Poster: Epigenetics & gene silencing

Abs # 836: An endogenous suppressor of RNA silencing in tobacco

Presenter:	Endres, Mathew W., endres@biol.sc.edu
Authors	Endres, Mathew W. (A)   Ge, Xin  (A)   Bryan, Appel  (A)   Bowman, Lewis  (A)   Vance, Vicki  (A)
Affiliations:	(A): University Of South Carolina

RNA silencing is a conserved RNA degradation mechanism that targets invading nucleic acids such as viruses, transgenes or transposons. HC-Pro is a plant viral protein that impairs RNA silencing, acting in a counter-defensive role. Here we report the identification of a tobacco protein (termed ntRAV) that interacts with HC-Pro in the yeast two-hybrid system. ntRAV shows relatedness to the Arabidopsis thaliana RAV family of transcription factors. Endogenous ntRAV mRNA accumulates to very high levels in young tobacco plants, then rapidly declines at around three weeks post-germination to a nearly undetectable level. To determine if ntRAV plays a role in RNA silencing, we produced transgenic tobacco lines that either over-express or are silenced for ntRAV and crossed these lines to a transgenic line (line 6b5) that is silenced in response to a sense-transgene encoding GUS. Using histochemical staining and northern blot analyses, we find that ectopic over-expression of ntRAV delays the developmental onset of GUS silencing in both the blade and the vein tissues of 6b5 leaves. Although delayed by about two weeks, once begun, the pattern of RNA silencing is similar in ntRAV over-expressing lines and wt controls. In both cases, silencing begins in the veinal tissues of older leaves and spreads into adjacent blade tissue over the next two weeks. In contrast to the ntRAV over-expressing lines, GUS RNA silencing is enhanced in the older leaves of adult 6b5 plants that have reduced ntRAV expression. We hypothesize that ntRAV encodes an endogenous suppressor of RNA silencing that may act early in development to regulate the developmental onset of RNA silencing.