Horner, Harry

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Nectar biosynthesis is conserved among floral and extrafloral nectaries

2021-04 , Chatt, Elizabeth C. , Mahalim, Siti-Nabilla , Mohd-Fadzil, Nur-Aziatull , Roy, Rahul , Klinkenberg, Peter M. , Horner, Harry , Hampton, Marshall , Carter, Clay J. , Nikolau, Basil , Biochemistry, Biophysics and Molecular Biology , Genetics, Development and Cell Biology

Nectar is a primary reward mediating plant–animal mutualisms to improve plant fitness and reproductive success. Four distinct trichomatic nectaries develop in cotton (Gossypium hirsutum), one floral and three extrafloral, and the nectars they secrete serve different purposes. Floral nectar attracts bees for promoting pollination, while extrafloral nectar attracts predatory insects as a means of indirect protection from herbivores. Cotton therefore provides an ideal system for contrasting mechanisms of nectar production and nectar composition between different nectary types. Here, we report the transcriptome and ultrastructure of the four cotton nectary types throughout development and compare these with the metabolomes of secreted nectars. Integration of these datasets supports specialization among nectary types to fulfill their ecological niche, while conserving parallel coordination of the merocrine-based and eccrine-based models of nectar biosynthesis. Nectary ultrastructures indicate an abundance of rough endoplasmic reticulum positioned parallel to the cell walls and a profusion of vesicles fusing to the plasma membranes, supporting the merocrine model of nectar biosynthesis. The eccrine-based model of nectar biosynthesis is supported by global transcriptomics data, which indicate a progression from starch biosynthesis to starch degradation and sucrose biosynthesis and secretion. Moreover, our nectary global transcriptomics data provide evidence for novel metabolic processes supporting de novo biosynthesis of amino acids secreted in trace quantities in nectars. Collectively, these data demonstrate the conservation of nectar-producing models among trichomatic and extrafloral nectaries.

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Microscopic Characterization of a Transposon-Induced Male-Sterile, Female-Sterile Mutant in Glycine max L.

2017-10-01 , Thilges, Katherine , Chamberlin, Mark , Horner, Harry , Albertsen, Marc , Horner, Harry , Genetics, Development and Cell Biology

Premise of research. A male-sterile, female-sterile mutant was discovered in a w4-m mutable line of Glycine max L. The mechanism of its sterility was not well understood. Therefore, different cytological and microscopic techniques were undertaken to better understand the process of mutant phenotype development. Molecular research indicated that mer3 was responsible for the sterility.

Methodology. Macro images were collected of whole plants, flowers, anthers, pods, and ovules. Chromosome spreads from anthers at various meiotic stages were examined. Confocal scanning laser microscopy using optical sectioning was utilized on whole anthers and ovules at various developmental stages. Whole mature anthers and isolated pollen images were collected and studied with SEM.

Pivotal results. In observations of the mutant, male cell development was found to begin normally and then digresses at metaphase I of meiosis, when abnormal segregation of chromosomes with reduced bivalent formation was observed. It was the abnormal formation of univalents and bivalents that led to male sterility. On the female side, the progression of development was arrested in the megagametophyte stage likely because of abnormal meiosis, leading to ovule abortion and female sterility.

Conclusions. The G. max male-sterile, female-sterile mutant was shown to have the same phenotype of mer3 sterility already shown in Arabidopsis, rice, yeast, and some animal systems.

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Comparison of Susceptible and Resistant Maize Hybrids to Colonization by Clavibacter michiganensis subsp. nebraskensis

2016-04-01 , Robertson, Alison , Sernett, Jeff , Horner, Harry , Robertson, Alison , Horner, Harry , Plant Pathology and Microbiology , Genetics, Development and Cell Biology

Clavibacter michiganensis subsp. nebraskensis causes Goss’s bacterial wilt and blight on maize and is managed primarily with C. michiganensis subsp. nebraskensis-resistant hybrids. To understand the mechanisms of resistance to infection by C. michiganensissubsp. nebraskensis, leaves of a susceptible and a resistant maize hybrid at the V4 to V5 developmental stage were wound inoculated with the pathogen. Blight lesion length was monitored, C. michiganensis subsp. nebraskensis colonizing ability was determined, and structural changes were observed using microscopy. Bacterial colonization preceded lesion development that occurred 4 to 5 days postinoculation in both hybrids. Lesion expansion in the susceptible hybrid was associated with a faster rate of C. michiganensis subsp. nebraskensis spread and multiplication in the tissues. In the resistant hybrid, spread and multiplication was reduced (P < 0.0001) and, at 16 days postinoculation, became imperceptible. Initially, C. michiganensis subsp. nebraskensis showed a preference for colonization of the metaxylem vessels in both hybrids. Spread from cell to cell was accomplished through disruption of cell walls, presumably from abundance of bacterial cells or enzymatic activity. Morphological responses of the resistant maize hybrid to infection by C. michiganensis subsp. nebraskensis were similar to those reported in maize inbred lines that were resistant to Stewart’s wilt caused by Pantoea stewartii. Resistance to C. michiganensis subsp. nebraskensis was associated with production of a dense matrix in the xylem that deformed and restricted movement of the bacterial cells.

