First Report of Brown Rot Caused by Monilinia fructicola on Apple in Italy

Monilinia fructicola (G. Wint.) Honey, the causal agent of brown rot, is one of the most important fungal pathogens of stone fruit but may also affect pome fruits. The pathogen is common in North America, Oceania, South America, and Asia. It is a quarantined pathogen in Europe (3), but was recently detected in apple from the Czech Republic, Germany, and Serbia (1,2,4). In January 2012, during a survey for fungal postharvest pathogens, stored apple (Malus domestica Borkh.) belonging to the cultivars Gala and Pink Lady showing brown rot symptoms were observed in the Emilia Romagna region, Italy. Typical decay spots were circular and brown, tending toward black. Decayed tissues remained firm, and numerous grayish pustules containing spores appeared on rotted areas. The pathogen was isolated on V8 juice agar and culture plates were incubated at 25°C in darkness for 5 days. A conidial suspension was spread on malt extract agar and single spores were selected. The colonies were morphologically identified as M. fructigena. Two colonies developing a gray mass of spores in concentric rings with the reverse side black were further studied by molecular tools. The colony margins were even and the conidia were one-celled, limoniform, hyaline, and 12.1 to 17.4 × 8.4 to 11.2 μm. The ribosomal ITS1-5.8S-ITS2 region was PCR-amplified from genomic DNA obtained from mycelium using primers ITS1 and ITS4. A BLAST search in GenBank revealed the highest similarity (99%) to M. fructicola sequences (GenBank Accession Nos. HQ893748.1 and FJ515894.1). Pathogenicity was confirmed using surface-sterilized mature 'Gala' apples, wounded with a sterile needle, and inoculated with an isolate conidial suspension (10³ spores/ml). A 20 μl droplet was placed in the wound; control fruits received sterile water without conidia. After 5 days of incubation at 20°C in plastic containers with high humidity, typical symptoms of brown rot developed on inoculated fruits, while control fruits remained symptomless. The fungus isolated from inoculated fruit exhibited the same morphological and molecular features shown by the original isolates. To our knowledge, this is the first report of the fungus M. fructicola on apple in Italy. Further studies are necessary to determine geographic distribution, prevalence and economic importance of this quarantine organism in Italy. References: (1) J. Duchoslavovà et al. Plant Dis.91:907, 2007. (2) A. Grabke et al. Plant Dis. 95:772, 2011. (3) OEPP/EPPO. EPPO A2 list of pests recommended for regulation as quarantine pests. Version 2010-09. Retrieved from http://www.eppo.int/QUARANTINE/listA2.htm , 2010. (4) M. Vasic et al. Plant Dis. 96:456, 2012.

A role for Atg8-PE deconjugation in autophagosome biogenesis

Formation of the autophagosome is likely the most complex step of macroautophagy, and indeed it is the morphological and functional hallmark of this process; accordingly, it is critical to understand the corresponding molecular mechanism. Atg8 is the only known autophagy-related (Atg) protein required for autophagosome formation that remains associated with the completed sequestering vesicle. Approximately one-fourth of all of the characterized Atg proteins that participate in autophagosome biogenesis affect Atg8, regulating its conjugation to phosphatidylethanolamine (PE), localization to the phagophore assembly site and/or subsequent deconjugation. An unanswered question in the field regards the physiological role of the deconjugation of Atg8-PE. Using an Atg8 mutant that bypasses the initial Atg4-dependent processing, we demonstrate that Atg8 deconjugation is an important step required to facilitate multiple events during macroautophagy. The inability to deconjugate Atg8-PE results in the mislocalization of this protein to the vacuolar membrane. We also show that the deconjugation of Atg8-PE is required for efficient autophagosome biogenesis, the assembly of Atg9-containing tubulovesicular clusters into phagophores/autophagosomes, and for the disassembly of PAS-associated Atg components.

