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Digital gene expression profiling for maize development - 2mm ear libraries, B73 vs. ramosa3 mutant

ABSTRACT: Genome-wide expression signatures detect specific perturbations in developmental programs and contribute to functional resolution of key regulatory networks. In maize (Zea mays) inflorescences, mutations in the RAMOSA (RA) genes affect determinacy of axillary meristems and thus alter branching patterns, an important agronomic trait. In this work, we developed and tested a framework for analysis of tag-based, digital gene expression (DGE) profiles using Illumina’s high-throughput sequencing technology and the newly-assembled B73 maize reference genome. We also used a mutation in the RA3 gene to identify putative expression signatures specific to stem cell fate in determinacy of axillary meristems. The RA3 gene encodes a trehalose-6-phosphate-phosphatase and may act at the interface between developmental and metabolic processes. Deep sequencing of DGE libraries, representing three biological replicate ear samples from wild-type and ra3 plants, generated 27 million 20-21nt reads with frequencies spanning four orders of magnitude. Unique sequence tags were anchored to 3´-ends of individual transcripts by DpnII and NlaIII digests, which were multiplexed during sequencing. We mapped 86% of non-redundant signature tags to the maize genome, which associated with 37,117 working gene models and un-annotated regions of expression. 66% of maize genes were detected at ≥ nine reads in immature maize ears. We used comparative genomics to leverage existing information from Arabidopsis and rice in functional analyses of differentially expressed maize genes. Results from this study provide a basis for analysis of short-read expression data in maize and resolved specific expression signatures that will help define mechanisms of action for the RA3 gene.

ORGANISM(S): Zea mays

PROVIDER: GSE24788 | GEO | 2010/10/20

SECONDARY ACCESSION(S): PRJNA132241

REPOSITORIES: GEO

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Project description:Genome-wide expression signatures detect specific perturbations in developmental programs and contribute to functional resolution of key regulatory networks. In maize (Zea mays) inflorescences, mutations in the RAMOSA (RA) genes affect determinacy of axillary meristems and thus alter branching patterns, an important agronomic trait. In this work, we developed and tested a framework for analysis of tag-based, digital gene expression (DGE) profiles using Illumina’s high-throughput sequencing technology and the newly-assembled B73 maize reference genome. We also used a mutation in the RA3 gene to identify putative expression signatures specific to stem cell fate in determinacy of axillary meristems. The RA3 gene encodes a trehalose-6-phosphate-phosphatase and may act at the interface between developmental and metabolic processes. Deep sequencing of DGE libraries, representing three biological replicate ear samples from wild-type and ra3 plants, generated 27 million 20-21nt reads with frequencies spanning four orders of magnitude. Unique sequence tags were anchored to 3´-ends of individual transcripts by DpnII and NlaIII digests, which were multiplexed during sequencing. We mapped 86% of non-redundant signature tags to the maize genome, which associated with 37,117 working gene models and un-annotated regions of expression. 66% of maize genes were detected at ? nine reads in immature maize ears. We used comparative genomics to leverage existing information from Arabidopsis and rice in functional analyses of differentially expressed maize genes. Results from this study provide a basis for analysis of short-read expression data in maize and resolved specific expression signatures that will help define mechanisms of action for the RA3 gene. 3' tag-based DGE libraries were generated using Illumina 1G technology. Libraries were prepared from 2mm ear samples and represent: 3 biological replicates of wild-type B73, 3 biological replicates of ramosa3 (ra3) mutants, and 1 technical replicate of a ra3 sample. Each sample was sequenced in a single lane of a flow cell. Each lane includes library preparations from both DpnII and NlaIII digests for that sample. Sequences from DpnII digests start with GATC and those from NlaIII digests start with ATG.

Project description:In this study we used the maize (Zea mays) inflorescence to investigate gene networks that modulate determinacy, specifically the decision to allow branch growth. We characterized developmental transitions by associating spatiotemporal expression profiles with morphological changes resulting from genetic perturbations that disrupt steps in a pathway controlling branching. These are the RNA-seq datasets used in this study. We profiled changes in gene expression during normal maize ear and tassel development and in developing maize ear primordia upon genetic perturbation of the RAMOSA branching pathway. For the wild-type ear and tassel developmental series, greenhouse-grown B73 inbred plants were used. 10mm ears were collected and sectioned as follows from tip to base along the developmental gradient: tip 1mm sampled (tip; Inflorescence Meristem/Spikelet Pair Meristem), next 1mm discarded, next 1mm sampled (mid; Spikelet Meristem), next 2mm discarded, next 2 mm sampled (base; Floral Meristem), and immediately frozen in liquid nitrogen. Sections from ~30 sampled ears were pooled for each of 2 biological replicates to represent tip, mid, and base stages. Tassels were hand-dissected, measured, separated by stage: 1-2mm (stg1), 3-4mm (stg2), and 5-7mm (stg3), and immediately frozen in liquid N. For each stage, ~20-30 tassels were pooled for each of 2 biological replicates. For ramosa mutant series, segregating families (1:1) of ra1-R, ra2-R, and ra3-fea1 mutant alleles, all introgressed at least 6 times into the B73 inbred background, were grown at CSHL Uplands Farm. Field-grown plants were genotyped and collected 6-7 weeks after germination (V7-V8 stage). First and second ear primordia were immediately hand-dissected, measured, and frozen in liquid nitrogen. For ra1, ra2 and ra3 mutants and wild-type controls, ears were pooled into two size classes: 1) 1mm class included a range of 0.7-1.5mm sized ears and nine ears were pooled for each of 2 biological replicates; 2) 2mm class included a range of 1.8-2.5mm sized ears and six ears were pooled for each of three biological replicates. Wild-type samples were proportional mixtures of heterozygote siblings segregating in ra1, ra2, and ra3 populations. Variability factors (e.g. ear size within class, ear rank on the plant, and time of collection) were distributed evenly across pooled samples.

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Digital gene expression profiling for maize development - 2mm ear libraries, B73 vs. ramosa3 mutant

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