Endoreduplication and gene expression in somaclonal variants of clonally propagated Phalaenopsis 'Wedding Promenade'

In the current study, we studied somaclonal variants of Phalaenopsis 'Wedding Promenade' (WP) to identify the factors that determine variation in this ornamental orchid. We grouped somaclonal variants of Phalaenopsis 'Wedding Promenade' based on their flower morphology (WP-N, WP-V1, WP-V2, and WP-V3). Morphological characteristics and histological studies were conducted in addition to flow cytometry and gene expression analyses of the flowers, leaves, and flower stalks. Morphological changes were observed in all WP groups; particularly, the width of the flower and the thickness of each organ were significantly increased when compared with those of normal flowers. The ploidy level of WP-V2 and WP-V3 was doubled in all organs, resulting in hexaploidy, while WP-N and WP-V1 were triploids. A high level of endoreduplication (3C-48C) was detected in the petals, leaves, and flower stalks of the WP Phalaenopsis variants. The expression patterns of HIGH PLOIDY 2 (HPY2) and MADS box transcription factor (PMADS4) isolated from Phalaenopsis were analyzed by real time quantitative PCR. HPY2 expression was the highest in the leaves of WP-V1, whereas its expression in flowers was similar in WP-V1 and normal flowers. Among the various flower organs analyzed, HPY2 expression was the highest in petals and lips of WP-V2. PMADS4 expression was not affected in the floral organs of the Phalaenopsis WP variants. The data identify a simple way to detect somaclonal variation in the Phalaenopsis WP variants and also provide insight into the causes of these variations.