The Effect Of Mutant ADP Glucose Pyrophosphorylase Gene On The Starch Content Of Transgenic Maize Kernels

Starch is an important raw material in food and chemical industry. At present, starch production in the world is about46million tons, of which90%is corn starch. Corn starch has been used to product more than2500kinds of industrial products and plays an important role in human life. Therefore, the breeding of high-starch corn to meet the human needs has great practical significance.Most of corn starch is synthesized in the corn grain endosperm. In this process, ADP-glucose pyrophosphorylase is the rate-limiting enzyme of starch synthesis pathway. It plays a crucial role in maize kernel development and starch synthesis. It is possible to improve the heat stability of AGPase and promote the synthesis of starch by the modification of AGPase gene.In this paper, in order to get the transgenic plants that has been produced by the transformation of the mutant AGPase gene from maize inbred lines Chang7-2and Zheng58, the progeny of transformed plants were screened by herbicide and identified by PCR assay. And we choose transgenic lines from the different independent transformation events to study the transgene expression, starch synthesis, grain yield and other agronomic traits of the transgenic homozygous plants. The result of Real-time quantitative RT-PCR analysis and enzymatic determination of AGPase activity at different grain filling stage (10DAP,15DAP,20DAP,30DAP) were accomplished. In the grain development AGPase activity showed a gradual increase at early stage, but peaked at20DAP, followed by a slow decline. And the expression of AGPase gene in transgenic plants is significantly higher than the non-transgenic plants (Chang7-2and Zheng58) in the process, and the enzyme activity changes correspondingly. Between the transgenic plants with the transgene mutant Sh2hs33and the transgenic plants with the transgene mutant Sh2hs33and Bt2gene slight differences were existent in the expression of AGPase gene and AGPase activity. The determination of starch content of mature kernels showed that the changes of the kernel starch content present a consistent trend with the gene expression and AGPase activity changes. In the transgenic lines transformed with mutant Sh2hs33and Bt2gene, the starch content increased to71%-74%compared with the wild-type (Chang7-2) or65%(Zheng58), respectively, about13.6%over the wild type. And in the transgenic lines transformed mutant Sh2hs33gene, the starch content in transgenic plants increased to71%-73%compared with the wild-type (Chang7-2) or65%(Zheng58), respectively, about12.3%over the wild type.100grain weight also had significant increase in transgenic lines, there were about20%(Sh2hs33) and22%(Sh2hs33Bt2) increase compared with non transgenic plant Chang7-2, and22%(Sh2hs33) and18%(Sh2hs33Bt2) increase compared with non transgenic plant Zheng58.In this work, the use of the maize endosperm-specific promoter, zein gene promoter, greatly enhanced AGPase gene expression in maize endosperm. It was reported the modified Sh2gene could enhance the thermal stability of AGPase. Maize plants could encounter over-thermal environment at the grain filling stage. It is significant to improve AGPase activity under the environment by enhancement of the thermal stability of the enzyme, which could accelerate the starch synthesis in endosperm and increase kernel weight, and eventually improve the yield of maize.