| Summary: | 博士 === 國立臺灣大學 === 園藝學研究所 === 96 === Papaya (Carica papaya L.) is an economically important fruit. The harvested area around the world is about 400 thousand hectares in 2006. Papaya plants are trioecious, with female, male and hermaphrodite, respectively. In hermaphrodite papaya, male flower and imperfect hermaphrodite flower are often observed because the floral organ development may be influenced by environmental and hormonal factors. Despite various causes led to malformation of papaya fruits, hermaphrodite papayas are favored worldwide for economic production. However, several drawbacks were observed during the formation of bisexual flowers, such as pistil degeneration and carpel-like anthers, which led to fruit malformation and resultant yield loss.
Sex expression in papaya flowers probably is determined very early during floral differentiation. In order to understand the roles played by the MADS-box genes in flower development and sex determination, cDNAs of E-class genes CpMADS1, CpMADS3 and a TM6 lineage of the B-class gene CpMADS2 were cloned from young flower buds of papaya. RT-PCR and real-time PCR analyses revealed that CpMADS1 and CpMADS3 were preferentially expressed in the carpel and also expressed in petals and stamens. CpMADS2 was expressed in both petals and stamens. These genes all expressed early during floral development. Comparison of ten papaya genotypes with 5 different sex phenotypes, viz. hermaphrodite, male, female, progeny-all-hermaphrodite, progeny-all-male, by Southern blot analysis of the genomic DNAs using probes of the three genes revealed similar restriction pattern and copy number, suggesting low correlation at genomic level of the three CpMADS genes with sex expression of papaya plants.
The CpMADS1 and CpMADS3 genes were constructed respectively in a binary vector and introduced into tobacco (Wisconsin 38) genome using Agrobacterium- mediated transformation. Amplification by polymerase chain reaction of genomic DNA confirmed the integration of the CpMADS1 and CpMADS3 genes into the transgenic tobacco genome. However, the phenotype of tansgenic tobacco plants carrying CpMADS1 or CpMADS3 were similar to the wild type.
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