Abstract
Background: Sucrose synthase (SUS), a crucial enzyme in the sucrose metabolism pathway, has synthesis and decomposition activities to promote the sucrose involved in plant growth and development, or stress response. SUS gene family members in more and more species have been identified and analyzed until now. However, the studies on SUS gene family and its functional characteristics in tea plant, is limited. Results: Here, we identified seven SUS genes (CsSUS1-CsSUS7) from the genome of tea plant ('Tieguanyin'). These seven CsSUSs with similar genetic structures were distributed on five chromosomes. CsSUSs were classified into SUSI, SUSII, and SUSIII subgroups. In the CsSUSs promoter, cis-elements related to light, phytohormone, and stress were observed. Transcriptome or quantitative real-time PCR (RT-qPCR) analysis results showed that in different tissues, during leaf growth processes, and under different stress (drought, shading, withering, salt, cold) treatments, the transcription levels of CsSUS1 and CsSUS3 were relatively high and the transcriptional patterns were varied, while CsSUS2, CsSUS4, CsSUS6 and CsSUS7 expression levels were relatively low or almost not expressed. CsSUS1 and CsSUS3 were discovered be located in the plasma membrane and cytosol. Meanwhile, after withering treatment, the decomposition activity of SUS gradually increased, while the synthesis activity gradually decreased, and the transcription level of CsSUS3 also gradually increased. Further silencing CsSUS3 expression by virus induced gene silencing (VIGS) technology reduced the SUS activity (especially the decomposition activity), increased sucrose content, and decreased fructose and glucose content. Conclusions: CsSUS3 was involved in sucrose metabolism during withering and mainly endows SUS with decomposition activity, to decompose sucrose and further generate hexose (fructose and glucose). Our results will help to further revealing the function of CsSUSs in sucrose metabolism of tea plant and provide theoretical reference for tea postharvest processing.