The secreted PAMP-induced peptide StPIP1_1 activates immune responses in potato

Treatment of potato plants with the pathogen-associated molecular pattern Pep-13 leads to the activation of more than 1200 genes. One of these, StPIP1_1, encodes a protein of 76 amino acids with sequence homology to PAMP-induced secreted peptides (PIPs) from Arabidopsis thaliana. Expression of StPIP1_1 is also induced in response to infection with Phytophthora infestans, the causal agent of late blight disease. Apoplastic localization of StPIP1_1-mCherry fusion proteins is dependent on the presence of the predicted signal peptide. A synthetic peptide corresponding to the last 13 amino acids of StPIP1_1 elicits the expression of the StPIP1_1 gene itself, as well as that of pathogenesis related genes. The oxidative burst induced by exogenously applied StPIP1_1 peptide in potato leaf disks is dependent on functional StSERK3A/B, suggesting that StPIP1_1 perception occurs via a receptor complex involving the co-receptor StSERK3A/B. Moreover, StPIP1_1 induces expression of FRK1 in Arabidopsis in an RLK7-dependent manner. Expression of an RLK from potato with high sequence homology to AtRLK7 is induced by StPIP1_1, by Pep-13 and in response to infection with P. infestans. These observations are consistent with the hypothesis that, upon secretion, StPIP1_1 acts as an endogenous peptide required for amplification of the defense response.

Microtubule-associated IQD9 orchestrates cellulose patterning in seed mucilage

Arabidopsis seeds release large capsules of mucilaginous polysaccharides, which are shaped by an intricate network of cellulosic microfibrils. Cellulose synthase complexes are guided by the microtubule cytoskeleton, but it is unclear which proteins mediate this process in the seed coat epidermis. Using reverse genetics, we identified IQ67 DOMAIN 9 (IQD9) and KINESIN LIGHT CHAIN-RELATED 1 (KLCR1) as two highly expressed genes during seed development and comprehensively characterized their roles in cell wall polysaccharide biosynthesis. Mutations in IQD9 as well as in KLCR1 lead to compact mucilage capsules with aberrant cellulose distribution, which can be rescued by transgene complementation. IQD9 physically interacts with KLCR1 and localizes to cortical microtubules (MTs) to maintain their organization in seed coat epidermal (SCE) cells. IQD9 as well as a previously identified TONNEAU1 (TON1) RECRUITING MOTIF 4 (TRM4) protein act to maintain cellulose synthase velocity. Our results demonstrate that IQD9, KLCR1 and TRM4 are MT-associated proteins that are required for seed mucilage architecture. This study provides the first direct evidence that members of the IQD, KLCR and TRM families have overlapping roles in cell wall biosynthesis. Therefore, SCE cells provide an attractive system to further decipher the complex genetic regulation of polarized cellulose deposition.

IQ67 DOMAIN proteins facilitate preprophase band formation and division-plane orientation

Spatiotemporal control of cell division is essential for the growth and development of multicellular organisms. In plant cells, proper cell plate insertion during cytokinesis relies on the premitotic establishment of the division plane at the cell cortex. Two plant-specific cytoskeleton arrays, the preprophase band (PPB) and the phragmoplast, play important roles in division-plane orientation and cell plate formation, respectively1. Microtubule organization and dynamics and their communication with membranes at the cortex and cell plate are coordinated by multiple, mostly distinct microtubule-associated proteins2. How division-plane selection and establishment are linked, however, is still unknown. Here, we report members of the Arabidopsis IQ67 DOMAIN (IQD) family3 as microtubule-targeted proteins that localize to the PPB and phragmoplast and additionally reside at the cell plate and a polarized cortical region including the cortical division zone (CDZ). IQDs physically interact with PHRAGMOPLAST ORIENTING KINESIN (POK) proteins4,5 and PLECKSTRIN HOMOLOGY GTPase ACTIVATING (PHGAP) proteins6, which are core components of the CDZ1. The loss of IQD function impairs PPB formation and affects CDZ recruitment of POKs and PHGAPs, resulting in division-plane positioning defects. We propose that IQDs act as cellular scaffolds that facilitate PPB formation and CDZ set-up during symmetric cell division.

