Functional characterization and analysis of Carica papaya SHORT VEGETATIVE PHASE (CpSVP)

Carica papaya (papaya), a fruit cultivated in tropical and sub-tropical regions, is known for its nutritional benefits and medicinal applications. Sex in papaya is controlled by a pair of nascent sex chromosomes with two slightly different Y chromosomes that distinguish males (XY) and hermaphrodites (XYh). These two Y chromosomes diverged about 4,000 years ago with only 0.4% sequence difference between them. The hermaphrodite specific region of the Yh chromosome (HSY), its X chromosome counterpart, and the male specific region of the Y (MSY) were sequenced. This relatively small region contains the sex determination genes as well as gene responsible for sex-linked traits such as peduncle length. Carica papaya contains three types of sex chromosome-female X, male Y and hermaphrodite Yh, and the male plant is the only sex type that bears long peduncle with numerous flowers. This sexual morphology provides a reproductive advantage by optimizing male inflorescence structure to maximize the number of flowers it can bear. However, the gene(s) responsible for this male-linked trait is not identified. There are two genes that differentiate males and hermaphrodites: a carpel suppressor gene and a gene promoting the elongation of peduncle length. SHORT VEGETATIVE PHASE (CpSVP) is present in Y chromosome but absent from X chromosome and is disrupted in Yh chromosome made it one of the ideal candidate genes for controlling peduncle length or sex determination. Using Arabidopsis as a heterologous system, CpSVP-Y male allele is sub-functionalized on both pedicel length and flowering time regulation while the autosomal allele is only involved in the former function. The CpSVP-Yh allele had no effect on pedicel length or flowering time. In Arabidopsis, we studied the spatial and temporal expression of CpSVP during vegetative and reproductive stages. CpSVP-Y and CpSVP-Yh are expressed transcriptionally in the floral organs, pedicels and leaves under its native 2kb promoter regulation but only CpSVP-Y allele can cause pedicel elongation, with no defects in reproductive organs. CpSVP-A(2kb) also is expressed in the same tissues, albeit weakly in the pedicels. Under its native 1kb promoter, CpSVP-Y and CpSVP-Yh is not expressed in the floral organs and negligible expression in pedicels. We identified a GA response cis-element, a pyrimidine box (P-box) at -461 bp, that enhances CpSVP expression and pedicels with no effect on flowering time, elongating pedicels only for CpSVP-Y allele. Determining the gene responsible for peduncle elongation will enhance our understanding of sex determination and the evolution of sex chromosomes of papaya. These findings implicate that the P-box at -461 bp promoter region plays a major role in controlling the spatial and temporal expression of CpSVP-Y, which leads to peduncle length and flowering time regulation but not sex determination.U of I OnlyAuthor requested U of I Only Access for two years through thesis offic