Poster: Chromatin Remodeling & Epigenetics

Abs # 1027: Influence of internal and external factors on transgene silencing in barley

Presenter:	Meng, Ling , mengling@uclink4.berkeley.edu
Authors	Meng, Ling  (A)   Ziv, Meira  (B)   Fessenden, Rachel  (A)   Rangel, Sergio  (A)   Zhang, Shibo  (A)   Lemaux, Peggy G. (A)
Affiliations:	(A): Department of Plant and Microbial Biology, University of California, Berkeley (B): Hebrew University of Jerusalem

Many internal and external factors, like transgene structure and stress, affect transgene expression stability. Transgene introduction in barley via bombardment results in high frequency, transgene silencing, while Ds -mediated gene delivery leads to more stable transgene expression. To study the role of these factors on gene expression, T₆ transgenic barley plants from either bombardment- or Ds-mediated gene delivery were used. Line T₃ #30 from bombardment, containing ubiquitin -1 promoter complex driving uidA and bar, has a complex, multi-copy transgene structure. This line had stable transgene expression up to T₆ generation, while an identical sibling line, T₃#31, had unstable expression. Imposing certain environmental stresses, i.e. water, nutrient deprivation and heat shock, did not reproducibly affect transgene expression in T₃#30; however, high frequencies of complete or partial transcriptional gene silencing (TGS) resulted from in vitro culturing of the line. Complete TGS was correlated with hypermethylation of the untranslated exon and intron in ubi1 promoter complex and condensed chromatin around the insertion site, while partial TGS was correlated with hypermethylation of the untranslated exon and parial methylation of the intron. Epigenetic modification occurred mainly during regeneration and was heritable and homozygous. Three Ds-mediated, single-copy T₆ lines, containing bar driven by the ubi1promoter complex, were also introduced into in vitro culture and no silencing was observed in regenerated plants from the three lines. These results suggest that internal factors, i.e., transgene structure, can affect the tendency of a transgene locus to silence as a result of external stresses, i.e., in vitro culture.