Overexpression of both AcSVP1 and AcSVP4 delays budbreak in kiwifruit A. chinensis var. deliciosa, but only AcSVP1 delays flowering in model plants

Kiwifruit SHORT VEGETATIVE PHASE (AcSVP) genes have been implicated in regulation of dormancy and flowering. Previously, we have shown that AcSVP2 and AcSVP3 have different effects on dormancy and flowering in transgenic kiwifruit and model plants. The role of two homologous genes, AcSVP1 and AcSVP4, remained unclear. Here, AcSVP1 and AcSVP4 were functionally characterized by ectopic expression in Actinidia species which show different chilling requirements for budbreak, as well as the model plant tobacco. Overexpression of AcSVP1 and AcSVP4 delayed spring budbreak in a high-chill A. chinensis var. deliciosa, but did not affect budbreak and flowering in a low-chill A. eriantha. Overexpression of AcSVP1 delayed flowering and seed germination in tobacco, while overexpression of AcSVP4 had only minor effects. Analysis of cis-regulatory motifs in the promoter regions of AcSVP1 and AcSVP4 and promoter transactivation assays revealed that AcSVP1 and AcSVP4 may be controlled by similar transcription factors, suggesting a conserved regulatory mechanism and a synergistic role for AcSVP1 and AcSVP4 in preventing premature kiwifruit budbreak during winter.