Microtubule-associated protein IQ67 DOMAIN5 regulates morphogenesis of leaf pavement cells in Arabidopsis thaliana

Plant microtubules form a highly dynamic intracellular network with important roles for regulating cell division, cell proliferation, and cell morphology. Their organization and dynamics are co-ordinated by various microtubule-associated proteins (MAPs) that integrate environmental and developmental stimuli to fine-tune and adjust cytoskeletal arrays. IQ67 DOMAIN (IQD) proteins recently emerged as a class of plant-specific MAPs with largely unknown functions. Here, using a reverse genetics approach, we characterize Arabidopsis IQD5 in terms of its expression domains, subcellular localization, and biological functions. We show that IQD5 is expressed mostly in vegetative tissues, where it localizes to cortical microtubule arrays. Our phenotypic analysis of iqd5 loss-of-function lines reveals functions of IQD5 in pavement cell (PC) shape morphogenesis. Histochemical analysis of cell wall composition further suggests reduced rates of cellulose deposition in anticlinal cell walls, which correlate with reduced anisotropic expansion. Lastly, we demonstrate IQD5-dependent recruitment of calmodulin calcium sensors to cortical microtubule arrays and provide first evidence for important roles for calcium in regulation of PC morphogenesis. Our work identifies IQD5 as a novel player in PC shape regulation and, for the first time, links calcium signaling to developmental processes that regulate anisotropic growth in PCs.

Microtubule-associated protein IQ67 DOMAIN5 regulates morphogenesis of leaf pavement cells in Arabidopsis thaliana

Plant microtubules form a highly dynamic intracellular network with important roles for regulating cell division, cell proliferation, and cell morphology. Their organization and dynamics are co-ordinated by various microtubule-associated proteins (MAPs) that integrate environmental and developmental stimuli to fine-tune and adjust cytoskeletal arrays. IQ67 DOMAIN (IQD) proteins recently emerged as a class of plant-specific MAPs with largely unknown functions. Here, using a reverse genetics approach, we characterize Arabidopsis IQD5 in terms of its expression domains, subcellular localization, and biological functions. We show that IQD5 is expressed mostly in vegetative tissues, where it localizes to cortical microtubule arrays. Our phenotypic analysis of iqd5 loss-of-function lines reveals functions of IQD5 in pavement cell (PC) shape morphogenesis. Histochemical analysis of cell wall composition further suggests reduced rates of cellulose deposition in anticlinal cell walls, which correlate with reduced anisotropic expansion. Lastly, we demonstrate IQD5-dependent recruitment of calmodulin calcium sensors to cortical microtubule arrays and provide first evidence for important roles for calcium in regulation of PC morphogenesis. Our work identifies IQD5 as a novel player in PC shape regulation and, for the first time, links calcium signaling to developmental processes that regulate anisotropic growth in PCs.

The IQD Family of Calmodulin-Binding Proteins Links Calcium Signaling to Microtubules, Membrane Subdomains, and the Nucleus

Calcium (Ca2+) signaling and dynamic reorganization of the cytoskeleton are essential processes for the coordination and control of plant cell shape and cell growth. Calmodulin (CaM) and closely related calmodulin-like (CML) polypeptides are principal sensors of Ca2+ signals. CaM/CMLs decode and relay information encrypted by the second messenger via differential interactions with a wide spectrum of targets to modulate their diverse biochemical activities. The plant-specific IQ67 DOMAIN (IQD) family emerged as possibly the largest class of CaM-interacting proteins with undefined molecular functions and biological roles. Here, we show that the 33 members of the IQD family in Arabidopsis (Arabidopsis thaliana) differentially localize, using green fluorescent protein (GFP)-tagged proteins, to multiple and distinct subcellular sites, including microtubule (MT) arrays, plasma membrane subdomains, and nuclear compartments. Intriguingly, the various IQD-specific localization patterns coincide with the subcellular patterns of IQD-dependent recruitment of CaM, suggesting that the diverse IQD members sequester Ca2+-CaM signaling modules to specific subcellular sites for precise regulation of Ca2+-dependent processes. Because MT localization is a hallmark of most IQD family members, we quantitatively analyzed GFP-labeled MT arrays in Nicotiana benthamiana cells transiently expressing GFP-IQD fusions and observed IQD-specific MT patterns, which point to a role of IQDs in MT organization and dynamics. Indeed, stable overexpression of select IQD proteins in Arabidopsis altered cellular MT orientation, cell shape, and organ morphology. Because IQDs share biochemical properties with scaffold proteins, we propose that IQD families provide an assortment of platform proteins for integrating CaM-dependent Ca2+ signaling at multiple cellular sites to regulate cell function, shape, and growth.

[Usability of smartphones for dose alerts]

PURPOSE

Smartphone apps for measuring ionizing radiation use the capability of (CMOS) camera chips to detect not only perceivable light but also electromagnetic wave radiation. The present study evaluates the accuracy of hardware and software and defines possible applications for the detection of X-ray radiation fields.

MATERIALS AND METHODS

2 apps and 2 different devices were tested in comparison with a calibrated ionization chamber and a personal electronic dosimeter. A calibration curve was determined for dose rates between 12 700 µSv/h and 5.7 µSv/h generated by a C-arm system.

