Abstract
Extensin, a hydroxyproline-rich glycoprotein, is abundant in the cell walls of higher plants. The regulation of the Brassica napus extA extensin gene was investigated by the construction of a series of 5' promoter truncations linked to the P-glucuronidase (gus) reporter gene. These truncations terminated -940bp, -789bp, -664bp, -433bp and -159bp, relative to the transcription start site. Transgenic tobacco plants containing these promoter truncations were regenerated using the disarmed Agrobacterium vector pBI101.2, and extA-driven gus expression analysed.Fluorescence assays located an activator region between -159bp to -433bp and a repressor region between -664bp to -789bp. Histochemical analysis of transgenics containing the -940bp, -789bp and -664bp truncations found that GUS activity was localised solely in the phloem, whereas the -433bp and -159bp truncations showed GUS activity in all cell-types. The phloem-activating region was found to be located within -159bp of the transcription start. A negative regulatory region located between -664bp and -433bp repressed expression in non-phloem cells. In areas of the plant subject to tensile stress, such as axillary branch nodes, the repression exerted by the negative regulatory region was overcome, and expression was seen in all cell-types. It appears therefore, that the activation of the extA gene in response to tensile stress is controlled by a negative regulatory element.
Northern hybridisations demonstrated that extA transcripts were induced in wounded stems and petioles, and a wound-activating region was located between -940bp and -3500bp.
Thus, the extA gene is under complex control, being regulated by at least five positively- and negatively-acting cis-regions, which control wound-inducibility, activation in response to tensile stress, and quantitative expression levels. A number of potential cis-elements have been identified by their similarity to known plant transcription factor binding sites. The actual role of these potential elements in the regulation of extA gene expression remains to be determined.
| Date of Award | 30 Sept 1998 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Sir william Roberts Memorial Studentship |
| Supervisor | Anil Shirsat (Supervisor) |