Abbott, Aaron (2010) The isolation of flowering time genes from lettuce to enable the manipulation of bolting time. PhD thesis, University of Warwick.

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Abstract

The time of bolting is an important factor in lettuce production because it
affects the yield and quality of the harvested crop. Bolting is promoted by
higher temperatures and is an increasing problem for growers with the current
trend for warmer summers. Lettuce plants that are in the early stages of
bolting are visibly indistinguishable from non-bolting plants, however there are
changes in the biosynthesis of secondary metabolites which are produced to
protect the young floral bud from insect attack. These compounds give the
lettuce plant a bitter taste and render the crop unsaleable. The development of
late bolting varieties, which would have a greater ‘holding ability’ in the field,
would result in reduced crop losses and an extension to the growing season.
In many plants, the timing of the transition from vegetative growth to flowering
is controlled by environmental cues which serve to communicate growth
conditions favourable for sexual reproduction and seed maturation. Studies in
Arabidopsis have led to the identification of several different pathways that
come together to regulate flowering time. Little research has been done on
these response pathways in lettuce, however, research has shown that
components of these pathways are conserved between Arabidopsis and other
crop species.
The aim of this project is to isolate genes regulating flowering time in lettuce in
order that novel alleles of these genes can be used to manipulate bolting time. A
lettuce BAC library has been screened and homologues of eight Arabidopsis
flowering time genes, principally from the autonomous pathway, have been
isolated. Functional orthologues of FLOWERING LOCUS T (FT) and the
autonomous pathway gene, FLK have been characterised in lettuce, suggesting
that there is conservation of the genes involved in flowering time in Arabidopsis
and lettuce.
Lettuce lines with a range of bolting times, including lines which bolt
significantly later than wild-type have been identified from EMS mutagenised
populations of cultivated lettuce and a diversity set of wild lettuce. Homozygous
lines from a Lactuca sativa cv. Larissa EMS population with a reproducible late
bolting phenotype when tested under commercial growing conditions have been
identified. These lines have been made available to Rijk Zwaan® for inclusion
in future breeding programs aimed at delaying bolting and improving the
‘holding’ ability’ of commercial lettuce crops.
Genomic sequence of selected lettuce flowering time genes have been compared
between the late bolting lines and wild-type looking for polymorphisms that
may account for the late bolting phenotype. Polymorphisms within these genes
were identified in some of the late bolting lines, however through analysing the
polymorphism in segregating backcross populations they have been shown not
to be causing the late bolting phenotype. Transcriptome sequencing has also
been performed to identify polymorphisms in other, possibly novel, genes which
may be causing the late bolting phenotype, as yet, no mutation segregating
within the late bolting lines has been identified.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QK Botany S Agriculture > SB Plant culture
Library of Congress Subject Headings (LCSH):	Lettuce -- Effect of temperature on, Lettuce -- Flowering time, Lettuce -- Genetics
Official Date:	September 2010
Dates:	Date Event September 2010 Submitted
Institution:	University of Warwick
Theses Department:	Warwick HRI
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Jackson, Stephen
Sponsors:	Biotechnology and Biological Sciences Research Council (Great Britain) (BBSRC)
Extent:	xviii, 356 leaves : ill., charts.
Language:	eng

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