RESULTS

The measured scattered radiation produced by an Alderson-Rando phantom ranged from 117 µSv/h (at a distance of 2 m) to 5910 µSv/h (at a distance of 0.3 m) and was 1.4 times less than the values of the ionization chamber. The exposure rate for the operator's thyroid was within 4200 - 4400 µSv/h. We found a strong dependence of the measurements on the angulation of the Smartphone, especially for short distances from the phantom (at a distance of 0.3 m, a 45° rotation downwards in a vertical direction caused a decrease from 3000 µSv/h to 972 µSv/h, while an upwards rotation resulted in an increase to 5000 µSv/h). For a distance of 1 m, this effect was remarkably smaller.

CONCLUSION

Smartphones can be used to detect ionizing radiation but showed limited accuracy and are heavily dependent on the angulation of the device. Qualitative measurements and utilization for dose alerts are possible.

Arabidopsis calmodulin-binding protein IQ67-domain 1 localizes to microtubules and interacts with kinesin light chain-related protein-1

Calcium (Ca(2+)) is a key second messenger in eukaryotes and regulates diverse cellular processes, most notably via calmodulin (CaM). In Arabidopsis thaliana, IQD1 (IQ67 domain 1) is the founding member of the IQD family of putative CaM targets. The 33 predicted IQD proteins share a conserved domain of 67 amino acids that is characterized by a unique arrangement of multiple CaM recruitment motifs, including so-called IQ motifs. Whereas IQD1 has been implicated in the regulation of defense metabolism, the biochemical functions of IQD proteins remain to be elucidated. In this study we show that IQD1 binds to multiple Arabidopsis CaM and CaM-like (CML) proteins in vitro and in yeast two-hybrid interaction assays. CaM overlay assays revealed moderate affinity of IQD1 to CaM2 (K(d) ∼ 0.6 μm). Deletion mapping of IQD1 demonstrated the importance of the IQ67 domain for CaM2 binding in vitro, which is corroborated by interaction of the shortest IQD member, IQD20, with Arabidopsis CaM/CMLs in yeast. A genetic screen of a cDNA library identified Arabidopsis kinesin light chain-related protein-1 (KLCR1) as an IQD1 interactor. The subcellular localization of GFP-tagged IQD1 proteins to microtubules and the cell nucleus in transiently and stably transformed plant tissues (tobacco leaves and Arabidopsis seedlings) suggests direct interaction of IQD1 and KLCR1 in planta that is supported by GFP∼IQD1-dependent recruitment of RFP∼KLCR1 and RFP∼CaM2 to microtubules. Collectively, the prospect arises that IQD1 and related proteins provide Ca(2+)/CaM-regulated scaffolds for facilitating cellular transport of specific cargo along microtubular tracks via kinesin motor proteins.

Comparison of the image quality of various fixed and dose modulated protocols for soft tissue neck CT on a GE Lightspeed scanner

PURPOSE

Up-to-date CT scanners provide high quality soft tissue imaging of the neck, but scanning protocols often are not optimized regarding radiation dose. Thus, we tried to find a dose-optimized protocol for soft tissue imaging of the neck.

MATERIAL AND METHODS

70 patients were scanned with a 16-row CT-scanner (Lightspeed, GE) with seven different protocols. We used four fixed tube current settings (225, 200, 175 and 150 mA; corresponding CTDI(vol)=10.6, 9.5, 8.3 and 7.1 mGy) and three z-axis dose modulations with a relatively high, moderate and low dose (calculated CTDI(vol)=10.5, 9.1, 7.7 mGy). Representative slices of seven anatomical regions (from the nasopharynx to the aortic arch) were subjectively judged by two radiologists with respect to image quality (five-point rating scale for noise and sharpness). For each protocol and for each judged anatomical region we determined and compared mean values regarding image quality and local tube current. For each protocol, mean values regarding the volume CT dose index (CTDI(vol)) and the dose-length product (DLP) were statistically compared. Moreover, using the software CT-Expo the respective effective doses and the cumulative organ doses of the thyroid gland were compared.

RESULTS

For a fixed tube current of at least 200 mA (CTDI(vol)=9.5 mGy) and for dose modulations with a moderate or high dose adjustment (calculated CTDI(vol)=9.1 and 10.5 mGy) the image quality was sufficient to excellent. As compared to a fixed tube current of 200 mA, dose modulation with a moderate dose adjustment improved the image quality in regions more vulnerable to noise-related artifacts such as at the level of the shoulder, without a noteworthy difference regarding the DLP. However, the cumulative organ dose of the thyroid gland was 17% lower using dose modulation with a moderate dose adjustment as compared to the fixed tube current of 200 mA. Thus, for a comparison with other scanners, we recommend dose modulation and an averaged CTDI(vol)<9 mGy (or a DLP<250 mGycm).

