The Effect of Poplar Overexpression on Growth, Secondary Cell Wall, and Fiber Characteristics in Tobacco.

The glutamine synthetase (GS1) is a key enzyme that catalyzes the reaction of glutamate and ammonia to produce glutamine in the nitrogen (N) metabolism. Previous studies on in several plant species suggest that overexpression of GS1s can enhance N utilization, accelerate plant vegetative growth, and change wood formation. In this study, we isolated a gene, termed , from This gene was expressed at a higher level in roots, and relatively lower but detectable levels in xylem, leaves and phloem of . The protein encoded by is primarily located in the cytoplasm. Overexpression of in tobacco led to the increased GS1 activity and IAA content, the augmented N assimilation, and the enlarged leaves with altered anatomical structures. These changes presumably promoted photosynthetic, growth, and biomass productivity. It was noteworthy that the secondary cell walls and fiber characteristics changed remarkably in transgenic tobacco. These changes aligned well with the altered expression levels of the genes involved in fiber development, secondary cell wall component biosynthesis, IAA biosynthesis, amino acid transport, and starch breakdown. Taken together, the results from our study suggest that catalytic functions of on N assimilation and metabolism in transgenic tobacco had significant effects on vegetative growth, leaf development, and secondary cell wall formation and properties through acceleration of photosynthesis and IAA biosynthesis, and redirection of carbon flux to synthesis of more cellulose and hemicellulose.