A novel dual-targeting signal at the C-terminus of AtPAP2 is essential to its growth-promoting effects

Abstract

Transgenic Arabidopsis thaliana overexpressing the purple acid phosphatase AtPAP2 displayed faster growth and higher seed yield phenotypes. AtPAP2 overexpression lines exhibited (a) higher biomass and seed yield (>50%); (b) higher sugars and TCA metabolities, and; (c) higher SPS and NR activities. A unique feature of AtPAP2, comparing to the other plant PAPs, is that it carries an additional hydrophobic motif at its C-terminus. Attachment of this hydrophobic motif to the C-terminus of GFP targeted it to both plastids and mitochondria in Arabidopsis cell line PSBD, whereas the putative signal peptide of AtPAP2 directed GFP to the cytosol. Ectopic expression of a truncated AtPAP2 without this C-terminal motif in Arabidopsis resulted in a loss of the fast-growing phenotypes, whereas ectopic expression of a truncated AtPAP2 without its putative N-terminal signal peptide in Arabidopsis did not hamper the fast-growing phenotypes. Hence, the unique C-terminal motif of AtPAP2 is a novel dual-targeting transit peptide to plastids and mitochondria and the biological actions of AtPAP2 are dependent on its targeting to these two organelles.