Abstract
Methods for the delivery of exogenous substances to specific organelles are important because each organelle functions according to its own role. Specifically, mitochondria play an important role in energy production. Recently, plant mitochondrial transformation via delivery methods to mitochondria has been actively researched. Mitochondrial targeting sequences (MTSs) are essential for transporting bioactive molecules, such as nucleic acids, to mitochondria. However, the selectivity and efficacy of MTSs as carrier molecules in plants are not yet sufficient. In this study, we developed an effective MTS in plants via a quantitative comparison of the targeting functions of several MTSs. The presequence of HSP60 from Nicotiana tabacum, which is highly similar to that of several other model plants, showed high mitochondrial-targeting ability among the MTSs tested. This result suggests the applicability of the HSP60 presequence for MTSs in various plants. We further investigated this HSP60 presequence through stepwise shortening on the basis of secondary structure prediction, aiming to simplify synthesis and increase the solubility of the peptides. As shown by assessment of the mitochondrial targeting ability, the 15 residues from the N-terminus of the HSP60 presequence for the MTS, which is particularly conserved among various model plants, retained a targeting efficacy comparable to that of the full-length HSP60 presequence. This developed sequence from the HSP60 sequence is a promising MTS for transfection into plant mitochondria.