|Levy, Laurene - USDA, APHIS, PPQ|
|Ravelonandro, Michel - INRA, BORDEAUX, FRANCE|
Submitted to: International Biotechnology Congress
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2003
Publication Date: June 23, 2002
Citation: Callahan, A.M., Scorza, R., Levy, L., Damsteegt, V.D., Ravelonandro, M. 2002. The effect of cold-induced dormancy on PTGS in plum clones containing the plum pox coat protein gene. International Biotechnology Congress, 10th International Association of Plant Tissue Culture & Biotechnology Congress Proceedings, P-1261, pp 99. Technical Abstract: Plum trees containing the coat protein gene (CP) from plum pox potyvirus (PPV) were inoculated with PPV through graft inoculation in a containment greenhouse. Only one line, C5, was highly resistant to infection by PPV. The mechanism of resistance appears to be post-transcriptional gene silencing (PTGS). In herbaceous systems, PTGS has been shown to be 're- set' following seed germination. It is important to know in a perennial fruit tree, if PTGS can be maintained rather than 're-set', through the yearly cycles of growth and dormancy. Leaf samples were collected from several clones of PPV- CP transformed plums over a period of three years before and after cold-induced dormancy (CID) periods that simulated winter dormancy and spring growth. The levels of viral RNA and transgene CP RNA were measured and compared in susceptible PPV-CP transgenic clones and the resistant C5 clone prior to CID, one month after CID (first leaf expansion) )and three months post-CID. There was at least tenfold more viral RNA and two-to fivefold more transgene RNA detected in the susceptible clones than in C5 as would be expected since the PPV-CP transgene is silenced in C5. The levels of both transgene and virus increased following CID in both the susceptible lines and C5, although the increases in C5 was significantly lower than in the susceptible clones. Either a re-setting of PTGS (in C5), or the effects of release from dormancy (in all clones) allowed more virus to be detected and a higher level of transgene accumulation immediately post-CID. Our results indicate an environmental influence on PTGS in a temperate woody perennial. This phenomenon has implications for the deployment of this resistance mechanism under field conditions.