These results indicate that chlorantraniliprole has toxicity against S. cosmioides larvae. Sublethal effects on the biological and reproductive performance of this species can help optimize integrated pest management programs. © 2018 Society of Chemical Industry.
SummaryCitrus is an economically important fruit crop that is severely afflicted by citrus canker, a disease caused by the bacterial phytopathogen, Xanthomonas citri subsp. citri (Xcc). GenBank houses a large collection of Expressed Sequence Tags (ESTs) enriched with transcripts generated during the defence response against this pathogen; however, there are currently no strategies in citrus to assess the function of candidate genes. This has greatly limited research as defence signalling genes are often involved in multiple pathways. In this study, we demonstrate the efficacy of RNA interference (RNAi) as a functional genomics tool to assess the function of candidate genes involved in the defence response of Citrus limon against the citrus canker pathogen. Double-stranded RNA expression vectors, encoding hairpin RNAs for citrus host genes, were delivered to lemon leaves by transient infiltration with transformed Agrobacterium. As proof of principle, we have established silencing of citrus phytoene desaturase (PDS) and callose synthase (CalS1) genes. Phenotypic and molecular analyses showed that silencing vectors were functional not only in lemon plants but also in other species of the Rutaceae family. Using silencing of CalS1, we have demonstrated that plant cell wall-associated defence is the principal initial barrier against Xanthomonas infection in citrus plants. Additionally, we present here results that suggest that H 2 O 2 accumulation, which is suppressed by xanthan from Xcc during pathogenesis, contributes to inhibition of xanthan-deficient Xcc mutant growth either in wild-type or CalS1-silenced plants. With this work, we have demonstrated that high-throughput reverse genetic analysis is feasible in citrus.
Xanthomonas citri ssp. citri (X. citri) is the causal agent of Asiatic citrus canker, a disease that seriously affects most commercially important Citrus species worldwide. We have identified previously a natural variant, X. citri A , that triggers a host-specific defence response in Citrus limon. However, the mechanisms involved in this canker disease resistance are unknown. In this work, the defence response induced by X. citri A was assessed by transcriptomic, physiological and ultrastructural analyses, and the effects on bacterial biofilm formation were monitored in parallel. We show that X. citri A triggers a hypersensitive response associated with the interference of biofilm development and arrest of bacterial growth in C. limon. This plant response involves an extensive transcriptional reprogramming, setting in motion cell wall reinforcement, the oxidative burst and the accumulation of salicylic acid (SA) and phenolic compounds. Ultrastructural analyses revealed subcellular changes involving the activation of autophagy-associated vacuolar processes. Our findings show the activation of SA-dependent defence in response to X. citri A and suggest a coordinated regulation between the SA and flavonoid pathways, which is associated with autophagy mechanisms that control pathogen invasion in C. limon. Furthermore, this defence response protects C. limon plants from disease on subsequent challenges by pathogenic X. citri. This knowledge will allow the rational exploitation of the plant immune system as a biotechnological approach for the management of the disease.
