Regulación hormonal del desarrollo temprano del fruto en Arabidopsis thaliana.

RESUMEN El fruto es un órgano esencial para las plantas, dado que permite que las semillas se desarrollen y maduren correctamente, y que se dispersen una vez completada su maduración. Desde hace varias décadas se ha propuesto que el proceso de desarrollo del fruto está modulado por fitohormonas, fundamentalmente giberelinas y auxinas, y que las semillas en desarrollo impulsarían el crecimiento del fruto mediante la síntesis de estas hormonas en su interior. Los mecanismos molecularres que rigen la actuación de estas hormonas, sin embargo, no se conocen. En diversas especies se ha descrito desde los años 30 que auxinas y giberelinas pueden inducir desarrollo del fruto independientemente de la fertilización, y en la planta modelo Arabidopsis thaliana también se ha comprobado, más recientemente, este efecto. En este trabajo se ha querido determinar qué mecanismos moleculares median la acción de estas hormonas, así como cuál es la naturaleza de la interacción entre auxinas y giberelinas en este proceso del desarrollo. Para facilitar el estudio de la fructificación y las fases iniciales del desarrollo del fruto, se ha utilizado el mutante de esterilidad masculina condicional cer6-2. En primer lugar, se ha demostrado que el ácido giberélico (GA3) y la auxina sintética 2,4-D son capaces de inducir desarrollo partenocárpico del fruto en el mutante cer6-2. El inhibidor del transporte polar de auxinas NPA, cuya capacidad de desencadenar desarrollo de fruto en pepino fue descrita en los años 70, también induce partenocarpia en este mutante de Arabidopsis. Experimentos de localización de auxinas, utilizando plantas transgénicas que expresan la proteína verde fluorescente (GFP) bajo la dirección del promotor sintético de respuesta a auxinas DR5, han demostrado que el primer paso del proceso de fructificación inducida por polinización y fertilización de los óvulos consiste en una acumulación de auxinas en los óvulos, y que el tratamiento con NPA mimetiza este efecto. Esta acumulación se restringe a los óvulos, ya que en el pericarpo del fruto no se aprecia incremento de la señal de GFP. Las giberelinas no tienen ningún efecto sobre la distribución de auxinas, lo que sugiere que su actuación en este proceso tiene lugar independientemente o con posterioridad a las auxinas. La polinización, así como los tratamientos inductores de partenocarpia con 2,4-D o NPA inducen la expresión de genes que codifican enzimas implicadas en la biosíntesis de giberelinas, y reprimen la expresión de genes que codifican enzimas implicadas en la inactivación de estas hormonas. La fructificación, inducida tanto por polinización como por todos los tratamientos, induce eventos de señalización por giberelinas: una fusión traduccional de GFP a la proteína de señalización por giberelinas RGA se degrada en respuesta a todos los tratamientos. Además, la capacidad de respuesta a los distintos tratamientos de diferentes mutantes en la ruta de señalización por giberelinas se ve afectada. Estos resultados apoyan la hipótesis de que las giberelinas medien la acción de las auxinas en el proceso de fructificación. Por último, un análisis transcriptómico de la respuesta a la inducción de partenocarpia mediante tratamiento con GA3 mostró que numerosos genes de respuesta a auxinas se inducen a consecuencia de tratamiento. Este resultado sugiere que la vía de señalización debe de ser compleja, con las giberelinas mediando la acción de las auxinas, pero actuando posteriormente, o en una rama independiente, también a través de la acción de las auxinas. __________________________________________________________________________________________________Fruit development is an essential process in the plant life cycle, because the fruit allows the correct development and maturation of the seeds, and also their dispersal. It has long been proposed that phytohormones, especially gibberellins and auxins, synthesized in developing seeds, would play a determinant role in fruit development, although their molecular mechanism of action remains unknown. Auxins and gibberellins have been shown to induce parthenocarpy, i.e. seedless fruit development, in several species, including Arabidopsis thaliana. The aim of this work has been to decipher the molecular mechanisms of action of auxins and gibberellins in fruit set, and to determine whether these hormones act independently, in a concerted manner, or sequentially, and which is the hierarchy between them. In order to simplify the study of fruit set, a conditional male sterile mutant, cer6-2, has been used. The capacity of different hormones to induce fruit development independent of fertilization in this mutant was assessed: gibberellic acid (GA3), the synthetic auxin 2,4-D, and the inhibitor of polar auxin transport NPA were found to induce parthenocarpy, although with a limited effect compared to pollination. Auxin distribution analysis showed that pollination triggers a strong accumulation of auxins in the ovules, but not in the pericarp of the fruit. NPA treatment mimicked this effect, whereas GA3 treatment had no effect upon auxin distribution, suggesting that GAs act downstream of auxins in fruit set. Induction of fruit set via pollination, auxin or NPA treatment resulted in an upregulation of GA biosynthetic genes, further supporting the role of GAs as mediators of auxin action. GA signaling events were activated after fruit set induction by all treatments and pollination, as shown by the degradation of the GA signaling protein RGA, and by the altered response to all treatments shown by GA signaling mutants. Finally, microarray analysis showed that fruit set induction by GA3-treatment triggers changes in the expression of several auxin-responsive genes, which suggests that the signaling pathway in early fruit development is more complex, with gibberellins acting downstream of auxins, but also triggering auxin signaling events further downstream, perhaps on an independent branch of the pathway

