Stability of the Expression of Acyl‐ACP Thioesterase Transgenes in Oilseed Rape Doubled Haploid Lines

Abstract

stable for more than five generations, without any apparent genetic instability or loss of the transgenic pheno-Transgene stability in doubled haploid (DH) lines is an important type. However, instability in the expression of other consideration for transgenic cultivar development programs. The objective of this study was to assess the expression stability of acyl-acyl transgenes has been observed in some studies (Assaad carrier protein (ACP) thioesterase (TE) transgenes in oilseed rape Scheid et al., 1991; Zhong et al., 1999). For (Brassica napus L.) DH lines. The DH lines were developed from example, in a population of Arabidopsis thaliana (L.) microspores of F 1 plants from the crosses between transgenic parents Heynh. plants transgenic for a hygromycin resistance carrying the bay-TE (Uc FatB1), elm-TE (Ua FatB1), nutmeg-TE gene (hpt), 50% of the plants failed to transmit the (Mf FatB1), or cuphea-TE (Ch FatB1) transgenes and three nontransresistance trait to the progeny, although the complete genic cultivars having distinct seed oil fatty acid compositions. Of 333 transgene was detected in all the plants (Scheid et al., DH 1 plants developed from microspore-derived embryos that had 1991). undergone selection for kanamycin resistance (the selectable marker) Unstable expression of transgenes has been associated with bay-TE F 1 and cuphea-TE F 1 plants as the microspore donors, with gene silencing (Charrier et al., 2000; Meyer and 20 plants did not show TE transgene expression. Polymerase chain reaction (PCR) and Southern blotting analyses confirmed that the Saedler, 1996; Scott et al., 1998). Gene silencing is due absence of TE transgene expression in these 20 DH 1 plants was due to somatically or meiotically heritable repression of gene to escape of embryos from kanamycin selection or existence of an expression that is potentially reversible and is not due to incomplete T-DNA copy without the TE transgene. No DH 1 plant mutation (Kaeppler et al., 2000). Gene silencing could with completely silenced TE transgenes was detected. Thirty of 34 result from the blocking of transcription initiation, trantransgenic DH lines showed a stable level of the target fatty acid, scriptional gene silencing (TGS), or from the degradation lauric acid (C12:0) for the bay-TE and palmitic acid (C16:0) for the of mRNA after transcription, posttranscriptional gene other three TE transgenes, over the two or three consecutive generasilencing (PTGS) (Chandler and Vaucheret, 2001; Matzke tions tested (DH 2 , DH 3 , and/or DH 4 plants). Target fatty acids were and Matzke, 1998; Wassenegger, 2000). Possible factors significantly affected by temperature during seed development. DH inducing gene silencing include growth conditions of the lines carrying the elm-TE or the cuphea-TE transgene grown under high temperature conditions (25/20؇C, day/night) during seed develop-

Developing transgenic wheat to encounter rusts and powdery mildew by overexpressing barley chi26 gene for fungal resistance

“…They ascribed this behavior to the use of CaMV–35S promoter driving the transgene. Transgene silencing has also been reported by other investigators [44, 45], with this as well other promoters, e.g., CaMV–35S [45, 46], Act1D [44], and maize ubi1 [43, 47], with different transformation methods, such as Agrobacterium -mediated transformation of oilseed rape [48, 49] and microprojectile bombardment for wheat [43, 47]. These reports and the current study support the conclusion that transgene silencing is not correlated to any specific promoter or transformation method used.…”

Relationship of seed quality traits for greenhouse-grown versus field-grown high erucic acid rapesseed: Is seed quality trait selection for greenhouse-grown seed worthwhile?

“…Temperatures in the greenhouse in both the fall and spring greenhouse cycles averaged approximately 208C, near to the optimum temperature for maximum phenotypic expression for oil, protein, erucic acid and glucosinolate concentrations (Canvin 1965;Mailer and Wratten 1985;Tang et al 2004). The means for all seed quality traits for fall and spring greenhouse cycles were not significantly different, so the experiments from the two greenhouse cycles were combined to increase sample size and simplify data presentation.…”

“…Similarly, Wilmer et al (1996) reported that that erucic acid concentration of the rapeseed cultivar Reston decreased as temperature increased from 15 to 258C in controlled environment studies. Tang et al (2004) also reported that very long chain fatty acids (C 20 and higher) decreased when temperature increased from 208C/158C day/night to 258C/208C day/night for cross progeny involving the rapeseed cultivar Mercury. Field experiments have shown that rapeseed exhibits significant cultivar and site variability in seed quality (Mailer and Wratten 1985;Shi et al 2003).…”

Molecular regulation of seed oil accumulation

“…Success of these transgenic approaches has been affected by various factors that include the insertion number, the location of the transgene in the genome and the stability of the desired trait [51] . While genetic transformation has resulted in some success in modifying fatty acid composition [54,58,59] , limitations are encountered during attempts to increase seed oil content [16,35] .…”