Volume 55(1):197-212, 2011 Acta Biologica Szegediensis h t t p : / / w w w . s c i . u - s z e g e d . h u / A B S
levels of the hormone. O u r observations, however, indicated BR effects are also influenced by differential h o r m o n e responsiveness.
T h e aim of our studies w a s to characterize the expression of BRII and find out if it can influence d e v e l o p m e n t a l and o r g a n - s p e c i f i c changes in BR sensitivity. In order to determine the transcriptional activity, we generated transgenic plants carrying BRII promoter-reporter gene fusions. In BR!I p r o m - G t / 5 plants histochemical analysis of glucuronidase activity revealed close correlation b e t w e e n B R - d e p e n d e n t elongation and transgene activity. On the other hand, time-course m e a s u r e m e n t s with BRII p r o m- L U C lines s h o w e d strong induction of BRII activity upon germination, and that the expression level w a s increased by dark, whereas d e c r e a s e d by light treatments. T o test h o w differential B R I I accumulation can influence m o r p h o g e n i c events, we prepared transgenic lines that e x p r e s s in bril m u t a n t b a c k g r o u n d BRII ::LUC fusions, with full receptor activity, under the control of various organ-specific promoters. We f o u n d that BRII::LUC expression via the photosynthesis-associated CAB3. vascular SUC2, and procambial ATHB8 promoters resulted in different types of partial c o m p l e - mentation. which all resulted in disproportionate organ development. T h e o b s e r v e d expression patterns and m o r p h o g e n i c e f f e c t s of BRII expression strongly suggest a role for the receptor abundance in determining the intensities of local BR responses.
Supervisor: Miklós Szekeres E-mail: lidia@brc.hu
Identification of Novel Regulatory Factors of Plant Stress Responses Using New Genetic Approaches
Imma Pérez-Salamó
I n s t i t u t e o f P l a n t B i o l o g y , B i o l o g i c a l Research Center, H u n g a r i a n A c a d e m y o f Sciences, S z e g e d , H u n g a r y
Plants frequently encounter abiotic stress conditions, such as drought, soil salinity, unfavorable temperature, s u b m e r g e n c e or high light.
T h e s e conditions severely limit plant growth, development and productivity; plants have developed various d e f e n s e m e c h a n i s m s to increase stress adaptation. Drought and salinity are regarded as the m a j o r environmental stresses primarily i m p o s e o s m o t i c stress on plants. Still poorly understood how plant defense mechanisms is actually performed against salt and osmotic stresses. To dissect plant signaling pathways Arabidopsis lhaliana is the s u p r e m e genetic model, however as a glycophyte its tolerance to salt stress is limited.
Thellungiella salsuginea (halophila) is a close halophyte relative of Arabidopsis, tolerates drought and salinity as well as e x t r e m e cold, accordingly has turned to be a model system in salt tolerance research (Bressan 2001). Thellungiella possesses m a n y p r o s p e r o u s attributes of Arabidopsis, like short life cycle, self-pollination, small g e n o m e size (about 2X of Arabidopsis), and even its genetic t r a n s f o r m a t i o n c a n be accomplished by simple floral dipping. In addition Thellungiella genes show 9 0 - 9 5 % s e q u e n c e identity to Arabidopsis.
We have developed new genetic technologies to identify novel regulatory factors controlling salt tolerance. R a n d o m c D N A libraries of Arabidopsis and Thellungiella have been cloned into the estradiol inducible p E R 8 plant expression vector ( Z u o et al. 2 0 0 1 ) T h e transfor- mation competent c D N A library of Thellungiella has been introduced randomly into Arabidopsis plants, a n d 20,(XX) t r a n s f o r m a n t seedlings have been screened for salt tolerance in the presence of estradiol. Fourteen estradiol dependent salt tolerant lines have been isolated, and the inserted c D N A clones of these lines have been cloned and sequenced, the corresponding Thellungiella g e n e s were identified by Arabi- dopsis sequence homology search. Salt tolerance w a s confirmed by repeated germination and growth a s s a y s in 10 lines, and 2 lines have been selected for further characterization. T h e line T L I - 2 expressed the c D N A of a Thellungiella putative translational initiation factor, the insertion of T L l - 2 6 line contained the c D N A of a putative R N A - b i n d i n g aminopeptidase.
Another approach has been devised to identify salt stress regulatory factors at cellular level. Arabidopsis cell culture has been trans- f o r m e d with the Arabidopsis c D N A library and the transformed cells have been selected on plant culture media s u p p l e m e n t e d with salt and estradiol. Four cell colonies have been selected with superior growth on selective m e d i u m . c D N A inserts of these calli have been cloned and identified by sequencing. O n e of these c D N A inserts encoded a novel heat shock factor, its overexpression could improve various abiotic stress tolerance of transgenic Arabidopsis plants.
Bressan RA. Zhang C. Zhang H. Hasegawa PM. Bohnert HJ. Zhu J - K (200I) Learning from ihc Arabidopsis experience. The next gene search paradigm.
Planl Physiol 127:1354-1360
Zuo J. Niu QW. Chua N H (2000) An estrogen receptor-based transaclivator X V E mediates highly inducible gene expression in transgenic plants. Plant J 24:265-273
Supervisor: László Szabados E-mail: imma@brc.hu
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