![]() Examples of tissue specific genes in maize include the zeins (Kriz et al., (1987)) which are abundant storage proteins found only in the endosperm of seed. “Regulated” promoters are typically expressed in only certain tissue types (tissue specific promoters) or at certain times during development (temporal promoters). Examples of constitutively expressed genes in maize include actin and ubiquitin. ![]() Genes encoding proteins with housekeeping functions are often driven by constitutive promoters. Expression from a constitutive promoter is more or less at a steady state level throughout development. “Constitutive” promoters are expressed in most tissues most of the time. Promoters can be classified into two general categories. Such sequences are often found within 400 bp of the CAP site, but may extend as far as 1000 bp or more. Other sequences conferring tissue specificity, response to environmental signals or maximum efficiency of transcription may be found interspersed with these promoter elements or found further in the 5′ direction from the CAP site. ![]() In plants the CCAAT “box” is sometimes replaced by the AGGA “box”. However, genes which have this sequence appear to be efficiently expressed. This sequence is not well conserved in many species including maize. Further upstream, often between −80 and −100, there can be a promoter element with homology to the consensus sequence CCAAT. In most instances the TATA box is required for accurate transcription initiation. Most maize genes have a TATA box 29 to 34 base pairs upstream of the CAP site. Eukaryotic promoters generally contain a sequence with homology to the consensus 5′-TATAAT-3′ (TATA box) about 10-35 base pairs (bp) upstream of the transcription start (CAP) site. Initiation of transcription of a gene is regulated by a sequence, called the promoter, located upstream (5′) of the coding sequence. The DNA sequences involved in these regulatory processes can be located upstream, downstream or even internally to the structural DNA sequences encoding the protein product of a gene. Regulation can be transcriptional or post-transcriptional and can include, for example, mechanisms to enhance, limit, or prevent transcription of the DNA, as well as mechanisms that limit the life span of the mRNA after it is produced. For example, a root specific or root preferential expression in maize would be highly desirable for use in expressing a protein toxic to pests that attack the roots of maize.Ĭells use a number of regulatory mechanisms to control which genes are expressed and the level at which they are expressed. Depending upon the particular project, there may be a need for constitutive expression, which directs transcription in most or all tissues at all times, or there may be a need for tissue specific expression. The selectable marker may not require the same expression level or pattern as that required for the gene of interest. To express agronomically important genes in crops at desired levels through genetic engineering requires the ability to control the regulatory mechanisms governing expression in plants, and this requires access to suitable regulatory sequences that can be coupled with the genes it is desired to express.Ī given project may require use of several different expression elements, for example one set to drive a selectable marker or reporter gene and another to drive the gene of interest. However, obtaining desired levels of expression remains a challenge. Through the use of recombinant DNA technology and genetic engineering, it has become possible to introduce desired DNA sequences into plant cells to allow for the expression of proteins of interest. Specific constructs of the invention use novel regulatory sequences derived from a maize root preferential cationic peroxidase gene. More particularly, the invention provides DNA sequences and constructs that are useful to control expression of recombinant genes in plants. This invention relates to genetic engineering of plants. This application claims the priority of U.S.
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