Several genes involved in the regulation of postembryonic organ initiation and growth have been identified. However, it remains largely unclear how developmental cues connect to the cell cycle. ...RETINOBLASTOMA RELATED (RBR) is a plant homolog of the tumor suppressor Retinoblastoma (pRb), which is a key regulator of the cell cycle. Using inducible RNA interference (RNAi) against Arabidopsis thaliana RBR (RBRi), we reduced RBR expression levels at different stages of plant development. Conditional reduction or loss of RBR function disrupted cell division patterns, promoted context-dependent cell proliferation, and negatively influenced establishment of cell differentiation. Several lineages of toti- and pluripotent cells, including shoot apical meristem stem cells, meristemoid mother cells, and procambial cells, failed to produce appropriately differentiated cells. Meristem activity was altered, leading to a disruption of the CLAVATA-WUSCHEL feedback loop and inhibition of lateral organ formation. Release of RBR from RNAi downregulation restored meristem activity. Gene profiling analyses soon after RBRi induction revealed that a change in RBR homeostasis is perceived as a stress, even before genes regulated by RBR-E2F become deregulated. The results establish RBR as a key cell cycle regulator required for coordination of cell division, differentiation, and cell homeostasis.
Post‐translational chromatin modifications are an important regulatory mechanism in light signalling and circadian clock function. The regulation of diurnal transcript level changes requires ...fine‐tuning of the expression of generally active genes depending on the prevailing environmental conditions. We investigated the association of histone modifications H3K4me3, H3K9ac, H3K9me2, H3S10p, H3K27ac, H3K27me3 and H3S28p with diurnal changes in transcript expression using chromatin immunoprecipitations followed by sequencing (ChIP‐Seq) in fully expanded leaves 6 of Arabidopsis thaliana grown in short‐day optimal and water‐deficit conditions. We identified a differential H3K9ac, H3K27ac and H3S28p signature between end‐of‐day and end‐of‐night that is correlated with changes in diurnal transcript levels. Genes with this signature have particular over‐represented promoter elements and encode proteins that are significantly enriched for transcription factors, circadian clock and starch catabolic process. Additional activating modifications were prevalent in optimally watered (H3S10p) and in water‐deficit (H3K4me3) plants. The data suggest a mechanism for diurnal transcript level regulation in which reduced binding of repressive transcription factors facilitates activating H3K9ac, H3K27ac and H3S28p chromatin modifications. The presence of activating chromatin modification patterns on genes only at times of the day when their expression is required can explain why some genes are differentially inducible during the diurnal cycle.
Regulation of diurnal transcript level changes requires fine‐tuning of the expression of generally active genes. We identified changes in a signature of activating H3K9ac, H3K27ac and H3S28p histone modifications between the end‐of‐day and end‐of‐night that correlate with diurnal transcript level fluctuations. Genes with this signature have particular over‐represented promoter elements, and they are enriched for transcription factors, circadian clock and starch catabolic process. This suggests a mechanism for diurnal transcript level regulation involving the H3K9ac|H3K27ac|H3S28p signature and explains why some genes are differentially inducible during the diurnal cycle.
Following the conceptual development of virus resistance strategies ranging from coat protein-mediated interference of virus propagation to RNA-mediated virus gene silencing, much progress has been ...achieved to protect plants against RNA and DNA virus infections. Geminiviruses are a major threat to world agriculture, and breeding resistant crops against these DNA viruses is one of the major challenges faced by plant virologists and biotechnologists. In this article, we review the most recent transgene-based approaches that have been developed to achieve durable geminivirus resistance. Although most of the strategies have been tested in model plant systems, they are ready to be adopted for the protection of crop plants. Furthermore, a better understanding of geminivirus gene and protein functions, as well as the native immune system which protects plants against viruses, will allow us to develop novel tools to expand our current capacity to stabilize crop production in geminivirus epidemic zones.
Summary
African cassava mosaic virus (ACMV) is a major contributor to cassava mosaic disease (CMD), the economically most important and devastating disease of cassava in Africa. We have developed ...transgenic cassava plants with increased ACMV resistance using improved antisense RNA technology by targeting the viral mRNAs of Rep (AC1), TrAP (AC2) and REn (AC3). Viral DNA replication assays in detached leaves demonstrated that replication of two ACMV isolates was strongly reduced or inhibited in most transgenic lines. After ACMV infection of plants using biolistic inoculation, several lines remained symptomless at lower infection pressure (100 ng viral DNA/plant). Symptom development was reduced and attenuated even at higher DNA doses. Transgenic ACMV‐resistant plants had significantly reduced viral DNA accumulation in their infected leaves. Short sense and antisense RNAs specific to AC1 were identified in transgenic lines expressing AC1 antisense RNA, suggesting that the short RNAs mediate interference by post‐transcriptional gene silencing. Our results demonstrate that resistance to ACMV infection of cassava can be achieved with high efficacy by expressing antisense RNAs against viral mRNAs encoding essential non‐structural proteins, providing a new tool to combat CMD in Africa.
