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Functional analysis of MAPK phosphatase AtMKP2 Cheng, Jia


Plants have evolved complex signal transduction pathways to sense and respond to the fast-changing environment. Among several crucial signaling pathways, MAPK pathways are known to be involved in regulating many biological processes, including development, cytokinesis, biotic and abiotic stress signaling and hormone signaling. As negative regulators of MAP kinases (MPKs), MAPK phosphatases (AtMKPs) can reverse the activation status of AtMPKs by dephosphorylating the activation sites of AtMPKs. There are 5 putative AtMKPs in the Arabidopsis genome and previous research has shown they play an important role in MAP kinase control. AtMKP2 has been shown to be a novel regulator for ozone stress responses, but how it might be involved in other biological aspects of Arabidopsis development and growth remains unknown. In this study, I examined the biological functions of AtMKP2 in trichome development. Phenotype analysis showed that in AtMKP2-RNAi mutants, trichome density as well as trichome branching number were affected. Both proAtMKP2: GUS signal and proAtMKP2:YFP signal showed that AtMKP2 was expressed in all development stages of developing trichomes. RT-PCR showed that the expression levels of several known trichome development regulators were affected in AtMKP2-RNAi plants. Genetic analysis of AtMKP2 RNAi x try and AtMKP2 RNAi x cpc double mutants showed phenotype consistent with the involvement of AtMKP2 in trichome development. To characterize the biological processes in which AtMKP2 plays a role, I also employed microarray approaches to examine the short-term transcriptional events in AtMKP2 LOF and GOF mutants. I was able to validate the microarray data of AtMKP2 LOF mutants using qRT-PCR. However, the gene expression patterns in AtMKP2 GOF mutants were not verified. This might result from the different overexpression levels of AtMKP2 in different biological replicates. Several defense-related genes showed transcriptional changes in both AtMKP2 LOF and GOF mutants, suggesting AtMKP2 might function in response to pathogen attack. In all, I studied the biological function of AtMKP2 in Arabidopsis trichome development and placed AtMKP2 within the network of known trichome development regulators. My microarray experiments provided some useful clues suggesting other biological functions of AtMKP2.

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