ABA-overproduction response under salinity

[SPA] Con el fin de comprender la influencia de la fitohormona ácido abscísico (ABA) en la adaptación al riego salino, dos líneas transgénicas independientes de tomate (Solanum lycopersicum L.), sp12 y sp5, que sobreexpresan constitutivamente el gen NCED1 (codifica para la enzima que cataliza un paso limitante en la biosíntesis de ABA) y la variedad silvestre Ailsa Craig, se han estudiado en experimentos o bien i) como planta entera o ii) como portainjerto bajo condiciones control y de estrés salino. Aunque la expresión constitutiva de NCED disminuye el crecimiento bajo condiciones control, minimiza los efectos producidos por la sal (planta completa) y mejora significativamente el crecimiento cuando se usa como portainjerto. El análisis de la savia xilemática de raíz mostró que los fenotipos resultantes bajo las diferentes condiciones de cultivo eran difíciles de explicar en términos de sobreproducción de ABA. Para intentar explicar estos resultados se llevó a cabo un análisis de expresión de un conjunto de genes relacionados con hormonas y estrés mediante PCR cuantitativa, así como un estudio transcriptómico mediante microarrays en la raíz. Los resultados sugieren que la sobreexpresión de NCED parece alterar diversas rutas de señalización, derivando en una respuesta adaptativa al estrés que podría ayudar a explicar los fenotipos observados. [ENG] With the aim of better understanding the influence of the plan hormone abscisic acid (ABA) in adaptation to saline irrigation, two independent transgenic tomato (Solanum lycopersicum L.) lines, sp12 and sp5, overexpressing constitutively NCED1 (the enzyme that catalyzes a key rate-limiting step in ABA biosynthesis) and the wild type Ailsa Craig, have been studied in experiments either i) as whole plants or ii) as rootstocks under control and salinity conditions. While NCED overexpression penalizes growth under control conditions, it minimized the effect of salinity (whole plants) or significantly improved plant growth and yield when used as rootstocks. The analysis of the root xylem sap revealed that the phenotypes resulting under the different conditions were difficult to explain in terms of ABA overproduction. With the aim of explaining these results, the expression of a set of hormone and stress associated genes (analysed by real time PCR) as well as a transcriptomic analysis (by using one-color microarray) were performed in roots. The results suggest that NCED overexpression seems to alter several signalling pathways leading to stress adaptive responses that could help to explain the observed phenotypes.The authors thank Andrew J. Thompson from Cranfield University, the NCED seeds set. This work was supported by CICYT-FEDER (project AGL2011-27996) and European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 289365(ROOTOPOWER project)

Impact of overexpression of 9-cis-epoxycarotenoid dioxygenase on growth and gene expression under salinity stress

To better understand abscisic acid (ABA)’s role in the salinity response of tomato (Solanum lycopersicum L.), two independent transgenic lines, sp5 and sp12, constitutively overexpressing the LeNCED1 gene (encoding 9-cis-epoxycarotenoid dioxygenase, a key enzyme in ABA biosynthesis) and the wild type (WT) cv. Ailsa Craig, were cultivated hydroponically with or without the addition of 100 mM NaCl. Independent of salinity, LeNCED1 overexpression (OE) increased ABA concentration in leaves and xylem sap, and salinity interacted with the LeNCED1 transgene to enhance ABA accumulation in xylem sap and roots. Under control conditions, LeNCED1 OE limited root and shoot biomass accumulation, which was correlated with decreased leaf gas exchange. In salinized plants, LeNCED1 OE reduced the percentage loss in shoot and root biomass accumulation, leading to a greater total root length than WT. Root qPCR analysis of the sp12 line under control conditions revealed upregulated genes related to ABA, jasmonic acid and ethylene synthesis and signalling, gibberellin and auxin homeostasis and osmoregulation processes. Under salinity, LeNCED1 OE prevented the induction of genes involved in ABA metabolism and GA and auxin deactivation that occurred in WT, but the induction of ABA signalling and stress-adaptive genes was maintained. Thus, complex changes in phytohormone and stress-related gene expression are associated with constitutive upregulation of a single ABA biosynthesis gene, alleviating salinity-dependent growth limitation

Overproduction of ABA in rootstocks alleviates salinity stress in tomato shoots

To determine whether root-supplied ABA alleviates saline stress, tomato (Solanum lycopersicum L. cv. Sugar Drop) was grafted onto two independent lines (NCED OE) overexpressing the SlNCED1 gene (9-cis-epoxycarotenoid dioxygenase) and wild type rootstocks. After 200 days of saline irrigation (EC = 3.5 dS m−1), plants with NCED OE rootstocks had 30% higher fruit yield, but decreased root biomass and lateral root development. Although NCED OE rootstocks upregulated ABA-signalling (AREB, ATHB12), ethylene-related (ACCs, ERFs), aquaporin (PIPs) and stress-related (TAS14, KIN, LEA) genes, downregulation of PYL ABA receptors and signalling components (WRKYs), ethylene synthesis (ACOs) and auxin-responsive factors occurred. Elevated SlNCED1 expression enhanced ABA levels in reproductive tissue while ABA catabolites accumulated in leaf and xylem sap suggesting homeostatic mechanisms. NCED OE also reduced xylem cytokinin transport to the shoot and stimulated foliar 2-isopentenyl adenine (iP) accumulation and phloem transport. Moreover, increased xylem GA3 levels in growing fruit trusses were associated with enhanced reproductive growth. Improved photosynthesis without changes in stomatal conductance was consistent with reduced stress sensitivity and hormone-mediated alteration of leaf growth and mesophyll structure. Combined with increases in leaf nutrients and flavonoids, systemic changes in hormone balance could explain enhanced vigour, reproductive growth and yield under saline stress

