Chloroplast and Nuclear Transcripts for Plastid Proteins inArabidopsis thaliana: Tissue Distribution in Mature Plants and During Seedling Development and Embryogenesis

Transcriptional profiling of the Arabidopsis embryo

We have used laser-capture microdissection to isolate RNA from discrete tissues of globular, heart, and torpedo stage embryos of Arabidopsis (Arabidopsis thaliana). This was amplified and analyzed by DNA microarray using the Affymetrix ATH1 GeneChip, representing approximately 22,800 Arabidopsis genes. Cluster analysis showed that spatial differences in gene expression were less significant than temporal differences. Time course analysis reveals the dynamics and complexity of gene expression in both apical and basal domains of the developing embryo, with several classes of synexpressed genes identifiable. The transition from globular to heart stage is associated in particular with an up-regulation of genes involved in cell cycle control, transcriptional regulation, and energetics and metabolism. The transition from heart to torpedo stage is associated with a repression of cell cycle genes and an up-regulation of genes encoding storage proteins, and pathways of cell growth, energy, and metabolism. The torpedo stage embryo shows strong functional differentiation in the root and cotyledon, as inferred from the classes of genes expressed in these tissues. The time course of expression of the essential EMBRYO-DEFECTIVE genes shows that most are expressed at unchanging levels across all stages of embryogenesis. We show how identified genes can be used to generate cell type-specific markers and promoter activities for future application in cell biology.

The Arabidopsis embryo mutant schlepperless has a defect in the chaperonin-60alpha gene

We identified a T-DNA-generated mutation in the chaperonin-60alpha gene of Arabidopsis that produces a defect in embryo development. The mutation, termed schlepperless (slp), causes retardation of embryo development before the heart stage, even though embryo morphology remains normal. Beyond the heart stage, the slp mutation results in defective embryos with highly reduced cotyledons. slp embryos exhibit a normal apical-basal pattern and radial tissue organization, but they are morphologically retarded. Even though slp embryos are competent to transcribe two late-maturation gene markers, this competence is acquired more slowly as compared with wild-type embryos. slp embryos also exhibit a defect in plastid development-they remain white during maturation in planta and in culture. Hence, the overall developmental phenotype of the slp mutant reflects a lesion in the chloroplast that affects embryo development. The slp phenotype highlights the importance of the chaperonin-60alpha protein for chloroplast development and subsequently for the proper development of the plant embryo and seedling.

Rosetteness in Portulaca grandiflora: an altered genetic expression

Rosetteness is either developmentally controlled or induced by various biotic and abiotic stresses. Prolonged vegetative growth and/or pruning seems to be inducing rosetteness in Portulaca grandiflora. Analysis of cellular extracts from rosette stems by SDS-PAGE, revealed induction of a polypeptide of high molecular mass (approximately equal to 58 kDa) and over-expression of a few lower molecular weight polypeptides. However, leaves showed no differences in the protein profiles.

Sequence and expression characteristics of three G-box-binding factor cDNAs from Brassica napus [corrected]

G-box-binding factors (GBFs) are bZIP proteins that have been implicated in the transcriptional control of a number of plant genes including the family for the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase. Using rbcS promoter regions as recognition site probes, we have cloned three Brassica GBFs designated as BnGBF1a, 1b and 2a. RNA gel blot analyses showed that all three BnGBF sequences give transcripts of the same size (1.3 kb) but in different amounts at a constant ratio in various tissues and developmental stages (1a > 2a > 1b). Transcript pools were largest in photosynthetically active organs such as leaves and cotyledons. Pool sizes correlated with those of total rbcS transcripts.