MIKC type MADS-box transcription factor LcSVP2 is involved in dormancy regulation of the terminal buds in evergreen perennial litchi (Litchi chinensis Sonn.)

SHORT VEGETATIVE PHASE (SVP), a member of the MADS-box transcription factor family, has been reported to regulate bud dormancy in deciduous perennial plants. Previously, three LcSVPs were identified from litchi genome, and LcSVP2 was highly expressed in the terminal buds of litchi during growth cessation or dormancy stages and down-regulated during growth stages. In this study, the roles of LcSVP2 in governing litchi bud dormancy was examined. LcSVP2 was highly expressed in the shoots, especially in the terminal buds at growth cessation stage, whereas low expression was showed in roots, female flowers and seeds. LcSVP2 was found to be located in the nucleus and have transcription inhibitory activity. Over-expression of LcSVP2 in Arabidopsis thaliana resulted in a later flowering phenotype compared to the wild-type control. Silencing LcSVP2 in growing litchi terminal buds delayed re-entry of dormancy, resulting in significantly lower dormancy rate. The treatment also significantly up-regulated litchi FLOWERING LOCUS T2 (LcFT2). Further study indicates that LcSVP2 interacts with an AP2-type transcription factor, SMALL ORGAN SIZE1 (LcSMOS1). Silencing LcSMOS1 promoted budbreak and delayed bud dormancy. ABA (200 mg/L), which enforced bud dormancy, induced a short-term increase in the expression of LcSVP2 and LcSMOS1. Our study reveals that LcSVP2 may play a crucial role, likely together with LcSMOS1, in dormancy onset of the terminal bud and may also serve as a flowering repressor in evergreen perennial litchi.