75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

351 Potent Induction of flowering by elevated growth temperature in Arabidopsis thaliana
Sureshkumar Balasubramanian 1 , Sridevi Sureshkumar 1 , Janne Lempe 1 , Detlef Weigel 1, 2
1
Max-Planck Institute for Developmental Biology, 2 Salk Institute, La Jolla, USA
The transition from the vegetative to reproductive development in plants is influenced by endogenous developmental
cues as well as environmental signals. The major environmental factors that modulate floral transition include photoperiod,
light quality, vernalization (exposure to winter conditions) and growth temperature. In addition biotic and abiotic stress
have also been implicated in floral transition. Uncoupling and studying the specific effects of each of these variables have
been challenging. While the photoperiod and vernalization pathways have been explored in greater detail, the molecular
genetic basis of the effects other environmental variables on flowering remains enigmatic. We have addressed the effects
of growth temperature, using an assay that allows us to study the specific effects of temperature on floral transition,
through a combinatorial analysis of mutant and natural genetic variants. We report a strong induction of flowering in short
day grown plants at elevated growth temperature (27ºC as opposed to the commonly used 23ºC). The floral induction is
as strong as plant growth long day conditions at lower temperatures (16ºC LD) and there is extensive natural variation
in this response. Analysis of natural variants and flowering time mutants show FLOWERING LOCUS C (FLC) to be
a potent suppressor of thermal induction similar to its effects on photoperiodic induction. However suppression of
flowering at lower temperatures (23ºC) is not brought about exclusively through FLC. We have performed QTL mapping
to uncover additional loci involved in thermal response. Using recombinant inbred lines derived from parental lines that
differ in thermo sensitivity, we show a quantitative trait locus (QTL) for thermo sensitivity maps to the floral repressor
FLOWERING LOCUS M (FLM) indicating the thermal inductive pathway acts in the same genetic cascade that of FLM.
While flc mutants are more sensitive to temperature consistent with the repressive effect of FLC, the flm mutants are
less sensitive to temperature indicating the thermal induction acts in the same genetic cascade to that of FLM. Thermal
induction is independent of CONSTANS and is integrated at the level of floral pathway integrators. Microarray analysis
reveals the genomic response to thermal and photoperiodic floral induction differs and factors involved in alternative
splicing are enriched specifically during thermal shift. This enrichment appears to be associated with changes in splicing
patterns of at least some of the flowering time regulators.
352 Natural Variation in the Arabidopsis Ionome
Ivan Baxter 1 , Ana Rus 1 , Brett Lahner 1 , Elena Yakubova 1 , Monica Borghi 1 , Owen Hoekenga 2 , David Salt 1
1
Purdue University, 2 Boyce Thompson Institute for Plant Research, Cornell University
Uncovering the genes that underpin mineral ion homeostasis in plants is a critical first step towards understanding
the biochemical networks that regulate the plants ionome. The natural accessions of Arabidopsis thaliana provide a rich
source of genetic diversity that leads to phenotypic differences. Additionally, changes in the ionome in natural accession
may represent adaptations to the local growth environment. To identify genes responsible for variation in mineral ion
homeostasis among accessions, we measured the levels of Li, B, Na, Mg, P, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo
and Cd, in the shoots of 96 different accessions. The majority of accessions assayed showed significant differences in
the shoot accumulation of at least one element when compared with the reference accession Col-0. We also analyzed the
seed ionome of 12 of the accessions. Interestingly, there was very little correspondence between the elemental differences
in the shoots and seeds of the same accession. To determine the degree of overlap between the loci which control the
ionome in different accessions, we measured the elemental accumulation in the leaves of three Recombinant Inbred
Line populations: Col-4 x Ler-0, Bay-0 x Sha, and Cvi-1x Ler-2. Over 100 QTLs were identified in the populations,
including at least one for each element analyzed. More than 65% of the loci identified were unambiguously unique to a
single population. Analysis of the Cvi-1x Ler-2 population under Fe deficient growth conditions, revealed an additional
18 QTLs, only four of which were found in the original, Fe sufficient, growth condition. We have identified novel alleles
of three genes which alter the accumulation of Na, Mo and Co in different Arabidopsis accessions.