A dual role for K63-linked ubiquitin chains in multivesicular body biogenesis and cargo sorting

In yeast, the sorting of transmembrane proteins into the multivesicular body (MVB) internal vesicles requires their ubiquitylation by the ubiquitin ligase Rsp5. This allows their recognition by the ubiquitin-binding domains (UBDs) of several endosomal sorting complex required for transport (ESCRT) subunits. K63-linked ubiquitin (K63Ub) chains decorate several MVB cargoes, and accordingly we show that they localize prominently to the class E compartment, which accumulates ubiquitylated cargoes in cells lacking ESCRT components. Conversely, yeast cells unable to generate K63Ub chains displayed MVB sorting defects. These properties are conserved among eukaryotes, as the mammalian melanosomal MVB cargo MART-1 is modified by K63Ub chains and partly missorted when the genesis of these chains is inhibited. We show that all yeast UBD-containing ESCRT proteins undergo ubiquitylation and deubiquitylation, some being modified through the opposing activities of Rsp5 and the ubiquitin isopeptidase Ubp2, which are known to assemble and disassemble preferentially K63Ub chains, respectively. A failure to generate K63Ub chains in yeast leads to an MVB ultrastructure alteration. Our work thus unravels a double function of K63Ub chains in cargo sorting and MVB biogenesis.

First Report of Colletotrichum acutatum Causing Bitter Rot on Apple in Italy

Italy could be considered the main apple-producing country in the European Union. Italian apple (Malus domestica L. Borkh.) production is estimated at approximately 2.1 million tons and encompasses a wide range of cultivars, harvested from August to November. Colletotrichum acutatum, which causes severe losses to strawberry production, was a regulated organism for all European countries until 2008, when it was removed from the EPPO quarantine pathogen list because of its wide distribution in strawberry-production areas. During the growing season of 2010, fungi were isolated from apple fruits exhibiting bitter rot symptoms after 4 months of storage in several packinghouses in the Emilia Romagna Region. The apples belonged to the Golden Delicious, Granny Smith, Pink Lady and Crisp Pink cultivars. Lesions on the fruit surface were circular and 1 to 3 cm in diameter. When lesions enlarged, they became sunken with relatively firm rotten tissues. The fungal fruiting structures, acervuli, were distributed sparsely or densely on old lesions, and under humid conditions, they discharged an orange conidial mass. Conidia observed with a light microscope appeared hyaline and fusiform, 8 to 16 × 2.5 to 4 μm, with two pointed ends or one rounded end. The fungal isolates were grown on potato dextrose agar (PDA) plates incubated at 25°C. After 7 days, colonies were white, becoming gray to pale orange, and when viewed from the reverse side, the color ranged from pink to reddish orange. Both cultural and morphological characteristics of the pathogen were similar to those described for C. acutatum J.H. Simmonds (3), which is responsible for bitter rot of apple (2). Koch's postulates were performed with one representative isolate from each host by artificial inoculation of 30 healthy apples from the cultivars listed above. Fruit surfaces were disinfected with 70% ethanol, wounded with a sterile needle, and then inoculated with 20 μl of a spore suspension (10⁵ conidia ml^-1) prepared from a 15-day-old culture on PDA. Inoculated fruits were sealed in a plastic bag and incubated at 25°C for 10 days. In 92% of fruits, symptoms appeared 10 days later, forming lesions with cream-to-salmon pink fruiting structures. The fungus was reisolated onto PDA from the lesions on the inoculated apples. After 7 days of incubation, the colonies and the morphology of conidia were the same as those of the original isolates. The tests were performed on all four cultivars with similar results. The PCR analysis, carried out using universal primers ITS1 and ITS4 (4) directly from single-spore-derived mycelium (1), resulted in an amplification product with 100% sequence homology with C. acutatum isolate AB626881 from GenBank database. Considering the results obtained, to our knowledge, this is the first report of C. acutatum in Italy causing bitter rot on apple. The disease is common in practically all countries where apples are commercially grown and since the losses could be severe under prolonged warm and wet weather conditions, C. acutatum could represent a serious issue for the Italian apple industry. References: (1) M. Iotti and A. Zambonelli. Mycol. Res. 110:60, 2006. (2) A. L. Jones et al. Plant Dis. 80:1294, 1996. (3) B. C. Sutton. Page 1 in: Colletotrichum: Biology, Pathology and Control. Brit. Soc. Plant Pathol. Oxon. UK 1992. (4) T. J. White et al. Page 315 in: PCR Protocols. A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990.

