Cloning Of A Cytosolic Small Subunit Gene Of AGPase In Maize And Genetic Transformation Into Wheat

Wheat is one of the most important food crops in the world，whichproductivity and supply-demand situation often impact national economic development and foodsecurity. In wheat grains, starch is the primary sink product, and accounts for approximately65-75% of seed weight. ADP-glucose pyrophosphorylase (AGPase) carries out the first committedstep in the starch synthesis routes in photosynthetic and non-photosynthetic plant tissues, andincreasing activities of AGPase improves seed weights significantly.A cDNA sequence encoding a cytosolic small subunit gene of AGPase was isolated frommaize by RT-PCR and designated as ZmSSU I (GenBank Accession No. GU550073), and thetranscription levels of ZmSSU I in maize kernels were analyzed with semi-quantitative RT-PCRmethod. Then, the expression vector of ZmSSU I gene were constructed, and transformed intowheat plants by pollen tube method. The results were as follows:1. Length of ZmSSU I gene isolated in this study was 1554 bps, containing an openreading frame (ORF) of 1428 bp encoding a putative protein of 476 amino acids. Sequencealignment indicated that the putative amino acid sequence of ZmSSU I shared high identitiesto those of other plants such as Zea mays (AAN39299), Sorghum bicolor (ABK97531), Oryzasativa (ACJ86322) and Triticum aestivum (AAF61173), 96%, 94%, 91% and 89%, respectively.2. ZmSSU I expressed abundantly in endosperms, moderately in leaves, and weakly in rootsand stems. The expression of ZmSSU I in developing kernels had a single-peak curve occurringafter pollination. Transcript levels for ZmSSU I increased and reached the peak on day 40 afterpollination, and then gradually decreased. This was concident with activities of AGPase and ratesof starch synthesis in grains. The results showed that ZmSSU I gene played an important role inmaize starch biosynthesis in grains.3. In order to increase grain weight by genetic engineering pathway, the plant expressionvectors of ZmSSU I gene were constructed with pWM101 vector, and transformed into a commonwheat cultivar (Yujiao 34) by pollen tube method. PCR amplification indicated that threetransgenic plants of ZmSSU I were obtained.