Identification of SHORT VEGETATIVE PHASE (SVP)-like genes and necessary responsibility of CmSVPc for the development of lateral branches in melon (Cucumis melo L.)

SVP acts as a central suppressor for floral transition and floral organ identity but also involves in the diverse functions among different species, such as abscission zones formation, plant height and dormancy. In this study, four SVP homologs were identified in melon and designated as CmSVPa, CmSVPb, CmSVPc and CmSVPd based on the similarity of their proteins to AtSVP. CmSVPc exhibited a clear difference in gene structure from the other CmSVP-like genes owing to its longer first and fifth introns. The results of exogenous gibberellin (GA3) and treatments with temperature and light suggested that CmSVPc and CmSVPd could be regulated by exogenous GA3 and all four CmSVPs involved in temperature and light responsive pathways. The results of RT-PCR indicated that transcripts of four CmSVPs were highly accumulated in shoot apices (MA and LA) and young leaves (YL) but they were present at relatively low levels in opening corolla (MF and BF). Compared with CmSVPa, CmSVPb and CmSVPd, the transcripts of CmSVPc were highest in all detected tissues except for LA in which CmSVPb accumulated to the highest level. Due to the specificity of gene structure and abundant transcripts of CmSVPc in melon, CmSVPc was chosen for further study. Subcellular localization revealed that CmSVPc was localized to the nucleus. Overexpression of CmSVPc in Arabidopsis led to increased numbers of lateral branches, delayed floral transition, and abnormal flower development compared with the wild type. However, CmSVPc-RNAi plants in melon inhibited the normal development of lateral branches, and the transgenic plants in which CmSVPc was downregulated also displayed shorter internodes, smaller petals and shorter fruits compared with the control. These results indicated that CmSVPc plays an important role in maintaining the growth of lateral branches in melon.