Phylogenetic analysis indicates that NtSUS2 is ortholog of StSUS3
We have previously cloned potato sucrose synthase 3(StSUS3 ) and inserted in the sense direction into tobacco guard cells in order to investigate the function of this gene in guard cell metabolism and stomatal movements (Daloso et al., 2016b). The reasons to use StSUS3 and tobacco plants are based in the fact thatStSUS3 and its ortholog AtSUS3 has been previously shown to be highly expressed in guard cells (Bates et al., 2012; Bauer et al., 2013; Kopka et al., 1997; Yao et al., 2020) and that tobacco produce large leaves, which is crucial to harvest sufficient guard cells for metabolomics analysis (Daloso et al., 2015). Here, StSUS3 was inserted in the antisense orientation into tobacco leaves under control of the KST1 promoter (Figure 1A). In order to identify which tobacco SUS (NtSUS ) isoform corresponds to StSUS3 , we first aligned all seven SUS CDS sequences from tobacco with StSUS3 . The phylogenetic tree confirmed previous study (Wang et al., 2015) indicating that StSUS3 is ortholog of NtSUS2 . (Figure 1B). Here, after we refer to NtSUS2 expression. In fact, qRT-PCR analysis showed that the NtSUS2 expression decreased by almost 40% in guard cells of L3 and L13 lines compared to wild type (WT), whilst no difference in leaf gene expression was observed (Figure 1C). Although StSUS3 is also similar to NtSUS1 (Figure 1B), we did not detect the expression of this isoform in guard cells and leaves, in agreement with a previous study (Wang et al., 2015).