissues. By RNA-seq analysis, we found 204 genes whose expression decreased by drought in WT plants and expressed independently of the water condition in BBX21-OE lines as SAP12, MYB73, EGYP1, TIP2-1 and DREB2A, and expressions were confirmed by quantitative polymerase chain reaction. These results suggest that BBX21 interplays with the ABA and growth signaling networks, improving the photosynthetic behavior in suboptimal water conditions with an increase in potato tuber yield.
Assuntos
Ácido Abscísico/metabolismo , Fotossíntese , Reguladores de Crescimento de Plantas/metabolismo , Solanum tuberosum/genética , Fatores de Transcrição/metabolismo , Água/metabolismo , Clorofila/metabolismo , Cloroplastos/metabolismo , Secas , Transporte de Elétrons , Folhas de Planta/genética , Folhas de Planta/fisiologia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Tubérculos/genética , Tubérculos/fisiologia , Transdução de Sinais , Solanum tuberosum/fisiologia , Fatores de Transcrição/genéticaRESUMO
Competition for light between neighboring plants has important consequences for plant fitness and crop productivity. Studies on the molecular mechanisms of plant responses to neighbor proximity have been largely based on the model species Arabidopsis thaliana grown under controlled light environments. These controlled conditions commonly use fluorescent tubes for the main light source for photosynthesis and filtered light form incandescent bulbs to adjust the ratio of red (R) to far-red (FR) radiation. However, both of these types of bulbs are being discontinued and replaced by more efficient sources based on light emitting diodes (LEDs). For that reason, there is a need to evaluate alternative light sources, which can phenocopy the physiological and molecular results obtained with traditional lighting systems. Here we evaluate a custom-made LED culture module that can be used to effectively evaluate shade-avoidance responses, yielding results that, in Arabidopsis, are comparable to those obtained using traditional lighting systems.
Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Perfilação da Expressão Gênica/métodos , Arabidopsis/genética , Arabidopsis/efeitos da radiação , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Luz/efeitos adversos , Fenótipo , Fotossíntese/efeitos da radiaçãoRESUMO
Plants are challenged by biotic and abiotic stress factors and the incidence of one can increase or decrease resistance to another. These relations can also occur transgenerationally. For instance, progeny plants whose mothers experienced herbivory can be more resistant to herbivores. Certain fungal endophytes that are vertically transmitted endow plants with alkaloids and resistance to herbivores. However, endophyte-symbiotic plants exposed to the oxidative agent ozone became susceptible to aphids. Here, we explored whether this effect persists transgenerationally. We exposed Lolium multiflorum plants with and without fungal endophyte Epichloë occultans to ozone (120 or 0 ppb), and then, challenged the progeny with aphids (Rhopalosiphum padi). The endophyte was the main factor determining the resistance to aphids, but its importance diminished in plants with ozone history. This negative ozone effect on the endophyte-mediated resistance was apparent on aphid individual weights. Phenolic compounds in seeds were increased by the symbiosis and diminished by the ozone. The endophyte effect on phenolics vanished in progeny plants while the negative ozone effect persisted. Independently of ozone, the symbiosis increased the plant biomass (≈24%). Although ozone can diminish the importance of endophyte symbiosis for plant resistance to herbivores, it would be compensated by host growth stimulation.
