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

257 Two NRT1 (PTR) Genes, When Overexpressed in Roots, Exhibited Cd-sensitive Phenotype
Chyn-Bey Tsai, Yi-Fang Tsay
Institute of Molecular Biology, Academia Sinica, Taipei 115, Taiwan
To date, there are only few of the 53 Arabidopsis NRT1 (Nitrate Transporter family 1 or PTR, Peptide Transporter
family) family members being characterized including 3 nitrate transporters (AtNRT1:1, AtNRT1:2 and AtNRT1:4)
and 2 peptide transporters (AtPTR2 and AtPTR1). Therefore, the in vivo functions of the majority in this gene family
remained unclear. To investigate physiological functions of these homologs, we took reverse genetic approach and
established a cadmium sensitivity assay by comparing the root elongation between the T-DNA insertion mutants of 53
NRT1 genes and wild type. Interestingly, mutants of At3g01350 and At5g14940 were found to be cadmium sensitive.
At3g01350 and At5g14940 are redundant genes due to the Chromosome duplication event. Quantitative real time PCR
reveals that the cadmium-sensitive phenotype was correlated with overexpression of either At5g14940 or At3g01350
in roots. Two-electrode voltage clamping analysis of Xenopus oocytes expressing At5g14940 indicates that, in addition
to nitrate, this transporter is capable to transport glutathione, and γ-EC which are precursors of phytochelatins used for
plant cadmium detoxification. In this study, we identify new substrates, glutathione and γ-EC, and new physiological
role for the NRT1 (PTR) family.
258 Arabidopsis Mitochondrial Prohibitin AtPHB4 Regulates A Stress Regulon Involved In Auxin
Homeostasis
Olivier Van Aken 2 , Kris Morreel 2 , Brigitte van de Cotte 2 , Hillel Fromm 1 , Wout Boerjan 2 , Dirk Inze 2 , Frank Van
Breusegem 2
1
Department of Plant Sciences, Tel Aviv, Israel, 2 Plant Systems Biology - VIB2, Ghent, Belgium
Prohibitins are evolutionarily conserved proteins with diverse roles in eukaryotic cell cycle progression, mitochondrial
electron transport, cellular signaling, aging and apoptosis. We demonstrate that prohibitins of Arabidopsis thaliana are
targeted to the mitochondria and are primarily expressed in apical tissues and dividing cells. Overexpression of AtPHB4
in transgenic Arabidopsis plants leads to increased shoot branching and leaf shape aberrations. A genome‐wide microarray
analysis of AtPHB4 OE transgenic plants revealed differential expression of a confined regulon of 34 transcripts. We infer
from a microarray meta‐analysis that this regulon is strongly co‐regulated during abiotic stress conditions and show that
one of its genes, a putative UDP‐glucosyltransferase UGT74E2, is a novel indole‐3‐butyric acid glucosyltransferase that
is involved in the increased shoot branching of AtPHB4 OE . We suggest that increased UGT74E2 activity steers auxin
catabolism in the apical tissues under unfavorable growth conditions and propose that AtPHB4 provides a previously
unidentified mitochondrial interface between stress perception and auxin homeostasis.