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Promoter of a cotton fibre MYB gene functional in trichomes of Arabidopsis and glandular trichomes of tobacco.

ABSTRACT: Cotton fibres are unicellular seed trichomes. Our previous study suggested that the cotton R2R3 MYB transcript factor GaMYB2 is a functional homologue of the Arabidopsis trichome regulator GLABRA1 (GL1). Here, the GaMYB2 promoter activity is reported in cotton (Gossypium hirsutum), tobacco (Nicotiana tabacum), and Arabidopsis plants. A 2062 bp promoter of GaMYB2 was isolated from G. arboreum, and fused to a beta-glucuronidase (GUS) reporter gene. In cotton, the GaMYB2 promoter exhibited activities in developing fibre cells and trichomes of other aerial organs, including leaves, stems and bracts. In Arabidopsis the promoter was specific to trichomes. Different from Arabidopsis and cotton that have unicellular non-glandular simple trichomes, tobacco plants contain more than one type of trichome, including multicellular simple and glandular secreting trichomes (GSTs). Interestingly, in tobacco plants the GaMYB2 promoter directed GUS expression exclusively in glandular cells of GSTs. A series of 5'-deletions revealed that a 360 bp fragment upstream to the translation initiation codon was sufficient to drive gene expression. A putative cis-element of the T/G-box was located at -233 to -214; a yeast one-hybrid assay showed that Arabidopsis bHLH protein GLABRA3 (GL3), also a trichome regulator, and GhDEL65, a GL3-like cotton protein, had high binding activities to the T/G-box motif. Overexpression of GL3 or GhDEL65 enhanced the GaMYB2 promoter activity in transgenic Arabidopsis plants. A comparison of GaMYB2 promoter specificities in trichomes of different plant species with different types of trichomes provides a tool for further dissection of plant trichome structure and development.

SUBMITTER: Shangguan XX

PROVIDER: S-EPMC2561158 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundSesquiterpene lactones are characteristic metabolites of Asteraceae (or Compositae) which often display potent bioactivities and are sequestered in specialized organs such as laticifers, resin ducts, and trichomes. For characterization of sunflower sesquiterpene synthases we employed a simple method to isolate pure trichomes from anther appendages which facilitated the identification of these genes and investigation of their enzymatic functions and expression patterns during trichome development.ResultsGlandular trichomes of sunflower (Helianthus annuus L.) were isolated, and their RNA was extracted to investigate the initial steps of sesquiterpene lactone biosynthesis. Reverse transcription-PCR experiments led to the identification of three sesquiterpene synthases. By combination of in vitro and in vivo characterization of sesquiterpene synthase gene products in Escherichia coli and Saccharomyces cerevisiae, respectively, two enzymes were identified as germacrene A synthases, the key enzymes of sesquiterpene lactone biosynthesis. Due to the very low in vitro activity, the third enzyme was expressed in vivo in yeast as a thioredoxin-fusion protein for functional characterization. In in vivo assays, it was identified as a multiproduct enzyme with the volatile sesquiterpene hydrocarbon delta-cadinene as one of the two main products with alpha-muuorlene, beta-caryophyllene, alpha-humulene and alpha-copaene as minor products. The second main compound remained unidentified. For expression studies, glandular trichomes from the anther appendages of sunflower florets were isolated in particular developmental stages from the pre- to the post-secretory phase. All three sesquiterpene synthases were solely upregulated during the biosynthetically active stages of the trichomes. Expression in different aerial plant parts coincided with occurrence and maturity of trichomes. Young roots with root hairs showed expression of the sesquiterpene synthase genes as well.ConclusionThis study functionally identified sesquiterpene synthase genes predominantly expressed in sunflower trichomes. Evidence for the transcriptional regulation of sesquiterpene synthase genes in trichome cells suggest a potential use for these specialized cells for the identification of further genes involved in the biosynthesis, transport, and regulation of sesquiterpene lactones.

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Promoter of a cotton fibre MYB gene functional in trichomes of Arabidopsis and glandular trichomes of tobacco.

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