Cloning And Functional Analysis Of GA20-oxidase And GASA Genes In Populus Deltoides×Populus Nigra

In most tree-breeding programs worldwide, enhancing the trees’height and growth rates are important aims. Now many studies have been done to advance that task by increasing the concentration of the plant hormone gibberellin, or its signalling. The plant hormone gibberellin (GA) regulates numerous developmental processes throughout the life cycle of plants. The most studied gibberellin biosynthesis enzyme is the GA20-oxidase which catalyses the rate limiting step of the pathway and is of particular importance in determining GA concentration in many plant species. Although the early signaling pathway of the hormone has been elucidated, the downstream molecular events linking signaling to developmental responses are largely unknown. GASA(GA-Stimulated in Arabidopsis) family usually is regulated by GA in Arabidopsis thaliana. Studies in various plant species have suggested the role of these genes in cell growth and differentiation. This stduy about functional analysis of GA20-oxidase and GASA genes would provide some clues to raise the rapid-growing strain of poplar and elucidate the function of GASA proteins in the gibberellin signal transduction pathway.We cloned the GA20-oxidase gene from R270(Populus deltoides×Populus nigra) and Arabidopsis thaliana separately by the PCR method. Transgenic plants were obtained through the flower dipping method mediated by Agrobacterium tumefaciens and we analyzed the biological function of poplar GA20-oxidase gene. The results showed that compared to the phenotype of overexpressing ATGA20oxl, overexpression of PdGA20ox resulted in earlier seedling establishment and flowering, longer hypocotyl and primary root, larger leaf areas, increasing stem elongation.Based on the previous results of Microarray analysis, some members of the GASA family, the PdGASA1, PdGASA2, PdGASA4were cloned. To study the biological function of PdGASA, transgenic Arabidopsis plants that constitutively expressed the PdGASA genes were constructed. Overexpression of PdGASA resulted in early seedling establishment, longer primary roots, larger leaf areas and increasing stem elongation. In vitro-grown poplar seedlings that were treatmented by phytohormone, the effects on the transcript levels of PdGASA were monitored. The results suggested that the expression patterns of the three poplar GASA genes were related to gibberellin.The poplar has been transformed separately with GA20-oxidase and PdGASA genes, and two poplar lines were gained. The results of PCR indicated that the PdGA20ox and PdGASA2genes had expressed separately in the two lines. The efficient transformation system was established in poplar. The results lay a foundation for promoting the study of the mechanisms of rapid growth in poplar.