RESUMO
An increasing interest in the development of products of natural origin for crop disease and pest control has emerged in the last decade. Here we introduce a new family of strawberry acyl glycosides (SAGs) formed by a trisaccharide (GalNAc-GalNAc-Glc) and a monounsaturated fatty acid of 6 to 12 carbon atoms linked to the glucose unit. Application of SAGs to Arabidopsis thaliana (hereafter Arabidopsis) plants triggered a transient oxidative burst, callose deposition and defense gene expression, accompanied by increased protection against two phytopathogens, Pseudomonas viridiflava and Botrytis cinerea. SAGs-induced disease protection was also demonstrated in soybean infected with the causal agent of target spot, Corynespora cassiicola. SAGs were shown to exhibit important antimicrobial activity against a wide-range of bacterial and fungal phytopathogens, most probably through membrane destabilization, and the potential use of SAGs as a biofungicide for postharvest disease protection was demonstrated on lemon fruits infected with Penicillium digitatum. Plant growth promotion by application of SAGs was shown by augmented primary root elongation, secondary roots development and increased siliques formation in Arabidopsis, whereas a significant increment in number of seed pods was demonstrated in soybean. Stimulation of radicle development and the induction of an auxin-responsive reporter system (DR5::GUS) in transgenic Arabidopsis plants, suggested that SAGs-stimulated growth at least partly acts through the auxin response pathway. These results indicate that strawberry fatty acid glycosides are promising candidates for the development of environmental-friendly products for disease management in soybean and lemon.
Assuntos
Antibacterianos/química , Antibacterianos/farmacologia , Fragaria/química , Glicosídeos/química , Glicosídeos/farmacologia , Doenças das Plantas/prevenção & controle , Arabidopsis/efeitos dos fármacos , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/microbiologia , Bioensaio , Botrytis/efeitos dos fármacos , Botrytis/fisiologia , Doenças das Plantas/microbiologia , Pseudomonas/efeitos dos fármacos , Pseudomonas/fisiologiaRESUMO
Circular RNAs (circRNAs) are a widespread class of endogenous noncoding RNAs and they have been studied in the past few years, implying important biological functions in all kingdoms of life. Recently, circRNAs have been identified in many plant species, including cereal crops, showing differential expression during stress response and developmental programs, which suggests their role in these process. In the following years, it is expected that insights into the functional roles of circRNAs can be used by cereal scientists and molecular breeders with the aim to develop new strategies for crop improvement. Here, we briefly outline the current knowledge about circRNAs in plants and we also outline available computational resources for their validation and analysis in cereal species.
Assuntos
Biologia Computacional , Grão Comestível/genética , Regulação da Expressão Gênica de Plantas , RNA Circular , RNA de Plantas , Biologia Computacional/métodos , Bases de Dados Genéticas , Perfilação da Expressão Gênica , Melhoramento Vegetal , Software , NavegadorRESUMO
Developing disease resistance is one of the most important components of any plant breeding program. Citrus traditional breeding methods (bud sport selection, crossbreeding, and other breeding channels) are a laborious task and often hampered by long juvenility, a high degree of heterozygosity, polyembryony, self-incompatibility, and abortion of reproductive organs. An interesting alternative to the classical breeding approach is the use of genetic transformation, which provides the means for adding a single agronomic trait to a plant without otherwise altering its phenotype. Agrobacterium tumefaciens-mediated transformation has been carried out with numerous hybrids and citrus species. This technique allowed us to introduce the Bs2 gene in Citrus, as well as to increase citrus canker resistance in transgenic Bs2 gene-expressing lines.
Assuntos
Citrus sinensis/genética , Plantas Geneticamente Modificadas/genética , Transformação Genética , Resistência à Doença/genética , Resistência à Doença/imunologia , Vetores Genéticos/genética , Melhoramento Vegetal/métodos , Doenças das Plantas/genética , Doenças das Plantas/imunologia , Doenças das Plantas/microbiologia , Folhas de Planta , Proteínas de Plantas/genética , Proteínas de Plantas/imunologia , Plasmídeos/genética , Xanthomonas/patogenicidadeRESUMO
HeT (1-0-galloyl-2,3; 4,6-bis-hexahydroxydiphenoyl-ß-D-glucopyranose) is a penta-esterified ellagitannin obtained from strawberry leaves. Previous studies have shown that foliar application of HeT prior to inoculation with a virulent pathogen increases the resistance toward Colletotrichum acutatum in strawberry plants and to Xanthomonas citri subsp. citri in lemon plants. In this work we report that HeT induces an immediate leak of electrolytes, the hyperpolarization of the cellular membrane, a rapid Ca2+ influx to the cytoplasm during the first few seconds, which in turn modulates the accumulation of nitric oxide 5â¯min after treatment. At longer times, a biphasic accumulation of H2O2 with peaks at 2 and 5â¯h post treatment could be observed. In addition, HeT elicited the increase of alternative oxidase capacity during the first 12â¯h post treatment.
