Glutamine synthetase genes family mediates nitrogen metabolism and disease responses in Kentucky bluegrass.

BACKGROUND

Kentucky bluegrass (Poa pratensis L.), an important cool-season turfgrass species, requires adequate nitrogen (N) fertilization for normal growth and development. It is also susceptible to infection by pathogens. The glutamine synthetase (GS) gene family, known to play central roles in plant N metabolism and disease responses across higher plants, has functions that remain uncharacterized in Kentucky bluegrass.

RESULTS

We identified and characterized four GS genes (PpGS1.1, PpGS1.2, PpGS1.3, and PpGS2) in Kentucky bluegrass. Phylogenetic analysis revealed a close relationship with perennial ryegrass (Lolium perenne), and structural analysis confirmed conserved functional domains and critical residues involved in substrate binding, phosphotransfer activity, thermostability, and cation coordination. Expression analyses showed that under low-nitrogen (LN) stress, PpGS1.1 was strongly upregulated (∼200%), while PpGS1.3 and PpGS2 showed modest increases (∼20%), and PpGS1.2 was unresponsive. Conversely, powdery mildew infection inhibits PpGS1.1 (∼79.4%), PpGS1.3(∼40.2%), and PpGS2 (∼76.2%) expression level, with PpGS1.2 unchanged. Transgenic tobacco overexpressing PpGS genes exhibited enhanced growth under LN stress, with higher N metabolism and antioxidant enzyme activities, reduced superoxide accumulation, and increased root length and fresh weight. However, upon tobacco mosaic virus (TMV) inoculation, these lines developed larger lesions and showed reduced antioxidant enzyme activities.

CONCLUSION

The study reveals GS genes family mediates N metabolism and disease responses in Kentucky bluegrass. The findings provide a theoretical foundation for turfgrass N management and disease resistance breeding, which is critical for developing elite Kentucky bluegrass cultivars with LN input and durable disease resistance.