QTL mapping of seedling tolerance to exposure to low temperature in the maize IBM RIL population.

Maize is a cold sensitive crop that exhibits severe retardation of growth and development when exposed to cold spells during and right after germination, including the slowdown in development of new leaves and in formation of the photosynthetic apparatus. Improving cold tolerance in maize would allow early sowing to improve crop yield by prolonging a growing season and by decreasing the negative effects of summer drought, diseases, and pests. Two maize inbreds widely incorporated into American maize germplasm, B73 and Mo17, exhibit different levels of tolerance to low temperature exposure at seedling stage.

Natural variation for gene expression responses to abiotic stress in maize.

Plants respond to abiotic stress through a variety of physiological, biochemical, and transcriptional mechanisms. Many genes exhibit altered levels of expression in response to abiotic stress, which requires concerted action of both cis- and trans-regulatory features. In order to study the variability in transcriptome response to abiotic stress, RNA sequencing was performed using 14-day-old maize seedlings of inbreds B73, Mo17, Oh43, PH207 and B37 under control, cold and heat conditions.

Killing two birds with one stone: Model plant systems as a tool to teach the fundamental concepts of gene expression while analyzing biological data.

Plants are ideal systems to teach core biology concepts due to their unique physiological and developmental features. Advances in DNA sequencing technology and genomics have allowed scientists to generate genome sequences and transcriptomics data for numerous model plant species. This information is publicly available and presents a valuable tool to introduce undergraduate students to the fundamental concepts of gene expression in the context of modern quantitative biology and bioinformatics.

RNA-directed DNA methylation enforces boundaries between heterochromatin and euchromatin in the maize genome.

The maize genome is relatively large (∼ 2.3 Gb) and has a complex organization of interspersed genes and transposable elements, which necessitates frequent boundaries between different types of chromatin. The examination of maize genes and conserved noncoding sequences revealed that many of these are flanked by regions of elevated asymmetric CHH (where H is A, C, or T) methylation (termed mCHH islands).

Authentic Research Experience and "Big Data" Analysis in the Classroom: Maize Response to Abiotic Stress.

Integration of inquiry-based approaches into curriculum is transforming the way science is taught and studied in undergraduate classrooms. Incorporating quantitative reasoning and mathematical skills into authentic biology undergraduate research projects has been shown to benefit students in developing various skills necessary for future scientists and to attract students to science, technology, engineering, and mathematics disciplines. While large-scale data analysis became an essential part of modern biological research, students have few opportunities to engage in analysis of large biological data sets.

Transposable elements contribute to activation of maize genes in response to abiotic stress.

Transposable elements (TEs) account for a large portion of the genome in many eukaryotic species. Despite their reputation as "junk" DNA or genomic parasites deleterious for the host, TEs have complex interactions with host genes and the potential to contribute to regulatory variation in gene expression. It has been hypothesized that TEs and genes they insert near may be transcriptionally activated in response to stress conditions.

Genomic distribution of maize facultative heterochromatin marked by trimethylation of H3K27.

Trimethylation of histone H3 Lys-27 (H3K27me3) plays a critical role in regulating gene expression during plant and animal development. We characterized the genome-wide distribution of H3K27me3 in five developmentally distinct tissues in maize (Zea mays) plants of two genetic backgrounds, B73 and Mo17. There were more substantial differences in the genome-wide profile of H3K27me3 between different tissues than between the two genotypes.

Spreading of heterochromatin is limited to specific families of maize retrotransposons.

Transposable elements (TEs) have the potential to act as controlling elements to influence the expression of genes and are often subject to heterochromatic silencing. The current paradigm suggests that heterochromatic silencing can spread beyond the borders of TEs and influence the chromatin state of neighboring low-copy sequences. This would allow TEs to condition obligatory or facilitated epialleles and act as controlling elements.

Brd1 gene in maize encodes a brassinosteroid C-6 oxidase.

The role of brassinosteroids in plant growth and development has been well-characterized in a number of plant species. However, very little is known about the role of brassinosteroids in maize. Map-based cloning of a severe dwarf mutant in maize revealed a nonsense mutation in an ortholog of a brassinosteroid C-6 oxidase, termed brd1, the gene encoding the enzyme that catalyzes the final steps of brassinosteroid synthesis.

Parent-of-origin effects on gene expression and DNA methylation in the maize endosperm.

Imprinting describes the differential expression of alleles based on their parent of origin. Deep sequencing of RNAs from maize (Zea mays) endosperm and embryo tissue 14 d after pollination was used to identify imprinted genes among a set of ~12,000 genes that were expressed and contained sequence polymorphisms between the B73 and Mo17 genotypes. The analysis of parent-of-origin patterns of expression resulted in the identification of 100 putative imprinted genes in maize endosperm, including 54 maternally expressed genes (MEGs) and 46 paternally expressed genes (PEGs).