RESUMO
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
B-box (BBX) proteins are zinc-finger transcription factors containing one or two B-box motifs. BBX proteins act as key factors in the networks regulating growth and development. The relevance of BBX21 to light and abscisic acid signaling in seedling development is well established; however, its importance in adult plant development and agronomic species is poorly understood. Therefore, we studied the effect of heterologous expression of Arabidopsis (Arabidopsis thaliana) BBX21 in potato (Solanum tuberosum) var Spunta. Three independent AtBBX21-expressing lines and the wild-type control were cultivated under sunlight and at controlled temperatures in a greenhouse. By anatomical, physiological, biochemical, and gene expression analysis, we demonstrated that AtBBX21-expressing plants were more robust and produced more tubers than wild-type plants. Interestingly, AtBBX21-expressing plants had higher rates of photosynthesis, with a significant increase in photosynthetic gene expression, and higher stomatal conductance, with increased size of the stomatal opening, without any associated decline in water use efficiency. Furthermore, AtBBX21-expressing potato plants had reduced photoinhibition associated with higher production of anthocyanins and phenolic compounds, and higher expression of genes in the phenylpropanoid biosynthesis pathway. To gain insights into the mechanism of BBX21, we evaluated the molecular, morphological, metabolic, and photosynthetic behavior in adult BBX21-overexpressing Arabidopsis. We conclude that BBX21 overexpression improved morphological and physiological attributes, and photosynthetic rates in nonoptimal, high-irradiance conditions, without associated impairment of water use efficiency. These characteristics of BBX21 may be useful for increasing production of potatoes, and potentially of other crops.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Luz , Fotossíntese/efeitos da radiação , Solanum tuberosum/fisiologia , Solanum tuberosum/efeitos da radiação , Fatores de Transcrição/metabolismo , Antocianinas/metabolismo , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Fenóis/metabolismo , Estômatos de Plantas/fisiologia , Estômatos de Plantas/efeitos da radiação , Tubérculos/crescimento & desenvolvimento , Plantas Geneticamente Modificadas , Propanóis/metabolismo , Transdução de Sinais , Solanum tuberosum/genéticaRESUMO
In response to canopy shade, plant vegetative structures elongate to gain access to light. However, the mechanism that allows a plastic transcriptional response to canopy shade light is not fully elucidated. Here we propose that the activity of PIF4, a key transcription factor in the shade signalling network, is modulated by the interplay between the BBX24 transcriptional regulator and DELLA proteins, which are negative regulators of the gibberellin (GA) signalling pathway. We show that GA-related targets are enriched among genes responsive to BBX24 under shade and that the shade-response defect in bbx24 mutants is rescued by a GA treatment that promotes DELLA degradation. BBX24 physically interacts with DELLA proteins and alleviates DELLA-mediated repression of PIF4 activity. The proposed molecular mechanism provides reversible regulation of the activity of a key transcription factor that may prove especially relevant under fluctuating light conditions.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Proteínas Repressoras/metabolismo , Transativadores/metabolismo , Arabidopsis/efeitos dos fármacos , Arabidopsis/genética , Arabidopsis/efeitos da radiação , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Genes de Plantas , Giberelinas/farmacologia , Hipocótilo/anatomia & histologia , Hipocótilo/efeitos dos fármacos , Hipocótilo/efeitos da radiação , Luz , Modelos Biológicos , Mutação/genética , Picloram/farmacologia , Reguladores de Crescimento de Plantas/farmacologia , Ligação Proteica/efeitos dos fármacos , Ligação Proteica/efeitos da radiação , Nicotiana/metabolismo , Técnicas do Sistema de Duplo-HíbridoRESUMO
The B-box domain is conserved in a large number of proteins involved in cell growth control, differentiation and transcriptional regulation among animal and plant species. In Arabidopsis thaliana, some works have found that B-box proteins (BBX) play central developmental functions in flowering, light and abiotic stress signaling. Despite the functional importance of this protein family, evolutionary and structural relationships of BBX proteins have not been extensively investigated in the plant kingdom. Using a phylogenetic approach, we conducted a comprehensive evolutionary analysis of the BBX protein family in twelve plant species (four green algae, one moss, one lycophyte, three monocots and three dicots). The analysis classified 214 BBX proteins into five structure groups, which evolved independently at early stages of green plant evolution. We showed that the B-box consensus sequences of each structure groups retained a common and conserved domain topology. Furthermore, we identified seven novel motifs specific to each structure group and a valine-proline (VP) pair conserved at the C-terminus domain in some BBX proteins suggesting that they are required for protein-protein interactions. As it has been documented in mammalian systems, we also found monopartite and bipartite amino acid sequences at the C-terminus domain that could function as nuclear localization signals (NLSs). The five BBX structure groups evolved constrained by the conservation of amino acid sequences in the two B-boxes, but radiating variation into NLSs and novel motifs of each structural group. We suggest that these features are the functional basis for the BBX protein diversity in green plants.