Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 4.22

BARLEY LEAVES SUBJECTED TO FAST- AND SLOW-OCCURRING WATER STRESS SHOW DIFFERENT TRANSCRIPT PROFILES

TALAME’ V.*, OZTURK N.Z.**, BOHNERT H.J.***, TUBEROSA R.*

*) Department of Agroenvironmental Science and Technology, University of Bologna, Italy

**) TUBITAK, Research Institute for Genetic Engineering and Biotechnology, Gebze/Kocaeli, Turkey

***) Departments of Plant Biology and of Crop Sciences, University of Illinois, Urbana, IL 61801, USA

microarray, barley, drought stress, mRNA, candidate gene

Transcriptome analysis through cDNA microarrays provides unprecedented opportunities to monitor genome-wide expression profiles and allows for the simultaneous determination of transcript abundance for a large number of genes. Commonly, microarray analyses for drought-stress responses are performed on samples collected from plants subjected to rather high-intensity stress treatments usually developed in a very short time (“shock” treatments); this experimental approach precludes the identification of those long-term responses in gene expression which may play an important role in the adaptation to drought under field conditions. The objective of this study was to monitor expression changes of regulated sequences in leaves of barley plants subjected to slow naturally-occurring drying conditions in soil (“stress” experiment) and to compare the results with those observed after rapid water loss in “shock” experiments. For this purpose, a cDNA microarray, including 1563 ESTs prevalently obtained from drought-stressed barley leaf and root tissues, was utilized in order to characterize the transcript profiles of two barley varieties (Tadmor and Er/Apm) well-adapted to low rainfall conditions. These varieties have been used as parental lines for identifying QTLs for yield and other agronomic traits under water-limited conditions (Telaut et al. 1997, Plant Breeding 116: 519-523). In the shock experiment, RNA was isolated from leaves of well-watered plants and from leaves of uprooted plants following a 20% loss in fresh weight. The results of this experiment have been reported in Ozturk et al. (2002, Plant Mol. Biol. 2002, 48: 551-573). In the stress experiment, leaf samples for RNA isolation were collected from plants grown in replicated pots and either maintained well-watered or subjected to an increasingly higher water deficit during a 10-day interval. At each sampling, soil moisture values, leaf relative water content (RWC) and the concentration of abscisic acid (ABA) and L-proline were determined. The two genotypes showed different drought-stress response courses for leaf RWC, ABA and proline concentrations, with Tadmor showing a higher capacity of osmotic adjustment. A significant but low correlation (from 0.29 to 0.41) was detected between changes in expression profiles of leaves subjected to the shock treatment compared with plants exposed to the slower and more natural drought treatment. The up-regulated transcripts include proteins known to be involved in drought stress responses such as, for example, dehydrins, jasmonate-responsive, metallothionein-like and late embryogenesis abundant (LEA) proteins. The majority of the strongly down-regulated transcripts are related to photosynthesis, photorespiration and the metabolism of amino acids and carbohydrates. When similar classes of transcripts were up- or down-regulated in both experiments, the shock treatment typically showed a higher number of transcripts and higher intensity ratios between water-stressed and control samples. These results indicate that changes in expression profiles may vary considerably according to the dynamics of the dehydration episode and suggest that only in a limited number of cases the results obtained with intense dehydration may predict the changes occurring when dehydration develops in the natural fashion that characterizes field conditions. To further investigate this issue, the results reported here will be compared with those obtained from RNA samples of Tadmor and Er/Apm plants which are being grown directly in soil in well-watered and drought stressed conditions. Our long-term goals are (I) to identify EST clones expressed under a wide range of drought treatments and (II) to map the most interesting EST clones. Analysis of the coincidence of the map position of EST clones with that of major QTLs controlling yield and other agronomically relevant traits in drought stressed barley and/or other related cereals may lead to the identification of candidate genes with an important adaptive role in sustaining yield under conditions of limited water availability.