Most proteins in chloroplasts are encoded by the nuclear genome and imported from the cytosol. Our lab is interested in understanding the regulations and sequential steps of the import process, from both the structural and the evolutionary perspectives. We have shown that functionality of translocon complexes are under tissue- and cell-type-specific regulations. We further found that chloroplast precursors can be divided into age-selective groups and identified the first functional motif within transit peptides for targeting old chloroplasts and leucoplasts. We have also identified a channel component and a co-chaperone in the translocon complex. Through analyzing the molecular function and structure of individual translocon components, and the interactions among components and with preproteins, we aim to understand how the translocon works at a molecular level and how it has evolved.