Thus, tomato is a valid model for further study of this system. The analysis revealed that there are four Toc159 homologues (slToc159-1, -2, -3 and -4) and two Toc34 homologues (slToc34-1 and -2) in tomato, and it was shown that tomato Toc159 and Toc34 homologues share high sequence similarity with the comparable import apparatus components from Arabidopsis and pea. In the work reported here, the Toc GTPase cDNAs from tomato were identified, cloned and analyzed. With the completion of the tomato genome sequencing project, it is now possible to identify putative homologues of the chloroplast import components in tomato. The majority of the known Toc components that mediate chloroplast protein import were originally identified in pea, and more recently have been studied most extensively in Arabidopsis. These proteins are translated in the cytosol as precursor proteins with cleavable amino-terminal targeting sequences called transit peptides. The translocon at the outer envelope membrane of chloroplasts (Toc) mediates the recognition and initial import into the organelle of thousands of nucleus-encoded proteins.
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