The puzzling origin of the autophagosomal membrane

Autophagy is one of the newest and fastest emerging research areas in biomedical life sciences. Autophagosomes, large double-membrane vesicles enclosing cytoplasmic components targeted for degradation, are the hallmark of this catabolic pathway. The origin of the lipid bilayers composing these transport carriers has been the central enigma of the field since the discovery of autophagy. A series of recent studies has implicated several cellular organelles as the possible source of the autophagosomal membranes, if anything further clouding our view. In this compendium, we will discuss these apparently contradictory results and briefly emphasize the relevance of determining the lipid source used for autophagy for future translational research, for example in drug discovery programs.

Lipid droplets are functionally connected to the endoplasmic reticulum in Saccharomyces cerevisiae

Cells store metabolic energy in the form of neutral lipids that are deposited within lipid droplets (LDs). In this study, we examine the biogenesis of LDs and the transport of integral membrane proteins from the endoplasmic reticulum (ER) to newly formed LDs. In cells that lack LDs, otherwise LD-localized membrane proteins are homogenously distributed in the ER membrane. Under these conditions, transcriptional induction of a diacylglycerol acyltransferase that catalyzes the formation of the storage lipid triacylglycerol (TAG), Lro1, is sufficient to drive LD formation. Newly formed LDs originate from the ER membrane where they become decorated by marker proteins. Induction of LDs by expression of the second TAG-synthesizing integral membrane protein, Dga1, reveals that Dga1 itself moves from the ER membrane to concentrate on LDs. Photobleaching experiments (FRAP) indicate that relocation of membrane proteins from the ER to LDs is independent of temperature and energy, and thus not mediated by classical vesicular transport routes. LD-localized membrane proteins are homogenously distributed at the perimeter of LDs, they are free to move over the LD surface and can even relocate back into the ER, indicating that they are not restricted to specialized sites on LDs. These observations indicate that LDs are functionally connected to the ER membrane and that this connection allows the efficient partitioning of membrane proteins between the two compartments.

Phosphorylation of a membrane curvature-sensing motif switches function of the HOPS subunit Vps41 in membrane tethering

An AP-3–binding site required for vesicle–vacuole fusion is masked when Vps41 is associated with highly curved membranes, such as endosomes, but is exposed at membranes with lower curvature, such as vacuoles, because of phosphorylation of the membrane-binding motif.

Tethering factors are organelle-specific multisubunit protein complexes that identify, along with Rab guanosine triphosphatases, transport vesicles and trigger their SNARE-mediated fusion of specific transport vesicles with the target membranes. Little is known about how tethering factors discriminate between different trafficking pathways, which may converge at the same organelle. In this paper, we describe a phosphorylation-based switch mechanism, which allows the homotypic vacuole fusion protein sorting effector subunit Vps41 to operate in two distinct fusion events, namely endosome–vacuole and AP-3 vesicle–vacuole fusion. Vps41 contains an amphipathic lipid-packing sensor (ALPS) motif, which recognizes highly curved membranes. At endosomes, this motif is inserted into the lipid bilayer and masks the binding motif for the δ subunit of the AP-3 complex, Apl5, without affecting the Vps41 function in endosome–vacuole fusion. At the much less curved vacuole, the ALPS motif becomes available for phosphorylation by the resident casein kinase Yck3. As a result, the Apl5-binding site is exposed and allows AP-3 vesicles to bind to Vps41, followed by specific fusion with the vacuolar membrane. This multifunctional tethering factor thus discriminates between trafficking routes by switching from a curvature-sensing to a coat recognition mode upon phosphorylation.

An Atg9-containing compartment that functions in the early steps of autophagosome biogenesis

A reservoir of Atg9-containing vesicles and tubules provides the initial membranes necessary for autophagophore formation in yeast.

