Project description:Genetic control of branching is a primary determinant of yield, regulating seed number and harvesting ability, yet little is known about the molecular networks that shape grain-bearing inflorescences of cereal crops. Here, 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. Developmental dynamics of genes targeted in vivo by the transcription factor RAMOSA1, a key regulator of determinacy, revealed potential mechanisms for repressing branches in distinct stem cell populations, including interactions with KNOTTED1, a master regulator of stem cell maintenance. Our results uncover discrete developmental modules that function in determining grass-specific morphology and provide a basis for targeted crop improvement and translation to other cereal crops with comparable inflorescence architectures.
Project description:In this study we investigated the developmental dynamics of genes targeted in vivo by the transcription factor RAMOSA1, a key regulator of determinacy, and revealed potential mechanisms for repressing branches in distinct stem cell populations in developing maize inflorescences. To identify targets of RA1 and to distinguish direct vs. indirect interactions, we performed Chromatin Immunoprecipitation (ChIP)-seq and compared the results to gene expression data (RNA-seq datasets for Eveland et al., 2013, submitted). We mapped genome-wide occupancy of RA1 and showed that it differently regulates modules of target genes based on spatiotemporal context. Plants expressing complementing RA1 transgenes tagged with HA or YFP were used in parallel experiments. Ear and tassel primordia were collected and tag-specific antibodies were used to pull down RA1 bound to its target loci. Genome-wide analysis of RA1 occupancy revealed thousands of putative binding sites (i.e. peaks significantly enriched (p < 1e-05) compared to input DNA).
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.
Project description:In this study we investigated the developmental dynamics of genes targeted in vivo by the transcription factor RAMOSA1, a key regulator of determinacy, and revealed potential mechanisms for repressing branches in distinct stem cell populations in developing maize inflorescences. To identify targets of RA1 and to distinguish direct vs. indirect interactions, we performed Chromatin Immunoprecipitation (ChIP)-seq and compared the results to gene expression data (RNA-seq datasets for Eveland et al., 2013, submitted). We mapped genome-wide occupancy of RA1 and showed that it differently regulates modules of target genes based on spatiotemporal context.
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.
Project description:In plants, small groups of pluripotent stem cells called axillary meristems are required for the formation of the branches and flowers that eventually establish shoot architecture and drive reproductive success. To ensure the proper formation of new axillary meristems, the specification of boundary regions is required for coordinating their development. We have identified two maize genes, BARREN INFLORESCENCE1 and BARREN INFLORESCENCE4 (BIF1 and BIF4), that regulate the early steps required for inflorescence formation. BIF1 and BIF4 encode AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) proteins, which are key components of the auxin hormone signaling pathway that is essential for organogenesis. Here we show that BIF1 and BIF4 are integral to auxin signaling modules that dynamically regulate the expression of BARREN STALK1 (BA1), a basic helix-loop-helix (bHLH) transcriptional regulator necessary for axillary meristem formation that shows a striking boundary expression pattern. These findings suggest that auxin signaling directly controls boundary domains during axillary meristem formation and define a fundamental mechanism that regulates inflorescence architecture in one of the most widely grown crop species.
Project description:Selection during evolution, whether natural or artificial, acts through the phenotype. For multifaceted phenotypes such as plant and inflorescence architecture, the underlying genetic architecture is comprised of a complex network of interacting genes rather than single genes that act independently to determine the trait. As such, selection acts on entire gene networks. Here, we begin to define the genetic regulatory network to which the maize domestication gene, teosinte branched1 (tb1), belongs. Using a combination of molecular methods to uncover either direct or indirect regulatory interactions, we identified a set of genes that lie downstream of tb1 in a gene network regulating both plant and inflorescence architecture. Additional genes, known from the literature, also act in this network. We observed that tb1 regulates both core cell cycle genes and another maize domestication gene, teosinte glume architecture1 (tga1). We show that several members of the MADS-box gene family are either directly or indirectly regulated by tb1 and/or tga1, and that tb1 sits atop a cascade of transcriptional regulators controlling both plant and inflorescence architecture. Multiple members of the tb1 network appear to have been the targets of selection during maize domestication. Knowledge of the regulatory hierarchies controlling traits is central to understanding how new morphologies evolve.
Project description:BackgroundOptimization of shade avoidance response (SAR) is crucial for enhancing crop yield in high-density planting conditions in modern agriculture, but a comprehensive study of the regulatory network of SAR is still lacking in monocot crops.ResultsIn this study, the genome-wide early responses in maize seedlings to the simulated shade (low red/far-red ratio) and also to far-red light treatment were transcriptionally profiled. The two processes were predominantly mediated by phytochrome B and phytochrome A, respectively. Clustering of differentially transcribed genes (DTGs) along with functional enrichment analysis identified important biological processes regulated in response to both treatments. Co-expression network analysis identified two transcription factor modules as potentially pivotal regulators of SAR and de-etiolation, respectively. A comprehensive cross-species comparison of orthologous DTG pairs between maize and Arabidopsis in SAR was also conducted, with emphasis on regulatory circuits controlling accelerated flowering and elongated growth, two physiological hallmarks of SAR. Moreover, it was found that the genome-wide distribution of DTGs in SAR and de-etiolation both biased toward the maize1 subgenome, and this was associated with differential retention of various cis-elements between the two subgenomes.ConclusionsThe results provide the first transcriptional picture for the early dynamics of maize phytochrome signaling. Candidate genes with regulatory functions involved in maize shade avoidance response have been identified, offering a starting point for further functional genomics investigation of maize adaptation to heavily shaded field conditions.