Abstract: A SVP-like MADS-box gene PhSVP was isolated from Phalaenopsis hybrida‘Big Chilli’. The full-length cDNA of PhSVP was obtained using the RACE method and the open reading frame was 687 bp which encoded 228 amino acids. Multiple protein sequence alignment revealed that PhSVP protein contained a highly conserved MEF2-like MADS domain and moderately conserved K-box domain and shared high identity with the homologs of SVP/AGL24 from the orchid family. Phylogenetic analysis also showed that PhSVP protein was more closely related to SVP/AGL24 homologues of other orchid species. The spatial expression pattern of PhSVP showed that it was highly expressed in vegetative organs and weakly expressed in reproductive organs such as sepals，lateral petals and lips. Further analysis of PhSVP expression in the inflorescence apex during the floral transition and flower development revealed that there was no significant change in the level of PhSVP transcript during progression from vegetative phase to inflorescence meristem phase and only a slight increase of PhSVP expression level was found in inflorescence meristem phase，whereas the expression of PhSVP was upregulated in the floral meristem phase during the early stage of flower development and gradually decreased in the late stages when sepal，petal and column primordia are sequentially formed. In addition，we also found the expression pattern of A-class MADS-box gene PhAP1 in the inflorescence apex during the flower development was similar to the expression pattern of PhSVP，whereas the expression levels of B-class gene PhPI and C-class gene PhAG were the highest in petal and column primordia stage. Finally，the expression of PhSVP in various tissues such as root，leaf and scape during scape elongation stage，floral bud stage and blooming flower stage was investigated. The result showed that PhSVP expression level in root was slightly higher at floral bud stage and its expression level in leaf at different flowering stages remained unchanged. However，the PhSVP transcript in the scape accumulated to higher levels at scape elongation stage than floral bud stage and blooming flower stage. These results suggest that PhSVP may play a regulatory role in maintaining floral meristem identity and preventing precocious differentiation of floral organ primordia.

Key words: Phalaenopsis, SVP gene, expression analysis, flower development, floral meristem identity