Poster: Oxidative Stress

Abs # 147: Overexpression Nicotiana protein kinase gene (NPK1) in maize enhanced tolerance to freezing

Presenter:	Shou, Huixia , huixia@iastate.edu
Authors	Shou, Huixia  (A)   Bordallo, Patricia  (A)   Frame, Bronwyn E (A)   Sheen, Jen  (B)   Wang, Kan  (A)
Affiliations:	(A): Department of Agronomy, Iowa State University (B): Department of Molecular Biology, Massachusetts General Hospital
Web Site:	http://www.agron.iastate.edu/ptf/Web/mainframe.htm

NPK1 gene is a mitogen-activated protein kinase kinase kinase (MAPKKK) isolated from tobacco. It involves the transduction of the oxidative stress signal and mimics H₂O₂ signal to induce specific stress-responsive genes. We generated transgenic maize lines, in which transgene NPK1 gene was driven by 35S promoter. The freezing tolerance of the transgenic lines was examined by measuring the electrolyte leakage (EL, an indicator of cell membrane damage) of plants under graduated freezing, in which growth chamber temperature was decreased one degree per hour starting from 0ºC, and -5ºC constant freezing conditions. Under graduated freezing, transgenic line A4-9 and A4-15, the highest expressers of NPK1 gene in the lines tested, maintained low EL (30%) when temperature dropped to –4ºC and –5ºC, respectively, while those of the negative segregants reached 80-100%. Under constant freezing (-5ºC), transgenic line A4-9 and A4-15 survived 3 and 4 hours, whereas the negative counterparts survived 2 and 3 hours, respectively. We observed that the NPK1 transgenic maize lines had elevated soluble sugar content compared with its negative segregants. Sugars are considered as cryoprotectants that increase in cold acclimated plants. Our data suggests that the constitutively expression of NPK1 gene in maize induced acclimation-like biochemical processes and protected maize plants from freezing stress.