Comparative Study on Nitrogen Assimilation and Gene Regulation of different Kentucky bluegrass Cultivars in response to Nitrate supply

Abstract Background: Kentucky bluegrass (Poa pratensis L) is one of the most popular cool-season turfgrass worldwide, but the mechanisms of this species in response to low nitrogen (N) still remain unclear. In this study, we characterized two cultivars ‘Bluemoon’ and ‘Balin’ distinctly in morphological, chromosomal, physiological and molecular attributes to N supply.Results: Bluemoon was more tolerant to low N than Balin by exhibiting higher turf quality (TQ), photosynthetic ability, activities of N reductases and synthetases and nitrogen use efficiency (NUE). Gene expression profiling showed that there were 968 and 336 differentially expressed genes (DEGs) after eliminating genetic background differences in Bluemoon and Balin respectively during low N stress, and these DEGs highly enriched in ‘Nitrogen metabolism’, ‘Pyruvate metabolism’ and ‘Carbon fixation in photosynthetic’ pathways. The identified genes related to carbon (C) metabolism highly expressed in Bluemoon, which could generate more NADPH then result in more N reduction comparing with Balin. Moreover, R2R3-MYB transcription factors were predicted to bind the promoter of GS to enhance the efficiency of GS/GOGAT cycle.Conclusion: These results could be crucial molecular regulations for improving the tolerance to low N and NUE in Bluemoon. The climate and geography in origins may shape the N assimilation patterns in Kentucky bluegrass via long-term domestication. Taken together, the findings help elucidate the low N tolerance mechanisms in Kentucky bluegrass and would be valuable for the genetic improvement of NUE aiming to promote low-input turfgrass management.