Borna disease virus 1 infection in alpacas: Comparison of pathological lesions and viral distribution to other dead-end hosts.

Borna disease is a progressive meningoencephalitis caused by spillover of the Borna disease virus 1 (BoDV-1) to horses and sheep and has gained attention due to its zoonotic potential. New World camelids are also highly susceptible to the disease; however, a comprehensive description of the pathological lesions and viral distribution is lacking for these hosts. Here, the authors describe the distribution and severity of inflammatory lesions in alpacas (n = 6) naturally affected by this disease in comparison to horses (n = 8) as known spillover hosts. In addition, the tissue and cellular distribution of the BoDV-1 was determined via immunohistochemistry and immunofluorescence. A predominant lymphocytic meningoencephalitis was diagnosed in all animals with differences regarding the severity of lesions. Alpacas and horses with a shorter disease duration showed more prominent lesions in the cerebrum and at the transition of the nervous to the glandular part of the pituitary gland, as compared to animals with longer disease progression. In both species, viral antigen was almost exclusively restricted to cells of the central and peripheral nervous systems, with the notable exception of virus-infected glandular cells of the Pars intermedia of the pituitary gland. Alpacas likely represent dead-end hosts similar to horses and other spillover hosts of BoDV-1.

Associations of cow and farm characteristics with cow-level lameness using data from an extensive cross-sectional study across 3 structurally different dairy regions in Germany.

The aim of the present study was to evaluate the associations between milk recording data, body condition score (BCS), housing factors, management factors, and lameness in freestall-housed dairy cows in 3 structurally different regions in Germany. These regions substantially vary regarding herd size, breeds, access to pasture, farm management (family run or company owned), and percentage of organic farms. The data used was collected in a large cross-sectional study from 2016 to 2019. A total of 58,144 cows from 651 farms in 3 regions of Germany (North, East, and South) was scored for locomotion and body condition. Additionally, data on milk yield, milk composition, breed, age, as well as information on housing and management were retrieved. One mixed-logistic regression model was fitted per region to evaluate the association of the data with the target variable "lame" and to allow for a comprehensive reflection across different kinds of farming types. In all regions, undercondition (BCS lower than recommended for the lactation stage; North: odds ratio [OR] 2.15, CI 1.96-2.34; East: OR 2.66, CI 2.45-2.88; South: OR 2.45, CI 2.01-2.98) and mid-lactation stage (102-204 d in milk; North: OR 1.15, CI 1.05-1.27; East: OR 1.24, CI 1.17-1.32; South: OR 1.38, CI 1.18-1.62) were associated with higher odds for lameness, whereas overcondition (BCS higher than recommended for the lactation stage; North: OR 0.51, CI 0.44-0.60; East: OR 0.51, CI 0.48-0.54; South: OR 0.65, CI 0.54-0.77) and parity of 1 or 2 was associated with lower odds (parity 1 = North: OR 0.32, CI 0.29-0.35; East: OR 0.19, CI 0.18-0.20; South: OR 0.28, CI 0.24-0.33; parity 2 = North: OR 0.51, CI 0.47-0.46; East: OR 0.41, CI 0.39-0.44; South: OR 0.49, CI 0.42-0.57), irrespective of the regional production characteristics. Low energy-corrected milk yield was associated with higher odds for lameness in South and North (North: OR 1.16, CI 1.05-1.27; South: OR 1.43, CI 1.22-1.69). Further factors such as pasture access for cows (North: OR 0.64, CI 0.50-0.82; and South: OR 0.65, CI 0.47-0.88), milk protein content (high milk protein content = North: OR 1.34, CI 1.18-1.52; East: OR 1.17, CI 1.08-1.28; low milk protein content = North: OR 0.79, CI 0.71-0.88; East: OR 0.84, CI 0.79-0.90), and breed (lower odds for "other" [other breeds than German Simmental and German Holstein] in East [OR 0.47, CI 0.42-0.53] and lower odds both for German Holstein and "other" in South [German Holstein: OR 0.62, CI 0.43-0.90; other: OR 0.46, CI 0.34 - 0.62]) were associated with lameness in 2 regions, respectively. The risk of ketosis (higher odds in North: OR 1.11, CI 1.01-1.22) and somatic cell count (higher odds in East: increased (>39.9 cells × 1,000/mL): OR 1.10; CI 1.03-1.17; high (>198.5 cells × 1,000/mL): OR 1.08; CI 1.01-1.06) altered the odds for lameness in 1 region, respectively. Cows from organic farms had lower odds for lameness in all 3 regions (North: OR 0.18, CI 0.11-0.32; East: OR 0.39, CI 0.28-0.56; South: OR 0.45, CI 0.29-0.68). As the dairy production systems differed substantially between the different regions, the results of this study can be viewed as representative for a wide variety of loose-housed dairy systems in Europe and North America. The consistent association between low BCS and lameness in all regions aligns with the previous literature. Our study also suggests that risk factors for lameness can differ between geographically regions, potentially due to differences in which dairy production system is predominantly used and that region-specific characteristics should be taken into account in comparable future projects.

