Genetic Transformation Of Potato With Soluble Starch Synthase SSIII Gene

Potato is one of the most important crops in the application of starch. Starch is the major storage carbohydrate in many plants, which is composed of amylose and amylopectin. Amylopectin represent in 75%-80%, which is consist of linear polymerα-1,4 glucose residues linked viaα-1,6 glucosidic bonds, whereas amylose consist of linear polymerα-1,4 glucosidic linkage. The potato starch is utilized for many food and manufacturing industries, although it is not ideal that gelling temperature, stickiness and freeze-thawing stability of potato cultivars in the field planting. Therefore, breeding the new variety potato of suitable processing industries is of important significance in the starch production. In this paper, Soluble starch synthase (SSⅢ)gene of RNA interference expression vectors driven by the constitutive expression promoter CaMV 35S were introduced into two potato cultivar Kexin1 and Kexin4 by Agrobacterium-mediated transformation method. It could provid the foundation for investigating function of SSIII gene in potato starch synthesis and obtaining the new potato germplasm resources. The main results as following:1. The RNAi plant expression vectors pBI-SSIII-RNAi and pBIC-SSIII-RNAi driven by the constitutive expression promoter CaMV 35S and the tuber-specific expression promoter CIPP, respectively. The potato cultivars Kexin 1 and Kexin 4 were transformed with Agrobacterium tumefaciens using the microtuber discs. PCR assay showed that the interference fragment of SSIII gene of thirty-one putative transgenic plants was integrated into potato genome.2. The potato transgenic plant with well-developed roots were transferred into the pots and grown in the greenhouse and obtained the transgenic mini-tubers about four months. RT-PCR assay showed that expression of SSIII gene of nineteen putative transgenic plants was decreased apparently in the transgenic lines.3. The starch granules morphology of potato transgenic plant was observed, and the amylose, amylopectin -to- amylose ratio of starch and phosphorus content was determined. The results showed that the nine transgenic lines have distinctly changed in the morphology of starch granules, such as cracks centered on the hilum. The amylose content of the nine transgenic lines increased 2.68%-29.05% compared with non-transgenic lines. The lowest amylose content for the plant line 1 was 14.55%, while the highest amylose content for the plant line 9 of was 17.59%. The amylopectin -to- amylose ratio of starch had declined discernibly. The phosphorus content of the six transgenic plant lines of Kexin 1 were reduced 9.94%-58.36%. Reduction of the phosphorus content was 34.76%-56.04% in the three transgenic lines of Kexin 4.