Grad Student Exit Seminar
Julie Nguyen
Thursday, May 2, 2019 at 3:00pm
Room 138 ERML
Title: Functional characterization and analysis of Carica
papaya SHORT VEGETATIVE PHASE (CpSVP)
Abstract: Carica papaya (papaya) is a tropical fruit, known for its nutritional benefits. Papaya contains three types of sex chromosomes-female X, male Y and hermaphrodite Yh , and the male plant is the only sex type that bears a long peduncle with numerous flowers. 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 peduncle length. SHORT VEGETATIVE PHASE (CpSVP) is present in Y chromosome, 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. CpSVP-Yh allele had no effect on pedicel length or flowering time. Under its native 1kb promoter, CpSVP-Y and CpSVP-Yh was not expressed in the floral organs with negligible expression in pedicels. We identified a GA response cis-element, a pyrimidine box (P-box) at -461 bp, that enhances CpSVP expression in reproductive organs and pedicels, with no effect on flowering time. 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, and allows males with their elongated peduncles to remain competitive against hermaphrodites.
