Gibberellin biosynthesis and signalling in Arabidopsis root growth

Using targeted expression of a constitutively active repressor of GA signalling Susana Ubeda-Tomas et al., (2007) demonstrated that GA action in endodermal cells is necessary for correct root growth. However, GUS studies have shown the final and penultimate GA-biosynthetic genes are not expressed in the endodermis, indicating movement of GAs may be required. This study used the targeted mis-expression of GA degrading enzymes in Col-0 and the attempted targeted rescue of GA biosynthetic and signalling mutants, using the corresponding GA metabolic or signalling component, to gain an insight into the localisation of important GA biosynthesis and signalling sites. This study has demonstrated that GA12 can be made by epidermal, cortical and endodermal cells. However, the ground tissue of the elongation zone does not contain GA12 due to the early GA biosynthetic enzymes only being expressed within cells with a close proximity to the QC. Subsequently the 20-oxidation converts GA12 to GA15, to GA24 to GA9. These reactions mobilise GA allowing it to move from the meristematic region to the elongation zone. GA20ox and GA3ox activity is required in both the meristematic region and the elongation zone for correct root growth to occur. In addition, GA metabolic components are subject to tissue specific GA feedback regulation as a result of post-transcriptional processing and/or post-translational modifications to their protein stability. GA perception in any tissue of the elongation zone can promote complete cell elongation, suggesting that any one tissue can elongate it neighbours, or that each cell is capable of releasing a signal to ensure they all elongate proportionally. The transcriptional network within the endodermis has a disproportionately important role in GAs regulation of cell division within the root proximal meristem but GA action in other cell types is also required. The cambian and bundle sheath cells in aerial tissue like the endodermis in the root contain an important transcriptional network that promotes GA dependant growth.EThOS - Electronic Theses Online ServiceGBUnited Kingdo