Chiasma

Newspaper reporting on events at the Boston University School of Medicine in the 1960s

DSS-28: a novel wide bandwidth radio telescope devoted to educational outreach

We have recently equipped the 34-meter DSS-28 radio telescope at the Goldstone Deep Space Communications Complex with a novel wide bandwidth radiometer and digital signal processor as part of the Goldstone Apple Valley Radio Telescope (GAVRT) educational outreach program operated by the Jet Propulsion Laboratory and the Lewis Center for Educational Research. The system employs a cryogenically cooled wide bandwidth quad-ridge feed and InP low noise amplifiers to achieve excellent noise performance from 2.7 to 14 GHz; a fractional bandwidth better than 4:1. Four independently tunable dual-polarization receivers each down-convert a 2 GHz block to baseband, providing access to 8 GHz of instantaneous bandwidth. A flexible FPGA-based signal processor has been constructed using CASPER FPGA hardware and tools to take advantage of this enormous bandwidth. This system demonstrates many of the enabling wide bandwidth technologies that will be crucial to maximizing the utility of future large centimeter-wavelength arrays, in particular the Square Kilometer Array. The GAVRT program has previously used narrow bandwidth total power radiometers to study flux variability of quasars and the outer planets. The versatility of DSS-28 will enable other projects including spectroscopy and SETI. Finally, the wide instantaneous bandwidth available makes this system uniquely suited for studying transient radio pulses. A configuration of the digital signal processor has been developed which provides the capability of recording a burst of raw baseband voltage data triggered by a real-time incoherent dedispersion system which is very sensitive to pulses from a known source, such as the Crab Nebula pulsar

Substantial deletion overlap among divergent Arabidopsis genomes revealed by intersection of short reads and tiling arrays

A new approach to detect deletions in divergentgenomes combines short read sequencing and tilling array data. Its utility is demonstrated on Arabidopsis strains

Governance for sustainability of estuarine areas: assessing alternative models using the case of Ria de Aveiro, Portugal

Estuaries are one of the most productive and complex types of ecosystems supporting a wide range of economic activities. Departing from a set of governance problems and emergent goals, such as sustainability or climate change adaptation faced by an estuarine case study area, Ria de Aveiro, in Portugal, this article assesses the adequacy of alternative governance models under the existing water resources legal framework and traditional political culture. It shows that apart from the centrally-based compliance model, all other alternatives require high degrees of institutional reforms. Moreover, although the model based on a dedicated new agency, long preferred by many users of Ria de Aveiro, is the most understandable and focused, it does not assure the pursuance of adaptability or collaboration, which are considered essential for estuary governance. As it relies on collective action and multi-level and multi-agent contexts, estuarine governance may require a new institutional design. Where one begins a process of institutional change, however, is not a simple issue to address and demands a deeper analysis, particularly on the types of required institutional changes, as well as on their impacts on policy and decision-making outcomes over estuarine environments and associated socio-ecological networkspublishe