Eukaryotes use the process of autophagy, in which structures targeted for lysosomal/vacuolar degradation are sequestered into double-membrane autophagosomes, in numerous physiological and pathological situations. The key questions in the field relate to the origin of the membranes as well as the precise nature of the rearrangements that lead to the formation of autophagosomes. We found that yeast Atg9 concentrates in a novel compartment comprising clusters of vesicles and tubules, which are derived from the secretory pathway and are often adjacent to mitochondria. We show that these clusters translocate en bloc next to the vacuole to form the phagophore assembly site (PAS), where they become the autophagosome precursor, the phagophore. In addition, genetic analyses indicate that Atg1, Atg13, and phosphatidylinositol-3-phosphate are involved in the further rearrangement of these initial membranes. Thus, our data reveal that the Atg9-positive compartments are important for the de novo formation of the PAS and the sequestering vesicle that are the hallmarks of autophagy.

The CORVET subunit Vps8 cooperates with the Rab5 homolog Vps21 to induce clustering of late endosomal compartments

Membrane tethering, the process of mediating the first contact between membranes destined for fusion, requires specialized multisubunit protein complexes and Rab GTPases. In the yeast endolysosomal system, the hexameric HOPS tethering complex cooperates with the Rab7 homolog Ypt7 to promote homotypic fusion at the vacuole, whereas the recently identified homologous CORVET complex acts at the level of late endosomes. Here, we have further functionally characterized the CORVET-specific subunit Vps8 and its relationship to the remaining subunits using an in vivo approach that allows the monitoring of late endosome biogenesis. In particular, our results indicate that Vps8 interacts and cooperates with the activated Rab5 homolog Vps21 to induce the clustering of late endosomal membranes, indicating that Vps8 is the effector subunit of the CORVET complex. This clustering, however, requires Vps3, Vps16, and Vps33 but not the remaining CORVET subunits. These data thus suggest that the CORVET complex is built of subunits with distinct activities and potentially, their sequential assembly could regulate tethering and successive fusion at the late endosomes.

Mitochondrial cholesterol in health and disease

Cholesterol is a critical component of biological membranes, which not only plays an essential role in determining membrane physical properties, but also in the regulation of multiple signaling pathways. Cells satisfy their need for cholesterol either by uptake from nutrients and lipoproteins or de novo synthesis from acetyl-CoA. The latter process occurs in the endoplasmic reticulum, where transcription factors that regulate the expression of enzymes involved in the de novo cholesterol synthesis reside. Cholesterol is distributed to different membranes most prominently to plasma membrane, where it participates in the physical organization of specific membrane domains. Mitochondria, however, are considered cholesterol-poor organelles, and obtain their cholesterol load by the action of specialized proteins involved in its delivery from extramitochondrial sources and trafficking within mitochondrial membranes. Although mitochondrial cholesterol fulfills vital physiological functions, such as the synthesis of bile acids in the liver or the formation of steroid hormones in specialized tissues, recent evidence indicates that the accumulation of cholesterol in mitochondria may be a key step in disease progression, including steatohepatitis, carcinogenesis or Alzheimer disease.

Vps41 phosphorylation and the Rab Ypt7 control the targeting of the HOPS complex to endosome-vacuole fusion sites

Membrane fusion depends on multisubunit tethering factors such as the vacuolar HOPS complex. We previously showed that the vacuolar casein kinase Yck3 regulates vacuole biogenesis via phosphorylation of the HOPS subunit Vps41. Here, we link the identified Vps41 phosphorylation site to HOPS function at the endosome-vacuole fusion site. The nonphosphorylated Vps41 mutant (Vps41 S-A) accumulates together with other HOPS subunits on punctate structures proximal to the vacuole that expand in a class E mutant background and that correspond to in vivo fusion sites. Ultrastructural analysis of this mutant confirmed the presence of tubular endosomal structures close to the vacuole. In contrast, Vps41 with a phosphomimetic mutation (Vps41 S-D) is mislocalized and leads to multilobed vacuoles, indicative of a fusion defect. These two phenotypes can be rescued by overproduction of the vacuolar Rab Ypt7, revealing that both Ypt7 and Yck3-mediated phosphorylation modulate the Vps41 localization to the endosome-vacuole junction. Our data suggest that Vps41 phosphorylation fine-tunes the organization of vacuole fusion sites and provide evidence for a fusion "hot spot" on the vacuole limiting membrane.