Assuntos
Cálcio/metabolismo , Fragaria/metabolismo , Peróxido de Hidrogênio/metabolismo , Taninos Hidrolisáveis/farmacologia , Óxido Nítrico/metabolismo , Sinalização do Cálcio , Eletrólitos/metabolismo , Fragaria/microbiologia , Doenças das Plantas/microbiologia , Xanthomonas/metabolismoRESUMO
Transgenic expression of the pepper Bs2 gene confers resistance to Xanthomonas campestris pv. vesicatoria (Xcv) pathogenic strains which contain the avrBs2 avirulence gene in susceptible pepper and tomato varieties. The avrBs2 gene is highly conserved among members of the Xanthomonas genus, and the avrBs2 of Xcv shares 96% homology with the avrBs2 of Xanthomonas citri subsp. citri (Xcc), the causal agent of citrus canker disease. A previous study showed that the transient expression of pepper Bs2 in lemon leaves reduced canker formation and induced plant defence mechanisms. In this work, the effect of the stable expression of Bs2 gene on citrus canker resistance was evaluated in transgenic plants of Citrus sinensis cv. Pineapple. Interestingly, Agrobacterium-mediated transformation of epicotyls was unsuccessful when a constitutive promoter (2× CaMV 35S) was used in the plasmid construction, but seven transgenic lines were obtained with a genetic construction harbouring Bs2 under the control of a pathogen-inducible promoter, from glutathione S-transferase gene from potato. A reduction of disease symptoms of up to 70% was observed in transgenic lines expressing Bs2 with respect to non-transformed control plants. This reduction was directly dependent on the Xcc avrBs2 gene since no effect was observed when a mutant strain of Xcc with a disruption in avrBs2 gene was used for inoculations. Additionally, a canker symptom reduction was correlated with levels of the Bs2 expression in transgenic plants, as assessed by real-time qPCR, and accompanied by the production of reactive oxygen species. These results indicate that the pepper Bs2 resistance gene is also functional in a family other than the Solanaceae, and could be considered for canker control.
Assuntos
Capsicum/genética , Citrus sinensis/genética , Citrus sinensis/microbiologia , Doenças das Plantas/microbiologia , Xanthomonas campestris/patogenicidade , Agrobacterium tumefaciens/genética , Resistência à Doença/genética , Regulação da Expressão Gênica de Plantas , Doenças das Plantas/genética , Brotos de Planta/genética , Plantas Geneticamente Modificadas , Regiões Promotoras Genéticas , Transformação GenéticaRESUMO
Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), has an important economic impact on the citrus industry. Extensive information is available about the disease but, nevertheless, the study of plant-pathogen interactions could provide new information in the understanding of citrus canker disease. A new isolate has been identified, Xcc AT, which has a high genetic similarity (> 90 %) to the virulent Xcc T strain based on genetic clustering analyses of the rep-PCR fingerprinting patterns, but it does not produce cankerous lesions in Citrus limon. In this study, we compared C. limon responses to Xcc AT and to the virulent Xcc T strain at both histological and transcriptional levels. Histologically, leaves inoculated with Xcc AT exhibited neither a typical disordering of the spongy mesophyll, nor a swelling of epidermis. A particular content (undetermined) was also found in mesophyll cells near the stomata, together with increased starch accumulation. The transcriptomic profiles were compared by cDNA-AFLP technique. A total of 121 fragments derived from transcript (TDF) were either specifically induced or repressed by the isolates, and 62 were sequenced. Analysis of global expression identified different classes of genes known to be involved in plant-pathogen interactions. This study constitutes the first approach of the specific interaction between the avirulent Xcc AT isolate and C. limon.(AU)
Assuntos
Noxas , Doenças das Plantas , Interações Hospedeiro-Patógeno , Xanthomonas , Infecções por Bactérias Gram-Negativas , Citrus/parasitologia , 24444 , Produtos Agrícolas , Expressão GênicaRESUMO
Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), has an important economic impact on the citrus industry. Extensive information is available about the disease but, nevertheless, the study of plant-pathogen interactions could provide new information in the understanding of citrus canker disease. A new isolate has been identified, Xcc AT, which has a high genetic similarity (> 90 %) to the virulent Xcc T strain based on genetic clustering analyses of the rep-PCR fingerprinting patterns, but it does not produce cankerous lesions in Citrus limon. In this study, we compared C. limon responses to Xcc AT and to the virulent Xcc T strain at both histological and transcriptional levels. Histologically, leaves inoculated with Xcc AT exhibited neither a typical disordering of the spongy mesophyll, nor a swelling of epidermis. A particular content (undetermined) was also found in mesophyll cells near the stomata, together with increased starch accumulation. The transcriptomic profiles were compared by cDNA-AFLP technique. A total of 121 fragments derived from transcript (TDF) were either specifically induced or repressed by the isolates, and 62 were sequenced. Analysis of global expression identified different classes of genes known to be involved in plant-pathogen interactions. This study constitutes the first approach of the specific interaction between the avirulent Xcc AT isolate and C. limon.
