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

259 Characterization of Flowering Time Responses to Photoperiod and Temperature in Diverse
Ecotypes of Arabidopsis thaliana and its Modification by the Gene CO
Daniel Villegas, Jose Alcalde
Facultad de Agronomia e Ingenieria Forestal. Pontificia Universidad Catolica de Chile. Casilla 306-22 Santiago,
Chile.
Flowering time is the most important phenological event in plant life because determines adaptation to environment.
Among several environmental factors that affect flowering time, temperature and photoperiod are the most important, plants
show genetic variation in the responses to them. Roberts and Summerfield (1987) proposed a simple Linear Photothermal
Model to predict flowering time (f) in which rate of progress to flowering (i.e. the inverse of f or 1/f) is a linear and additive
function of average T and/or P from sowing to flowering. This model has been shown to fit well to several crop plants (peas,
soybean, etc) allowing quantification of the effects of different genes that modify the responses of the rate of progress to
flowering to T and P, and their influence on adaptability to different environments. This association between gene effects
on flowering and the parameters of the linear photothermal model allowed quantitative biological-functional interpretation
of the model. First, we tested this model on different ecotypes of Arabidopsis (representing wide range from early to very
late types) to know if their responses can be adequately represented by the model; and second, considering the advances
in understanding the molecular aspects of flowering control in this species, we studied the effect of genes that may play a
role in modulating control the flowering in Arabidopsis such CONSTANS, to determine if this gene has a major modifying
effect on specific parameters of the model. To do this, we create twelve different photothermal environments covering a 10
to 25 °C temperature range and a 10 to 20 h d -1 photoperiod range. All ecotypes were grown in these different environments
and days from sowing to flower, number of leaves at bolting and number of leaves at flowering were registered. The results
show that in all the ecotypes the linear photothermal model described well the response of rate of progress to flowering,
defining at least two planes of response (Thermal and Photothermal planes). With these results, time to flowering under
any photothermal environment covered by this study can be accurately predicted. Ecotype Wassilewskija was the earliest
to flower (33 d at 20 o C and 20 h d -1 ) while Zurich shows no flower response after 120 d at 14 o C and 10 h d -1 .
Research funded by FONDECYT, Chile. Project No 1040551. A CONICYT Scholarship for doctoral studies for D.V. is gratefully
acknowledged.
260 Sumoylation facilitates basal thermotolerance in Arabidopsis through salicylic acid–
independent processes
Chan Yul Yoo 1 , Kenji Miura 1 , Jing Bo Jin 1 , Jiyoung Lee 2 , Dae-Jin Yun 2 , Ray Bressan 1 , Paul Hasegawa 1
1
Center for Plant Environmental Stress Physiology, Purdue University, 2 Division of Applied Life Science
(BK21), Gyeongsang National University
AtSIZ1 is a SUMO (small ubiquitin modifier) E3 ligase that is an ortholog of PIAS-type proteins, which facilitates
SUMO conjugation to substrate target proteins (sumoylation) in Arabidopsis (Arabidopsis thaliana). siz1 T-DNA mutations
(siz1-2 and siz1-3) cause basal, but not acquired, thermosensitivity that is associated with hyper-accumulation of salicylic
acid (SA). Expression of NahG, which encodes a salicylate hydroxylase, effectively reduces endogenous SA accumulation
but enhances thermosensitivity resulting from siz1-2. High temperature induces SUMO1/2 conjugation to peptides in
wild type, but to a substantially lesser degree in siz1 mutants. In other organisms, heat shock transcription factor (HSF)
sumoylation regulates DNA binding and activation of heat shock protein (HSP) gene expression that facilitates thermal
adaptation. However, heat shock–induced expression of genes, including HSPs, APX1 and APX2, is similar in siz1 and
wild-type seedlings, further indicating that SIZ1 does not regulate acquired thermotolerance. Together, these results
indicate that sumoylation through SIZ1 facilitates basal thermotolerance through processes that are SA independent and
supersedes negative regulation of SA accumulation by the E3 ligase.