genetic and physical maps around the sex-determining m -locus of the dioecious plant asparagus
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Genetic and physical maps around the sex-determining M-
locus of the dioecious plant asparagus
Telgmann-Rauber et al. 2007
Background
• The M-locus controls sexual dimorphism– MM = supermale– Mm = male– mm = female
• In breeding male genotypes are desired– Higher yield– Longevity
• Markers at this locus would be useful to differentiate MM and Mm genotypes
Author’s goals
• Clone the region determining sex in asparagus from its position in the genome
• Develop markers in this region to use in asparagus breeding programs
Previous work
• The M-locus was fine-mapped to the sex chromosome L5 (Reamon-Büttner et al. 1998)
• 15 markers were used to construct a high density map around the M-locus (Jamsari et al. 2004)
Materials and Methods
• Bulked Segregant Analysis was used to develop new AFLPs– BSA uses two bulked pools of segregants differing
for 1 trait, where the pools differ is likely to be the region controlling the trait
• 809 F3 individuals were used for mapping – F3 individuals were created by selfing 3
andromonoecious plants in the F2 generation• 1-2% plants are andromonoecious
• New markers were mapped using JoinMap
Materials and Methods• Used a BAC library with 86,784 clones (5.5X
coverage)• BACs were screened with 5 AFLP primer
combinations• Positive clones were then aligned into contigs
using FPC software• 4 BACS were partially sequenced to identify
consensus sequences– Sequences were then blasted to identify putative ORFs
• Also ran FISH for physical mapping
Results
• Found 12 novel AFLPs cosegregating with the M-locus
• 11 BACs identified using 5 AFLP combos
• 39 BACs identified by chromosome walking– Aligned BACS still miss the M-locus
Markers
BACs
Figure 1 - Genetic and Physical Map
Figure 2 - sequencing results
53% of hits had homology to transposons/retrotransposons
FISH results
Probes based off BACs were found to hybridize to centromericand pericentromeric regions
Conclusions
• Created a detailed map with 26 markers spanning 8.01cM around the M-locus
• Could not close the gap around the M-locus– Marker density not high enough– M-locus not evenly represented in BACs
Conclusions
• Recombination frequency is reduced in the M-locus region
• Gene density in this region is low• The sex locus is enriched for repetitive
sequences• The locus is likely to be near a
cetromeric or pericentromeric region
Future direction
• Create more markers
• Use a different BAC library
• Expression profiling using subtractive hybridization/microarray technologies
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