Isolation and characterization of the papaya MADS-box E-class genes, CpMADS1 and CpMADS3, and a TM6 lineage gene CpMADS2.

Papaya (Carica papaya L.) plants are polygamous, with female, male, and hermaphroditic flowers. To understand the roles of MADS-box genes in flower development and sex determination, we cloned cDNAs of E-class genes CpMADS1 and CpMADS3 and a TM6 lineage of the B-class gene CpMADS2 from young flower buds of papaya. Reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR analyses revealed that CpMADS1 and CpMADS3 were preferentially expressed in the carpel and also in petals and stamens. CpMADS2 was expressed in both petals and stamens early during floral development. Comparison of 10 papaya genotypes of 5 different sex phenotypes - hermaphrodite, male, female, progeny-all-hermaphrodite, and progeny-all-male - by Southern blot analysis of genomic DNAs with probes of the 3 genes revealed similar restriction patterns and copy number, suggesting a low relationship of the 3 CpMADS genes with sex expression of papaya plants at the genomic level.