Transgene‐mediated suppression of chalcone synthase expression in Petunia hybrida results from an increase in RNA turnover

Abstract

SummaryCo.suppreseion of the pigmentation gene chelcone synthese (chs) in Petunia hybrida by chs transgenes leads to white or variegated flowers and is characterized by a reduction in steady-state mRNA levels. To determine the level at which suppression occurs different petunia transformants were analysed containing CaMV-35S RNA promoter-driven hybrid genes consisting of the ~glucuronidase gene (uidA) linked to the full-length chsA cDNA, the 5' half or to the 3' half. With these transgenes one out of 12-15 primary transformants showed suppression of the transgenes and of the resident chs genes throughout the flower or in sectors. The reduction in steady-state chs mRNA was not the result of a transcriptional inactivation event. As determined by nuclear run-on experiments, transcription of suppressed chs genes was similar to that of nonsuppressed genes. This indicates that co.suppression occurs post-transcriptionally. Among individual transformants the transgenes were transcribed at different levels but neither a high nor a low level correlated with a particular degree or pattern of suppression. Surprisingly, even a promoterless chs transgene construct was found to suppress the endogenous chs genes in three out of 15 transformanta. It remains, however, unknown whether or not transcription of the transgene locus is required to induce co-suppression. The data suggest that properties of the chs transgene locus other than the expression level are important for inducing cosuppression. The possible role of antisense RNA, which was detected in all transformants, ectopic pairing and the structure of the integrated T-DNAs in the mechanism of the selective increase in chs RNA turnover are discussed.

Alternative processing of the maize Ac transcript in Arabidopsis

“…Previously published studies have illustrated that partial sense mRNA from introduced DNA can interact with native gene product from homologous genes to form RNA complexes, which can lead to a down regulation of overall gene activity (reviewed by Matzke andMatzke (1995) andFlavell (1994)). However, these observations are nearly always associated with a decrease in mRNA levels within the cytoplasm (van Blokland et al, 1994). As discussed earlier and illustrated in Figure 5, there seems to be no decrease in Ac mRNA in Arabidopsis in comparison to other heterologous hosts species.…”

How and Why Do Plants Inactivate Homologous (Trans)genes?

“…Current research concerning silencing is leading in severa1 directions: In addition to these questions that arise from mechanistic differences, there is a common interest in isolating genes whose products modify the degree or timing of a11 types of silencing (Dehio and Schell, 1994) and in determining T-DNA modifications and/or configurations that are associated with silencing loci (A. Matzke et al, 1994;van Blokland et al, 1994). Finally, there is a pressing need to clarify the involvement of methylation in silencing by increased use of genomic sequencing and to study alternative forms of stable gene repression, such as chromatin condensation.…”

Antisense and Sense CHS cDNA Expressed by a Tapetum-specific Promoter Causes Partial Male Sterility in Transgenic Tobacco

“…3) . The reduction of the number of fertile pollen grains might be caused by co-suppression as reported earlier in many transgenic plants [27][28][29][30] . It is also possible that the inappropriate timing, location, or level of transgene expression might lead to a collapse of biosynthesis of phenylpropanoid.…”