Expression Of Exogenous Xylanase Gene Atx In Rice And Study The Characteristics Of Transgenic Rice Plants

Xylanase (EC 3.2.1.8) can degrade the xylan backbone into xylooligosaccharides, so it plays an important role in the degradation of cell wall of plants and has many applications. A hybrid xylanase gene (atx) was introduced into rice variety Zhonghua 11 via Agrobacterium-mediated transformation, by using the rice mature embryo-derived callus as explants. Hygromycin resistance detection, PCR amplification and southern blot analysis had all demonstrated that the target gene had been integrated into the genome of transgenic rice. RT-PCR and fluorescence quantitative PCR (FQ-PCR) analysis of the total RNA extracted from the fresh leaves of several transgenic lines showed that the introduced xylanase gene could be normally expressed in rice under the control of CaMV 35S promoter, but the expression levels were different in each of transgenic rice plants. For further studying the characteristics of the transgenic rice plants, some physiology-biochemistry parameters were determined. In each growth stage, no difference was found between transgenic plants and non-transgenic plants (WT) under identical conditions. And there were also no significant differences between them in plant height, panicle length and tillering number. These results suggest that expression of exogenous xylanase gene (atx) had no adverse effect on phenotype of rice. All of the examined transgenic lines exhibited xylanase activity and the activity was significantly higher than that of the control rice plants before the stage of grain filling. Interestingly, the xylanase activity in leaves of transgenic lines conceitedly reduced during their growth stage, and this enzyme activity is relatively high at stage of seedling, such as the xylanase activity of 'X1-3' transgenic line was up to 3.51 U·g^-1 fresh leaf. These results indicate that exogenous xylanase gene (atx) can express successfully during the development stages of transgenic rice plants and the exogenous xylanase expressed in the transgenic rice plants was active. By analyzing the net photosynthesis (P_N) rate, it was indicated that there were no obvious difference between transgenic rice lines and WT at stage of tillering, heading-flowering and grain filling, whereas only P_N of the 'X2-5' transgenic line was significantly increased at stage of jointing-booting as compared to the WT. These results suggest that expression of exogenous xylanase gene (atx) had no negative impact on photosynthesis of rice. Furthermore, no significant differences between the transgenic lines and WT were observed for traits of spikes per plant, full grains per spike and setting percentage. Though the WT had greater trait values for 1000-grain weight, but the transgenic lines had greater trait values for total grains per spike. Thus, these results indicate that expression of exogenous xylanase gene (atx) would not cut the yield of rice on the whole. By measuring the content of cell wall composition, it was found that cell wall polysaccharides, including pectin, hemicellulose 1, and hemicellulose 2 were no significantly different between the transgenic lines and the WT in rice root apex. A similar observation was found for pectin content of rice leaves. However, the content of hemicellulose 1 of the 'X2-5' transgenic line in rice leaf was declined by 25.5%, as compared to the WT. These results demonstrate that expression of exogenous xylanase gene (atx) would not change the cell wall composition of rice root apex, but may have some effect on the cell wall composition of rice leaf.In conclusion, exogenous xylanase gene (atx) would be successfully expressed in rice. Growth and reproduction of the transgenic rice plants were not affected by the expression of foreign xylanase. So it would be an economic way for xylanase production via transgenic rice.