![]() thaliana seedlings, developed in the light or darkness, displaying normal or etiolated morphology. (A) Five-day-old, norflurazon-bleached A. Representative pictures are shown in all panels. thaliana seedlings is dependent on MYB12 and MYB111 activity. Although the light-dependent factor AtMYB12 and the light-independent factor AtMYB111 control flavonol glycoside accumulation in different parts of the seedling (Figure 1), as well as in various organs of adult plants, MYB11 activity is restricted to certain organs of adult plants. Because these factors specifically control flavonol glycoside accumulation, AtMYB12, AtMYB11, and AtMYB111 are also referred to as production of flavonol glycosides 1 to 3 (PFG1, PFG2, and PFG3), respectively. These three TFs form subgroup 7 (SG7) of the R2R3-MYB family of TFs. thaliana, namely, MYB11 ( At3g62610) and MYB111 ( At5g49330), which are structurally and functionally related to MYB12. Two additional R2R3-MYB TFs were identified in A. AtMYB12 was found to be a flavonol-specific activator of flavonoid biosynthesis, with the two flavonoid biosynthesis genes CHS ( At5g13930, encoding chalcone synthase) and FLS1 ( At5g08640, encoding flavonol synthase) as its primary targets. The Arabidopsis thaliana protein MYB12, encoded by the locus At2g47460, is a member of the R2R3-MYB family of TFs that share the MYB DBD. ![]() įlavonols are products of flavonoid biosynthesis, which forms various C15 molecules that vary in oxidation level and decoration, and they accumulate in their glycosylated form in the vacuoles of plant cells. Domains reported to be responsible for transcriptional activation contain acidic, glutamine-rich, or proline-rich stretches of amino acids. The latter two might both be part of the DBD, and the sum of the functional regions defines the characteristics, the localization, and the regulatory role of a given TF. A typical modular TF usually contains, in addition to a DBD that is used to sort TFs into TF families, a transcription regulation domain, a nuclear localization signal, and often a dimerization interface as well. The identification of distinct regulatory domains allows the investigation of interactions with other proteins present in initiation complexes. Although factors that do not contain a DBD are sometimes regarded as TFs, the standard TF consists of a domain that is responsible for sequence-specific binding to regulatory cis-acting elements in promoters, and additional domains with regulatory functions. These complexes direct the transcriptional machinery, composed of RNA polymerase II and many additional factors, to the start site of gene transcription. The process is dependent on the assembly of regulatory multiprotein complexes at promoter sequences, which include TFs responsible for cell type-specific or stimulus-responsive gene expression. ![]() An essential component of gene regulation is the transcriptional activation of genes, which takes place at promoters. Therefore, understanding plant TF function is an important step toward understanding plant development, adaptation, and evolution. Because many biological processes in metazoans, including plants, are regulated at the level of transcription, the evolution of many traits during the domestication of plants has not surprisingly been associated with changes in TFs or their regulation and/or their expression patterns. They are largely responsible for the selectivity in gene regulation, and are often expressed in a tissue-specific, developmental stage-specific, or stimulus-dependent manner. Generally, TFs contain a sequence-specific DNA-binding domain (DBD). Transcription factors (TFs) are proteins that are capable of activating and/or repressing transcription.
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