Background: Overexpression of GA20 oxidase gene has been a recent trend for improving plant growth and biomass. Constitutive expression of GA20ox has successfully improved plant growth and biomass in several plant species. However, the constitutive expression of this gene causes side-effects, such as reduced leaf size and stem diameters, etc. To avoid these effects, different tissue-specific promoters had been identified and employed for GA20ox overexpression. In this study, we demonstrate the potential of At1g, a root-preferential promoter, for GA20ox expression to enhance plant biomass.
Results: We examined the utility of At1g promoter to drive the expression of GUS (b-glucuronidase) reporter and GA20ox genes in tobacco and Melia azedarach. Histochemical GUS assays in tobacco showed that At1g was a root-preferential promoter whose expression was particularly strong in root tips. The ectopic expression of AtGA20ox gene under the control of At1g promoter showed the improved plant growth and biomass of both tobacco and M. azedarach transgenic plants compared to wild-type (WT) control plants. Stem length as well as stem and root fresh weights increased by up to 1.5-3 folds in transgenic tobacco and 2 folds in transgenic M. azedarach. Both tobacco and M. azedarach transgenic plants showed increases in the root xylem width, xylem over phloem ratio by 50%-100% as compared to WT plants. Importantly, no significant difference in the leaf shape and size was observed between At1g::AtGA20ox transgenic and WT plants. Moreover, transgenic M. azedarach showed a 135% increase in stem diameter even though no change was found in transgenic tobacco.
Conclusions: These results demonstrate the great utility of At1g promoter, when driving AtGA20ox gene, for growth and biomass improvements in woody plants and potentially some other plant species.