4.2 CsTPS1 is involved in regulating the defense response via AS in tea plants
The transcriptional regulation of TPS genes is critically important for volatile terpenoid biosynthesis (Nagegowda, 2010. The substrate and product specificity of TPS s can regulate terpenoid biosynthesis at the enzyme level (Fischer et al., 2013). In addition to regulating transcriptional processes such as splicing, TPS genes also regulate other complex aspects of transcription. AS, which produces multiple mRNA subtypes from a single gene, is widespread in plants and often produces a variety of transcripts with diverse functions (Reddy et al., 2013). The full-length sequences and short AS forms ofCsTPS1 were obtained from the young leaves of tea plants. Although both CsTPS1 and its AS forms could catalyze the formation of geraniol in vitro , CsTPS1 and its AS forms confer different levels of disease resistance. The expression ofCsTPS1-AS , but not the full-length sequences of CsTPS1 , was induced in response to pathogen infection (Figure 5C and 5G). This might explain differences in the distribution and localization of CsTPS1 and CsTPS1-AS in the chloroplasts.
The silencing of CsTPS1-AS significantly decreased the content of geraniol and the resistance of tea plants to infection by the two pathogens (Figure 5B and 5C); however, no changes in disease symptoms were observed when CsTPS1 was silenced (Figure 5G and 5H). Hence, the shorter AS form of CsTPS1 plays a critical role in enhancing the resistance of tea plants to pathogen infection.