255:	The regulatory role of ASN1 in nitrogen status of Arabidopsis thaliana.

Authors:	Chan, Hiu-Ki(A)Coruzzi, Gloria, M.(B)Lam, Hon-Ming(A)
Affiliations:	(A): Department of Biology, The Chinese University of Hong Kong (B): Department of Biology, New York University
Presenter:	Chan, Hiu-Ki , s980740@mailserv.cuhk.edu.hk

Asparagine, which plays an important role in nitrogen transport and storage in higher plants, is synthesized by the action of asparagine synthetase. In Arabidopsis thaliana, asparagine synthetase activities are encoded by a small gene family (ASN1, ASN2 and ASN3). Levels of free asparagine in the leaves and green siliques are high in dark-adapted plants and low in light-grown plants and parallel to the changes in ASN1 (but not ASN2 and ASN3) mRNA levels. We also reported previously that the gene expression of ASN1 is regulated by the relative carbon and nitrogen status in plant cells. To further investigate the role of ASN1 enzyme in controlling nitrogen status of the whole plant, we constructed transgenic plants that ectopically express the sense or antisense ASN1 mRNA. Northern blot analysis showed that the sense and antisense transgenic lines over-produced or under-produced ASN1 mRNA, respectively, in both dark-adapted and light-grown plants. These changes in mRNA levels were reflected in the differences of free asparagine levels in the leaves and siliques of these transgenic lines. Since asparagine in siliques may act as nitrogen resources during seed formation, we also determined the nitrogen status in the seeds of these transgenic plants. Preliminary data showed that both the percentage of total nitrogen and the total nitrogen to carbon ratio are higher in transgenic lines overproducing asparagine in leaves and siliques. These results suggest that ASN1 enzyme may play a crucial role in controlling the nitrogen status in Arabidopsis thaliana. [U.S. DOE support to GC and H.K. RGC support to HML]