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Research insights in Goss’s wilt and leaf blight

2014-12-03 , Nutter, Forrest , Horner, Harry , Eggenberger, Sharon , Robertson, Alison , Horner, Harry , Mallowa, Sally , Nutter, Forrest , Sernett, Jeff , Shepherd, Lisa

Goss’s wilt and leaf blight is caused by the bacterium Clavibacter michiganensis subsp. nebraskensis (Cmn). The disease was first reported in Nebraska in 1969 and soon after in the surrounding states including Iowa. Corn breeders identified resistance to the bacterium and by the 1980s the disease was no longer a threat to corn production except in eastern Nebraska. In 2008, Goss’s leaf blight was reported in eight counties in Iowa. In 2011, the disease was widespread throughout the state and up to 50 percent yield losses occurred in some fields.

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New insights on the functions of carbon‐calcium‐inclusions in plants

2020-06-24 , Karabourniotis, George , Horner, Harry , Horner, Harry , Bresta, Panagiota , Nikolopoulos, Dimosthenis , Liakopoulos, Georgios , Genetics, Development and Cell Biology

The carbon-calcium-inclusions (CCaIs) either as calcium oxalate crystals (CaOx) or amorphous calcium carbonate cystoliths are spread among most photosynthetic organisms. They represent dynamic structures with a significant construction cost and their appearance during evolution indicates an ancient origin. Both types of inclusions share some similar functional characteristics providing adaptive advantages, such as the regulation of Ca level, and the release of CO2 and water molecules upon decomposition. The latter seems to be essential under drought conditions and explains the intense occurrence of these structures in plants thriving in dry climates. It seems, however, that for plants CaOx may represent a more prevalent storage system compared to CaCO3 due to the multifunctionality of oxalate. This compound participates in a number of important soil biogeochemical processes, creates endosymbiosis with beneficial bacteria and provides tolerance against a combination of abiotic (nutrient deprivation, metal toxicity) and biotic (pathogens, herbivores) stress factors. We suggest a reevaluation of the roles of these fascinating plant structures under a new and holistic approach that could enhance our understanding of carbon sequestration at the whole plant level and provide future perspectives.

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Peruvian Window-Leaved Peperomia Taxa Display Unique Crystal Macropatterns in High-Altitude Environments

2017-02-01 , Horner, Harry , Wanke, Stefan , Horner, Harry , Oelschlägel, Birgit , Samain, Marie-Stéphanie , Genetics, Development and Cell Biology

Premise of research. Window-leaved Peperomia taxa (WPs) occur in the Peruvian Andes from near sea level to high altitudes and display curled leaves that are generally exposed to high irradiance and periodic drought, far different from the typically uncurled humid-forest, often-shaded Peperomia taxa. Even though representatives of the latter taxa, as well as other members of the Piperales, have been observed for the presence (type) and location (macropattern) of leaf crystals in previous studies, this special group of WP taxa has missed scrutiny. It was important to determine whether the WP taxa contained the same types of crystals in the same tissue locations and, if not, what any differences could be that are related to their anatomy, environment, and physiology.

Methodology. Living leaves of 35 available accessions from the 42 currently recognized taxa of WPs were chemically fixed, some cleared and/or vibratome sectioned or fractured to observe the internal leaf tissues for the presence of crystals composed of calcium oxalate with polarizing microscopy and SEM.

Pivotal results. WPs variably displayed three types of crystals, i.e., druses, prisms, and crystal sand, in the three major leaf tissues (multiple epidermis/hydrenchyma and palisade and spongy parenchymas). The WPs are distinctly different from uncurled humid-forest, often-shaded Peperomia taxa by often having prisms and crystal sand in their hydrenchyma and consistently having crystal sand in their spongy parenchyma. These results are additional synapomorphies for WPs belonging to the distinct subgenus Fenestratae within the genus Peperomia.

Conclusions. The partial or complete enclosing of the hydrenchyma by leaf curling and the resulting increased exposure of the abaxial leaf surface, with the subtending spongy parenchyma containing primarily crystal sand, suggests that these adaptations may provide protection for the primary internal photosynthetic tissue (palisade parenchyma) against photoinhibition by filtering and dispersing the solar irradiance and moderating the internal leaf temperature, two critical conditions allowing these taxa to live in extreme environments.