Retrobulbar Adenocarcinoma with Subconjunctival Extension in a Common Buzzard (Buteo buteo).

A free ranging, fledged common buzzard (Buteo buteo) was found with severe feather damage and left periorbital swelling. Clinical examination revealed a 3.0 × 2.5 × 1.5 cm left medial subconjunctival mass. The abnormal tissue extended over most of the left cornea, severely impairing the bird's vision in that eye. Additionally, the left globe was displaced in a temporal direction. Computed tomography revealed the origin of the mass to be retrobulbar tissue. An ultrasound examination of the mass found cystic areas, and a sanguineous fluid was aspirated. Cytological examination of the aspirated fluid revealed numerous erythrocytes and a few round cells with oval nuclei, single large nucleoli, and abundant foamy cytoplasm. After a poor prognosis for rehabilitation to the wild, the bird was humanely euthanatized. A postmortem examination of the bird confirmed the retrobulbar mass with extension around the bulbus. Histological examination of the mass was consistent with an invasive adenocarcinoma, likely arising from the lacrimal glands. Neoplasia in the orbit has occasionally been described in Psittaciformes, but only rarely in birds of prey such as Accipitriformes.

Prospective phenotyping of long-term survivors of generalized arterial calcification of infancy (GACI).

PURPOSE: Generalized arterial calcification of infancy (GACI), characterized by vascular calcifications that are often fatal shortly after birth, is usually caused by deficiency of ENPP1. A small fraction of GACI cases result from deficiency of ABCC6, a membrane transporter. The natural history of GACI survivors has not been established in a prospective fashion. METHODS: We performed deep phenotyping of 20 GACI survivors. RESULTS: Sixteen of 20 subjects presented with arterial calcifications, but only 5 had residual involvement at the time of evaluation. Individuals with ENPP1 deficiency either had hypophosphatemic rickets or were predicted to develop it by 14 years of age; 14/16 had elevated intact FGF23 levels (iFGF23). Blood phosphate levels correlated inversely with iFGF23. For ENPP1-deficient individuals, the lifetime risk of cervical spine fusion was 25%, that of hearing loss was 75%, and the main morbidity in adults was related to enthesis calcification. Four ENPP1-deficient individuals manifested classic skin or retinal findings of PXE. We estimated the minimal incidence of ENPP1 deficiency at ~1 in 200,000 pregnancies. CONCLUSION: GACI appears to be more common than previously thought, with an expanding spectrum of overlapping phenotypes. The relationships among decreased ENPP1, increased iFGF23, and rickets could inform future therapies.

Neoplasia and Tumor-Like Lesions in Pet Rabbits (Oryctolagus cuniculus): A Retrospective Analysis of Cases Between 1995 and 2019.