Seedless Fruit Production by Hormonal Regulation of Fruit Set

Seed and fruit development are intimately related processes controlled by internal signals and environmental cues. The absence of seeds is usually appreciated by consumers and producers because it increases fruit quality and fruit shelf-life. One method to produce seedless fruit is to develop plants able to produce fruits independently from pollination and fertilization of the ovules. The onset of fruit growth is under the control of phytohormones. Recent genomic studies have greatly contributed to elucidate the role of phytohormones in regulating fruit initiation, providing at the same time genetic methods for introducing seedlessness in horticultural plants

Comparison of global responses to mild deficiency and excess copper levels in Arabidopsis seedlings

[EN] Copper is an essential micronutrient in higher plants, but it is toxic in excess. The fine adjustments required to fit copper nutritional demands for optimal growth are illustrated by the diverse, severe symptoms resulting from copper deficiency and excess. Here, a differential transcriptomic analysis was done between Arabidopsis thaliana plants suffering from mild copper deficiency and those with a slight copper excess. The effects on the genes encoding cuproproteins or copper homeostasis factors were included in a CuAt database, which was organised to collect additional information and connections to other databases. The categories overrepresented under copper deficiency and copper excess conditions are discussed. Different members of the categories overrepresented under copper deficiency conditions were both dependent and independent of the general copper deficiency transcriptional regulator SPL7. The putative regulatory elements in the promoter of the copper deficiency overrepresented genes, particularly of the iron superoxide dismutase gene FSD1, were also analysed. A 65 base pair promoter fragment, with at least three GTAC sequences, was found to be not only characteristic of them all, but was responsible for most of the FSD1 copper-dependent regulations. Moreover, a new molecular marker for the slight excess copper nutritional status is proposed. Taken together, these data further contribute to characterise copper nutritional responses in higher plants.We thank Dr Toshiharu Shikanai for the spl7 mutant and the Unitat d'Analisi Elemental, Serveis Cientificotecnics at the Universitat de Barcelona. This work has been supported by Grants BIO2011-24848 and CSD2007-00057 to L.P. from the Spanish Ministry of Economy and Competitiveness, and by FEDER funds from the European Union and the Generalitat Valenciana (Regional Valencian Government; ACOMP07-159). N.A.-C., A.G.-M. and A.P.-G were recipients of predoctoral fellowships from the Spanish Ministry of Economy and Competitiveness.Andres-Colas, N.; Perea García, A.; Mayo, S.; Garcia-Molina, A.; Dorcey, E.; Rodríguez-Navarro, S.; Perez Amador, MA.... (2013). Comparison of global responses to mild deficiency and excess copper levels in Arabidopsis seedlings. Metallomics. 5(9):1234-1246. https://doi.org/10.1039/c3mt00025g123412465

Reduction of indole-3-acetic acid methyltransferase activity compensates for high-temperature male sterility in Arabidopsis

High temperature is a general stress factor that causes a decrease in crop yield. It has been shown that auxin application reduces the male sterility caused by exposure to higher temperatures. However, widespread application of a hormone with vast effects on plant physiology may be discouraged in many cases. Therfore, the generation of new plant varieties that locally enhance auxin in reproductive organs may represent an alternative strategy. We have explored the possibility of increasing indoleacetic acid (IAA) in ovaries by reducing IAA METHYLTRANSFERASE1 (IAMT1) activity in Arabidopsis thaliana. The iamt1 mutant showed increased auxin signaling in funiculi, which correlated with a higher growth rate of wild-type pollen in contact with mutant ovaries and premature ovule fertilization. While the production of seeds per fruit was similar in the wild type and the mutant at 20°C, exposure to 29°C caused a more severe decrease in fertility in the wild type than in the mutant. Loss of IAMT1 activity was also associated with to the production of more nodes after flowering and higher tolerance of the shoot apical meristem to higher temperatures. As a consequence, the productivity of the iamt1 mutant under higher temperatures was more than double of that of the wild type, with almost no apparent trade-off