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Abstract

Wild strains of Arabidopsis thaliana grow and reproduce in a wide range of
environments on the Northern hemisphere. These wild strains show extensive
genetically-controlled phenotypic variation, which is a valuable resource both
for mechanistic studies and for understanding the basis of genomic and
genetic variation.
In order to explore the natural variation of flowering time, a systematic
flowering time screen was performed. Flowering time is influenced mostly by
light, ambient growth temperature and vernalization. Therefore, 165 A. thaliana
wild strains and several flowering time mutants were examined under
four growth conditions, differing in light, ambient growth temperature and
vernalization (16°C long day, 23°C long day, 23°C short day, 16°C long day
with vernalization). These studies revealed that there is substantial variation
in the flowering behaviour of A. thaliana wild strains. The large number of
investigated wild strains confirmed FRIGIDA (FRI) and FLOWERING LOCUS C
(FLC) as major determinants of flowering time, conferring the winter annual
habit. But even within the groups of winter annuals and rapidly cycling wild
strains there remains extensive continuous variation that cannot be explained
by FRI/FLC. In addition, much of the variation that remains after vernalization
is likely to be independent of FRI/FLC. Several interesting wild strains with
an attenuated response to ambient temperature, photoperiod or vernalization
respectively, could be identified.
Further analyses of FRIGIDA (FRI) and FLOWERING LOCUS C (FLC)
were undertaken. Non-functionality of FRI or FLC leads to an early flowering
response. Although the two known deletions in FRI (Col- and Ler-type
deletions) were present in almost half of the surveyed wild strains, we also
found early flowering strains that lacked these FRI deletions. Thirteen early
flowering strains without these prevalent deletions in FRI were further analyzed
by complementation crosses to FRI flc, fri FLC, fri flc and FRI FLC, as well
as sequence analysis. The early flowering phenotype of these strains could
be explained by new weak or non-functional alleles of FRI and FLC.