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Determination of the Gelation Mechanism of Freeze–Thawed Hen Egg Yolk

2015-11-02 , Horner, Harry , Acevedo, Nuria , Horner, Harry , Wang, Tong , Wang, Tong , Food Science and Human Nutrition , Genetics, Development and Cell Biology

A study of yolks stored up to 168 d at −20 °C was conducted to determine the gelation behavior and mechanism of freeze–thawed yolk. Methods used were rheology, native and sodium dodecyl sulfate polyacrylamide gel electrophoresis (native- and SDS-PAGE), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), particle size analysis, and proton nuclear magnetic resonance (1H NMR) spectroscopy for matrix mobility. Results indicate that both constituents of plasma and granules contributed to gelation of yolk under freezing. PAGE analyses suggest that granular proteins participated in aggregation during freeze–thaw. Increasing gel strength and particle size and decreasing water and lipid–water mobility indicate that lipoproteins or apolipoproteins aggregated. At storage times ≥84 d, increased protein and lipid mobility, the detection of smaller particles, and secondarily increased gel strength suggest the liberation of protein or lipoprotein components from previously formed aggregates and further aggregation of these constituents. Disruption of the gelled yolk matrix observed with TEM supported that ice crystal formation was required for gelation to occur. A two-stage dynamic gelation model is thus proposed.

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Systems analyses of key metabolic modules of floral and extrafloral nectaries of cotton

2019-11-27 , Nikolau, Basil , Horner, Harry , Mohd-Fadzil, Nur-Aziatull , Roy, Rahul , Klinkenberg, Peter , Horner, Harry , Hampton, Marshall , Carter, Clay , Nikolau, Basil , Genetics, Development and Cell Biology , Genetics, Development and Cell Biology

Nectar is a primary reward mediating plant-animal mutualisms to improve plant fitness and reproductive success. In Gossypium hirsutum (cotton), four distinct trichomatic nectaries develop, one floral and three extrafloral. The secreted floral and extrafloral nectars serve different purposes, with the floral nectar attracting bees to promote pollination and the extrafloral nectar attracting predatory insects as a means of indirect resistance from herbivores. Cotton therefore provides an ideal system to contrast mechanisms of nectar production and nectar composition between floral and extrafloral nectaries. Here, we report the transcriptome, ultrastructure, and metabolite spatial distribution using mass spectrometric imaging of the four cotton nectary types throughout development. Additionally, the secreted nectar metabolomes were defined and were jointly composed of 197 analytes, 60 of which were identified. Integration of theses datasets support the coordination of merocrine-based and eccrine-based models of nectar synthesis. The nectary ultrastructure supports the merocrine-based model due to the abundance of rough endoplasmic reticulum positioned parallel to the cell walls and profusion of vesicles fusing to the plasma membranes. The eccrine-based model which consist of a progression from starch synthesis to starch degradation and to sucrose biosynthesis was supported by gene expression data. This demonstrates conservation of the eccrine-based model for the first time in both trichomatic and extrafloral nectaries. Lastly, nectary gene expression data provided evidence to support de novo synthesis of amino acids detected in the secreted nectars.

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IRE1, a component of the unfolded protein response signaling pathway, protects pollen development in Arabidopsis from heat stress

2016-10-01 , Deng, Yan , Srivastava, Renu , Quilichini, Teagen , Dong, Haili , Bao, Yan , Horner, Harry , Horner, Harry , Howell, Stephen , Computer Science , Plant Pathology and Microbiology , Genetics, Development and Cell Biology , Plant Sciences Institute

The unfolded protein response (UPR) is activated by various stresses during vegetative development in Arabidopsis, but is constitutively active in anthers of unstressed plants. To understand the role of the UPR during reproductive development, we analyzed a double mutant, ire1a ire1b. The double mutant knocks out the RNA splicing arm of the UPR signaling pathway and is fertile at room temperature, but is male sterile at modestly elevated temperature (ET). The conditional male sterility in the mutant is a sporophytic trait, and when the double mutant was grown at ET, defects appeared in the structure of the tapetum. As a result, the tapetum in the double mutant failed to properly deposit the pollen coat at ET, which made pollen grains clump and prevented their normal dispersal. IRE1 is a dual protein kinase/ribonuclease involved in the splicing of bZIP60 mRNA, and through complementation analysis of various mutant forms of IRE1b, it was demonstrated that the ribonuclease activity of IRE1 was required for protecting male fertility from ET. It was also found that overexpression of SEC31A rescued the conditional male sterility in the double mutant. SEC31A is involved in ER to Golgi trafficking and a major target of the IRE1-mediated UPR signaling in stressed seedlings. Thus, IRE1, a major component of the UPR, plays an important role in protecting pollen development from ET.

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Where Goes the BSA Endowment: A Legacy Yet to be Written

2015-01-01 , Horner, Harry , Horner, Harry , Genetics, Development and Cell Biology

As a longtime BSA member (64 years), I have attended all but two BSA annual meetings and have literally rubbed shoulders with some of the best and most famous botanists in the world (in audience at my first talk as a young graduate student were Ledyard Stebbins, Katherine Esau, Ernest Gifford and Vernon Cheadle)! How fortunate (and scared) can one be! And now as a long-time member of BSA, I reflect on how I have committed part of my professional outside-of-the-university time in a variety of ways to the Society—they include financial support, oral and poster presentations, publications in AJB, section chair, committee member, Board of Directors and Council member, Treasurer, and yes, President. All of these involvements have been extremely rewarding to me both professionally and personally.