Poster: Epigenetics & gene silencing

Abs # 830: Homology-Dependent Post-Transcriptional Gene Silencing (hdPTGS) Is Not Completely Recovered in Maize Hybrids

Presenter:	Gupta, Manju , mgupta@dow.com
Authors	Gupta, Manju  (A)   Bing, James  (A)   Higgins, Laura  (B)   Schulenberg, Greg  (A)   Thompson, Steve  (A)   Wang, Jimei  (B)   Xu, Deping  (B)   Zhong, Gan-Yuan  (B)
Affiliations:	(A): Dow AgroSciences LLC (B): Pioneer Hi-Bred International, Inc., A DuPont Company

The characterization of transgenic events for gene silencing takes multiple plant generations. According to the literature, hdPTGS, which frequently is more pronounced when transgenes are in the homozygous state, can be reversed when the transgenes are returned to a hemizygous state. This phenomenon may have value in breeding certain traits. During the event-sorting process created for the cry1F transgene, we identified a rare event, TC1360, in which cry1F was expressed consistently during the hemizygous backcross generations, but silenced almost completely when homozygous. The presence of small interfering RNAs (siRNA) corresponding to the coding region, a characteristic feature of PTGS, was observed in the silenced homozygous plants. We asked the question whether the silenced homozygous state of this event would be completely reversed when the transgene was returned to the hemizygous state in maize hybrids. To answer this question, the event was fully introgressed into two maize lines through backcross breeding. No gene silencing was observed in the backcrossed plants. Selected lines were then selfed consecutively for four generations. Most of the plants in the S2 generation were completely silenced. Hybrids were produced from the S4 silenced lines. We report here that the cry1F expression did not completely return to its hemizygous level in these S4 hybrids. As a result, this event was discarded from further development. Data will be presented to discuss this concept in greater detail.