| Plants can reduce oxygen into H2O to power their growth and development. It isinevitable to produce reactive oxygen species (ROS) if the reduction is carried out partly.Although it has been reported that a trace of ROS could play a pivotal role in growth andmetabolism, the accumulation of ROS would cause threat to plant, such as to impair proteinsmembrane lipids and other cytoplasm components, to introduce programmed cell death (PCD),to give rise to developmental abnormality of root hair and to bring about male sterility.Mitochondrial phosphate transporter/Phosphate carrier (MPT/PiC), which lies in themitochondrial inner membrane, plays an essential role in transferring orthophosphate (Pi)from cytoplast into the mitochondrial matrix. A total of three MPT genes have been clonedfrom the Arabidopsis genome, and overexpression of those three genes could cause thesensitivity to salt stress. However, there is much to be done to find out the relationshipbetween MPT and ROS and the mechanism by which MPT affects growth and development.Plants are faced with a variety of biotic and abiotic stresses in their growth anddevelopment, such as salt stress, drought stress and low temperature. Those stresses couldattenuate photosynthesis and respiration which in turn results in a serious of psychologicalmetabolic and molecular events. Although it has been proven MPTs could regulate theresponse of plants to salt stress by adjusting the synthesis of ATP and the metabolism ofgibberellin, it is not very clear about the relationship between MPT and osmotic stress.This research focuses on a member of MPT family, AtMPT3. We use OEMPT3plants tostudy the gene function in development and growth, which laid a solid foundation on futureresearch. The results are as follows:(1) By hydropathy plot analysis and three dimensional structure predictions, AtMPT3protein had character of mitochondrial phosphate transporter. The AtMPT3have three tandemdomains, which are made up of two transmembrane a-helices separated by a hydrophilic extramembrane loop. These domains, which are essential for mitochondrial targeting, are alsoconserved in all analyzed mitochondrial transporter proteins.(2) Expression patterns showed that AtMPT3was induced in many tissues at severaldevelopmental stages including pollens, especially in leaves, which indicated that it played acritical role in development.(3) Overexpression lines of AtMPT3had various defective phenotypes including dwarf,short curly dark leaf, pine-shape flowers, sterile pollens and cell death, which indicatedAtMPT3had a crucial role in development.(4) By chip analysis, overexpression of AtMPT3gived rise to many changes tometabolism processes in plant. Among them, the expression of genes related to ROS andelectron transport chain changed remarkably.(5) By quantitative real-time reverse transcription-PCR and histological stain, it has beenshowed that ROS level accumulated excessively in both cellular and transcriptional level inOEMPT3lines, which verified the gene chip results. Meanwhile, our results implied the levelof AtMPT3might affect ROS metabolism in plants.(6) Respiration rate analysis to OEMPT3lines showed that their electron transportationwas not changed, which excluded the possibility that the arrest of the respiration rate leads tothe accumulation of ROS. Therefore much needs to be done to clarify how the overexpressionof AtMPT3causes the accumulation of ROS.(7) The expression of AtMPT3was obviously induced by osmotic stress which can alsoinhibit seed germination and seedling establishment of OEMPT3lines. An increase ofrespiration rate and ATP contents could occur in OEMPT3lines compared with WT underosmotic stress condition. The changes of available energy might lead to the high osmoticsensitive phenotypes of OEMPT3lines. |
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