"Frontmatter". In: Plant Genomics and Proteomics
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Christopher A. Cullis - Plant Genomics and Proteomics-J. Wiley & Sons (2004)
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PECIFIC P ROMOTER S EQUENCES A RE R EQUIRED FOR R EGULATED G ENE E XPRESSION There are numerous types of promoters that can regulate gene expression. These promoters can be constitutive or inducible. A constitutive promoter is one that functions in all tissues under all conditions, whereas an inducible promoter is only activated in response to specific stimuli. A constitutive pro- moter may still drive differential levels of expression but should not be com- pletely silent in any tissue. Table 5.1 lists a series of plant promoters and the expression patterns that are observed when they are used in transformation experiments (Lessard et al., 2002). The identification of such specific pro- moters is of use in controlling the expression of a transgene when it is nec- essary or desirable to target the expression of that transgene to specific organs, tissues, or developmental stages. In addition to using plant-specific promoters for this task, a number of chemically induced promoters have been developed to enable a controlled activation of constructs. T HE E FFECT OF E NHANCER E LEMENTS ON G ENE E XPRESSION An enhancer is a DNA sequence that greatly increases the expression of a gene in its vicinity. The sequence can reside upstream or downstream, its T H E E F F E C T O F E N H A N C E R E L E M E N T S O N G E N E E X P R E S S I O N 9 1 9 2 5. C O N T R O L O F G E N E E X P R E S S I O N T ABLE 5.1. E XAMPLES OF D IFFERENT T YPES OF P LANT P ROMO TERS U SED FOR C ONSTRUCTION OF T RANSGENES T ype of pr omoter Name Comments Refer ence Constitutive Ubiquitin Plant-origin pr omoter that drives Plesse et al., 2001 high-level constitutive expr ession, but expr ession level during development may vary Constitutive tCUP Cryptic pr omoter fr om tobacco W u et al., 2003 T issue-specific b -Conglycinin A well-characterized pr omoter Chen et al., 1986 embryo pr omoter that dir ects embryo-specific expr ession T issue-specific Opaque-2 These pr omoters show developmental Rossi et al., 1997 endosperm regulation and expr ession pr omoter T issue-specific 2A1 1 2A1 1 is a fr uit-specific pr omoter V an Haar en and Houck, 1993 fr uit derived fr om tomato T issue-specific Lhcb3 pr omoter Lhcb3 pr omoter is a light-r egulated Ali and T aylor , 2001 leaf leaf-specific pr omoter fr om Arabidopsis T issue-specific Stgan Exclusive expr ession in stolons T rindade et al., 2003 stolon Pollen specific lat52 pr omoter Developmentally r egulated but Bate and T well, 1998 drives high expr ession during pollen maturation Reprinted fr om Metab. Eng . 4, Lessar d et al. Manipulating gene expr ession for the metabolic engineering of plants, 67–79, Copyright 2002, with permission fr om Elsevier . orientation is not fixed, and enhancers can still function when placed at some distance from the transcription start site. These elements do not control whether or not the promoter is active, but they do affect the level of expres- sion. Their effects can be magnified if they are present in multiple copies. They can also have a greater enhancement when present in various combi- nations. For example, analysis of the tCUP promoter (Wu et al., 2003) demon- strated that when the long AT-rich region (between positions –350 and –161 bp relative to the transcription start site) was deleted a significant decrease in promoter activity was observed, whereas oligomerization of this region enhanced activity. A 21-bp sequence (TAGCCCCAA TTTCAAATTCAA) was also identified in a similar fashion and defined a novel cryptic constitutive enhancer element the activity of which was depen- dent on the AT-rich element itself. As well as enhancing gene expression, some cis-acting regions can also silence the expression of adjacent genes. A bidirectional mannopine synthase (MAS) promoter contains elements that both enhance and silence gene expression (Guevara-Garcia et al., 1999; Figure 5.2). The bidirectional pro- moter controls the expression of two genes that encode enzymes for the syn- thesis of mannopine in plant tissues infected with Agrobacterium tumefaciens. The use of different MAS promoter regions in transformation experiments demonstrated that the regulatory properties of these divergent promoters result from the presence of orientation-dependent negative and positive reg- ulatory regions. In particular, some of these elements have the unusual prop- erty of acting as enhancers in one orientation and as silencers in the other. This is an example of the complexity of the control and response elements over a short region adjacent to the gene. Download 1.13 Mb. Do'stlaringiz bilan baham: |
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