Prevalence and age distribution of tumors is largely unknown in pet rabbits. Currently available studies focused on specific organ systems or specific tumor types and never covered a comparative examination of all tumor types. Previous studies on laboratory rabbits suggested a low tumor prevalence but were mostly limited to young adult animals. In the present study, all tumor types and several tumor-like lesions of all organ systems were analyzed retrospectively in archived pet rabbit samples of all ages. Cases included necropsy cases (n = 2,014) or postmortem tissue samples (n = 102) as well as surgical biopsies (n = 854). All lesions suspicious of neoplasia were reevaluated by histopathology and, when indicated, by immunohistochemistry. Necropsy cases had a tumor prevalence of 14.4% in both sexes or 19.8% in female intact rabbits of all age groups, and up to 47.2% or 66.7%, respectively, in rabbits older than 6 years. Overall, the most common tumor types were uterine adenocarcinoma (prevalence in female intact animals: 13.1%), lymphoma (prevalence: 2.8%), and thymoma (prevalence: 2.1%). Lymphoma, the most common tumor of rabbits ≤24 months of age, were of B-cell immunophenotype in 96% of cases and most commonly located in the lymph nodes (57%), gastrointestinal tract (54%), kidneys (48%), spleen (42%), and liver (41%). Tumors accounted for 81.1% of surgical biopsies and mostly comprised cutaneous, mammary, and uterine tumors. In conclusion, tumor types and prevalence varied significantly with respect to age, revealing some differences from previous studies on laboratory rabbits.

Cognitive behavioral therapy in adolescents with early-onset psychosis: a randomized controlled pilot study.

Cognitive behavioral therapy for psychosis (CBT) is an effective treatment in adult patients with schizophrenia. However, no randomized controlled and blinded trial in adolescents with early-onset psychosis (EOP) has been conducted. Therefore, the present pilot study explores the acceptance, tolerability, feasibility, and safety of a modified CBT in adolescents with EOP. Twenty-five adolescents with EOP were randomized to either 9 months (20 sessions) of CBT + treatment as usual (TAU) or TAU alone. The primary endpoint was the PANSS-positive subscale (P1-7). Secondary endpoints included psychopathology, global functioning, and quality of life (QoL). Acceptance, tolerability, feasibility, and safety were assessed. Blinded assessments took place by the end of the treatment (9 months) and at 24-month follow-up. Despite improvements in both groups and lack of statistical significance between CBT + TAU and TAU regarding the primary endpoint, we observed between-group effect sizes of at least d = 0.39 in favor of CBT + TAU at post-treatment for delusions, negative symptoms, functioning and QoL after the intervention and effect sizes of at least d = 0.35 after 24 months. CBT in EOP was highly acceptable (73.5% agreed to randomization), well-tolerated (83.1% attendance rate, no drop-outs), and safe (one serious adverse event (SAE) in CBT + TAU in comparison with six SAEs in TAU). These findings suggest that CBT adapted to the needs of adolescents with EOP is a promising approach regarding negative symptoms, functioning, and QoL. CBT is a safe and tolerable treatment. However, due to the small sample size and the pilot character of the study, these conclusions are limited, and should be tested in a larger, adequately powered randomized controlled trial.

Pseudodiverticula of the Small Intestine Associated With Idiopathic Smooth Muscle Hypertrophy in Domestic Rabbits ( Oryctolagus cuniculus).

Acquired outpouches of the intestinal tract are referred to as pseudodiverticula or false pulsion diverticula. In contrast to true diverticula, in which the wall contains all layers of the intestinal tract, the wall of pseudodiverticula lacks the tunica muscularis. Smooth muscle hypertrophy of the small intestine is commonly considered a cause of pseudodiverticulosis in animals due to increased intraluminal pressure. This study reports pseudodiverticula associated with idiopathic smooth muscle hypertrophy of the small intestine in lagomorphs. Four domestic rabbits had single or multiple (up to 200) pseudodiverticula of various size in the small intestine. In all cases the tunica muscularis was diffusely thickened, significantly exceeding reference thickness of 14 rabbits (mean, 112.3 µm; range, 26.3-389.0 µm). Clinical signs were considered to be caused by severe necrosis and inflammation of the wall of large pseudodiverticula, leading to perforation with subsequent peritonitis and mesenteric and omental abscess formation in 2 cases.

A predominantly glial origin of axonal ribosomes after nerve injury.

