Project description:Chloroplasts in differentiated bundle sheath (BS) and mesophyll (M) cells of maize (Zea mays) leaves are specialized to accommodate C4 photosynthesis. This study provides a reconstruction of how metabolic pathways, protein expression, and homeostasis functions are quantitatively distributed across BS and M chloroplasts. This yielded new insights into cellular specialization. The experimental analysis was based on high-accuracy mass spectrometry, protein quantification by spectral counting, and the first maize genome assembly. A bioinformatics workflow was developed to deal with gene models, protein families, and gene duplications related to the polyploidy of maize; this avoided overidentification of proteins and resulted in more accurate protein quantification. A total of 1,105 proteins were assigned as potential chloroplast proteins, annotated for function, and quantified. Nearly complete coverage of primary carbon, starch, and tetrapyrrole metabolism, as well as excellent coverage for fatty acid synthesis, isoprenoid, sulfur, nitrogen, and amino acid metabolism, was obtained. This showed, for example, quantitative and qualitative cell type-specific specialization in starch biosynthesis, arginine synthesis, nitrogen assimilation, and initial steps in sulfur assimilation. An extensive overview of BS and M chloroplast protein expression and homeostasis machineries (more than 200 proteins) demonstrated qualitative and quantitative differences between M and BS chloroplasts and BS-enhanced levels of the specialized chaperones ClpB3 and HSP90 that suggest active remodeling of the BS proteome. The reconstructed pathways are presented as detailed flow diagrams including annotation, relative protein abundance, and cell-specific expression pattern. Protein annotation and identification data, and projection of matched peptides on the protein models, are available online through the Plant Proteome Database.
Project description:Identification of target transcripts for the putative chloroplast RNA binding protein CFM2 in Zea mays. CFM2 was immunoprecipitated from a chloroplast extract. Chloroplast extracts were prepared from WT tissue. RNA from the pellet and from the supernatant for each pulldown was labelled with different fluoro-dyes and hybridized onto an array covering the complete maize chloroplast genome. Messages enriched in the immunoprecipitate from WT tissue are likely targets for CFM2.
Project description:Identification of target transcripts for the putative chloroplast RNA binding protein CRP1 in Zea mays. CRP1 was immunoprecipitated from a chloroplast extract. Chloroplast extracts were prepared from WT and CRP1-deficient tissue. RNA from the pellet and from the supernatant for each pulldown was labelled with different fluoro-dyes and hybridized onto an array covering the complete maize chloroplast genome. Messages enriched in the immunoprecipitate from WT tissue, but not enriched in mutant tissue are likely targets for CRP1.