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
Figure 1 - Genetic and Physical Map
Markers
BAC
s
Figure 2 - sequencing results
53% of hits had homology to transposons/retrotransposons
FISH results
Probes based off BACs were found to hybridize to centromeric
and 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