Enhancing plant growth and biomass production by overexpression of GA20ox gene under control of a root preferential promoter.

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 diameter, etc. To avoid these effects, we identified and employed different tissue-specific promoters for GA20ox overexpression. In this study, we examined the utility of At1g promoter to drive the expression of GUS (β-glucuronidase) reporter and AtGA20ox genes in tobacco and Melia azedarach. Histochemical GUS assays and quantitative real-time-PCR results 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 improved plant growth and biomass of both tobacco and M. azedarach transgenic plants. Stem length as well as stem and root fresh weight 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 root xylem width with xylem to phloem ratio over 150-200% as compared to WT plants. Importantly, no significant difference in leaf shape and size was observed between At1g::AtGA20ox transgenic and WT plants. 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.