In vivo imaging of neurodegeneration in Caenorhabditis elegans by third harmonic generation microscopy

In this study, neurodegeneration phenomena were investigated, by performing third harmonic generation imaging measurements on the nematode Caenorhabditis elegans, in vivo. The in vivo, precise identification of the contour of the degenerating neurons in the posterior part of the nematode and the monitoring, in real time, of the progression of degeneration in the worm, through third harmonic generation imaging measurements, were achieved. Femtosecond laser pulses (1028 nm) were utilized for excitation. Thus, the THG image contrast modality comprises a powerful diagnostic tool, providing valuable information and offering new insights into morphological changes and complex developmental processes in live biological specimens.

Effects of potassium sorbate on postharvest brown rot of stone fruit

The effect of potassium sorbate (K-sorb), a low-toxicity chemical, to control Monilinia spp. was investigated. Preliminary in vitro studies found the MIC of K-sorb for conidial germination and mycelial growth was, respectively, 260 and 1,250 mg/ liter. Immersion of naturally infected peach and nectarine fruit in a solution (15 g/liter) of K-sorb for 120 s reduced brown rot by over 80% in four of five trials. Although treated fruits showed a significant reduction in firmness with respect to the control, they did not reach the overripe stage and retained acceptable quality parameters. In an attempt to elucidate the mechanism of action for K-sorb, the inhibition of enzymatic activity by K-sorb was also tested. In a radial diffusion assay, the addition of K-sorb to agarose reduced polygalacturonase (PG) activity across the concentrations considered. The greatest reduction (54.3%, with respect to the control) was obtained at a sorbate concentration of 15 g/liter. PG kinetic activity of Monilinia laxa observed by a spectrophotometric assay peaked after 40 min in all samples tested. PG activity was significantly higher in the control than in the samples with increased K-sorb concentrations. In conclusion, based on these findings, K-sorb can be recommended as a low-toxicity antifungal compound against Monilinia spp. in peaches and nectarines with its mode of action probably depending in part on the inhibition of PG activity in M. laxa.

A cryosectioning procedure for the ultrastructural analysis and the immunogold labelling of yeast Saccharomyces cerevisiae

Yeast Saccharomyces cerevisiae has been a crucial model system for the study of a multitude of cellular processes because of its amenability to genetics, molecular biology and biochemical procedures. By contrast, the morphological analysis of this organism by immunoelectron microscopy (IEM) has remained in a primordial phase preventing researchers to routinely incorporate this technique into their investigations. Here, in addition to simple but detailed protocols to perform conventional electron microscopy (EM) on plastic embedded sections, we present a new IEM procedure adapted from the Tokuyasu method to prepare cryosections from mildly fixed cells. This novel approach allows an excellent cell preservation and the negatively stained membranes create superb contrast that leads to a unique resolution of the yeast morphology. This, plus the optimal preservation of the epitopes, permits combined localization studies with a fine resolution of protein complexes, vesicular carriers and organelles at an ultrastructural level. Importantly, we also show that this cryo-immunogold protocol can be combined with high-pressure freezing and therefore cryofixation can be employed if difficulties are encountered to immobilize a particular structure with chemical fixation. This new IEM technique will be a valuable tool for the large community of scientists using yeast as a model system, in particular for those studying membrane transport and dynamics.

Irs4p and Tax4p: two redundant EH domain proteins involved in autophagy

Proteins carrying EPS15 homology (EH) domains are present from yeast to mammals. The characterized members of this protein family are all involved in intracellular trafficking, typically endocytosis and endocytic recycling. We focused on two members of this family in Saccharomyces cerevisiae Irs4p and Tax4p, whose functions are less well characterized. We show that the deletion of IRS4 altered the function of a neighboring gene, VPS51, involved in endocytic recycling. The irs4Deltatax4Delta cells complemented for the loss of Vps51p (irs4Deltatax4Delta*) display no defects in endocytosis and endosomal recycling, clearly differentiating these two EH proteins from the other protein family members. Because Irs4p is phosphorylated when autophagy is induced, we studied the potential role of these two proteins in this latter process. We observed a loss of viability upon starvation in irs4Deltatax4Delta* cells because of a delay in bulk autophagy. Irs4p and Tax4p are also required for pexophagy but not for the cytoplasm-to-vacuole pathway. In growing cells, Irs4p and Tax4p colocalized to few cytoplasmic puncta distinct from endosomes and Golgi compartments. In conditions inducing autophagy, Irs4p and Tax4p partially localized to the pre-autophagosomal structure (PAS) and are required to efficiently recruit to the PAS Atg17p, a factor modulating the autophagic response. We propose that Irs4p and Tax4p are two redundant modulators of the autophagic processes acting upstream from Atg17p, possibly in the signaling events leading to the activation of the autophagic machinery in response to starvation.

