Plastids differentiate into various functional types (chloroplasts, leucoplasts, chromoplasts, etc.) that have distinct proteomes depending on the specific tissue. Most plastid proteins are encoded by the nuclear genome, synthesized as higher molecular mass preproteins with an N-terminal transit peptide, and then post-translationally imported from the cytosol. Evidence for tissue-specific regulation of import into plastids, and subsequent modulation of plastid proteomes, has been lacking. We quantified protein import into isolated pea leaf chloroplasts and root leucoplasts and identified two transit-peptide motifs that specifically enhance preprotein import into root leucoplasts. Using a plastid preprotein expressed in both leaves and roots of stable transgenic plants, we showed that losing one of the leucoplast motifs interfered with its function in root leucoplasts but had no effect on its function in leaf chloroplasts. We assembled a list of all Arabidopsis plastid preproteins encoded by recently duplicated genes and show that, within a duplicated preprotein pair, the isoform bearing the leucoplast motif usually has greater root protein abundance. Our findings represent a clear demonstration of tissue-specific regulation of organelle protein import and suggest that it operates by selective evolutionary retention of transit-peptide motifs, which enhances import into specific plastid types.

质体可分为多种功能类型（叶绿体，白质体，色质体等），这些功能类型取决于特定的组织而具有不同的蛋白质组。大多数质体蛋白由核基因组编码，合成为具有N末端转运肽的更高分子量的前蛋白，然后从细胞质中翻译后导入。缺乏组织特异性调节输入质体以及随后调节质体蛋白质组的证据。我们量化蛋白质导入到分离的豌豆叶叶绿体和根白质中，并确​​定了两个转运肽基序，这些基元可以特异性地增强前蛋白质导入根白质中。使用稳定转基因植物的叶和根中都表达的质体前蛋白，我们发现失去一种白质体基序会干扰其在根部白质体中的功能，但对其叶绿体中的功能没有影响。我们组装了由最近重复的基因编码的所有拟南芥质体前蛋白的列表，并显示在重复的前蛋白对中，带有白质体基序的同工型通常具有更大的根蛋白丰度。我们的发现代表了对细胞器蛋白质进口的组织特异性调节的明确证明，并表明其通过转运肽基序的选择性进化保留来起作用，从而增强了向特定质体类型的进口。具有白质体基序的同工型通常具有更大的根蛋白丰度。我们的发现代表了对细胞器蛋白质进口的组织特异性调节的明确证明，并表明其通过转运肽基序的选择性进化保留来起作用，从而增强了向特定质体类型的进口。具有白质体基序的同工型通常具有更大的根蛋白丰度。我们的发现代表了对细胞器蛋白质进口的组织特异性调节的明确证明，并表明其通过转运肽基序的选择性进化保留来起作用，从而增强了向特定质体类型的进口。