Una red de regulación génica o red de regulación genética (GRN) es una colección de segmentos de ADN en una célula que interactúan entre sí ( indirectamente a través de su ARN y productos de expresión de proteínas). Control de la expresión génica en eucariontes Niveles: DNA transcripcional postranscripcional traduccional postraduccionales. Hay disponibles más de 1,8 millones de ensayos de expresión génica TaqMan prediseñados que cubren más de 30 especies en formatos de un solo tubo.
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Chilean Journal geniva Agricultural Research 69 2: In crops, this variation from ideal growth conditions often results in lower yields and a high economic impact for producers and consumers. Understanding the mechanisms involved in the response of plants to adverse environmental conditions is, without a doubt, the first step in the generation of crops geniica higher tolerance to stress. Research at the level of genes genomicsproteins proteomicsmetabolites metabolomicsindividuals physiology, systemic biology and communities ecology has been fundamental in the current understanding of the response of plants to stress.
In particular, a huge development in the field of genomics in the last 20 years has led to a deeper understanding in areas such as gene expression, organization and its relationship to stress tolerance. Functional genomics studies the function of genes of an organism and focuses on dynamic processes such as transcription, translation, interaction of genes and how they are related to different phenotypes.
Connecting gene function and traits relevant to agriculture, such gemica yield, plant structure and tolerance to adverse environmental conditions has become of utmost interest considering global warming, urban development and an ever increasing population demand for food.
Genome analysis has been mostly limited to model plants that fulfil some specific requirements such as: In particular, two of the most important model species are Arabidopsis thaliana and rice Oryza sativa L.
Besides its importance as a crop, rice has a high degree of synteny with genomes of other cereals plants, such as maize, wheat, barley and other grasses because their genomes share a considerable similarity in their organization, as well as sequence similarity Gale and Devos, ; Bowers et al.
Great advances in the comparison of genomes and transcriptomes of different organisms have contributed to the development of comparative genomics as one of the most promising fields in the area Gale and Devos, ; Caicedo and Purugganan, In this way, finding variations in the genome or the transcriptome from the current model species related to interesting agronomic traits is of the highest importance for crop biotechnology van de Mortel and Aarts, The objective of this review is to summarize expresio techniques used in gene expression analysis in plants and their relevance to abiotic stress research.
Special emphasis is given to issues to be considered when comparing performance of crops in controlled conditions and in the field. Techniques used for evaluating gene expression in functional genomics studies A fundamental step in any functional genomics study is the analysis of gene expression. One of the greatest strengths of genomics compared to other disciplines is the prospect of analyzing the expression of thousands of genes expresipn, resulting in a more comprehensive picture of changes occurring in the transcriptome across different conditions Green et al.
The technology available for the analysis of gene expression can be divided into two categories: Closed systems are characterized by a finite number of genes that can be assessed by virtue of their inclusion by selection.
Therefore, the coverage of genes will be related to the completeness of the knowledge of the genome being studied, limiting this kind of analysis to the most well characterized species or systems Green et al. Typically, closed systems such as microarrays Table 2 and real-time polymerase chain reaction PCR have been extensively used in gene expression analysis in plants Ma et al.
On the other hand, with open systems there is no need for previous knowledge of the genome or transcriptome of the organism. Worth mentioning are sequencing technology and digital gene expression DGE that have recently been used to study the transcriptome of different organisms and promise to become an efficient and cost-effective alternative with high potential in crop research Mikkilineni et al.
Open and closed systems should not be considered as competitors, but rather as complementary technologies to be used depending on the subject to be analyzed and the objectives of the research. Most commonly used techniques for gene expression analysis in plants. Gene expression analysis through microarrays in expresiln crops. The amount of material available is an important variable to be considered in the selection of a technology for gene expression analysis.
Another variable to keep geinca mind is the selection of the sample to be analyzed. In this regard, the latest advances in microdissection techniques allow extraction of RNA from specific tissues and individual cells, opening the possibility of a highly detailed analysis and a expreskon reduction of noise generated by the natural heterogeneity of plant organs Brandt, ; Lee et al.
Abiotic stress variables to be considered in functional genomics studies The aim of most functional genomics studies concerned with abiotic stress is to relate gene function to traits of plant performance under adverse environmental conditions.
A recurring question is how representative are growth chamber studies compared to field studies. In this respect there is a lack of studies that comprehensively evaluate correlations between growth chambers and the field in terms of plant performance.
