Localization of MLPK and SSP for Self-Incompatibility of Brassica oleracea by Fluorescence in situ Hybridization

To understand the physical locations of self-incompatibility (SI) genes and their linkage relationship, this study conducted fluorescence in situ hybridization (FISH) in Brassica oleracea genome using the probes of MLPK and SSP genes on prometaphase chromosomes, early pachytene chromosomes, and extended DNA fibers. The results indicated that the MLPK probe was hybridized onto the short arm of a pair of homologous prometaphase chromosomes, and the average percent distance from the centromere to the signal point was 53.41±3.16. The SSP probe was hybridized onto the long arm of a pair of homologous prometaphase chromosomes with the satellite, and the average percent distance from the centromere to the signal point was 78.36±4.26. Hybridization signals from the 3 types of cytological targets with different FISH resolutions showed that both MLPK and SSP might be located at a single-copy locus in B. oleracea genome. Repeated FISH analysis indicated that both MLPK and 5S rDNA probes were hybridized onto the same chromosomes. According to the karyotype standard, MLPK is primarily inferred on chromosome 2, and SSP on chromosome 7. The results presumably revealed that neither MLPK nor SSP should be linked to S-locus, and they were located on different chromosomes of B. oleracea.