Axonal mRNA transport and local protein synthesis are crucial for peripheral axon regeneration. To date, it remains unclear how ribosomes localize to axons. They may be co-transported with mRNAs or, as suggested by recent studies, transferred from Schwann cells (SC). Here, we generated transgenic "RiboTracker" mice expressing tdTomato-tagged ribosomal protein L4 in specific cell types when crossed with Cre lines. Two neuronal RiboTracker-Cre lines displayed extremely low levels of axonal L4-tdTomato-positive ribosomes. In contrast, two glial RiboTracker-Cre lines revealed tagged ribosomes in sciatic nerve (SN) axons with increasing amounts after injury. Furthermore, non-RiboTracker dorsal root ganglia co-cultured with L4-tdTomato-expressing SCs displayed tagged ribosomes in axons. These data provide unequivocal evidence that SN axons receive ribosomes from SCs upon injury and indicate that glial cells are the main source of axonal ribosomes.

Repair of a Tibiotarsal Fracture in a Pomeranian Goose ( Anser anser) With a Locking Plate.

A 2-year-old Pomeranian goose ( Anser anser) weighing 8.1 kg was examined because of non-weight-bearing lameness of the right limb. A closed, transverse, diaphyseal fracture of the distal third of the right tibiotarsus with a craniolateral displacement of the distal fragment was diagnosed radiographically. Surgery under general anesthesia was performed to repair the fracture with a 14-hole, 2.7-mm locking plate fixed with 6 screws in a bicortical manner. Two days later, the bird was fully weight-bearing on the leg. Radiographs performed 4 and 8 weeks after surgery showed good healing of the affected bone with an appropriate callus formation bridging the fracture line. Sixteen weeks after surgery, the patient was readmitted because of lameness exhibited while staying outside exposed to subzero (°C) temperatures. On the basis of this finding, heat conduction was postulated as the possible cause of lameness because it disappeared after implant removal. To the best our knowledge, this case represents the first report of a surgical repair of a tibiotarsal fracture with a locking plate in waterfowl.

AtPME3, a ubiquitous cell wall pectin methylesterase of Arabidopsis thaliana, alters the metabolism of cruciferin seed storage proteins during post-germinative growth of seedlings.

AtPME3 (At3g14310) is a ubiquitous cell wall pectin methylesterase. Atpme3-1 loss-of-function mutants exhibited distinct phenotypes from the wild type (WT), and were characterized by earlier germination and reduction of root hair production. These phenotypical traits were correlated with the accumulation of a 21.5-kDa protein in the different organs of 4-day-old Atpme3-1 seedlings grown in the dark, as well as in 6-week-old mutant plants. Microarray analysis showed significant down-regulation of the genes encoding several pectin-degrading enzymes and enzymes involved in lipid and protein metabolism in the hypocotyl of 4-day-old dark grown mutant seedlings. Accordingly, there was a decrease in proteolytic activity of the mutant as compared with the WT. Among the genes specifying seed storage proteins, two encoding CRUCIFERINS were up-regulated. Additional analysis by RT-qPCR showed an overexpression of four CRUCIFERIN genes in the mutant Atpme3-1, in which precursors of the α- and ß-subunits of CRUCIFERIN accumulated. Together, these results provide evidence for a link between AtPME3, present in the cell wall, and CRUCIFERIN metabolism that occurs in vacuoles.

The Role of Dual-Phase Cone-Beam CT in Predicting Short-Term Response after Transarterial Chemoembolization for Hepatocellular Carcinoma.

PURPOSE: To identify computational and qualitative features derived from dual-phase cone-beam CT that predict short-term response in patients undergoing transarterial chemoembolization for hepatocellular carcinoma (HCC). MATERIALS AND METHODS: This retrospective study included 43 patients with 59 HCCs. Six features were extracted, including intensity of tumor enhancement on both phases and characteristics of the corona on the washout phase. Short-term response was evaluated by modified Response Evaluation Criteria in Solid Tumors on follow-up imaging, and extracted features were correlated to response using univariate and multivariate analyses. RESULTS: Univariate and multivariate analyses did not reveal a correlation between absolute and relative tumor enhancement characteristics on either phase with response (arterial P = .21; washout P = .40; ∆ P = .90). On multivariate analysis of qualitative characteristics, the presence of a diffuse corona was an independent predictor of incomplete response (P = .038) and decreased the odds ratio of objective response by half regardless of tumor size. CONCLUSIONS: Computational features extracted from contrast-enhanced dual-phase cone-beam CT are not prognostic of response to transarterial chemoembolization in patients with HCC. HCCs that demonstrate a diffuse, patchy corona have reduced odds of achieving complete response after transarterial chemoembolization and should be considered for additional treatment with an alternative modality.

