| Summary: | 碩士 === 國立臺灣大學 === 植物科學研究所 === 101 === Flooding is a common environmental stress. When it happened, the catabolism in plants switched from aerobic respiration to anaerobic fermentation. Previous studies showed that oxygen deficiency induced several genes in sugar metabolism, glycolytic and fermentative pathways, including ALCOHOL DEHYDROGENASE (ADH). Our lab has used a negative-selection approach to isolate mutants that were defective in regulating the expression of ADH gene during seed germination and in seedlings under hypoxia stress. This approach used a transgenic line, AG2, in which expression pattern of ADH::GUS gene reflecting the endogenous ADH gene, for ethyl methanesulfonate (EMS) mutagenesis. In order to screen mutants that affect ADH gene expression, seeds were treated with allyl alcohol and selected for survivors. The surviving plants, designed allyl alcohol resistance (aar) mutants, were candidates for hypoxic regulatory mutants. To map and characterize one of these aar mutants, aar1, which is a recessive mutant, we first checked the sequence of the endogenous ADH gene to confirm that the mutation is not located at the ADH locus. Then, we crossed another ecotype Lansberg and aar mutant (C24 background), and collect the F2 plants for genetic mapping. We used markers on different chromosomes, and already narrowed down to two possible regions both at chromosome 3. Through its segregation rate, we hypothesize that there are two mutation sites in the aar1 mutant. One is a deletion in NPC6 locus, and the other one locates at a locus that is proximal to NPC6.
To characterize aar1 mutant, we examined the expression level of several key glycolytic and fermentative genes. The results showed that AAR1 only affects ADH gene, indicating that AAR1 may be involved in other signaling pathway. We also used microarrays to identify the differential gene expressions in aar1 mutant under hypoxic condition. We found groups of genes, including core hypoxia responsive genes and water transport genes, are down regulated in aar1 mutant, while genes that incode peroxidase are up regulated in aar1 mutant. According to this result, we hypothesize that AAR1 plays a negative role, and represses activity of peroxidases under hypoxia. On the other hand, AAR1 regulates ADH and other genes that encode water transporters may be mediate via repressors. Although the identity of the aar1 mutation is still not determined in this study, the genetic mapping and microarray results gave us some clues about the location of AAR1 on chromosome III, and the role that AAR1 plays under hypoxia stress.
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