Over-expression of glutamine synthetase genes Gln1-3/Gln1-4 improved nitrogen assimilation and maize yields

Abstract

In agriculture, certain fertilizers that contain nitrogen generally tend to provide the most macronutrients for plant growth and development. The cDNAs of Gln1-3 and Gln1-4 genes, encoding glutamine synthetase isoenzymes (GS1), were fused to the rice actin1 promoter and over-expressed in the inbred maize line DH9632 by Agrobacte¬rium-mediated genetic transformation. PCR assays demonstrated the integration of these genes in six transgenic lines. Transcription of Gln1-3 or Gln1-4 in the transformants was also confirmed by semi-quantitative RT-PCR and qRT-PCR; the transgenic lines had significantly higher expression compared with wild type. Transgenic lines L2 and L7 expressed the most Gln1-3 and Gln1-4 mRNA, respectively, and had the most enzyme activity in leaves below the ear after pollination for 14 days. Over-expression of these two genes led to increased chlorophyll con¬tent and improved photosynthesis after 14 days. In addition, yield-related traits such as ear length, ear diameter, ear weight, grain weight per ear, and hundred-kernel weight were improved in the transgenic lines. The plot yield of transgenic L2 was increased by approximately 20%. These results suggest that overexpression of Gln1-3 and Gln1-4 in maize improves yields and enhances nitrogen using efficiency. Thus, transgenic lines overexpressing Gln1-3 or Gln1-4 in maize could potentially be used in maize breeding.