Molecular Cloning of a cDNA for Chrysanthemum morifolium Ramat Squalene Synthase Gene and Impact of Its Silencing on Transgenic Chrysanthemum Plants

The aim of this research was to study the impact of squalene synthase gene silencing on the features of transgenic chrysanthemum plants, and on the synthesis of some sesquiterpenes—caryophyllene, germacrene and farnesene. We have cloned chrysanthemum squalene synthase gene cDNA (CmSQS) and obtained five lines stably transformed with vector for CmSQS silencing. Silencing of CmSQS gene transcription was detected in all five transgenic lines, the decrease in the squalene content was found in three of them, by 1.8–2.0 times depending on the line. The content of triterpenes α- and β-amirin, derivatives of squalene, clearly correlated with its content in plants. The β-caryophyllene, germacrene D and β-farnesene were identified in chrysanthemum using GC-MS analysis; the content of these compounds in transgenic plants did not change appreciably compared to control ones. Silencing of squalene synthase had no effect on plants morphology. In two transgenic lines, a decrease in growth rate relative to non-transgenic plants was observed; the growth rate of three other lines did not differ from the control. Thus, in our experiments no well-defined relationship between CmSQS gene transcription level, the content of squalene and studied sesquiterpenes was found. The obtained data provide additional information on mechanisms of plant secondary metabolism regulation including the relation between β-caryophyllene, germacrene D and β-farnesene content with squalene synthesis level.