Assuntos
Citrus/parasitologia , Doenças das Plantas , Infecções por Bactérias Gram-Negativas , Interações Hospedeiro-Patógeno , Noxas , Xanthomonas , 24444 , Expressão Gênica , Produtos AgrícolasRESUMO
Huanglongbing (HLB), a devastating citrus disease caused by the bacterium Candidatus Liberibacter spp., is now responsible for significant economic losses worldwide. Yet, no effective disease control has been found, and the non-cultivability of the bacterium has severely hampered studies on the pathogen. The 16S rDNA gene is a well-characterized sequence, essential for cell survival, and is used for bacterial identification or assignment of close relationships at the genus and species levels. Quantitative Real-Time PCR (qPCR) assays based on 16S rDNA genes are widely used in the detection of Ca. Liberibacter spp. in multiplex reactions. We have developed for the first time a set of qPCR primers based on the conserved 16S rDNA gene, which specifically and simultaneously detects in a singleplex reaction, all three bacterial species associated with HLB, and can differentiateCa.Liberibacter asiaticus or africanus from americanus by their characteristic melting curves. The assay is very sensitive, and it was possible to amplify expected DNA fragments with an efficiency of 98 % using the Syber Green system and a Ct value lower than tested methods for HLB diagnosis. The application of this fast, simple and efficient detection methodology could also be important in the detection of all species of HLB-associated Liberibacters and could contribute to early pathogen detection, a crucial step in the development of preventive strategies aimed at avoiding the dissemination of this devastating disease in HLB-free areas.
Assuntos
Citrus/parasitologia , Doenças das Plantas , Reação em Cadeia da Polimerase , Rhizobiaceae/patogenicidadeRESUMO
Huanglongbing (HLB), a devastating citrus disease caused by the bacterium Candidatus Liberibacter spp., is now responsible for significant economic losses worldwide. Yet, no effective disease control has been found, and the non-cultivability of the bacterium has severely hampered studies on the pathogen. The 16S rDNA gene is a well-characterized sequence, essential for cell survival, and is used for bacterial identification or assignment of close relationships at the genus and species levels. Quantitative Real-Time PCR (qPCR) assays based on 16S rDNA genes are widely used in the detection of Ca. Liberibacter spp. in multiplex reactions. We have developed for the first time a set of qPCR primers based on the conserved 16S rDNA gene, which specifically and simultaneously detects in a singleplex reaction, all three bacterial species associated with HLB, and can differentiateCa.Liberibacter asiaticus or africanus from americanus by their characteristic melting curves. The assay is very sensitive, and it was possible to amplify expected DNA fragments with an efficiency of 98 % using the Syber Green system and a Ct value lower than tested methods for HLB diagnosis. The application of this fast, simple and efficient detection methodology could also be important in the detection of all species of HLB-associated Liberibacters and could contribute to early pathogen detection, a crucial step in the development of preventive strategies aimed at avoiding the dissemination of this devastating disease in HLB-free areas.(AU)
Assuntos
Reação em Cadeia da Polimerase , Doenças das Plantas , Citrus/parasitologia , Rhizobiaceae/patogenicidadeRESUMO
In an incompatible interaction between Colletotrichum fragariae and strawberry plants, the accumulation of phenolic compounds in plant leaves was observed. A particularly abundant penta-esterified ellagitannin that accumulated in response to pathogen attack was identified as 1-0-galloyl-2,3;4,6-bis-hexahydroxydiphenoyl-ß-d-glucopyranose (HeT) by mass spectroscopy and nuclear magnetic resonance. Foliar application of purified HeT prior to inoculation with a virulent pathogen was shown to increase resistance toward C. acutatum in strawberry plants and to Xanthomonas citri subsp. citri in lemon plants. The induced resistance in strawberry was associated with a rapid oxidative burst, callose deposition, a transient increase of salicylic acid in phloem, and induction of gene expression responsive to salicylic acid. Results obtained suggested that HeT could be a common plant defense response molecule capable of inducing pathogen resistance in different plant species.