Genes induced under anaerobic conditions in rice.

摘要

Anaerobiosis is one of the major stresses that affect plant growth and development. A lack of oxygen becomes a serious problem when plants are submerged for periods of one to two weeks. Plants respond to anoxia by regulation of gene expression at both the transcriptional and translational levels. The research presented in this dissertation involved isolation and characterization of two types of genes that are induced under anaerobic conditions. The first was a gene family that encodes the pyruvate decarboxylase (PDC) enzymes in rice. PDC is the first enzyme in the alcoholic fermentation pathway which is thought to play an important role in plant survival when plants are flooded. I isolated two pdc genes and their cDNAs, and investigated their temporal and spatial expression patterns under anaerobic conditions. The two genes were found to be regulated differently in shoots and roots of rice at different time periods of anoxia. These genes are now being used to modify their levels of expression in rice in order to assess whether a correlation exists between expression levels and flooding tolerance.;The second class of genes investigated includes the anaerobically induced early, or aie, genes those responding after 1-2 hours of anoxia. These genes have not been studied extensively in plants. I used differential display techniques to identify cDNA fragments which were induced within 90 minutes of anoxia. I isolated two partial cDNA fragments that were induced to high levels. These two partial cDNAs have 96% sequence homology and are members of a multigene family. Southern blots of genomic DNA and RNase protection assays showed that there were at least 2 to 3 different members present in the rice genome. Each member of this family was induced at different levels after different time periods of anaerobic conditions.;The anaerobic induction of both pdc and aie genes is down-regulated by translational inhibitors indicating that these genes require new protein synthesis for their induction. Sequencing of a full-length aie cDNA showed that this gene putatively encodes a 14 kD protein with 127 amino acid residues. The DNA and deduced amino acid sequence of this gene did not show any significant homology to any known genes or proteins present in the GenBank or SwissProt databases. This is the first report of a gene that is induced early under anoxia in rice. Both pdc and aie gene families may play important roles in plant metabolism under anaerobic conditions.