Abstract
BACKGROUND: Papaya is a major fruit crop in tropical and subtropical regions worldwide. It is trioecious with three sex forms: male, female, and hermaphrodite. Sex determination is controlled by a pair of nascent sex chromosomes with two slightly different Y chromosomes, Y for male and Yh for hermaphrodite. The sex chromosome genotypes are XY (male), XYh (hermaphrodite), and XX (female). The papaya hermaphrodite-specific Yh chromosome region (HSY) is pericentromeric and heterochromatic. Physical mapping of HSY and its X counterpart is essential for sequencing these regions and uncovering the early events of sex chromosome evolution and to identify the sex determination genes for crop improvement. RESULTS: A reiterate chromosome walking strategy was applied to construct the two physical maps with three bacterial artificial chromosome (BAC) libraries. The HSY physical map consists of 68 overlapped BACs on the minimum tiling path, and covers all four HSY-specific Knobs. One gap remained in the region of Knob 1, the only knob structure shared between HSY and X, due to the lack of HSY-specific sequences. This gap was filled on the physical map of the HSY corresponding region in the X chromosome. The X physical map consists of 44 BACs on the minimum tiling path with one gap remaining in the middle, due to the nature of highly repetitive sequences. This gap was filled on the HSY physical map. The borders of the non-recombining HSY were defined genetically by fine mapping using 1460 F2 individuals. The genetically defined HSY spanned approximately 8.5 Mb, whereas its X counterpart extended about 5.4 Mb including a 900 Kb region containing the Knob 1 shared by the HSY and X. The 8.5 Mb HSY corresponds to 4.5 Mb of its X counterpart, showing 4 Mb (89%) DNA sequence expansion. CONCLUSION: The 89% increase of DNA sequence in HSY indicates rapid expansion of the Yh chromosome after genetic recombination was suppressed 2-3 million years ago. The genetically defined borders coincide with the common BACs on the minimum tiling paths of HSY and X. The minimum tiling paths of HSY and its X counterpart are being used for sequencing these X and Yh-specific regions.
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Claims 11
Claim · model-written summary
The HSY map has a minimum tiling path of 68 overlapping BACs.
- Taxon
- Papaya
_-_DPLA_-_55200ec009622d7d42349f3583df310e.jpg?width=60)
Carica papayae1 - Outcome
- HSY physical mape0
- Value
- 68 overlapped BACse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
_-_DPLA_-_55200ec009622d7d42349f3583df310e.jpg?width=500)
Verbatim
e0“The HSY physical map consists of 68 overlapped BACs on the minimum tiling path”
e1“Papaya is a major fruit crop”
Claim · model-written summary
The HSY map covers all four HSY-specific Knobs.
- Taxon
- PapayaCarica papayae1
- Outcome
- HSY-specific Knobse0
- Value
- foure0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“covers all four HSY-specific Knobs”
e1“Papaya is a major fruit crop”
Claim · model-written summary
One gap remained near Knob 1 in the HSY map.
- Taxon
- PapayaCarica papayae1
- Outcome
- gap remained in the region of Knob 1e0
- Value
- One gape0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“One gap remained in the region of Knob 1”
e1“Papaya is a major fruit crop”
Claim · model-written summary
The X map comprises 44 BACs on its minimum tiling path.
- Taxon
- PapayaCarica papayae1
- Outcome
- X physical mape0
- Value
- 44 BACse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The X physical map consists of 44 BACs on the minimum tiling path”
e1“Papaya is a major fruit crop”
Claim · model-written summary
A repetitive-sequence gap remains in the X physical map and is filled on the HSY map.
- Taxon
- PapayaCarica papayae1
- Outcome
- one gap remaining in the middlee0
- Value
- one gape0
- Qualifier
- highly repetitive sequencese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“with one gap remaining in the middle, due to the nature of highly repetitive sequences. This gap was filled on the HSY physical map”
e1“Papaya is a major fruit crop”
Claim · model-written summary
Fine mapping in 1460 F2 individuals defined the non-recombining HSY borders.
- Taxon
- PapayaCarica papayae1
- Outcome
- borders of the non-recombining HSYe0
- Value
- 1460 F2 individualse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The borders of the non-recombining HSY were defined genetically by fine mapping using 1460 F2 individuals”
e1“Papaya is a major fruit crop”
Claim · model-written summary
The genetically defined HSY spans approximately 8.5 Mb.
- Taxon
- PapayaCarica papayae1
- Outcome
- genetically defined HSYe0
- Value
- 8.5 Mbe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The genetically defined HSY spanned approximately 8.5 Mb”
e1“Papaya is a major fruit crop”
Claim · model-written summary
The X counterpart extends about 5.4 Mb.
- Taxon
- PapayaCarica papayae1
- Outcome
- X counterparte0
- Value
- 5.4 Mbe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“its X counterpart extended about 5.4 Mb”
e1“Papaya is a major fruit crop”
Claim · model-written summary
The X counterpart includes a 900 Kb region containing shared Knob 1.
- Taxon
- PapayaCarica papayae1
- Outcome
- region containing the Knob 1 shared by the HSY and Xe0
- Value
- 900 Kbe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a 900 Kb region containing the Knob 1 shared by the HSY and X”
e1“Papaya is a major fruit crop”
Claim · model-written summary
The HSY sequence is expanded by 4 Mb relative to the corresponding X sequence.
- Taxon
- PapayaCarica papayae1
- Outcome
- DNA sequence expansione0
- Direction
- expansione0
- Value
- 4 Mb (89%)e0
- Comparator
- X counterparte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The 8.5 Mb HSY corresponds to 4.5 Mb of its X counterpart, showing 4 Mb (89%) DNA sequence expansion”
e1“Papaya is a major fruit crop”
Claim · model-written summary
Genetically defined borders coincide with shared BACs on the HSY and X tiling paths.
- Taxon
- PapayaCarica papayae1
- Outcome
- genetically defined borders coincide with the common BACse0
- Comparator
- minimum tiling paths of HSY and Xe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The genetically defined borders coincide with the common BACs on the minimum tiling paths of HSY and X”
e1“Papaya is a major fruit crop”