Uncovering the evolutionary history of dual-targeted proteins in land plants

Lin Xu

Research output: ThesisDoctoral Thesis

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Abstract

Over 107 proteins have been found to be dual-targeted to either mitochondria and plastids, or mitochondria/plastids and peroxisomes. To investigate whether the orthologs of dual-targeted proteins in Arabidopsis thaliana (Arabidopsis) were also dual-targeted in Physcomitrella patens (P. patens) and Oryza sativa (rice), the targeting ability of the predicted protein that showed the highest level of sequence identity to the Arabidopsis dual-targeted protein was tested using GFP tagging. Study 1 found that dual targeting of proteins arose early in evolution and is conserved. Rice contains an ortholog that was dual-targeted in 28 out of 38 cases that were previously reported to be dual-targeted to mitochondria and plastids in Arabidopsis, while nine out of 13 cases of dual-targeted proteins were also dual-targeted in rice and P. patens. Moreover, the study of targeting ability of a number of proteins encoded by small gene families revealed that dual targeting ability of ascorbate peroxidase (APX) arose sometime after Picea glauca (P. glauca) diverged from P. patens. Dual targeting of APX was lost in rice following monocot divergence; a duplication event resulted in two genes with each encoding organelle-specific proteins. Six of the P. patens hexokinase (HXK) are dual-targeted while none of the four HXK proteins from Arabidopsis are, indicating that P. patens HXKs underwent gene duplication from a dual-targeted HXK, and dual targeting arose after P. patens diverged from other land plants. Finally, examination of the targeting ability of P. patens mitochondrial intermembrane import and assembly machinery protein 40 (Mia40) and predicted targeting ability of a number of other plant species showed that mitochondrial targeting of Mia40, as well as dual targeting of Mia40 arose relatively late in plant evolution, as it is only dual-targeted in angiosperms.
Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - 2013

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