Manipulation of bolting time in lettuce for improved quality and greater sustainability.
Supervisor: Dr Steve Jackson, Warwick HRI, Warwick University, UK
Background
A recognised problem for lettuce growers is that the crop will sometimes initiate
bolting (i.e. flowering) in the field before it is harvested. When lettuce plants start to bolt
they produce secondary metabolites such as sesquiterpene lactones in the leaves which
have a bitter and unpleasant taste, thus rendering the crop unsaleable. As bolting is
promoted by higher temperatures this problem is likely to become more widespread with
the increasing average seasonal temperatures caused by global warming. Delayed bolting,
or greater holding ability in the field, is a desirable trait in commercial lettuce varieties as
it gives the grower more time to harvest the crop in the field, helps to preserve the quality
of lettuces sold for consumption, and increases sustainability by reducing wastage from
crop losses. We are exploiting our knowledge about genes controlling flowering time in
the model plant Arabidopsis to identify key genes that can be used to manipulate
flowering time in crop plants such as lettuce.
Aim: This project aims to understand the molecular mechanisms controlling bolting in
lettuce in order to be able to manipulate them to improve the holding ability of lettuce
plants in the field.
Lettuce genes that are homologous to genes known to control flowering in Arabidopsis
are being isolated. These genes affect flowering time specifically and do not have any
pleiotropic effects on plant growth. Induced variation in the sequences of these genes will
be identified in lines of an EMS mutagenised iceberg lettuce population, leading to the
isolation of lettuce lines with a defined genetic lesion causing delayed bolting/flowering
time. In addition we will screen a wild lettuce diversity set for natural sequence variation
in these specific genes that affect bolting time. The usefulness of naturally occurring
mutations in flowering time genes will be compared to that of induced mutations in the
same genes to see which is the most robust source of flowering time variation.
This project will use recently developed molecular biological techniques such as
TILLING and hybridisation to a lettuce tiling array to identify the mutations. The effect
of the mutations on the expression of key flowering time regulatory genes will be
analysed by real-time PCR. The project will also involve crossing the useful mutations
into lettuce breeding lines for the creation of new commercial lettuce varieties which will
be assessed for their usefulness by breeders. The student will be working as part of a
team with a post-doc and technician who are also working on the lettuce improvement
programme. This project is a prime example of knowledge transfer from model species to
crop plants.