Evaluation of 41 elite and exotic inbred\u3ci\u3e Sorghum\u3c/i\u3e genotypes for high quality callus production

Interest is high in the genetic study and improvement of sorghum(Sorghum bicolor L. Moench), a crop of worldwide agronomic importance. The ability to initiate and maintain high quality (pigmentless, mucilage-free, fast growing, type II) callus cultures from a variety of sorghum genotypes is important for certain tissue culture-based genetic studies. The objective of this study was to identify high-quality callus-producing genotypes from a group of 41 diverse inbred sorghum lines. Callus cultures of 20 elite inbred sorghum genotypes and 21 inbred genotypes of exotic background were initiated from immature inflorescences. The cultures were subjected to several cycles of subculturing with selection for high quality callus growth, then rated for the callus quality traits pigment/tannin production, mucilage production, embryogenesis, and friability. Genotypic effects on each of the traits was highly significant. The range in quality of callus produced by different sorghum genotypes was large. Based on mean ratings assigned for each of the traits, 7 elite inbred genotypes and 5 nonelite genotypes were identified as producers of high quality callus

Genome-wide association analysis of stalk biomass and anatomical traits in maize.

BackgroundMaize stover is an important source of crop residues and a promising sustainable energy source in the United States. Stalk is the main component of stover, representing about half of stover dry weight. Characterization of genetic determinants of stalk traits provide a foundation to optimize maize stover as a biofuel feedstock. We investigated maize natural genetic variation in genome-wide association studies (GWAS) to detect candidate genes associated with traits related to stalk biomass (stalk diameter and plant height) and stalk anatomy (rind thickness, vascular bundle density and area).ResultsUsing a panel of 942 diverse inbred lines, 899,784 RNA-Seq derived single nucleotide polymorphism (SNP) markers were identified. Stalk traits were measured on 800 members of the panel in replicated field trials across years. GWAS revealed 16 candidate genes associated with four stalk traits. Most of the detected candidate genes were involved in fundamental cellular functions, such as regulation of gene expression and cell cycle progression. Two of the regulatory genes (Zmm22 and an ortholog of Fpa) that were associated with plant height were previously shown to be involved in regulating the vegetative to floral transition. The association of Zmm22 with plant height was confirmed using a transgenic approach. Transgenic lines with increased expression of Zmm22 showed a significant decrease in plant height as well as tassel branch number, indicating a pleiotropic effect of Zmm22.ConclusionSubstantial heritable variation was observed in the association panel for stalk traits, indicating a large potential for improving useful stalk traits in breeding programs. Genome-wide association analyses detected several candidate genes associated with multiple traits, suggesting common regulatory elements underlie various stalk traits. Results of this study provide insights into the genetic control of maize stalk anatomy and biomass

Chromosome-level genome assembly of a regenerable maize inbred line A188.

BACKGROUND The maize inbred line A188 is an attractive model for elucidation of gene function and improvement due to its high embryogenic capacity and many contrasting traits to the first maize reference genome, B73, and other elite lines. The lack of a genome assembly of A188 limits its use as a model for functional studies. RESULTS Here, we present a chromosome-level genome assembly of A188 using long reads and optical maps. Comparison of A188 with B73 using both whole-genome alignments and read depths from sequencing reads identify approximately 1.1 Gb of syntenic sequences as well as extensive structural variation, including a 1.8-Mb duplication containing the Gametophyte factor1 locus for unilateral cross-incompatibility, and six inversions of 0.7 Mb or greater. Increased copy number of carotenoid cleavage dioxygenase 1 (ccd1) in A188 is associated with elevated expression during seed development. High ccd1 expression in seeds together with low expression of yellow endosperm 1 (y1) reduces carotenoid accumulation, accounting for the white seed phenotype of A188. Furthermore, transcriptome and epigenome analyses reveal enhanced expression of defense pathways and altered DNA methylation patterns of the embryonic callus. CONCLUSIONS The A188 genome assembly provides a high-resolution sequence for a complex genome species and a foundational resource for analyses of genome variation and gene function in maize. The genome, in comparison to B73, contains extensive intra-species structural variations and other genetic differences. Expression and network analyses identify discrete profiles for embryonic callus and other tissues

Genetic Fine-Mapping of a Quantitative Trait Locus (QTL) Associated with Embryogenic Tissue Culture Response and Plant Regeneration Ability in Maize (Zea mays L.)

