| Sweet potato is the sixth largest agricultural crop in the world,it is valuable because it is a low energy input crop with stable yields under sub-optimal conditions. Sweet potato is grown for its tuberous rootswhose starch is used both as a food and as anindustrial resource. Such characteristics have attracted worldwide interest by biomedical and plant science researchers.Starch, is the most common form of stored carbon in plants, and in the synthesis and accumulation of starch there were four important enzymes,as ADP-glucose pyrophosphorylase(AGpase) which synthesizes sugarnucleotide precursors, starch synthase, whichextends the a-1,4-linked glucan chains using ADP-Glc, and a starch-branching enzyme (SBE),which introduces a-1,6 branch points to form amylopectin. The SBE, 1,4-a-D-glucan-6-a-[1,4-aglucan]-transferase, is a key enzyme in starch biosy- nthesis.AGPase, one of the key enzymes in starch biosynthesis is the first committed step in the biosynthesis of both transient starch in chloroplasts/chromoplasts, and storage starch in amyloplasts. AGPase from higher plants is heterotetrameric,consisting of two large (AGP-L) subunits and two small(AGP-S) catalytic subunits encoded by at least two different genes (Preiss and Sivak,1996). The ratio of amylose to amylopectin has a great influence on the physicochemical properties of starch. Genetic engineering of starch has a high potential for the quality improvement of sweetpotato starch and helps in the development of new dietary and industrial applications.Total RNA was purified from high-starch sweet potato variety Chuanshu 34, and was reverse-transcripted into cDNAs. The cDNA of AGPal and AGPa2 gene was cloned by RT-PCR from. Chuanshu 34,The sequence analysis showed that the total length of the AGPal cDNA was 1569bp encoded a 522-amino acid polypeptide, AGPa2 cDNA was 1572bp encoded a 523-amino acid polypeptide,.Homology analysis of the nucleotide sequence and the deduced amino acid sequence showed that the two cDNA shared 99%identity with the published sequence. Molecular Weight (MW) and Isoelectric Point (pI) of AGPal was predicted to be 57.109 kDa and 7.23 respectively. AGPa2 was57.113 kDa and 7.89 respectively.There are 90% identity between the AGPal and AGPa2 amino acid sequence..AGPal and AGPa2 were acquired through digestion, electrophoresis and recover, and then were sub-cloned into pCambia1301 cloning site,pC-AGPal and pC-AGPa2 vectors were constracted, introduced into A. tumefaciens strain EHA105 and. transformed into embryos of sweetpotato via Agrobacterium tumefaciens system. Plantlets were regenerated in vitro by resistance selection on medium containing hygromycin.,14 resistant plants were obtained. tested by GUS staining and polymerase chain reaction (P.C.R.), the ruslts showed that 5of them may be tansgenic plants.at the same time,we transformed the two gene in tobacco, the tested Work is gonging on. |
