Abstract
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 GS1s 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 GS1 gene, termed PsnGS1.2, from Populus simonii × Populus nigra. This gene was expressed at a higher level in roots, and relatively lower but detectable levels in xylem, leaves and phloem of P. simonii × P. nigra. The protein encoded by PsnGS1.2 is primarily located in the cytoplasm. Overexpression of PsnGS1.2 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 PsnGS1.2 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 PsnGS1.2 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.
Highlights
Plants need to absorb inorganic nitrogen (N) in the form of ammonium (NH4+) or nitrate (NO3−) from soil to maintain their regular or accelerated growth and development (Jackson et al, 2008)
The PsnGS1.2 is not clustered into the same clade with well-characterized Pinus GS1 (Figure 1B), which means that the functions of PsnGS1.2 may not be inferable from other known functional GS1s of woody species
We found some distinct functions of PsnGS1.2
Summary
Plants need to absorb inorganic nitrogen (N) in the form of ammonium (NH4+) or nitrate (NO3−) from soil to maintain their regular or accelerated growth and development (Jackson et al, 2008). Since not all GS1s are regulated in the same manner and located in the same type of cells or organs (Ishiyama et al, 2004b; Martin et al, 2006; Bernard et al, 2008; Castro-Rodriguez et al, 2011), GS1s exhibit different functions in N assimilation and metabolism in some transgenic plants (Ishiyama et al, 2004b; Martin et al, 2006; Lothier et al, 2011) These earlier studies suggest that GS1s are worth studying and characterizing to benefit humans
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