REPAIR OF A FEMORAL FRACTURE IN A CONGO AFRICAN GREY PARROT ( PSITTACUS ERITHACUS ERITHACUS) WITH A PARACORTICAL-CLAMP-CERCLAGE TECHNIQUE.

A 1-yr-old female Congo African grey parrot ( Psittacus erithacus erithacus) was admitted with a lameness of the right pelvic limb. On the radiographs a closed, caudolaterally displaced, comminuted, diaphyseal fracture of the femur was diagnosed. Surgery under general anesthesia was performed in order to repair the fracture with a paracortical-clamp-cerclage technique. This straightforward and effective technique has been developed as a low-cost treatment for simple and comminuted diaphyseal fractures in dogs and cats. Fixation is obtained with clamps, shaped during surgery, and attached to the bone shaft with cerclage wire. This technique led to immediate weight-bearing, appropriate bone healing, and permanent fixation of the implants in the patient. To the best of the authors' knowledge, this case represents the first report of a surgical repair of a femoral fracture with a paracortical-clamp-cerclage technique in a bird.

Seed dormancy cycling in Arabidopsis: chromatin remodelling and regulation of DOG1 in response to seasonal environmental signals.

The involvement of chromatin remodelling in dormancy cycling in the soil seed bank (SSB) is poorly understood. Natural variation between the winter and summer annual Arabidopsis ecotypes Cvi and Bur was exploited to investigate the expression of genes involved in chromatin remodelling via histone 2B (H2B) ubiquitination/de-ubiquitination and histone acetylation/deacetylation, the repressive histone methyl transferases CURLY LEAF (CLF) and SWINGER (SWN), and the gene silencing repressor ROS1 (REPRESSOR OF SILENCING1) and promoter of silencing KYP/SUVH4 (KRYPTONITE), during dormancy cycling in the SSB. ROS1 expression was positively correlated with dormancy while the reverse was observed for CLF and KYP/SUVH4. We propose ROS1 dependent repression of silencing and a sequential requirement of CLF and KYP/SUVH4 dependent gene repression and silencing for the maintenance and suppression of dormancy during dormancy cycling. Seasonal expression of H2B modifying genes was correlated negatively with temperature and positively with DOG1 expression, as were histone acetyltransferase genes, with histone deacetylases positively correlated with temperature. Changes in the histone marks H3K4me3 and H3K27me3 were seen on DOG1 (DELAY OF GERMINATION1) in Cvi during dormancy cycling. H3K4me3 activating marks remained stable along DOG1. During relief of dormancy, H3K27me3 repressive marks slowly accumulated and accelerated on exposure to light completing dormancy loss. We propose that these marks on DOG1 serve as a thermal sensing mechanism during dormancy cycling in preparation for light repression of dormancy. Overall, chromatin remodelling plays a vital role in temporal sensing through regulation of gene expression.

HIGHLY METHYL ESTERIFIED SEEDS is a pectin methyl esterase involved in embryo development.

Homogalacturonan pectin domains are synthesized in a highly methyl-esterified form that later can be differentially demethyl esterified by pectin methyl esterase (PME) to strengthen or loosen plant cell walls that contain pectin, including seed coat mucilage, a specialized secondary cell wall of seed coat epidermal cells. As a means to identify the active PMEs in seed coat mucilage, we identified seven PMEs expressed during seed coat development. One of these, HIGHLY METHYL ESTERIFIED SEEDS (HMS), is abundant during mucilage secretion, peaking at 7 d postanthesis in both the seed coat and the embryo. We have determined that this gene is required for normal levels of PME activity and homogalacturonan methyl esterification in the seed. The hms-1 mutant displays altered embryo morphology and mucilage extrusion, both of which are a consequence of defects in embryo development. A significant decrease in the size of cells in the embryo suggests that the changes in embryo morphology are a consequence of lack of cell expansion. Progeny from a cross between hms-1 and the previously characterized PME inhibitor5 overexpression line suggest that HMS acts independently from other cell wall-modifying enzymes in the embryo. We propose that HMS is required for cell wall loosening in the embryo to facilitate cell expansion during the accumulation of storage reserves and that its role in the seed coat is masked by redundancy.

