NIMA-related kinases regulate directional cell growth and organ development through microtubule function in Arabidopsis thaliana.

NIMA-related kinase 6 (NEK6) regulates cellular expansion and morphogenesis through microtubule organizaiton in Arabidopsis thaliana. Loss-of-function mutations in NEK6 (nek6/ibo1) cause ectopic outgrowth and microtubule disorganization in epidermal cells. We recently found that NEK6 forms homodimers and heterodimers with NEK4 and NEK5 to destabilize cortical microtubules possibly by direct binding to microtubules and the β-tubulin phosphorylation. Here, we identified a new allele of NEK6 and further analyzed the morphological phenotypes of nek6/ibo1 mutants, along with alleles of nek4 and nek5 mutants. Phenotypic analysis demonstrated that NEK6 is required for the directional growth of roots and hypocotyls, petiole elongation, cell file formation, and trichome morphogenesis. In addition, nek4, nek5, and nek6/ibo1 mutants were hypersensitive to microtubule inhibitors such as propyzamide and taxol. These results suggest that plant NEKs function in directional cell growth and organ development through the regulation of microtubule organization

Easy-to-Use InDel Markers for Genetic Mapping between Col-0 and Ler-0 Accessions of Arabidopsis thaliana

Map-based gene cloning has played a key role in many genetic studies using the model plant,Arabidopsis thaliana. In the post-next generation sequencing era, identification of point mutations and their corresponding genes is increasingly becoming a powerful and important approach to define plant gene function. To perform initial mapping experiments efficiently on Arabidopsis mutants, enrichment of easy-to-use and reliable polymorphic DNA markers would be desirable. We present here a list of InDel polymorphic markers between Col-0 and Ler-0 accessions that can be detected in standard agarose gel electrophoresis

Chemical control of xylem differentiation by thermospermine, xylemin, and auxin

The xylem conducts water and minerals from the root to the shoot and provides mechanical strength to the plant body. The vascular precursor cells of the procambium differentiate to form continuous vascular strands, from which xylem and phloem cells are generated in the proper spatiotemporal pattern. Procambium formation and xylem differentiation are directed by auxin. In angiosperms, thermospermine, a structural isomer of spermine, suppresses xylem differentiation by limiting auxin signalling. However, the process of auxin-inducible xylem differentiation has not been fully elucidated and remains difficult to manipulate. Here, we found that an antagonist of spermidine can act as an inhibitor of thermospermine biosynthesis and results in excessive xylem differentiation, which is a phenocopy of a thermospermine-deficient mutant acaulis5 in Arabidopsis thaliana. We named this compound xylemin owing to its xylem-inducing effect. Application of a combination of xylemin and thermospermine to wild-type seedlings negates the effect of xylemin, whereas co-treatment with xylemin and a synthetic proauxin, which undergoes hydrolysis to release active auxin, has a synergistic inductive effect on xylem differentiation. Thus, xylemin may serve as a useful transformative chemical tool not only for the study of thermospermine function in various plant species but also for the control of xylem induction and woody biomass production

Coupled Simulation of Shock Waves in Gas-Particle Mixtures Introducing Motion Equations

In this work, direct numerical analyses for flow around particles passing a shock wave was carried out to predict effects of small particles in rocket plumes. A flow solver based on three-dimensional compressible Navier-Stokes equations is developed for the purpose of high accurate prediction of the acoustic field around rocket plumes. This flow solver is capable of analysing a flow around moving multiple particles and motion equations was introduced. The flow field and the drag coefficient after the shock wave passage were validated by comparing with the drag models at shock Mach number 1.2-2.8. The result was in good agreement with the drag models. In the flow around multiple particles, the interference between particles was confirmed

Determination of polyamines in Arabidopsis thaliana by capillary electrophoresis using salicylaldehyde-5-sulfonate as a derivatizing reagent

