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

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 1.23

A BRANCHED-CHAIN AMINO ACID AMINOTRANSFERASE ISOLATED FROM HORDEUM VULGARE IS DIFFERENTIALLY REGULATED BY ABIOTIC STRESS

M. MALATRASI*^,**, M. GULLI’*, M. CORRADI*, T.J. CLOSE**, N. MARMIROLI*

*) Dipartimento di Scienze Ambientali, Sez. Genetica e Biotecnologie Ambientali, Parco Area delle Scienze, 43100 Parma

**) Department of Botany and Plant Sciences, University of California, Riverside, USA

branched-chain amino acid aminotransferase, drought stress, barley, differential display, RT-PCR

Plants have developed several adaptive strategies to cope with environmental stress. Among the abiotic factors water availability is probably the most important in determining plant surviving and the most common to experience. The plant reacts to osmotic stress by a complex of responses leading to enhance the stress tolerance. These begin with stress perception, which initiates signal transduction pathways that cause changes at the cellular, physiological and developmental levels (involving hormones balance, modification of metabolites and repression or induction of many regulated genes). For genetic improvement programs the characterisation of new genes involved in stress response is fundamental. In fact many of the water-deficit induced genes encode for specific stress proteins with possible protective function, even if the only expression during stress does not guarantee that a gene product promote the ability of the plant to survive stress. In this research changes in the patterns of gene expression were analysed in drought, cold and ABA-treated seedlings of barley (Hordeum vulgare cv. Georgie) by differential display reverse transcriptase polymerase chain reaction (DDRT-PCR). Here we report the characterisation of the gene HvBCAT-1, corresponding to the clone DD12 isolated by DDRT-PCR, which belongs to the branched-chain amino acid aminotransferase (BCAT) gene family. BCAT catalyze the final transamination step in the pathway that produces essential amino acids leucine, isoleucine, and valine; these enzymes are also involved in the degradation of these three amino acids. BCAT activity has been detected in a wide range of eukariotic systems, including maize, spinach, peas, barley, tomato fruit, soybean, yeast, rats and human. So far identification and cloning of plant BACT genes has been successful in potato, where the two genes analyzed were demonstrated to be differentially expressed (Campbell et al., 2001) and in Arabidopsis where a family of seven members with different subcellular location was described (Diebold et al., 2002). Through the screening of a barley BAC library the genomic clone corresponding to DD12 has been isolated, and the structure of the gene has been elucidated. A comparative analysis with the corresponding genes from rice and Arabidopsis has been performed in order to identify conserved structural patterns. HvBCAT-1 has been mapped on chromosome 4H. The expression analysis of HvBCAT-1 transcript was analysed by both qualitative RT-PCR and Northern hybridisation and several conditions were tested. Through the RT-PCR analysis it was revealed the presence of the transcripts in all the analysed conditions, but Northern blot analysis demonstrated that the level of transcript increased under drought stress and ABA treatments as compared with control condition.

This is the first example of the identification of a BCAT gene in barley regulated by drought condition; this observation may suggest a role for BCAA metabolism in stress response that could be explained by the need for precursors for stress inducible secondary metabolites derived from these amino acids.