The Characterization of Arabidopsis mterf6 Mutants Reveals a New Role for mTERF6 in Tolerance to Abiotic Stress

Exposure of plants to abiotic stresses, such as salinity, cold, heat, or drought, affects their growth and development, and can significantly reduce their productivity. Plants have developed adaptive strategies to deal with situations of abiotic stresses with guarantees of success, which have favoured the expansion and functional diversification of different gene families. The family of mitochondrial transcription termination factors (mTERFs), first identified in animals and more recently in plants, is likely a good example of this. In plants, mTERFs are located in chloroplasts and/or mitochondria, participate in the control of organellar gene expression (OGE), and, compared with animals, the mTERF family is expanded. Furthermore, the mutations in some of the hitherto characterised plant mTERFs result in altered responses to salt, high light, heat, or osmotic stress, which suggests a role for these genes in plant adaptation and tolerance to adverse environmental conditions. In this work, we investigated the effect of impaired mTERF6 function on the tolerance of Arabidopsis to salt, osmotic and moderate heat stresses, and on the response to the abscisic acid (ABA) hormone, required for plants to adapt to abiotic stresses. We found that the strong loss-of-function mterf6-2 and mterf6-5 mutants, mainly the former, were hypersensitive to NaCl, mannitol, and ABA during germination and seedling establishment. Additionally, mterf6-5 exhibited a higher sensitivity to moderate heat stress and a lower response to NaCl and ABA later in development. Our computational analysis revealed considerable changes in the mTERF6 transcript levels in plants exposed to different abiotic stresses. Together, our results pinpoint a function for Arabidopsis mTERF6 in the tolerance to adverse environmental conditions, and highlight the importance of plant mTERFs, and hence of OGE homeostasis, for proper acclimation to abiotic stress

Zur Auslegung hochkonzentrierender Solarkollektoren und Solarkollektorsysteme

With 28 figs., 20 refs., 1 tab.SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Mutation of an Arabidopsis NatB N-Alpha-Terminal Acetylation Complex Component Causes Pleiotropic Developmental Defects

<div><p>N-α-terminal acetylation is one of the most common, but least understood modifications of eukaryotic proteins. Although a high degree of conservation exists between the N-α-terminal acetylomes of plants and animals, very little information is available on this modification in plants. In yeast and humans, N-α-acetyltransferase complexes include a single catalytic subunit and one or two auxiliary subunits. Here, we report the positional cloning of <i>TRANSCURVATA2</i> (<i>TCU2</i>), which encodes the auxiliary subunit of the NatB N-α-acetyltransferase complex in Arabidopsis. The phenotypes of loss-of-function <i>tcu2</i> alleles indicate that NatB complex activity is required for flowering time regulation and for leaf, inflorescence, flower, fruit and embryonic development. In double mutants, <i>tcu2</i> alleles synergistically interact with alleles of <i>ARGONAUTE10</i>, which encodes a component of the microRNA machinery. In summary, NatB-mediated N-α-terminal acetylation of proteins is pleiotropically required for Arabidopsis development and seems to be functionally related to the microRNA pathway.</p></div

Structure of the <i>AGO10</i> gene and its alleles studied in this work.

<p>Exons and introns are shown as black rectangles and lines, respectively. White boxes represent the 5′ and 3′ untranslated regions. Arrows point to the position of the <i>zll-2</i> and <i>pnh-2</i> point mutations.</p

Silique morphology in P14 6.3.

<p>(A, B) Siliques from (A) L<i>er</i> and (B) P14 6.3 plants. (C–E) Three valves with a rough surface were shown in most P14 6.3 siliques: (C) front and (D) lateral views of closed siliques and (E) a silique with longitudinally open septa. (F) Seeds containing mature embryos and (G) aborted or unfertilized ovules (red arrows) in dissected P14 6.3 siliques. Pictures were taken 35 das. Scale bars: (A, B) 2 mm, (C–E) 1 mm and (F, G) 200 µm.</p

Rosette phenotype of <i>amiR-TCU2</i> transgenic lines.

<p>Pictures were taken 16 das. Scale bars: 2 mm.</p

Inflorescence structure and floral morphology in P14 6.3.

<p>(A) Lateral view of L<i>er</i> and P14 6.3 inflorescences. (B, C) Details of abnormal structures observed in P14 6.3 stems: (B) a filamentous bulge, and (C) an aborted lateral flower. (D) Inflorescence apex in L<i>er</i> and P14 6.3 plants. The red arrow indicates an aborted lateral flower. (E, F) Flowers of the inflorescence apex from (E) L<i>er</i> and (F) P14 6.3. (G, H) Different sizes of (G) flowers from the inflorescence apex and (H) petals from L<i>er</i> and P14 6.3. Pictures were taken 35 das. Scale bars: (A) 2 cm, (B, C) 0.5 mm, (D–F) 2 mm and (G, H) 1 mm.</p