ResumenEl proceso de convergencia hacia el Espacio Europeo de Enseñanza Superior ha puesto de relieve la importancia del dominio de competencias transversales (CTs) durante la formación universitaria. Dichas competencias confieren al estudiante la capacidad de innovación y de adaptación a los cambios, siendo su adquisición necesaria para la vida profesional. En la Universidad Politécnica de Valencia, se han redactado 13 CTs que aúnan las competencias de la normativa vigente y las de las agencias de acreditación. En nuestro grupo de innovación educativa estudiamos diferentes métodos de enseñanza-aprendizaje y evaluación de las competencias transversales en asignaturas relacionadas con las ciencias de la vida. En concreto, en este trabajo presentamos una propuesta para evaluar la CT "Responsabilidad ética, medioambiental y profesional". Esta competencia pretende la obtención de conocimientos, habilidades, destrezas y actitudes útiles para interactuar con el entorno, de forma ética, responsable y sostenible, ante uno mismo y los demás. Las asignaturas relacionadas con las ciencias de la vida y, en particular, sus créditos de laboratorio, resultan un marco idóneo para la adquisición de dicha competencia. Nuestra propuesta de evaluación de la misma se basa en una rúbrica que ha de ser cumplimentada por los pares a través de una aplicación telemática.Palabras clave : competencia transversal, evaluación, e-rúbrica, laboratorio, responsabilidad ética, medioambiental y profesional IntroducciónLa adaptación de las titulaciones al Espacio Europeo de Educación Superior (EEES) ha supuesto un gran cambio metodológico en el sistema de autonomía en el aprendizaje y en la Evaluación de la competencia transversal "Responsabilidad ética, medioambiental y profesional" a través de una e-rúbrica en el laboratorio. 2015, Universitat Politècnica de ValènciaCongreso IN-RED (2015)
In Santa Fe, the central-east area of Argentina, the expansion of fruit tree crops requires the introduction and evaluation of low chilling varieties. The aims of this study was to characterize the phenological behaviour and the reproductive traits of peach (Prunus persica L. Batsch) and nectarine varieties with chilling requirements ranging from 150 to 650 chilling hours (CH). Low chilling varieties (≤ 450 CH) had higher flower density (22.0-56.5 flowers m -1 ), fruit set (26.0-56.7%), fruit yield (9.3-36.6 kg per plant), and low coefficient of fruit yield variability than varieties with a higher chilling requirement (>500 CH). The phenology of high chilling requirement varieties had the advantage that blooming and fruit set happened after the period of late frost occurrence. However, they did not satisfy their chilling requirement, showing an inadequate vegetative and reproductive behaviour. Low chilling varieties began to sprout during July, and the period of full bloom occurred from July 14 th to August 4 th . Fruit harvest was initiated on October 19 th with the cv. 'Flordastar' and it extended for 58 days. However, on low chilling varieties the harvest time was reduced in ten days. Flower density, fruit set and fruit yield showed a negative relationship with the chilling requirement of the variety.
Summary Transcription activator‐like effectors (TALEs) are important effectors of Xanthomonas spp. that manipulate the transcriptome of the host plant, conferring susceptibility or resistance to bacterial infection. Xanthomonas citri ssp. citri variant AT (X. citri AT) triggers a host‐specific hypersensitive response (HR) that suppresses citrus canker development. However, the bacterial effector that elicits this process is unknown. In this study, we show that a 7.5‐repeat TALE is responsible for triggering the HR. PthA4AT was identified within the pthA repertoire of X. citri AT followed by assay of the effects on different hosts. The mode of action of PthA4AT was characterized using protein‐binding microarrays and testing the effects of deletion of the nuclear localization signals and activation domain on plant responses. PthA4AT is able to bind DNA and activate transcription in an effector binding element‐dependent manner. Moreover, HR requires PthA4AT nuclear localization, suggesting the activation of executor resistance (R) genes in host and non‐host plants. This is the first case where a TALE of unusually short length performs a biological function by means of its repeat domain, indicating that the action of these effectors to reprogramme the host transcriptome following nuclear localization is not limited to ‘classical’ TALEs.
Field evaluations have shown that Satsuma mandarin (Citrus unshiu) ‘Okitsu’ is one of the mandarin cultivars that shows substantial resistance to Xanthomonas citri subsp. citri (X. citri), the causal agent of citrus bacterial canker disease. However, the mechanisms underlying this resistance are not well understood. In this study, we have shown that ‘Okitsu’ leaves are nevertheless susceptible to X. citri infection during a period of their development; however, this period is shorter than that seen in the susceptible mandarin ‘Clemenules’ (C. clementina). Under controlled growth conditions, the resistance of ‘Okitsu’ to X. citri was associated with the age of the leaf and was evident in spray-inoculated plants but not in those inoculated by infiltration. Furthermore, X. citri showed reduced attachment and biofilm formation in ‘Okitsu’ leaves compared with ‘Clemenules’. Taken together, our data suggest that structural features of the ‘Okitsu’ leaf surface, such as the physical properties of the cuticle, are involved in the resistance to X. citri.
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