Embryogenic and regenerable tissue cultures are widely utilized in plant transformation, clonal propagation, and biological research applications. Germplasm utilized in those applications are limited, however, due to genotype-dependent culture response. The goal of this study was to identify genomic regions controlling embryogenic and regenerable tissue culture response in the globally important crop, maize ( L.), toward the long-term objective of developing approaches for genotype-independent plant genetic engineering and clonal propagation systems. An inbred maize line, WCIC2, nearly-isogenic to reference inbred B73, was developed by phenotypic selection and molecular marker analysis. WCIC2 has over 50x increase in tissue culture response relative to the recurrent parent, B73. This line was used to genetically fine-map a region on chromosome 3 controlling embryogenic and regenerable tissue culture response to a 23.9 Mb region. WCIC2 and derivatives will be useful materials to enable maize research in a genetic background similar to B73, and our genetic mapping results will advance research to identify causal genes controlling somatic embryo formation and plant regeneration in maize

Whole transcriptome profiling of maize during early somatic embryogenesis reveals altered expression of stress factors and embryogenesis-related genes.

Embryogenic tissue culture systems are utilized in propagation and genetic engineering of crop plants, but applications are limited by genotype-dependent culture response. To date, few genes necessary for embryogenic callus formation have been identified or characterized. The goal of this research was to enhance our understanding of gene expression during maize embryogenic tissue culture initiation. In this study, we highlight the expression of candidate genes that have been previously regarded in the literature as having important roles in somatic embryogenesis. We utilized RNA based sequencing (RNA-seq) to characterize the transcriptome of immature embryo explants of the highly embryogenic and regenerable maize genotype A188 at 0, 24, 36, 48, and 72 hours after placement of explants on tissue culture initiation medium. Genes annotated as functioning in stress response, such as glutathione-S-transferases and germin-like proteins, and genes involved with hormone transport, such as PINFORMED, increased in expression over 8-fold in the study. Maize genes with high sequence similarity to genes previously described in the initiation of embryogenic cultures, such as transcription factors BABY BOOM, LEAFY COTYLEDON, and AGAMOUS, and important receptor-like kinases such as SOMATIC EMBRYOGENESIS RECEPTOR LIKE KINASES and CLAVATA, were also expressed in this time course study. By combining results from whole genome transcriptome analysis with an in depth review of key genes that play a role in the onset of embryogenesis, we propose a model of coordinated expression of somatic embryogenesis-related genes, providing an improved understanding of genomic factors involved in the early steps of embryogenic culture initiation in maize and other plant species

Spatial and Temporal Divergence of Expression in Duplicated Barley Germin-Like Protein-Encoding Genes

Subfunctionalization is the process by which a pair of duplicated genes, or paralogs, experiences a reduction of individual expression patterns or function while still reproducing the complete expression pattern and function of the ancestral gene. Two germin-like protein (GLP)-encoding genes, GerB and GerF, are paralogs that belong to a small gene family in barley (Hordeum vulgare). Both genes share high nucleotide sequence similarity in coding and noncoding regions and encode identical apoplastic proteins. The use of RNA gel blots, coupled with single-stranded conformation polymorphism (SSCP) analysis of RT–PCR products, elucidated the developmental and tissue-specific expression patterns of each gene. Individual expression patterns provided evidence of both overlapping redundancy and early subfunctionalization. GerB is predominantly expressed in developing shoots, while GerF is predominantly expressed in seedling roots, developing spikes, and pericarp/testa. GerF promoter deletion studies located a region (−356/−97) responsible for high promoter activity and showed the ability of GerB and GerF upstream regions to drive gfp expression in coleoptiles, epicarps, and lemma/palea of developing spikes. The observed expression patterns are consistent with proposed roles in plant development and defense mechanisms for this gene family. These roles may explain why redundancy has been selectively maintained in this duplicate gene pair

Highly expressed genes in immature zygotic embryo explants in tissue culture.^a

a<p>Fragments per kilobase of exon per million fragments mapped (FPKM) at 0, 24, 36, 48, and 72 h after placement on tissue culture initiation medium and the assigned gene cluster number determined by k-means analysis.</p><p>Highly expressed genes in immature zygotic embryo explants in tissue culture.^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0111407#nt101" target="_blank">a</a>}</p

K-means clustering of genes expressed during early somatic embryogenesis.

<p>Log2 values of fragments per kilobase of exon model per million fragments mapped (FPKM) in genes with greater than zero FPKM expressed in immature zygotic embryo explants of maize inbred line A188 at 0, 24, 36, 48, and 72 h after placement on culture initiation medium grouped by expression trends as uncentered Pearson’s correlation coefficient in six k-means clusters.</p