title: Developmental and cell type characterization of bundle sheath and mesophyll chloroplast transcript abundance in maize.
abstract: The C4 grass Zea mays separates light and light-independent photosynthetic processes into two leaf cell types: bundle sheath (BS) and mesophyll (M). When mature, BS and M cells have anatomically and biochemically distinct chloroplasts that must cooperate to complete the process of photosynthesis. This report compares changes in transcript abundance between young and mature maize BS and M chloroplasts from specific segments of the leaf developmental gradient. Representative transcripts encoding components of Photosystem I, Photosystem II, Cytochrome b (6) f, thylakoidal NADH dehydrogenase; and the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase as well as nine nuclear-coded transcripts encoding chloroplast proteins were measured using quantitative RT-PCR. In addition, 887 nuclear genes encoding plastid-localized proteins, as well as 64 chloroplast and 34 mitochondrial genes were assayed utilizing a cDNA microarray. In 9 out of the 18 chloroplast-encoded genes and 84 genes from the 985 element microarray revealed greater than twofold transcript abundance differences between developmental stages and/or cell types. Patterns for transcripts associated with operons and gene clusters suggest differing regulatory mechanisms for particular polycistronic stretches. In summary, this report provides evidence that cell type-specific transcript abundance varies more in the young developing chloroplast, and differences plateau or subside as chloroplasts mature.
authors.affiliation: Department of Biology, Middle Tennessee State University, Box 60, Murfreesboro, TN 37132, USA.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Sharpe
authors.forename: Aditya
authors.initials: A
authors.lastname: Mahajan
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Takacs
authors.forename: David B
authors.initials: DB
authors.lastname: Stern
authors.forename: A Bruce
authors.initials: AB
authors.lastname: Cahoon
mesh_terms: D002736:Chloroplasts / Q000235:genetics*; D058503:Mesophyll Cells / Q000378:metabolism*; D018515:Plant Leaves / Q000235:genetics; D014158:Transcription, Genetic; D003313:Zea mays / Q000033:anatomy & histology / Q000235:genetics*