On the consequences of aluminium stress in rye: repressionof two mitoch ondrial malate dehydrogenase mRNAs

Abstract

Plants have developed several external and internal aluminium (Al) tolerance mecha-nisms. The external mechanism best characterised is the exudation of organic acidsinduced by Al. Rye (Secale cereale L.), one of the most Al-tolerant cereal crops, secretesboth citrate and malate from its roots in response to Al. However, the role of malatedehydrogenase (MDH) genes in Al-induced stress has not been studied in rye. Wehave isolated the ScMDH1 and ScMDH2 genes, encoding two different mitochondrialMDH isozymes, in three Al-tolerant rye cultivars (Ailes, Imperial and Petkus) and onesensitive inbred rye line (Riodeva). These genes, which have seven exons and sixintrons, were located on the 1R (ScMDH1) and 3RL(ScMDH2) chromosomes. Exon 1of ScMDH1 and exon 7 of ScMDH2 were the most variable among the different ryes.The hypothetical proteins encoded by these genes were classified as putative mito-chondrial MDH isoforms. The phylogenetic relationships obtained using both cDNAand protein sequences indicated that the ScMDH1 and ScMDH2 proteins are ortholo-gous to mitochondrial MDH1 and MDH2 proteins of different Poaceae species. Theexpression studies of the ScMDH1 and ScMDH2 genes indicate that it is more intensein roots than in leaves. Moreover, the amount of their corresponding mRNAs in rootsfrom plants treated and not treated with Al was higher in the tolerant cultivar Petkusthan in the sensitive inbred line Riodeva. In addition, ScMDH1 and ScMDH2 mRNAlevels decreased in response to Al stress (repressive behaviour) in the roots of both thetolerant Petkus and the sensitive line Riodeva.