TOWARDS SPATIO-TEMPORALLY RESOLVING COMPLEXITIES IN LEAF FORM

157 pagesAll life arises from a single cell. Sometimes, many cells are created from one and allow for complex life. In complex organisms, cell activity must be carefully orchestrated to initiate and mature organs of the correct placement, size and shape. Arabidopsis leaves offer a unique opportunity to study these developmental processes at the cellular level. From early initiation, leaves are amenable to repetitive imaging on a confocal microscope and plant cells do not move. Thus, the growth rates and geometric properties of cells in the developing lamina can be tracked over time. In this work, I have increased the resolution at which we understand cellular changes in developing WT and jaw-D leaves. jaw-D leaves ripple and wave while WT leaves are flat. The jaw-D mutant was discovered in a screen and results from the overexpression of microRNA319 (miR319) at its endogenous locus (Palatnik et al., 2003). miR319 targets mRNAs of members of the class II TCP transcription factor family for degradation (Palatnik et al., 2003, 2007). TCPs have been shown to target genes associated with differentiation and cell division (Efroni et al., 2008; Koyama et al., 2007; Schommer et al., 2008, 2014; Sun et al., 2017; Bresso et al., 2018). Therefore, it is hypothesized that proper spatial expression of miR319 is necessary to create simple, flat leaves in WT by modulating tissue growth and development (Alvarez et al., 2016; Nag et al., 2009; Challa et al., 2019). My work sheds new light on how miR319 contributes to leaf shape through spatial regulation of cell growth, division and differentiation. Future work from our lab will investigate the spatial relationships between miR319 and other developmental gene regulatory networks and their resultant tissue patterning effects.2025-01-1

Disentangling the Effect of Species Traits and Soil Chemistry on Decomposition in a Temperate Forest Ecosystem

From the Washington University Undergraduate Research Digest: WUURD, Volume 10, 2014-2015. Published by the Office of Undergraduate Research, Joy Zalis Kiefer Director of Undergraduate Research and Assistant Dean in the College of Arts & Sciences; Stacy Ross, Editor; Kristin Sobotka, Editor; Jennifer Kohl. Mentor: Scott A. Mangon and Jonathan A. Myer

An optimized pipeline for live imaging whole Arabidopsis leaves at cellular resolution

Abstract Background Live imaging is the gold standard for determining how cells give rise to organs. However, tracking many cells across whole organs over large developmental time windows is extremely challenging. In this work, we provide a comparably simple method for confocal live imaging entire Arabidopsis thaliana first leaves across early development. Our imaging method works for both wild-type leaves and the complex curved leaves of the jaw-1D mutant. Results We find that dissecting the cotyledons, affixing a coverslip above the samples and mounting samples with perfluorodecalin yields optimal imaging series for robust cellular and organ level analysis. We provide details of our complementary image processing steps in MorphoGraphX software for segmenting, tracking lineages, and measuring a suite of cellular properties. We also provide MorphoGraphX image processing scripts we developed to automate analysis of segmented images and data presentation. Conclusions Our imaging techniques and processing steps combine into a robust imaging pipeline. With this pipeline we are able to examine important nuances in the cellular growth and differentiation of jaw-D versus WT leaves that have not been demonstrated before. Our pipeline is approachable and easy to use for leaf development live imaging

Maize Introgression Library Provides Evidence for the Involvement of liguleless1 in Resistance to Northern Leaf Blight

Plant disease resistance is largely governed by complex genetic architecture. In maize, few disease resistance loci have been characterized. Near-isogenic lines are a powerful genetic tool to dissect quantitative trait loci. We analyzed an introgression library of maize (Zea mays) near-isogenic lines, termed a nested near-isogenic line library for resistance to northern leaf blight caused by the fungal pathogen Setosphaeria turcica. The population was comprised of 412 BC5F4 near-isogenic lines that originated from 18 diverse donor parents and a common recurrent parent, B73. Single nucleotide polymorphisms identified through genotyping by sequencing were used to define introgressions and for association analysis. Near-isogenic lines that conferred resistance and susceptibility to northern leaf blight were comprised of introgressions that overlapped known northern leaf blight quantitative trait loci. Genome-wide association analysis and stepwise regression further resolved five quantitative trait loci regions, and implicated several candidate genes, including Liguleless1, a key determinant of leaf architecture in cereals. Two independently-derived mutant alleles of liguleless1 inoculated with S. turcica showed enhanced susceptibility to northern leaf blight. In the maize nested association mapping population, leaf angle was positively correlated with resistance to northern leaf blight in five recombinant inbred line populations, and negatively correlated with northern leaf blight in four recombinant inbred line populations. This study demonstrates the power of an introgression library combined with high density marker coverage to resolve quantitative trait loci. Furthermore, the role of liguleless1 in leaf architecture and in resistance to northern leaf blight has important applications in crop improvement

