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