| A cDNA sequence (EU586278) encoding plastidial small subunit (SSU II) of AGPase was cloned from grains of wheat (Triticum aestivum L.) with RT-PCR in this paper. Sequencing indicated that it lacked a long and uninterrupted fragment (114 bp) at 5′terimini. Temporal and spatial expression of SSU II during the grain filling period suggested that it could be positively related to starch synthesis in grains. In order to increase starch contents, kernel werghts and yields by genetic engineering technology, over-expression vectors of SSU II was constructed and transformed into wheat by pollen tube mediated transformation methods. Some transgenic plants, in which starch contents and grain weights significantly increased, were obtained. The main results showed as following:1. EU586278 included a sequence of 1 631 bp in length and its coding region was 1 428 bp. Sequence analysis showed that EU586278 was 83.2% identical to barely SSU II (Z48563) in the whole sequences, and 97% identical in their middle and 3′regions. Compared with Z48563, however, EU586278 lacked a long and uninterrupted fragment 114 bp at 5′unique region. Due to this lacked fragment, molecular weight(52.01 kDa)and isoelectric point(5.48)of EU586278 were difference from barely (Z48563), whose molecular weight and isoelectric point were 56.05 kDa and 6.11, respectively.2. Target P software predication indicated that the transit peptide of EU586278 was only 25 amino acids, much shorter other plant SSU IIs (58-70 amino acids). The shortage in EU586278 was mainly due to the lack fragment at 5′terimini in EU586278. Accordingly, EU586278 shared only 60.9% of the total transit peptides for barley and wheat (Z48563 and EU275212). The difference in sequences of SSU IIs among higher plants focused on their transit peptides. Dendrogram analysis of plant transit peptides showed that EU586278 was only 52-33% identical to barely SSU II (Z48563),wheat SSU II (AF536819),maize SSU II (AF334960) , suggesting that it could be a novel SSU II of AGPase. And it was found that there was a heat stable motif (QTCL) in N termini of EU586278, inferring that plastidial AGPase composed of SSU IIs and LSU IIs could play some role in starch synthesis during late period of grain filling.3. In order to explore the mechanism on deletion of a long fragment in EU586278. A 5′partial DNA sequence of SSU II (1146 bp, FJ907395), corresponding to 5′partial cDNA sequence of EU586278 in Chinese wheat cultivar (Yujiao 2) was also amplified. Sequencing indicated that FJ907395 included the deleted sequence of EU586278.This indicated that deletion in EU586278 was not occuerred at DNA levels, but at transcription levels.4. Semi-quantitive PCR analysis showed that SSU II expressed abundantly in leaves, moderately in stems and grains, and weakly in roots, indicated that SSU II plant an important role in starch synthesis in leaves, but also took part in starch synthesis in grains. In Yujiao 2 and Lankao Aizao 8, two large-size-seed wheat cultivars, transcript levels of SSU II were consistent with the rates of starch accumulation in grains during the grain filling period. This further suggested that SSU II could play an important role in starch synthesis in grains.5. In order to increase kernel werght by genetic engineering, the over-expression vectors of SSU II gene were constructed, and transformed to wheat plants by pollen tube method. PCR amplification and semi-quantitative RT-PCR indicated that T2 transgenic wheat plants of SSU IIs were obtained.6. AGPase activity in the kernels of T2 transgenic plants were 17%-32% higher than negative control. And 1000-kernel weights in transgenic SSU II wheat T2 lines were 5.1%-7.2% more than those in control plants. This suggested that over expression of SSU II in wheat plants provided a new way for increasing kernels weights and yields in wheat by gene engeneering way.
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