Identification and Characterization of Plasma Membrane Intrinsic Protein (PIP) Aquaporin Genes in Petals of Opening Carnation Flowers

Transport of water into cells is mediated by plasma membrane intrinsic protein (PIP) families of aquaporin, which are involved in petal cell expansion during flower opening. In this study, we performed comprehensive characterization of aquaporin family genes and analyzed the expression of PIP genes in petals of opening flowers to examine the role of PIPs in flower opening in the carnation (Dianthus caryophyllus L.). A database search of the genome sequence revealed the existence of 26 aquaporin genes with 8 members of the PIP subfamily in the carnation 'Francesco'. The expression of all the PIP genes was validated by the existence of expressed sequence tags, and expression analysis by quantitative reverse transcription-PCR showed that DcPIP2;1 and DcPIP1;1 are the two major PIP isoforms expressed in petals of the 'Pure Red' carnation. The transcripts of these two genes were also detected abundantly in other floral tissues including the calyx, style, receptacle, and ovary, as well as stems and leaves. The expression of DePIP2;1 and DcPIP1;1 in petals was maintained at a high level throughout the flower opening process. These data suggest a putative role of these PIPs in petal growth for flower opening.