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

245 How Imidazolinone Kills Plant – The Transcriptome Profiling Of csr1-2 Upon Imidazolinone
Herbicide Treatment
Yuzuki Manabe, Brian Miki
Bioproducts and Bioprocesses, Research Branch, Agriculture and Agri-Food Canada, Ottawa, ON K1A 0C6,
Canada
An herbicide tolerant mutant, csr1-2, carries an equivalent mutation to commercially available Clearfield © crops.
CSR1 encodes a catalytic subunit of acetohydroxyacid synthase (AHAS, EC 2.2.1.6), which catalyzes the first step of
branched-chain amino acids, Ile, Leu, and Val, biosynthesis. csr1-2 is a dominant mutation which retains the activity of
AHAS but make AHAS resistant towards Imidazolinone due to reduced binding capacities. Despite their widespread
usage, the mechanism by which Clearfield © crops gain Imidazolinone herbicide tolerance has not yet been fully
characterized.
Transcription profiling combined with physiological characterization of imidazolinone-tolerant mutants will provide
further insights into its well characterized biochemical and genetic features. In wild-type plants, primary root growth is
inhibited within several hours of Imidazolinone treatment, but inhibition of shoot growth takes 3 days. Both grafting and
microarray expression experiment indicate that there is no suppressing signal transduced from the shoot to the roots to
inhibit root growth following Imidazolinone treatment. Based on these data, it has been hypothesized that Imidazolinone
acts by separate and independent mechanisms upon root and shoot growth. Our data show that Imidazolinone inhibition
of the root growth is not due to the death of the root apical meristem, and is reversible. Use of the ATH1 genechip
microarray has also revealed that branched-chain amino acid biosynthesis, amino acid transport and senescence take
part in the Imidazolinone response.
246 Role of Arabidopsis Zeaxanthin Epoxidase Gene in Responses to Osmotic and Oxidative
Stresses
Hye-Yeon Seok 1 , Hee-Yeon Park 1 , Sun-Ho Kim 1 , Bo-Kyung Park 1 , Ho-Seung Kim 1 , Chin Bum Lee 2 , Choon-Hwan Lee 1 ,
Yong-Hwan Moon 1
1
Department of Molecular Biology, Pusan National University, Busan 609-735, Korea, 2 Department of Biology,
Dong-eui University, Busan 614-714, Korea
Stoichiometric conversions of three xanthophylls pigments, involving the cycling between violaxanthin, antheraxanthin
and zeaxanthin, are known as xanthophyllcycle. Zeaxanthin epoxidase (ZEP) catalyzes the conversion of zeaxanthin to
violaxanthin and antheraxanthin. This step is considered as the first committed step in abscisic acid (ABA) biosynthesis
pathway. ABA plays important roles in environmental stress responses and many cellular processes including seed
development, dormancy germination and vegetative growth. As an aspect of the xanthophyll cycle, ZEP also is related
to the protection of plants from photooxidation because zeaxanthin may protect from light stress by directly quenching
free radicals and by making the thylakoidmembrane less permeable to oxygen.
In this study, to elucidate the function of ZEP in stress-response, we have generated transgenic plants overexpressing
Arabidopsis ZEP gene, and investigated responses to salt-, drought- and oxidative-stresses in the transgenic plants. First,
the ZEP gene was ectopically expressed under CaMV35S promoter in transgenic plants, and the ectopic expression of the
ZEP gene in the transgenic plants was confirmed by semi-quantitative RT-PCR. The transgenic plants also had almost no
zeaxanthin content, indicating the products of the overexpressed ZEP function. Using selected transgenic plants, we had
investigated responses to a few salts such as NaCl, LiCl, and KCl with various concentrations. As results, the transgenic
plants were more tolerant to Na + and Li + than wild-type (WT) plants, although responses of the transgenic plants were
different between Na + and Li + . The transgenic plants also showed tolerance to mannitol, suggesting that the transgenic
plants are tolerant to drought, and indeed the transgenic plants on soil showed tolerance to drought. Interestingly, the
transgenic plants were less tolerant to MV than WT, revealing that the transgenicplants are sensitive to ROS.
Taken together, our results suggest that the ZEP gene would be very useful to generate transgenic plants tolerant to
salt- and drought-stresses.