Pharmacological targeting of NF-kappaB potentiates the effect of the topoisomerase inhibitor CPT-11 on colon cancer cells

NF-κB interferes with the effect of most anti-cancer drugs through induction of anti-apoptotic genes. Targeting NF-κB is therefore expected to potentiate conventional treatments in adjuvant strategies. Here we used a pharmacological inhibitor of the IKK2 kinase (AS602868) to block NF-κB activation. In human colon cancer cells, inhibition of NF-κB using 10 μM AS602868 induced a 30–50% growth inhibitory effect and strongly enhanced the action of SN-38, the topoisomerase I inhibitor and CPT-11 active metabolite. AS602868 also potentiated the cytotoxic effect of two other antineoplasic drugs: 5-fluorouracil and etoposide. In xenografts experiments, inhibition of NF-κB potentiated the antitumoural effect of CPT-11 in a dose-dependent manner. Eighty-five and 75% decreases in tumour size were observed when mice were treated with, respectively, 20 or 5 mg kg⁻¹ AS602868 associated with 30 mg kg⁻¹ CPT-11 compared to 47% with CPT-11 alone. Ex vivo tumour analyses as well as in vitro studies showed that AS602868 impaired CPT-11-induced NF-κB activation, and enhanced tumour cell cycle arrest and apoptosis. AS602868 also enhanced the apoptotic potential of TNFα on HT-29 cells. This study is the first demonstration that a pharmacological inhibitor of the IKK2 kinase can potentiate the therapeutic efficiency of antineoplasic drugs on solid tumours.

SNX1 defines an early endosomal recycling exit for sortilin and mannose 6-phosphate receptors

Mannose-6-phosphate receptors (MPRs) transport lysosomal hydrolases from the trans Golgi network (TGN) to endosomes. Recently, the multi-ligand receptor sortilin has also been implicated in this transport, but the transport carriers involved herein have not been identified. By quantitative immuno-electron microscopy, we localized endogenous sortilin of HepG2 cells predominantly to the TGN and endosomes. In the TGN, sortilin colocalized with MPRs in the same clathrin-coated vesicles. In endosomes, sortilin and MPRs concentrated in sorting nexin 1 (SNX1)-positive buds and vesicles. SNX1 depletion by small interfering RNA resulted in decreased pools of sortilin in the TGN and an increase in lysosomal degradation. These data indicate that sortilin and MPRs recycle to the TGN in SNX1-dependent carriers, which we named endosome-to-TGN transport carriers (ETCs). Notably, ETCs emerge from early endosomes (EE), lack recycling plasma membrane proteins and by three-dimensional electron tomography exhibit unique structural features. Hence, ETCs are distinct from hitherto described EE-derived membranes involved in recycling. Our data emphasize an important role of EEs in recycling to the TGN and indicate that different, specialized exit events occur on the same EE vacuole.

Monitoring metals near a hazardous waste incinerator. Temporal trend in soils and herbage

In recent years, incineration has been demonstrated to be a commercially available technology for hazardous waste (HW) disposal (Richter and Johnke, 2004). However, because of the potential adverse effects of toxic emissions, waste incinerators are still an important cause for concern for the public. In spite of that, compliance with current EU emissions has vastly reduced the probability of adverse health effects (Glorennec et al., 2005). With respect to metals, a number of studies have shown that these elements are emitted by industrial, medical and municipal waste incinerators (Schumacher et al., 1997; Rimmer et al., 2006). Filter ash is an especially problematic residue because it contains high metal concentrations (Lisk et al., 1989). After combustion in modern HW incinerators (HWIs), metals contained in HW are mainly collected in bottom and fly ash, with only small quantity of metals being discharged from the stack as particulate matter or vapor (Jung et al., 2004). However, the atmospheric emission of these elements is a matter of concern.