Transcriptional landscapes of floral meristems in barley.

Organ development in plants predominantly occurs postembryonically through combinatorial activity of meristems; therefore, meristem and organ fate are intimately connected. Inflorescence morphogenesis in grasses (Poaceae) is complex and relies on a specialized floral meristem, called spikelet meristem, that gives rise to all other floral organs and ultimately the grain. The fate of the spikelet determines reproductive success and contributes toward yield-related traits in cereal crops. Here, we examined the transcriptional landscapes of floral meristems in the temperate crop barley (Hordeum vulgare L.) using RNA-seq of laser capture microdissected tissues from immature, developing floral structures. Our unbiased, high-resolution approach revealed fundamental regulatory networks, previously unknown pathways, and key regulators of barley floral fate and will equally be indispensable for comparative transcriptional studies of grass meristems.

The transcriptional landscape of polyploid wheat.

The coordinated expression of highly related homoeologous genes in polyploid species underlies the phenotypes of many of the world's major crops. Here we combine extensive gene expression datasets to produce a comprehensive, genome-wide analysis of homoeolog expression patterns in hexaploid bread wheat. Bias in homoeolog expression varies between tissues, with ~30% of wheat homoeologs showing nonbalanced expression. We found expression asymmetries along wheat chromosomes, with homoeologs showing the largest inter-tissue, inter-cultivar, and coding sequence variation, most often located in high-recombination distal ends of chromosomes. These transcriptionally dynamic genes potentially represent the first steps toward neo- or subfunctionalization of wheat homoeologs. Coexpression networks reveal extensive coordination of homoeologs throughout development and, alongside a detailed expression atlas, provide a framework to target candidate genes underpinning agronomic traits in wheat.

Functional annotation of the Arabidopsis P450 superfamily based on large-scale co-expression analysis.

Cytochrome P450 mono-oxygenases play prominent roles in a diverse set of metabolic pathways, but the function of most of these enzymes remains obscure. A bottleneck in the functional genomics of this superfamily constitutes hypothesis generation to identify potential substrates (or substrate classes) individual P450s may act on. We used publicly available large-scale expression data to perform co-expression analysis comparing the expression matrix of each P450 with those from more than 4000 selected genes across thousands of microarrays. Based on functional annotations of co-expressed genes from a diverse set of databases, co-expressed pathways were thus identified for each P450. Using this approach, most P450s with known functions were placed into their respective pathways, thereby proofing the concept. As examples, pathway mapping results identifying novel P450s potentially acting on flower-specific monoterpenes and root-specific triterpenes are described. Co-expression results for all Arabidopsis P450s will be presented as a web resource on the 'CYPedia' web pages (http://ibmp.u-strasbg.fr/CYPedia/).

Potato guard cells respond to drying soil by a complex change in the expression of genes related to carbon metabolism and turgor regulation.

Altering stomatal function by a guard cell-targeted transgenic approach with the aim of increased stress tolerance and crop yield requires knowledge of the natural fluctuations of stomatal gene expression under stress conditions. We developed a fast method for the isolation of RNA from epidermal fragments of potato leaves (Solanum tuberosum L. cv. Désirée), demonstrated that this RNA preparation is highly enriched in guard cell transcripts and used this method to investigate the response of gene expression in guard cells to mild drought stress. Drought was applied in planta by withholding water over a period of 2-4 days. In the following work responses observed under these conditions are called 'long-term' in contrast to immediate (short-term) stomatal opening and closing responses to environmental stress. We observed both gene-specific increases and decreases of steady-state transcript levels. In particular, the mRNA levels of sucrose synthase and sucrose-phosphate synthase were elevated 5.5-fold and 1.4-fold, respectively. In contrast, expression of an inwardly rectifying K+ channel from guard cells (kst1) and of a plasma membrane H(+)-ATPase (pha2) was reduced to 26% and 36%, respectively, of the expression in watered controls. In addition, expression of vacuolar invertase, UDP-glucose pyrophosphorylase, ADP-glucose pyrophosphorylase (large subunit), cytosolic glyceraldehyde-3-phosphate dehydrogenase, a sucrose/H+ cotransporter, and a novel isoform of phosphoenolpyruvate carboxylase were also reduced. Other genes exhibited unaltered expression. Compared with the response in whole leaves, the transcript levels of phosphoenolpyruvate carboxylase, vacuolar invertase, and cytosolic glyceraldehyde-3-phosphate dehydrogenase were regulated guard cell specifically. Most importantly, changes in steady-state transcript levels were complete before the onset of a decrease in leaf water potential, when drought-induced stomatal closure was already obvious. These data support the hypothesis that a systemic drought-stress signal acts not only on short-term stomatal movements but also on long-term gene expression in guard cells. Such long-term changes in gene expression might contribute to the fine-tuning of guard cell responses to environmental stimuli.

Characterization of pea chloroplastic carbonic anhydrase. Expression in Escherichia coli and site-directed mutagenesis.

A cDNA encoding the mature, chloroplast-localized carbonic anhydrase in pea has been expressed in E. coli. The enzyme is fully active and yields of up to 20% of the total soluble protein can be obtained from the bacteria. This expression system was used to monitor the effects of site-directed mutagenesis of seven residues found within conserved regions in the pea carbonic anhydrase amino acid sequence. The effects of these modifications are discussed with respect to the potential of various amino acids to act as sites for zinc coordination or intramolecular proton shuttles.

Cloning and sequence comparison of the mouse, human, and chicken engrailed genes reveal potential functional domains and regulatory regions.

We have isolated and characterized genomic DNA clones for the human and chicken homologues of the mouse En-1 and En-2 genes and determined the genomic structure and predicted protein sequences of both En genes in all three species. Comparison of these vertebrate En sequences with the Xenopus En-2 [Hemmati-Brivanlou et al., 1991) and invertebrate engrailed-like genes showed that the two previously identified highly conserved regions within the En protein ]reviewed in Joyner and Hanks, 1991] can be divided into five distinct subregions, designated EH1 to EH5. Sequences 5' and 3' to the predicted coding regions of the vertebrate En genes were also analyzed in an attempt to identify cis-acting DNA sequences important for the regulation of En gene expression. Considerable sequence similarity was found between the mouse and human homologues both within the putative 5' and 3' untranslated as well as 5' flanking regions. Between the mouse and Xenopus En-2 genes, shorter stretches of sequence similarity were found within the 3' untranslated region. The 5' untranslated regions of the mouse, chicken and Xenopus En-2 genes, however, showed no similarly conserved stretches. In a preliminary analysis of the expression pattern of the human En genes, En-2 protein and RNA were detected in the embryonic and adult cerebellum respectively and not in other tissues tested. These patterns are analogous to those seen in other vertebrates. Taken together these results further strengthen the suggestion that En gene function and regulation has been conserved throughout vertebrate evolution and, along with the five highly conserved regions within the En protein, raise an interesting question about the presence of conserved genetic pathways.