Mapping maize genes: a series of research-based laboratory exercises.

Open-ended, inquiry-based multiweek laboratory exercises are the key elements to increasing students' understanding and retention of the major biological concepts. Including original research into undergraduate teaching laboratories has also been shown to motivate students and improve their learning. Here, we present a series of original laboratory exercises on fine mapping novel maize mutations producing interesting phenotypes.

Studying gene expression: database searches and promoter fusions to investigate transcriptional regulation in bacteria.

A laboratory project was designed to illustrate how to search biological databases and utilize the information provided by these resources to investigate transcriptional regulation in Escherichia coli. The students searched several databases (NCBI Genomes, RegulonDB and EcoCyc) to learn about gene function, regulation, and the organization of transcriptional units. A fluorometer and GFP promoter fusions were used to obtain fluorescence data and measure changes in transcriptional activity.

Aneuploidy causes tissue-specific qualitative changes in global gene expression patterns in maize.

Segmental aneuploidy refers to the relative excess or deficiency of specific chromosome regions. This condition results in gene dosage imbalance and often causes severe phenotypic alterations in plants and animals. The mechanisms by which gene dosage imbalance affects gene expression and phenotype are not completely clear.

High-throughput genetic mapping of mutants via quantitative single nucleotide polymorphism typing.

Advances in next-generation sequencing technology have facilitated the discovery of single nucleotide polymorphisms (SNPs). Sequenom-based SNP-typing assays were developed for 1359 maize SNPs identified via comparative next-generation transcriptomic sequencing. Approximately 75% of these SNPs were successfully converted into genetic markers that can be scored reliably and used to generate a SNP-based genetic map by genotyping recombinant inbred lines from the intermated B73 x Mo17 population.

Profiling expression changes caused by a segmental aneuploid in maize.

Background: While changes in chromosome number that result in aneuploidy are associated with phenotypic consequences such as Down syndrome and cancer, the molecular causes of specific phenotypes and genome-wide expression changes that occur in aneuploids are still being elucidated.

Results: We employed a segmental aneuploid condition in maize to study phenotypic and gene expression changes associated with aneuploidy. Maize plants that are trisomic for 90% of the short arm of chromosome 5 and monosomic for a small distal portion of the short arm of chromosome 6 exhibited a phenotypic syndrome that includes reduced stature, tassel morphology changes and the presence of knots on the leaves.

Natural variation for alleles under epigenetic control by the maize chromomethylase zmet2.

The contribution of epigenetic alterations to natural variation for gene transcription levels remains unclear. In this study, we investigated the functional targets of the maize chromomethylase ZMET2 in multiple inbred lines to determine whether epigenetic changes conditioned by this chromomethylase are conserved or variable within the species. Gene expression microarrays were hybridized with RNA samples from the inbred lines B73 and Mo17 and from near-isogenic derivatives containing the loss-of-function allele zmet2-m1.

Association of Arabidopsis topoisomerase IIA cleavage sites with functional genomic elements and T-DNA loci.

Topoisomerase IIA (Topo IIA) is an essential ubiquitous enzyme involved in controlling DNA topology during multiple processes of genome function, and has been implicated in the generation of double-stranded breaks (DSB) in genomic DNA prior to DNA integration in plant genomes. Despite extensive characterization of type II topoisomerases from bacteria, viruses and animals, no studies on the specificity of plant Topo IIA-mediated DNA cleavage have been reported. We mapped and characterized Arabidopsis thaliana Topo IIA (AtTopoIIA) cleavage sites and demonstrated that they were cleaved in vivo.

Transgene integration in plants: poking or patching holes in promiscuous genomes?

Transgene integration in plants transformed by either Agrobacterium or direct DNA delivery methods occurs through illegitimate recombination (IR). The precise mechanism(s) for IR-mediated transgene integration and the role of host double-strand break repair enzymes remain unknown. A recent wealth of sequenced transgene loci and investigations aimed at genetically dissecting transgene integration mechanism(s) have provided new insights into the process.

Complex transgene locus structures implicate multiple mechanisms for plant transgene rearrangement.

To more fully characterize the internal structure of transgene loci and to gain further understanding of mechanisms of transgene locus formation, we sequenced more than 160 kb of complex transgene loci in two unrelated transgenic oat (Avena sativa L.) lines transformed using microprojectile bombardment. The transgene locus sequences from both lines exhibited extreme scrambling of non-contiguous transgene and genomic fragments recombined via illegitimate recombination.