Improvement of biomass production in transgenic Meliaazedarach L. plants by the expression of a GA20-oxidase gene

Melia azedarach L. is a multipurpose timber tree that is important in forestry plantations. Genetic modification to improve the growth rate and wood quality is important to produce new cultivars of M. azedarach. In this study, the effects of AtGA20ox gene expression on plant growth, wood formation, and biomass production in transgenic M. azedarach plants were investigated. AtGA20ox was inserted into the binary vector pBI101 under the control of the xylem specific promoter CAD4 and transferred to M. azedarach via Agrobacterium-mediated method. The integration and expression of the transgenes were confirmed using PCR, RT-PCR, and Southern blotting. The specificity of CAD4 in the xylem was indicated by the higher expression of the AtGA20ox gene in the stem tissues compared to the leaves. The larger stem diameter resulted from higher xylem cell numbers and a wider xylem zone in all the transgenic plants. In addition, the transgenic plants also grew more quickly. Consequently, transgenic M. azedarach increased its biomass production 2- to 4-fold compared to the wild-type plants at 90 days under greenhouse conditions. Our results suggest that the expression of ectopic AtGA20ox under the control of a xylem-specific promoter is an appropriate method to improve plant growth, biomass production, and wood formation in M. azedarach and other forestry plants.