CONCLUSION

A combination of dose modulation and an averaged CTDI(vol)<9 mGy or a DLP<250 mGycm yields sufficient image quality for soft tissue CT-imaging of the neck.

[5 years of "concerted action dose reduction in CT" -- what has been achieved and what remains to be done?]

In May 1998, the German "Concerted Action Dose Reduction in CT" was founded by all parties involved in CT. Its intention was to achieve a significant reduction of the radiation exposure caused by CT, a matter that has increasingly been considered a major challenge since the early nineties. As a result of a number of joint efforts, the essential preconditions have been established by now. The fifth anniversary of the Concerted Action gave rise for both retrospection and outlook on the tasks that have already been accomplished and those that still need to be done. For this purpose, a one-day symposium took place in Berlin on November 4, 2003. The contents of a total of 18 contributions will be outlined here in brief.

Assessment of a theoretical formalism for dose estimation in CT: an anthropomorphic phantom study

Dose assessment in computed tomography (CT) is challenging due to the vast variety of CT scanners and imaging protocols in use. In the present study, the accurateness of a theoretical formalism implemented in the PC program CT-EXPO for dose calculation was evaluated by means of phantom measurements. Phantom measurements were performed with four 1-slice, four 4-slice and two 16-slice spiral CT scanners. Firstly, scanner-specific nCTDIw values were measured and compared with the corresponding standard values used for dose calculation. Secondly, effective doses were determined for three CT scans (head, chest and pelvis) performed at each of the ten installations from readings of thermoluminescent dosimeters distributed inside an anthropomorphic Alderson phantom and compared with the corresponding dose values computed with CT-EXPO. Differences between standard and individually measured nCTDIw values were less than 16%. Statistical analysis yielded a highly significant correlation (P < 0.001) between calculated and measured effective doses. The systematic and random uncertainty of the dose values calculated using standard nCTDIw values was about -9 and +/- 11%, respectively. The phantom measurements and model calculations were carried out for a variety of CT scanners and representative scan protocols validate the reliability of the dosimetric formalism considered-at least for patients with a standard body size and a tube voltage of 120 kV selected for the majority of CT scans performed in our study.

CT-basierte Lebervolumetrie im Tiermodell: Bedeutung für die klinische Volumetrie im Rahmen der Leberlebendspende

PURPOSE

Exact preoperative determination of the liver volume is of great importance prior to hepatobiliary surgery, especially in living donated liver transplantation (LDLT). In the current literature, a strong correlation between preoperatively calculated and intraoperatively measured liver volumes has been described. Such accuracy seems questionable, primarily due to a difference in the perfusion state of the liver in situ versus after explantation. Purpose of the study was to asses the influence of the perfusion state on liver volume and the validity of the preoperative liver volumetry prior to LDLT.

METHODS

In an experimental study, 20 porcine livers were examined. The livers were weighted and their volumes were determined by water displacement prior and after fluid infusion to achieve a pressure physiologically found in the liver veins. The liver volumes in the different perfusion states were calculated based on CT-data. The calculated values were compared with the volume measured by water displacement and the weight of the livers.

RESULTS

Assessment of calculated CT volumes and water displacements at identical perfusion states showed a tight correlation and differed on average by 4 +/- 5 %. However, livers before and after fluid infusion showed a 33 +/- 8 % (350 +/- 150 ml) difference in volume.

CONCLUSION

CT-volumetry acquires highly accurate data as confirmed by water displacement studies. However, the perfusion state has major impact on liver volume, which has to be accounted for in clinical use.

Radiation exposure in multi-slice versus single-slice spiral CT: results of a nationwide survey

Multi-slice (MS) technology increases the efficacy of CT procedures and offers new promising applications. The expanding use of MSCT, however, may result in an increase in both frequency of procedures and levels of patient exposure. It was, therefore, the aim of this study to gain an overview of MSCT examinations conducted in Germany in 2001. All MSCT facilities were requested to provide information about 14 standard examinations with respect to scan parameters and frequency. Based on this data, dosimetric quantities were estimated using an experimentally validated formalism. Results are compared with those of a previous survey for single-slice (SS) spiral CT scanners. According to the data provided for 39 dual- and 73 quad-slice systems, the average annual number of patients examined at MSCT is markedly higher than that examined at SSCT scanners (5500 vs 3500). The average effective dose to patients was changed from 7.4 mSv at single-slice to 5.5 mSv and 8.1 mSv at dual- and quad-slice scanners, respectively. There is a considerable potential for dose reduction at quad-slice systems by an optimisation of scan protocols and better education of the personnel. To avoid an increase in the collective effective dose from CT procedures, a clear medical justification is required in each case.