Seedling establishment is a crucial phase during plant development when the germinating heterotrophic embryo switches to autotrophic growth and development. Positive regulators of embryonic ...development need to be turned off, while the cell cycle machinery is activated to allow cell cycle entry and organ primordia initiation. However, it is not yet understood how the molecular mechanisms responsible for the onset of cell division, metabolism changes and cell differentiation are coordinated during this transition. Here, we demonstrate that the Arabidopsis thaliana RETINOBLASTOMA-RELATED protein (RBR) ortholog of the animal tumor suppressor retinoblastoma (pRB) not only controls the expression of cell cycle-related genes, but is also required for persistent shut-down of late embryonic genes by increasing their histone H3K27 trimethylation. Seedlings with reduced RBR function arrest development after germination, and stimulation with low amounts of sucrose induces transcription of late embryonic genes and causes ectopic cell division. Our results suggest a model in which RBR acts antagonistically to sucrose by negatively regulating the cell cycle and repressing embryonic genes. Thus, RBR is a positive regulator of the developmental switch from embryonic heterotrophic growth to autotrophic growth. This establishes RBR as a new integrator of metabolic and developmental decisions.
Quist and Chapela claim that transgenic DNA constructs have been introgressed into a traditional maize variety in Mexico, and furthermore suggest that these constructs have been reassorted and ...introduced into different genomic backgrounds. However, we show here that their evidence for such introgression is based on the artefactual results of a flawed assay; in addition, the authors misinterpret a key reference to explain their results, concluding that reassortment of integrated transgenic DNA occurs during transformation or recombination.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Quist and Chapela claim that transgenic DNA constructs have been introgressed into a traditional maize variety in Mexico, and furthermore suggest that these constructs have been reassorted and ...introduced into different genomic backgrounds. However, we show here that their evidence for such introgression is based on the artefactual results of a flawed assay; in addition, the authors misinterpret a key reference to explain their results, concluding that reassortment of integrated transgenic DNA occurs during transformation or recombination.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Cauliflower mosaic virus (CaMV) and Rice tungro bacilliform virus (RTBV) belong to distinct genera of pararetroviruses infecting dicot and monocot plants, respectively. In both viruses, polycistronic ...translation of pregenomic (pg) RNA is initiated by shunting ribosomes that bypass a large region of the pgRNA leader with several short (s)ORFs and a stable stem-loop structure. The shunt requires translation of a 5'-proximal sORF terminating near the stem. In CaMV, mutations knocking out this sORF nearly abolish shunting and virus viability.
Here we show that two distant regions of the CaMV leader that form a minimal shunt configuration comprising the sORF, a bottom part of the stem, and a shunt landing sequence can be replaced by heterologous sequences that form a structurally similar configuration in RTBV without any dramatic effect on shunt-mediated translation and CaMV infectivity. The CaMV-RTBV chimeric leader sequence was largely stable over five viral passages in turnip plants: a few alterations that did eventually occur in the virus progenies are indicative of fine tuning of the chimeric sequence during adaptation to a new host.
Our findings demonstrate cross-species functionality of pararetroviral cis-elements driving ribosome shunting and evolutionary conservation of the shunt mechanism. We are grateful to Matthias Müller and Sandra Pauli for technical assistance. This work was initiated at Friedrich Miescher Institute (Basel, Switzerland). We thank Prof. Thomas Boller for hosting the group at the Institute of Botany.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The development of control strategies is a challenge for optimal use of low-temperature heat in complex energy systems. In the energy system of the considered building, several different combinations ...of active system components lend themselves to supply a given energy demand. Within preceding research, we transformed the considered building into a multi-functional test bench for control techniques that offers optimal conditions for the demonstration and evaluation of control strategies. This paper describes a control strategy for the complex heat pump system based on operation modes. It enables us to integrate a geothermal field into the system with respect to exergetic principles. The paper presents results of the control strategy's first year of operation. It correlates between active operation modes and the respective electrical consumption of the building. We derive the potential of the implemented operation modes for demand response applications. A mode-based control strategy enables the robust and efficient operation of complex building energy systems. We show that the integration of renewable energy sources becomes easy and flexible.
•Generic control algorithm applicable to HVAC supply chains.•Control based on nonlinear minimization of exergy destruction and loss.•Dynamic simulation models used for predictive control.•Distributed ...control based on subsystem optimization and data exchange using look-up tables.•Combination of model-based and feedback control.•Simulation case study evaluating control quality and energy consumption in three scenarios.
Generic model-assisted control algorithms for building energy systems achieve an energy-efficient building operation while the implementation effort is lower than in the case of a taylor-made automation system. In this paper, a generic distributed simulation-model-assisted and exergy-based control algorithm is presented, which is applicable to typical building energy systems (BES). It exploits dynamic nonlinear simulation models from an open-source Modelica library and makes use of sequential neighbor communication. In the supply chains of a BES, the algorithm performs multiple optimizations of small subsystems by considering pre-defined values of pre-defined coupling variables. The objective function is the sum of the exergy destruction and loss, which is based only on measurements without additional information such as monetary costs. In a simulation case study, an open-loop and a closed-loop version of the algorithm are compared to a control system based on rules and feedback controllers that was optimized manually for this particular scenario to provide a benchmark. The tracking error of the closed-loop algorithm is close to the benchmark. The open-loop algorithm achieves an energy consumption close to the benchmark. These results show that the algorithm finds suitable solutions automatically whereas the rule-based control system cannot be expected to perform equally well if boundary conditions were changed.
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