An anaerobically inducible early (aie) gene family from rice

One of the major abiotic stresses that affect plant growth and development is anoxia or hypoxia. Plants respond to anoxia by regulation of gene expression at both the transcriptional and translational levels. Genes involved in such regulation are expected to be expressed soon after onset of anoxia. To date, however, anaerobically regulated genes that have been characterized predominantly encode enzymes for sugar phosphate metabolism, and are induced after several hours of anaerobic conditions. Early induced genes, those responding after 1-2 h of anoxia, have not been studied extensively. To study the early anaerobic response we investigated the most flooding-tolerant variety of rice, FR13A (flood-resistant). We used differential display techniques to identify cDNA fragments representing mRNAs that are induced within 90 min of anoxia. We isolated two cDNA fragments and one full-length cDNA that were induced to high levels. These cDNAs were found to be members of a family of 2-3 genes, which were called the aie (anaerobically inducible early) gene family. Northern blot analyses showed that the mRNA levels of aie genes peaked after 1.5 to 3 h of anoxia and were still at high levels after 72 h of anoxia. RNase protection assays showed 4-5 different protected bands indicating multiple transcripts from the aie gene family. Sequence analyses of the full-length cDNA showed an open reading frame that putatively encodes a 14 kDa protein of 127 amino acid residues. Neither the nucleotide nor the deduced amino acid sequences of this gene showed any significant homology to any known genes or proteins present in the GenBank or SwissProt databases. This novel gene, that is induced so early under anoxia in plants, may play an important role in plant metabolism under anaerobic conditions.