Litchi Flowering is Regulated by Expression of Short Vegetative Phase Genes

Abstract

Short vegetative phase (SVP), a MADS-domain transcription factor, was shown to act as a repressor of flowering in arabidopsis (Arabidopsis thaliana). Although the role of SVPs in flowering is well characterized in the model plant arabidopsis, little is known in evergreen woody litchi (Litchi chinensis). In this study, three litchi SVP homologs (LcSVP1, LcSVP2, and LcSVP3) were cloned, and the bioinformatic analysis of the LcSVPs was carried out to identify their molecular characteristics. Their expression patterns in the apical meristem (AM) during the transition from vegetative to reproductive phase were studied under natural flowering inductive conditions. Also, brassinosteroid (BR) treatment under low temperature conditions was performed to elucidate the role of LcSVPs in the BR-regulated flowering. The results showed that LcSVPs belonged to the MADS superfamily. LcSVP relative expression levels in AMs of the early- and late-flowering cultivars showed decreasing trends with the transition from vegetative to reproductive growth. Under low temperature condition, relative expression levels of LcSVP1, LcSVP2, and LcSVP3 in AMs or panicle primordia showed decreasing trends, whereas those in the AMs of the BR-treated trees remained at relatively high levels. Relative expression analysis of the litchi homolog, flowering locus t 1 (LcFT1), showed that the BR-treated leaves had lower relative expression level than nontreated control leaves. The findings suggest that LcSVPs act as repressors involved in flowering in natural conditions and the BR-regulated flowering.