Abstract
Consumer demand for year-round strawberry fruit has increased the need to extend the cropping season. Perpetual flowering cultivars, which produce fruit continuously throughout the growing season, offer a promising solution. However, these cultivars typically exhibit reduced runner production, due to a genetic trade-off between flowering and runnering, presenting challenges for propagation and breeding efforts. Additionally, limited understanding of the mechanisms controlling these traits in the cultivated strawberry (Fragaria × ananassa) has hindered the application of advanced breeding or crop improvement tools. This PhD work aimed to better understand the genetic and molecular mechanisms underlying perpetual flowering and continuous runnering in strawberry, to contribute to the development of perpetual flowering cultivars with extended fruiting periods and improved propagation potential. In this thesis the control of perpetual flowering was explored by functionally studying key f lowering genes TFL1 and FT1 in F. x ananassa seasonal flowering cultivar ‘Malling Centenary’ and perpetual flowering cultivar ‘Calypso’ using CRISPR/Cas9 genome editing and phenotyping. FaTFL1 mutant lines exhibited early flowering and reduced runner production under long day conditions, validating its role as a floral repressor and demonstrating the regulatory link between these traits. FaFT1 mutant lines presented alteration in floral and fruit morphology suggesting its role in floral development. Furthermore, the genetic regulation of the trade-off between flowering and runnering was studied through genotyping-by-sequencing based QTL mapping using a woodland strawberry (Fragaria vesca) F₂ mapping population developed from a cross between an ecotype from Spain with continuous runnering habit and an accession from Iceland with a “standard” runnering habit. Two additive QTLs associated with continuous runnering were identified using interval mapping. The most significant QTL was narrowed and validated using cleave amplified polymorphic sequences (CAPS) for genotyping in a second validation population. Candidate genes associated with dormancy and axillary bud outgrowth were identified in both QTLs. Gene expression analysis showed a significant downregulation of two candidate genes in continuous runnering individuals supporting their role in the control of this trait. Finally, the functional role of the two main candidate genes for continuous runnering was explored through CRISPR/Cas9 targeted mutagenesis in F. vesca. Two mutant lines for one of the main candidate genes were obtained, however the editing efficiency was very low and consequently this part of the study was not pursued to completion. The work developed within this thesis provides valuable insight into the mechanisms controlling perpetual flowering and the developmental trade-off between generative and vegetative reproduction that could inform future crop improvement strategies.
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Claims 10
Claim · model-written summary
FaTFL1 mutant lines flowered early under long days.
- Taxon
- strawberry
_single2.jpg?width=60)
Fragaria ×ananassat0 - Material
- FaTFL1 mutant linese0
- Treatment
- FaTFL1 mutant linese0
- Gene
- FaTFL1e0
- Outcome
- floweringe0
- Direction
- earlye0
- Qualifier
- under long day conditionse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
_single2.jpg?width=500)
Verbatim
t0“strawberry”
e0“FaTFL1 mutant lines exhibited early flowering and reduced runner production under long day conditions”
Claim · model-written summary
FaTFL1 mutant lines produced fewer runners under long days.
- Taxon
- strawberryFragaria ×ananassat0
- Treatment
- FaTFL1 mutant linese0
- Gene
- FaTFL1e0
- Outcome
- runner productione0
- Direction
- reducede0
- Qualifier
- under long day conditionse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“strawberry”
e0“FaTFL1 mutant lines exhibited early flowering and reduced runner production under long day conditions”
Claim · model-written summary
FaFT1 mutant lines had altered floral morphology.
- Taxon
- strawberryFragaria ×ananassat0
- Treatment
- FaFT1 mutant linese0
- Gene
- FaFT1e0
- Outcome
- florale0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“strawberry”
e0“FaFT1 mutant lines presented alteration in floral and fruit morphology”
Claim · model-written summary
FaFT1 mutant lines had altered fruit morphology.
- Taxon
- strawberryFragaria ×ananassat0
- Treatment
- FaFT1 mutant linese0
- Gene
- FaFT1e0
- Outcome
- fruit morphologye0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“strawberry”
e0“FaFT1 mutant lines presented alteration in floral and fruit morphology”
Claim · model-written summary
Two additive QTLs associated with continuous runnering were identified.
- Taxon
- woodland strawberry
Fragaria vesca subsp. americanae1 - Gene
- QTLse0
- Outcome
- Two additive QTLs associated with continuous runneringe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Two additive QTLs associated with continuous runnering were identified using interval mapping”
e1“woodland strawberry (Fragaria vesca) F₂ mapping population”
Claim · model-written summary
The most significant QTL was narrowed and validated in a second population.
- Taxon
- woodland strawberryFragaria vesca subsp. americanae1
- Gene
- QTLe0
- Outcome
- QTL was narrowed and validatede0
- Comparator
- second validation populatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The most significant QTL was narrowed and validated using cleave amplified polymorphic sequences (CAPS) for genotyping in a second validation population”
e1“woodland strawberry (Fragaria vesca) F₂ mapping population”
Claim · model-written summary
Candidate genes linked to dormancy and axillary bud outgrowth were identified in both QTLs.
- Taxon
- woodland strawberryFragaria vesca subsp. americanae1
- Gene
- Candidate genese0
- Outcome
- Candidate genes associated with dormancy and axillary bud outgrowthe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Candidate genes associated with dormancy and axillary bud outgrowth were identified in both QTLs”
e1“woodland strawberry (Fragaria vesca) F₂ mapping population”
Claim · model-written summary
Two candidate genes were significantly downregulated in continuous runnering individuals.
- Taxon
- woodland strawberryFragaria vesca subsp. americanae1
- Material
- continuous runnering individualse0
- Gene
- two candidate genese0
- Outcome
- Gene expressione0
- Direction
- downregulatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Gene expression analysis showed a significant downregulation of two candidate genes in continuous runnering individuals”
e1“woodland strawberry (Fragaria vesca) F₂ mapping population”
Claim · model-written summary
Two mutant lines for one candidate gene were obtained.
- Taxon
- woodland strawberryFragaria vesca subsp. americanae1
- Gene
- one of the main candidate genese0
- Outcome
- Two mutant linese0
- Value
- Twoe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Two mutant lines for one of the main candidate genes were obtained, however the editing efficiency was very low”
e1“woodland strawberry (Fragaria vesca) F₂ mapping population”
Claim · model-written summary
Editing efficiency for the candidate gene was very low.
- Taxon
- woodland strawberryFragaria vesca subsp. americanae1
- Outcome
- editing efficiencye0
- Value
- very lowe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Two mutant lines for one of the main candidate genes were obtained, however the editing efficiency was very low”
e1“woodland strawberry (Fragaria vesca) F₂ mapping population”