The issues in what follows should be considered when designing an experiment in controlled conditions with possible applications in the field: Most studies so far have been focused on the response to just one kind of stress. This strategy has led to key discoveries expreesion otherwise would not have been possible and that have helped us to understand in greater depth the way plants respond to stress.
However, it should be noted that plants in the field are usually exposed to more than one stress simultaneously. This combination of stresses is fundamental to understand differences between the performance of crops in controlled growth chambers and in the field Knight and Knight, ; Mittler, Length of the treatment.
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Despite the fact that valuable data can be obtained from short term experiments, it is longer term plant performance with respect to biomass, yield data and the degree of recovery from stress that has the most value in agriculture Vinocur and Altman, Intensity of the treatment. For example, the response of a plant to chilling stress will be different from the response to freezing stress, considering that the latter can lead to ice formation.
The intensity of the treatment will also be of the utmost importance for screening purposes, especially when a ranking of tolerance to stress is to exresion established.
Stage of crop development. Clearly, tolerance to stress is different throughout the lifecycle of any plant and the consequences of exposure to stress may also vary. As an example, rice is especially susceptible to low temperature during the germination and reproductive stages Board et al. In the first, a possible consequence is the failure to germinate. Exposure to cold during the reproductive stage will induce sterility rather than have an effect on plant survival. In this regard, it is important to have plants in similar stages of development when screening for tolerance to stress, especially with cultivars that complete their lifecycle at different times.
Designing experiments in functional crop genomics must consider all these recommendations in order to successfully extrapolate results to the field. exptesion
Red de regulación génica – Wikipedia, la enciclopedia libre
As well, it is important to keep in mind genotype x environment interactions G exprfsion E when evaluating the performance of any genotype in the field by including the range of adaptation of new varieties to different environments and the consistency of their performance over genida. In order to effectively recognize G x E in any breeding program, there must be a comprehensive characterization of the genotypes and environments being assayed, and these considerations are valid for genomics as well.
Functional genomics and stress response in crops Abiotic stresses are estimated to reduce yield to less than half compared to the potential under ideal growing conditions Boyer, Unlike plant expresionn to biotic stresses, which is mostly monogenic, tolerance to abiotic stresses are generally multigenic, quantitative and complex traits controlled by quantitative trait loci QTL.
This has clear consequences for the development of plants that are more tolerant to abiotic stresses by genetic engineering Vinocur and Altman, A further complication is that some genes may exert control over different traits, resulting in unwanted changes in agronomic plant traits. Cold expresin drought tolerance in crops constitute highly desired traits in Chile given the expreslon consequences of the current climatic trend of very low temperatures in winters and severe drought in summers.
Cold stress in plants causes a reduction in enzyme activities, reaction rates, energy imbalance and is accompanied by changes in the transcriptome, proteome and metabolome Guy et al.
On the other hand, when plants are exposed to drought, there exresion a characteristic response of a partial-to-total stomatal closure, resulting in a reduction of CO 2 uptake, transpiration and a major impact for photosynthesis and source-sink relationships Chaves et al.
The consequences of any stress will depend on its intensity. As an example, chilling temperatures will be responsible for lower metabolic rates and energy imbalance, while freezing temperatures will additionally cause membrane injury and severe dehydration when ice forms Graham and Patterson, ; Thomashow, ; Pearce, Drought and temperature stress might occur alone or in combination at any stage in plant development, causing reduced grain weight and yield loss Sreenivasulu et al.
It is known that exposure to one kind of stress usually involves an increased tolerance to other stresses given that similar effects are shared at the cellular level.
As an example, freezing temperatures, low water availability and high salinity can all cause lowering of the cellular osmotic potential and thereby activate osmotic stress responses Langridge et al. In this regard, it is not unexpected to find promoters that have sequences for transcription factors involved in drought, salt and cold response, suggesting points of convergence at the molecular level Knight and Knight, These results, added to a high overlapping of genes involved in the response to cold, drought and high salinity, suggest an intricate coordination of the response to genixa stresses in plants at molecular level Kreps et al.
At first glance, a shared regulatory network involved in the response gwnica multiple stresses opens possibilities for the development of multiple-stress-tolerant plants. However, it must not be forgotten that the combination of some stresses might require conflicting henica antagonistic responses. In this way, the acclimation of plants exoresion this combination would require an appropriate response to each individual stress, as well as compensation and adjustment for expreion of the expreslon aspects involved Exoresion, ; Rizhsky et al.
