Plastid proteomics in higher plants: current state and future goals.

Plastids are plant cell organelles with many essential functions in plant metabolism. Among these are photosynthesis, amino acid and fatty acid biosynthesis, as well as the synthesis of several secondary metabolites. All plastids originate from undifferentiated proplastids, which are restricted to meristematic tissues and undifferentiated cells. Depending on the tissue, proplastids can develop into different plastid types (e.g. amyloplasts in storage tissue, chloroplasts in photosynthetic tissues, and chromoplasts in fruits and flowers). Other specialized plastid types include gerontoplasts, the plastids of senescent leaves that are important for resource allocation, oleoplasts, which are oil storage plastids in olive (Olea europaea), and etioplasts, the final stage of proplastid development in photosynthetic tissues in the dark (Wise, 2006). Finally, plastid types can possibly specialize to different degrees depending on cell type, developmental state, and (a)biotic conditions. An extreme case are the highly specialized C4 chloroplasts in bundle-sheath and mesophyll cells in the maize (Zea mays) leaf, with strong differences in proteome composition (Friso et al., 2010).With the ability to develop and differentiate, plastids add versatile biosynthetic capacity to the plant cell and are responsible for unique biosynthetic pathways that make plants unrivaled biochemical factories that are essential for life on earth. Thus, significant research efforts are underway that aim at understanding plastid biology in depth. A decade ago, the first plastid proteomics study was published and the potential of plastid proteomics was outlined (van Wijk, 2000). Since then, proteomics of plastids and plant (sub)proteomes has delivered on its promise. Here, we provide an update on the current status of plastid proteome research a decade after the first reports. ADVANCES IN PLASTID PROTEOMICS AND PROTEOMICS TECHNOLOGY