The ABC transporter G subfamily in Arabidopsis thaliana.

ABC transporters are ubiquitously present in all kingdoms and mediate the transport of a large spectrum of structurally different compounds. Plants possess high numbers of ABC transporters in relation to other eukaryotes; the ABCG subfamily in particular is extensive. Earlier studies demonstrated that ABCG transporters are involved in important processes influencing plant fitness. This review summarizes the functions of ABCG transporters present in the model plant Arabidopsis thaliana. These transporters take part in diverse processes such as pathogen response, diffusion barrier formation, or phytohormone transport. Studies involving knockout mutations reported pleiotropic phenotypes of the mutants. In some cases, different physiological roles were assigned to the same protein. The actual transported substrate(s), however, still remain to be determined for the majority of ABCG transporters. Additionally, the proposed substrate spectrum of different ABCG proteins is not always reflected by sequence identities between ABCG members. Applying only reverse genetics is thereby insufficient to clearly identify the substrate(s). We therefore stress the importance of in vitro studies in addition to in vivo studies in order to (i) clarify the substrate identity; (ii) determine the transport characteristics including directionality; and (iii) identify dimerization partners of the half-size proteins, which might in turn affect substrate specificity.

Adult congenital open-heart surgery: emergence of a new mortality score.

OBJECTIVES: In revised 2018 American Heart Association/American College of Cardiology guideline for the management of adults with congenital heart disease (ACHD), the committee introduced a classification that combines lesion anatomy and physiological status: ACHD anatomic physiological (AP) classification. Anatomy is described as of simple (I), moderate (II) or great (III) complexity, whereas physiology is listed in 4 categories of increasing severity (A, B, C and D). Can this classification predict early postoperative mortality? METHODS: ACHD AP classification was determined for 339 adults who underwent open-heart surgery between September 2012 and August 2018. In addition, the adult congenital heart surgery (ACHS) and Society of Thoracic Surgery-European Association for Cardio-Thoracic Surgery (STAT) mortality scores were calculated. A model based on binary logistic regression was applied. The event was early postoperative death. Mortality scores were estimated for each ACHD AP class. RESULTS: All patients could be categorized by the ACHD AP classification. The 354 procedures were performed with an early mortality of 3.4% (12/354). The mortality risk for the new mortality score, simply called ACAP score, ranged from 0.2% (95% confidence interval 0.08-0.41%) for ACHD AP class IA to 20% (16.04-24.64%) for IIID class. Observed over expected ratios of early mortality amounted to 0.87, 1.54 and 1.14, whereas areas under the curve of receiver operator characteristic were found to be 0.78, 0.64 and 0.88 for STAT, ACHS and ACAP scores, respectively. CONCLUSIONS: ACHD AP classification could embrace all procedures. In our setting, the ACAP score was more predictive of early mortality than the ACHS and STAT mortality scores. It should be validated by further studies and other centres.

ABCG1 contributes to suberin formation in Arabidopsis thaliana roots.

Diffusion barriers enable plant survival under fluctuating environmental conditions. They control internal water potential and protect against biotic or abiotic stress factors. How these protective molecules are deposited to the extracellular environment is poorly understood. We here examined the role of the Arabidopsis ABC half-size transporter AtABCG1 in the formation of the extracellular root suberin layer. Quantitative analysis of extracellular long-chain fatty acids and aliphatic alcohols in the atabcg1 mutants demonstrated altered root suberin composition, specifically a reduction in longer chain dicarboxylic acids, fatty alcohols and acids. Accordingly, the ATP-hydrolyzing activity of heterologous expressed and purified AtABCG1 was strongly stimulated by fatty alcohols (C26-C30) and fatty acids (C24-C30) in a chain length dependent manner. These results are a first indication for the function of AtABCG1 in the transport of longer chain aliphatic monomers from the cytoplasm to the apoplastic space during root suberin formation.

Cloning and expression of selected ABC transporters from the Arabidopsis thaliana ABCG family in Pichia pastoris.

Phytohormones play a major role in plant growth and development. They are in most cases not synthesized in their target location and hence need to be transported to the site of action, by for instance ATP-binding cassette transporters. Within the ATP-binding cassette transporter family, Pleiotropic Drug Resistance transporters are known to be involved in phytohormone transport. Interestingly, PDRs are only present in plants and fungi. In contrast to fungi, there are few biochemical studies of plant PDRs and one major reason is that suitable overexpression systems have not been identified. In this study, we evaluate the expression system Pichia pastoris for heterologous overexpression of PDR genes of the model plant Arabidopsis thaliana. We successfully cloned and expressed the potential phytohormone transporters PDR2 and PDR8 in P. pastoris. Sucrose gradient centrifugation confirmed that the overexpressed proteins were correctly targeted to the plasma membrane of P. pastoris and initial functional studies demonstrated ATPase activity for WBC1. However, difficulties in cloning and heterologous overexpression might be particular obstacles of the PDR family, since cloning and overexpression of White Brown Complex 1, a half-size transporter of the same ABCG subfamily with comparable domain organization, was more easily achieved. We present strategies and highlight critical factors to successfully clone plant PDR genes and heterologously expressed in P. pastoris.

Effects of clonidine and superficial cervical plexus block on hemodynamic stability after carotid endarterectomy.

OBJECTIVES: To evaluate the effects of 2 interventions (intravenous clonidine and superficial cervical block) on hemodynamic stability after carotid endarterectomy and to identify variables associated with hemodynamic instability. DESIGN: Prospective, observational study, sequential enrollment. SETTING: University hospital. PARTICIPANTS: Two hundred seventy-five patients undergoing elective carotid endarterectomy under general anesthesia. INTERVENTIONS: Group NN (n = 50) received no intervention. In group CN (n = 85), 3 mug/kg of clonidine were administered intravenously 30 minutes before the end of the operation. Group CB (n = 140) additionally received a superficial cervical plexus block (SCB) with 20 mL of naropine 0.5% before the induction of anesthesia. MEASUREMENTS AND MAIN RESULTS: Clonidine alone (odds ratio [OR], 2.33; 95% confidence interval [CI], 1.45-3.76) and clonidine combined with an SCB (OR, 4.99; 95% CI, 3.19-7.82) resulted in a significant increase in hemodynamic stability after CEA (p < 0.001) from 53.3% (NN) to 70.0% (CN) and 83.3% (CB), respectively. The need for rescue medication decreased from 40.0% to 17.6% and 13.6% (p < 0.001). Both interventions significantly reduced the need for postoperative opioid analgesics (p < 0.01). Logistic regression analysis showed preoperative systolic blood pressure values greater than 170 mmHg (OR, 3.23; 95% CI, 1.76-5.93), previous cardiac interventions (OR, 3.3; 95% CI, 1.54-7.11), and the need for rescue medication in the awakening period (OR, 5.8; 95% CI, 2.88-11.52) to be independent risk factors for postoperative hemodynamic instability (p < or = 0.002). CONCLUSIONS: Intravenous clonidine and superficial cervical block significantly improve cardiovascular stability after carotid endarterectomy. Patients with pre-existing excessive hypertension and previous coronary interventions must be considered a high-risk group.