Abstract
Leucoplasts are important organelles for the synthesis and storage of starch, lipids and proteins. However, molecular mechanism of protein import into leucoplasts and how it differs from that of import into chloroplasts remain unknown. We used pea seedlings for both chloroplast and leucoplast isolations to compare within the same species. We further optimized the isolation and import conditions to improve import efficiency and to permit a quantitative comparison between the two plastid types. The authenticity of the import was verified using a mitochondrial precursor protein. Our results show that, when normalized to Toc75, most translocon proteins are less abundant in leucoplasts than in chloroplasts. A precursor shown to prefer the receptor Toc132 indeed had relatively more similar import efficiencies between chloroplasts and leucoplasts compared to precursors that prefer Toc159. Furthermore we found two precursors that exhibited very high import efficiency into leucoplasts. Their transit peptides may be candidates for delivering transgenic proteins into leucoplasts and for analyzing motifs important for leucoplast import.
Highlights
Plastids are essential plant organelles responsible for functions ranging from photosynthesis and biosynthesis of amino acids and fatty acids to assimilation of nitrogen and sulfur (Leister, 2003; Sakamoto et al, 2008)
We found that leucoplasts have a different stoichiometry of translocon components compared to chloroplasts
It has been shown that pea roots contain a higher phenol oxidase activity than do pea leaves (Henry et al, 1979) and it is possible that isolated leucoplasts are more sensitive to oxidative damages than do isolated chloroplasts
Summary
Plastids are essential plant organelles responsible for functions ranging from photosynthesis and biosynthesis of amino acids and fatty acids to assimilation of nitrogen and sulfur (Leister, 2003; Sakamoto et al, 2008). All plastids are derived from embryonic proplastids and differentiate into different functional types in different tissues, for example chloroplasts in green tissues for photosynthesis, chromoplasts in petals and fruits for carotenoid pigment accumulation, and leucoplasts in non-green tissues for nutrient storage (Wise, 2006). To perform these specific functions, different plastid types require different proteins (Kleffmann et al, 2007; Brautigam and Weber, 2009; Barsan et al, 2012). Tic is a co-chaperone coordinating the actions of Tic110 and Hsp (for reviews see Li and Chiu, 2010; Shi and Theg, 2013; Paila et al, 2015)
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