Promotion of testa rupture during garden cress germination involves seed compartment-specific expression and activity of pectin methylesterases.

Pectin methylesterase (PME) controls the methylesterification status of pectins and thereby determines the biophysical properties of plant cell walls, which are important for tissue growth and weakening processes. We demonstrate here that tissue-specific and spatiotemporal alterations in cell wall pectin methylesterification occur during the germination of garden cress (Lepidium sativum). These cell wall changes are associated with characteristic expression patterns of PME genes and resultant enzyme activities in the key seed compartments CAP (micropylar endosperm) and RAD (radicle plus lower hypocotyl). Transcriptome and quantitative real-time reverse transcription-polymerase chain reaction analysis as well as PME enzyme activity measurements of separated seed compartments, including CAP and RAD, revealed distinct phases during germination. These were associated with hormonal and compartment-specific regulation of PME group 1, PME group 2, and PME inhibitor transcript expression and total PME activity. The regulatory patterns indicated a role for PME activity in testa rupture (TR). Consistent with a role for cell wall pectin methylesterification in TR, treatment of seeds with PME resulted in enhanced testa permeability and promoted TR. Mathematical modeling of transcript expression changes in germinating garden cress and Arabidopsis (Arabidopsis thaliana) seeds suggested that group 2 PMEs make a major contribution to the overall PME activity rather than acting as PME inhibitors. It is concluded that regulated changes in the degree of pectin methylesterification through CAP- and RAD-specific PME and PME inhibitor expression play a crucial role during Brassicaceae seed germination.

Changes in hormone flux and signaling in white spruce (Picea glauca) seeds during the transition from dormancy to germination in response to temperature cues.

BACKGROUND: Seeds use environmental cues such as temperature to coordinate the timing of their germination, allowing plants to synchronize their life history with the seasons. Winter chilling is of central importance to alleviate seed dormancy, but very little is known of how chilling responses are regulated in conifer seeds. White spruce (Picea glauca) is an important conifer species of boreal forests in the North American taiga. The recent sequencing and assembly of the white spruce genome allows for comparative gene expression studies toward elucidating the molecular mechanisms governing dormancy alleviation by moist chilling. Here we focused on hormone metabolite profiling and analyses of genes encoding components of hormone signal transduction pathways, to elucidate changes during dormancy alleviation and to help address how germination cues such as temperature and light trigger radicle emergence. RESULTS: ABA, GA, and auxin underwent considerable changes as seeds underwent moist chilling and during subsequent germination; likewise, transcripts encoding hormone-signaling components (e.g. ABI3, ARF4 and Aux/IAA) were differentially regulated during these critical stages. During moist chilling, active IAA was maintained at constant levels, but IAA conjugates (IAA-Asp and IAA-Glu) were substantially accumulated. ABA concentrations decreased during germination of previously moist-chilled seeds, while the precursor of bioactive GA1 (GA53) accumulated. We contend that seed dormancy and germination may be partly mediated through the changing hormone concentrations and a modulation of interactions between central auxin-signaling pathway components (TIR1/AFB, Aux/IAA and ARF4). In response to germination cues, namely exposure to light and to increased temperature: the transfer of seeds from moist-chilling to 30 °C, significant changes in gene transcripts and protein expression occurred during the first six hours, substantiating a very swift reaction to germination-promoting conditions after seeds had received sufficient exposure to the chilling stimulus. CONCLUSIONS: The dormancy to germination transition in white spruce seeds was correlated with changes in auxin conjugation, auxin signaling components, and potential interactions between auxin-ABA signaling cascades (e.g. the transcription factor ARF4 and ABI3). Auxin flux adds a new dimension to the ABA:GA balance mechanism that underlies both dormancy alleviation by chilling, and subsequent radicle emergence to complete germination by warm temperature and light stimuli.

