Isolation and phylogenetic characterisation of LdSVP, SHORT VEGETATIVE PHASE (SVP) homologous gene from Lansium domesticum

SHORT VEGETATIVE PHASE (SVP), encoding a MADS-domain protein, is one of the central floral repressors in Arabidopsis thaliana besides FLOWERING LOCUS C. It is expressed in vegetative tissues and floral primordia but not in developed flowers, and acts in a dose-dependent manner. SVP homologous gene from Lansium domesticum, namely LdSVP, was isolated from young leaf tissues of 3-month old plants. Deduced amino acid sequence of LdSVP contains MADSbox, I-box, K-box and C-terminal domains, conforming to MIKC-type protein, and highly similar to SVP. LdSVP cDNA consists of 684 nucleotides of coding sequence, 226 nucleotides of 5’ untranslated region (UTR) and 266 nucleotides of 3’ UTR. Phylogenetic study of SVP and SVP homologous proteins of 23 plant species indicates that LdSVP is closely related to PtSVP, a SVP homologous protein of trifoliate orange (Poncirus trifoliata), and both share the same ancestor. It is phylogenetically further from PtAGL24, a MADS-box gene from P. trifoliata that is closely related to AGAMOUS-LIKE 24 (AGL24) of Arabidopsis, than PtSVP. Therefore, LdSVP is more likely to take on the functions of SVP than AGL24. Protein phylogenetic analysis and domain organisation study showed that LdSVP may have a similar function to PtSVP in flowering time regulation. PtSVP is highly expressed in dormant tissues and vegetative meristems, and induces late flowering when transformed into wild-type A. thaliana, suggesting that LdSVP may be involved in seasonal flowering of duku, and SVP homologous genes may be the main floral repressors in seasonal flowering regulation of tropical plants. Although SVP homologues have evolved among plant species, the functional domains are well conserved between Arabidopsis and L. domesticum.