| Summary: | 碩士 === 國立臺灣大學 === 生化科技學系 === 100 === Four functional-unknown proteins, AtMAPR2, AtMAPR3, AtMAPR4 and AtMAPR5, possessing sequence 30-40% similarity to MAPR (membrane associated progesterone receptor) are studied in this group. The cytochrome b5 like heme/steroid binding domain are highly conserved in these proteins, and they bind progesterone and heme in animals. The UV-visible absorption spectra showed AtMAPRs are hemoproteins. (Kao, 2010, unpublished)
To study the physiological role of heme-binding ability of AtMAPR3, we analyzed whether or not the expression of AtMAPR3 are subjected to the heme concentration. In this study, 10-day-old seedlings were treated with a precursor of heme, δ-aminolevulinic acid (ALA). The results showed AtMAPR3 expression was three-fold-increased by ALA treatment under 16 h light / 8 h dark, and two-fold-increased under 24 h dark; however, when adding dipyridyl (DPD), the inhibitor of Fe-chelatase, the induction was blocked. The expression of AtMAPR3 was also induced by H2O2 and tert-butyl hydroxide (tBHP) about six-fold. H2O2 could be used as a second messenger to express the defence-related genes by jasmonic acid (JA), and JA increased AtMAPR3 expression about four-fold. To further study the physiology roles of AtMAPR3, we need to analyze the phenotype of AtMAPR3-KO and other mutants. In this study, AtMAPR3-KO, AtMAPR3-OX and WT were treated with H2O2, tBHP and methyl viologen (MeV), and the survival rate of AtMAPR3-KO was lower than WT slightly. However, AtMAPR3-OX showed no differences with WT.
The results revealed that the downstream products of ALA, such as Mg-protoporphyrin IX or heme, could be a signal molecule which involved in the expression of AtMAPR3. The expression of AtMAPR3 in response to ROS needs to be further investigated in physiological aspect.
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