The plant hormone auxin regulates diverse aspects of plant growth and development. We report that in Arabidopsis, auxin response is dependent on a ubiquitin-ligase (E3) complex called SCF

Ceftazidime-avibactam (CAZ-AVI) is a recently approved ␤-lactam-␤-lactamase inhibitor combination with the potential to treat serious infections caused by carbapenem-resistant organisms. Few patients with such infections were included in the CAZ-AVI clinical trials, and clinical experience is lacking. We present a case series of patients with infections caused by carbapenem-resistant Enterobacteriaceae (CRE) or Pseudomonas aeruginosa (CRPa) who were treated with CAZ-AVI salvage therapy on a compassionate-use basis. Physicians who had prescribed CAZ-AVI completed a case report form. We used descriptive statistics to summarize patient characteristics and treatment outcomes. We used the Wilcoxon rank sum test and Fisher's exact test to compare patients by treatment outcome. The sample included 36 patients infected with CRE and two with CRPa. The most common infections were intra-abdominal. Physicians categorized 60.5% of patients as having life-threatening infections. All but two patients received other antibiotics before CAZ-AVI, for a median of 13 days. The median duration of CAZ-AVI treatment was 16 days. Twentyfive patients (65.8%) concurrently received other antibiotics to which their pathogen was nonresistant in vitro. Twenty-eight patients (73.7%, 95% confidence interval [CI], 56.9 to 86.6%) experienced clinical and/or microbiological cure. Five patients (20.8%) with documented microbiological cure died, whereas 10 patients (71.4%) with no documented microbiological cure died (P ϭ 0.01). In three-quarters of cases, CAZ-AVI (alone or combined with other antibiotics) cured infections caused by carbapenemresistant organisms, 95% of which had failed previous therapy. Microbiological cure was associated with improved survival. CAZ-AVI shows promising clinical results for infections for which treatment options are limited.

SummaryIn animals and fungi, a group of proteins called the cyclin-dependent kinase inhibitors play a key role in cell cycle regulation. However, comparatively little is known about the role of these proteins in plant cell cycle regulation. To gain insight into the mechanisms by which the plant cell cycle is regulated, we studied the cyclin-dependent kinase inhibitor KRP1 in Arabidopsis. KRP1 interacts with the CDKA;1/CYCD2;1 complex in planta and functions in the G1-S transition of the cell cycle. Furthermore, we show that KRP1 is a likely target of the ubiquitin/proteasome pathway. Two different ubiquitin protein ligases, SCF SKP2 and the RING protein RKP, contribute to its degradation. These results suggest that SCF SKP2b and RPK play an important role in the cell cycle through regulating KRP1 protein turnover.

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Studies on the CDC6 protein, which is crucial to the control of DNA replication in yeast and animal cells, are lacking in plants. We have isolated an Arabidopsis cDNA encoding the AtCDC6 protein and studied its possible connection to the occurrence of developmentally regulated endoreplication cycles. The AtCDC6 gene is expressed maximally in early S-phase, and its promoter contains an E2F consensus site that mediates the binding of a plant E2F/DP complex. Transgenic plants carrying an AtCDC6 promoter-␤-glucuronidase fusion revealed that it is active in proliferating cells and, interestingly, in endoreplicating cells. In particular, the extra endoreplication cycle that occurs in dark-grown hypocotyl cells is associated with upregulation of the AtCDC6 gene. This was corroborated using ctr1 Arabidopsis mutants altered in their endoreplication pattern. The ectopic expression of AtCDC6 in transgenic plants induced endoreplication and produced a change in the somatic ploidy level. AtCDC6 was degraded in a ubiquitin-and proteosome-dependent manner by extracts from proliferating cells, but it was degraded poorly by extracts from dark-grown hypocotyl endoreplicating cells. Our results indicate that endoreplication is associated with expression of the AtCDC6 gene and, most likely, the stability of its product; it also apparently requires activation of the retinoblastoma/E2F/DP pathway. These conclusions may apply to endoreplicating cells in other tissues of the plant and to endoreplicating cells in other eukaryotes.

In Arabidopsis, the root clock regulates the spacing of lateral organs along the primary root through oscillating gene expression. The core molecular mechanism that drives the root clock periodicity and how it is modified by exogenous cues such as auxin and gravity remain unknown. We identified the key elements of the oscillator (AUXIN RESPONSE FACTOR 7, its auxin-sensitive inhibitor IAA18/POTENT, and auxin) that form a negative regulatory loop circuit in the oscillation zone. Through multilevel computer modeling fitted to experimental data, we explain how gene expression oscillations coordinate with cell division and growth to create the periodic pattern of organ spacing. Furthermore, gravistimulation experiments based on the model predictions show that external auxin stimuli can lead to entrainment of the root clock. Our work demonstrates the mechanism underlying a robust biological clock and how it can respond to external stimuli.

Our findings suggest that early oseltamivir administration was associated with favourable outcomes among critically ill ventilated patients with 2009 H1N1 virus infection.

Summary Root‐knot nematodes (RKNs; Meloidogyne spp.) induce new post‐embryogenic organs within the roots (galls) where they stablish and differentiate nematode feeding cells, giant cells (GCs). The developmental programmes and functional genes involved remain poorly defined. Arabidopsis root apical meristem (RAM), lateral root (LR) and callus marker lines, SHORT‐ROOT/SHR, SCARECROW/SCR, SCHIZORIZA/SCZ, WUSCHEL‐RELATED‐HOMEOBOX‐5/WOX5, AUXIN‐RESPONSIVE‐FACTOR‐5/ARF5, ARABIDOPSIS‐HISTIDINE PHOSPHOTRANSFER‐PROTEIN‐6/AHP6, GATA‐TRANSCRIPTION FACTOR‐23/GATA23 and S‐PHASE‐KINASE‐ASSOCIATED‐PROTEIN2B/SKP2B, were analysed for nematode‐dependent expression. Their corresponding loss‐of‐function lines, including those for LR upstream regulators, SOLITARY ROOT/SLR/IAA14, BONDELOS/BDL/IAA12 and INDOLE‐3‐ACETIC‐ACID‐INDUCIBLE‐28/IAA28, were tested for RKN resistance/tolerance. LR genes, for example ARF5 (key factor for root stem‐cell niche regeneration), GATA23 (which specifies pluripotent founder cells) and AHP6 (cytokinin‐signalling‐inhibitor regulating pericycle cell‐divisions orientation), show a crucial function during gall formation. RKNs do not compromise the number of founder cells or LR primordia but locally induce gall formation possibly by tuning the auxin/cytokinin balance in which AHP6 might be necessary. Key RAM marker genes were induced and functional in galls. Therefore, the activation of plant developmental programmes promoting transient‐pluripotency/stemness leads to the generation of quiescent‐centre and meristematic‐like cell identities within the vascular cylinder of galls. Nematodes enlist developmental pathways of new organogenesis and/or root regeneration in the vascular cells of galls. This should determine meristematic cell identities with sufficient transient pluripotency for gall organogenesis.