Dynamic growth re-orientation orchestrates flatness in the Arabidopsis leaf

Abstract The growth and division of cells in plant leaves is highly dynamic in time and space, all while the cells cannot move relative to their neighbors. Given these constraints, models predict that long range regulatory systems must exist to maintain flat forms. Juxtaposed microRNA (miR-NA) networks could serve as one of these regulatory systems. One of these miRNAs, miR319 is thought to be expressed from the base of leaves and to promote growth by degrading class II TCP transcription factor mRNAs. A miR319 overexpression mutant, jagged and wavy ( jaw-D ) exhibits rippling and undulating leaves, consistent with biomechanical predictions that without genetic spatial coordination, tissues will deform. It has been theorized that jaw-D rippling results from overgrowth at the margins, however this does not fully address how miR319 expression from the base of wild-type (WT) leaves allows them to flatten. Here, we track the growth, cell division and cell maturation in live WT and jaw-D leaves to ask how miR319 expression in WT promotes flattening. This data revealed the importance of spatially distinct growth, division and differentiation patterns in WT leaves, which are missing in jaw-D. We propose that WT leaf cells respond to differentiation cues to dynamically re-orient growth in specific tissue locations and regulate flattening

The plant pathogen enzyme AldC is a long-chain aliphatic aldehyde dehydrogenase.

Aldehyde dehydrogenases are versatile enzymes that serve a range of biochemical functions. Although traditionally considered metabolic housekeeping enzymes because of their ability to detoxify reactive aldehydes, like those generated from lipid peroxidation damage, the contributions of these enzymes to other biological processes are widespread. For example, the plant pathoge

De Novo and Inherited Loss-of-Function Variants in TLK2 : Clinical and Genotype-Phenotype Evaluation of a Distinct Neurodevelopmental Disorder

Next-generation sequencing is a powerful tool for the discovery of genes related to neurodevelopmental disorders (NDDs). Here, we report the identification of a distinct syndrome due to de novo or inherited heterozygous mutations in Tousled-like kinase 2 (TLK2) in 38 unrelated individuals and two affected mothers, using whole-exome and whole-genome sequencing technologies, matchmaker databases, and international collaborations. Affected individuals had a consistent phenotype, characterized by mild-borderline neurodevelopmental delay (86%), behavioral disorders (68%), severe gastro-intestinal problems (63%), and facial dysmorphism including blepharophimosis (82%), telecanthus (74%), prominent nasal bridge (68%), broad nasal tip (66%), thin vermilion of the upper lip (62%), and upslanting palpebral fissures (55%). Analysis of cell lines from three affected individuals showed that mutations act through a loss-of-function mechanism in at least two case subjects. Genotype-phenotype analysis and comparison of computationally modeled faces showed that phenotypes of these and other individuals with loss-of-function variants significantly overlapped with phenotypes of individuals with other variant types (missense and C-terminal truncating). This suggests that haploinsufficiency of TLK2 is the most likely underlying disease mechanism, leading to a consistent neurodevelopmental phenotype. This work illustrates the power of international data sharing, by the identification of 40 individuals from 26 different centers in 7 different countries, allowing the identification, clinical delineation, and genotype-phenotype evaluation of a distinct NDD caused by mutations in TLK2

Distribution of influenza virus types by age using case-based global surveillance data from twenty-nine countries, 1999-2014

Background: Influenza disease burden varies by age and this has important public health implications. We compared the proportional distribution of different influenza virus types within age strata using surveillance data from twenty-nine countries during 1999-2014 (N=358,796 influenza cases)