Overexpression Of ZmDWF4 Improves Yield Traits In Maize

Maize is one of the most important crops. It is important to meet the needs of foodstuffs in the world that the yield of maize is improved. Molecular breeding can directionally change plant genetic traits using biological techniques, and has become an important approach in maize breeding.Brassinosteroid (BR) plays important roles in various processes of plant growth and development. The DWF4 gene encodes a rate-limiting mono-oxygenase named sterol C-22 hydroxylase, which mediates the C-22 hydroxylation in the pathway of BR biosynthesis. Due to its key role in maintaining BR homeostasis, the DWF4 gene has become a target for genetic manipulation of BR levels.Based on the preferred Agrobacterium-mediated transformation system in maize using immature embryos, we successfully introduced ZmDWF4 which plays an important role in BR biotechnology into the Qi 319 inbred. Seven hundred and twenty resistant plants from 2833 explants and the regeneration efficiency of resistant plants is about 25%.To identify the resistant plants, firstly, we carried out the PCR experiment using two pairs of specific primers that amplify NPTâ…¡and ZmDWF4, respectively. The results of PCR showed we obtained 22 positive plants from 720 resistant plants. Secondly, we used resistance gene NPTâ…¡as probe to detect parts of positive plants by southern blot. The result showed that exogenous ZmDWF4 had successfully integrated into the maize genome. In addition, the detection using semi-quantitative RT-PCR showed the expression of ZmDWF4 in the positive plants was significantly increased. The molecular detection using PCR, southern blot and semi-quantitative RT-PCR indicate that we have successfully obtained transgenic plants.To analysis the phenotypic effects resulting from ZmDWF4 over-expression, we measured the plant height, number and length of internodes, cell length, size and weight of seeds and senescence of leaf tissue of maize transgenic lines and wild type plants. The results are as follows. (1) The transgenic maize displayed vigorous growth. The results show the transgenic plants had more internodes numbers and the length of internodes is longer than WT did. The length of transgenic plants increased 17% or more.(2) Photosynthesis analysis indicated Pn of transgenic plants were higher than that of wild type plants. It revealed evidence of enhanced CO2 assimilation and improved photosynthesis.(3) Statistics of leaf senescence of transgenic maize and wild type plants showed that the leaves of wild type plants have been completely dead at 122 days after sowing, however, most of leaves of transgenic plants were dead at 139 days after sowing. It indicates senescence of transgenic plants has been delayed.(4) The length and diameter of transgenic ear, the size and weight of grain all increased. The kernel weight of transgenic plants was significantly higher than wild type grain.In summary, overexpression of ZmDWF4 gene not only increased vegetative growth and plant height, but also delayed leaf senescence. So, it has potential to enhance seed yield in maize. In addition, our work will be helpful to molecular breeding of maize.