Tuning of pectin methylesterification: consequences for cell wall biomechanics and development.

MAIN CONCLUSION: Recent publications have increased our knowledge of how pectin composition and the degree of homogalacturonan methylesterification impact the biochemical and biomechanical properties of plant cell walls, plant development, and plants' interactions with their abiotic and biotic environments. Experimental observations have shown that the relationships between the DM, the pattern of de-methylesterificaton, its effect on cell wall elasticity, other biomechanical parameters, and growth are not straightforward. Working towards a detailed understanding of these relationships at single cell resolution is one of the big tasks of pectin research. Pectins are highly complex polysaccharides abundant in plant primary cell walls. New analytical and microscopy techniques are revealing the composition and mechanical properties of the cell wall and increasing our knowledge on the topic. Progress in plant physiological research supports a link between cell wall pectin modifications and plant development and interactions with the environment. Homogalacturonan pectins, which are major components of the primary cell wall, have a potential for modifications such as methylesterification, as well as an ability to form cross-linked structures with divalent cations. This contributes to changing the mechanical properties of the cell wall. This review aims to give a comprehensive overview of the pectin component homogalacturonan, including its synthesis, modification, regulation and role in the plant cell wall.

Demethylesterification of cell wall pectins in Arabidopsis plays a role in seed germination.

The methylesterification status of cell wall homogalacturonans, mediated through the action of pectin methylesterases (PMEs), influences the biophysical properties of plant cell walls such as elasticity and porosity, important parameters for cell elongation and water uptake. The completion of seed germination requires cell wall extensibility changes in both the radicle itself and in the micropylar tissues surrounding the radicle. In wild-type seeds of Arabidopsis (Arabidopsis thaliana), PME activities peaked around the time of testa rupture but declined just before the completion of germination (endosperm weakening and rupture). We overexpressed an Arabidopsis PME inhibitor to investigate PME involvement in seed germination. Seeds of the resultant lines showed a denser methylesterification status of their cell wall homogalacturonans, but there were no changes in the neutral sugar and uronic acid composition of the cell walls. As compared with wild-type seeds, the PME activities of the overexpressing lines were greatly reduced throughout germination, and the low steady-state levels neither increased nor decreased. The most striking phenotype was a significantly faster rate of germination, which was not connected to altered testa rupture morphology but to alterations of the micropylar endosperm cells, evident by environmental scanning electron microscopy. The transgenic seeds also exhibited an apparent reduced sensitivity to abscisic acid with respect to its inhibitory effects on germination. We speculate that PME activity contributes to the temporal regulation of radicle emergence in endospermic seeds by altering the mechanical properties of the cell walls and thereby the balance between the two opposing forces of radicle elongation and mechanical resistance of the endosperm.

Transcriptional dynamics of two seed compartments with opposing roles in Arabidopsis seed germination.

Seed germination is a critical stage in the plant life cycle and the first step toward successful plant establishment. Therefore, understanding germination is of important ecological and agronomical relevance. Previous research revealed that different seed compartments (testa, endosperm, and embryo) control germination, but little is known about the underlying spatial and temporal transcriptome changes that lead to seed germination. We analyzed genome-wide expression in germinating Arabidopsis (Arabidopsis thaliana) seeds with both temporal and spatial detail and provide Web-accessible visualizations of the data reported (vseed.nottingham.ac.uk). We show the potential of this high-resolution data set for the construction of meaningful coexpression networks, which provide insight into the genetic control of germination. The data set reveals two transcriptional phases during germination that are separated by testa rupture. The first phase is marked by large transcriptome changes as the seed switches from a dry, quiescent state to a hydrated and active state. At the end of this first transcriptional phase, the number of differentially expressed genes between consecutive time points drops. This increases again at testa rupture, the start of the second transcriptional phase. Transcriptome data indicate a role for mechano-induced signaling at this stage and subsequently highlight the fates of the endosperm and radicle: senescence and growth, respectively. Finally, using a phylotranscriptomic approach, we show that expression levels of evolutionarily young genes drop during the first transcriptional phase and increase during the second phase. Evolutionarily old genes show an opposite pattern, suggesting a more conserved transcriptome prior to the completion of germination.