Herein, we report a novel method for the determination of polyamines in a sample extracted from Arabidopsis thaliana by capillary electrophoresis (CE) using salicylaldehyde-5-sulfonate (SAS) as a derivatizing reagent. An aldehyde group of SAS forms a Schiff base with amino groups of aliphatic polyamines, resulting in an anionic species with an absorption band in the ultraviolet region. The derivatization method was straightforward since the derivatives were formed by mixing a sample with the derivatizing reagent at a neutral pH. In addition, the negative charges induced by SAS led to a high resolution with a short analysis time. This method permitted the separation of five polyamines, which play important roles in plants. However, further improvement in sensitivity was needed for the determination of the polyamines in plant samples. Therefore, the CE method was coupled with solid-phase extraction (SPE) using an ion-pairing formation with sodium dodecyl benzene sulfonate. The SPE method improved the concentration limits of detection to sub-μM levels, which corresponded with a 10-fold enhancement. The calibration curves for cadaverine, putrescine, and spermidine were linear with concentrations that ranged from 1 to 20 μM and correlation coefficients (R2) were greater than 0.998. The proposed method was applied to the determination of spermidine in a plant sample, Arabidopsis thaliana

Bony island within the articular cartilage of the knee in a child: a rare condition for early osteoarthritis

Articular cartilage is a specific type of connective tissue composed of hydrated proteoglycans within a matrix of collagen fibrils. In the elderly population, it shows degenerative changes that may results in osteoarthritis. The more severe form of osteoarthritis occasionally demonstrates bone formation within the cartilage, which is designated as a bony protuberance, however, such lesions are rare in children. This report presents the case of a 10-year-old boy with a bony protuberance within the articular cartilage of the knee. The patient initially complained of knee pain and he subsequently developed flexion contracture. Radiological and arthroscopic examinations revealed a bony protuberance in the articular cartilage and degenerative changes of the cartilage above it. He was successfully treated by the removal of the bony protuberance and osteochondral grafting. The bony protuberance may have caused cartilage degradation since the thickness of the cartilage above it was thinner than that around the lesion. The bony protuberance within the articular cartilage formed in the younger population may be a possible cause of osteoarthritis. This case is a noteworthy with regard to the pathogenesis of osteoarthritis

The dwarf phenotype of the Arabidopsis acl5 mutant is suppressed by a mutation in an upstream ORF of a bHLH gene

Loss-of-function mutants of the Arabidopsis thaliana ACAULIS 5 (ACL5) gene, which encodes spermine synthase, exhibit a severe dwarf phenotype. To elucidate the ACL5-mediated regulatory pathways of stem internocle elongation, we isolated four suppressor of acaulis (sac) mutants that reverse the acl5 dwarf phenotype. Because these mutants do not rescue the dwarfism of known phytohormone-related mutants, the SAC genes appear to act specifically on the ACL5 pathways. We identify the gene responsible for the dominant sac51-d mutant, which almost completely suppresses the acl5 phenotype. sac51-d disrupts a short upstream open reading frame (uORF) of SAC51, which encodes a bHLH-type transcription factor. Our results indicate that premature termination of the uORF in sac51-d results in an increase in its own transcript level, probably as a result of an increased translation of the main ORF. We suggest a model in which ACL5 plays a role in the translational activation of SAC51, which may lead to the expression of a subset of genes required for stem elongation

Thermospermine suppresses auxin-inducible xylem differentiation in Arabidopsis thaliana

Thermospermine, a structural isomer of spermine, is synthesized by a thermospermine synthase designated ACAULIS5 (ACL5). Thermospermine-deficient acl5 mutant of Arabidopsis thaliana shows severe dwarfism and excessive xylem differentiation. By screening for compounds that affect xylem differentiation in the acl5 mutant, we identified auxin analogs that remarkably enhanced xylem vessel differentiation in the acl5 mutant but not in the wild type. The xylem-inducing effect of auxin analogs was clearly suppressed by thermospermine, indicating that auxin-inducible xylem differentiation is normally limited by thermospermine. Here, we further characterized xylem-inducing effect of auxin analogs in various organs. Auxin analogs promoted protoxylem differentiation in roots and cotyledons in the acl5 mutant. Our results indicate that the opposite action between thermospermine and auxin in xylem differentiation is common in different organs and also suggest that thermospermine might be required for the suppression of protoxylem differentiation