As an example, when plants are exposed to drought, their stomata are closed, which is clearly an antagonistic response if the plant is simultaneously exposed to heat, when transpiration is necessary to reduce leaf temperature. Higher tolerance to abiotic stress could be achieved by increasing protective mechanisms antioxidants, non-photochemical quenching, etc.
In this matter, the capacity of recovery from stress is usually overlooked, despite its relevance considering that cycles of stress and recovery are common under natural conditions and may have a major impact in yield Vinocur and Altman, In this regard, a successful approach in determining gene function comes from sequence comparison with databases and, more recently, the use of coexpression modules with promising expresioh Subramanian et al.
Comparative genomics constitute an increasingly important field in order to understand how similar model species and crops are, and how to transfer knowledge obtained from model species to applications in agriculture Paterson et al. ex;resion
12. Control de la expresión génica en eucariontes
In this matter, the choice of putative candidate genes is facilitated by the conservation of gene sequences, order and distribution among species and the existence of similar functional gene categories in morphologically similar organs Brady et al.
Changes in the transcriptome among related species under stress reported by different groups are usually hard to compare since treatments are usually performed with different tissues, exposure times, intensities, and using different technologies.
In this way, a careful experimental design with related plants that present different degrees of tolerance to stress can be extremely informative. A successful example is the comparison of the transcriptome of winter and spring wheat, cultivars with different tolerance to cold, exposed to low temperature. This study reports the correlation of gene expression kinetics with tolerance to low temperature, a subject usually overlooked that emphasizes the importance of sampling in functional genomics studies Gulick et al.
The availability of the complete genome sequence of some model plants, such as O. This constitutes a new powerful technology that has already made possible the identification of several unannotated transcripts responsive to abiotic stress Gregory et al. However, finding a gene responsive to stress does not necessarily guarantee its participation in tolerance to this condition. Identification and sequencing allow assigning a putative function to a sequence when a significant homology with genes of known function is found.
These results are then usually complemented with a proper validation by the use of transgenics. This approach has been especially important in the discovery of several candidate genes in crops in the last decade and, in some cases, it has led to significant improvements in tolerance to stress Table 3. An example showing the importance of transcription factors in the response to stress was observed in transgenic rice for the transcription factor ABF3 Arabidopsis ABRE-binding factor 3which showed increased tolerance to drought Oh et al.
Maize and rice transgenics and stress tolerance. It is also interesting that different responses are obtained by manipulation of genes within the same family.
A good example are calcineurin B-like protein-interacting protein kinases: These results demonstrate the participation of single genes in tolerance to a particular stress. However, it has also been shown that manipulation of single genes can lead to increased tolerance to more than one kind of stress.
As an example, the constitutive expression of the transcription factor DREB1A Arabidopsis DRE-binding protein 1 in rice determined increased tolerance to drought and salt stress. Similar multi-tolerance effects were observed by over-expressing genes such as OsCDPK7, a genicaa protein kinase, which resulted in rice with increased tolerance to cold, salt and drought stress Saijo et al.
Manipulation of genes with roles other than regulation, such as detoxification, protection and osmotic regulation, has also resulted in increased tolerance to stress in plants Xu et al. Targeting effector, rather than regulatory genes, may result in fewer side effects considering the unwanted activation of responsive genes involved in other metabolic pathways. Despite similarities among different plants, it must not be forgotten that species such as wheat and barley, with far less characterized genomes compared to model plants, may offer unique and interesting features.
Their high level of abiotic tolerance and diversity may provide important resources for validation of candidate genes and accelerate important breeding programs Langridge et al. Performance in the field of these species suggests that greater tolerance to abiotic stress is still achievable for other crops if proper research is conducted and should stimulate the exploration of new technologies and alliances between scientists and farmers.
Its application in crop research is just starting as technologies are becoming more accessible and cost-effective and are expected to fuel huge advances in agriculture in the coming decades. Currently, the importance of biotechnology is being acknowledged by breeding programs around the world and is resulting in the development of new techniques and approaches to increase crop tolerance to stress.
Whether Chile will continue to increase its share in the food market worldwide will depend on its ability to develop sustainable and cutting-edge crop research in the future.