Identification of a GA-Related Cis-Element Regulating Male Peduncle Elongation in Papaya

Papaya (Carica papaya L.) is a tropical trioecious crop with males, hermaphrodites, and females. There is a sequence difference between male and hermaphrodite SHORT VEGETATIVE PHASE (CpSVP), making SVP a strong candidate gene controlling peduncle length in papaya. To study the spatial and temporal expression and function of CpSVP in Arabidopsis, we constructed a translation fusion structure based on the native promoter of SVP in papaya. In the 2kb promoter, strong GUS staining was observed in the floral organs and pedicels. In the 1kb promoter, there is no GUS expression in the floral organs, and it is barely detectable in pedicels. Removal of a GA responsive P-box cis-element in the 1kb promoter enhanced expression in the floral organs and pedicels, and elongated pedicels. In the transgenic Arabidopsis plants expressing the male CpSVP allele, there was an increase in pedicel length, but not in the plants expressing the hermaphrodite CpSVP allele. CpSVP-Y is capable of pedicel elongation, with no defects in reproductive organs. These findings imply that CpSVP-Y and this P-box play a major role in peduncle elongation but not sex determination in papaya.