Multiple translocation of the AVR-Pita effector gene among chromosomes of the rice blast fungus Magnaporthe oryzae and related species

Magnaporthe oryzae is the causal agent of rice blast disease, a devastating problem worldwide. This fungus has caused breakdown of resistance conferred by newly developed commercial cultivars. To address how the rice blast fungus adapts itself to new resistance genes so quickly, we examined chromosomal locations of AVR-Pita, a subtelomeric gene family corresponding to the Pita resistance gene, in various isolates of M. oryzae (including wheat and millet pathogens) and its related species. We found that AVR-Pita (AVR-Pita1 and AVR-Pita2) is highly variable in its genome location, occurring in chromosomes 1, 3, 4, 5, 6, 7, and supernumerary chromosomes, particularly in rice-infecting isolates. When expressed in M. oryzae, most of the AVR-Pita homologs could elicit Pita-mediated resistance, even those from non-rice isolates. AVR-Pita was flanked by a retrotransposon, which presumably contributed to its multiple translocation across the genome. On the other hand, family member AVR-Pita3, which lacks avirulence activity, was stably located on chromosome 7 in a vast majority of isolates. These results suggest that the diversification in genome location of AVR-Pita in the rice isolates is a consequence of recognition by Pita in rice. We propose a model that the multiple translocation of AVR-Pita may be associated with its frequent loss and recovery mediated by its transfer among individuals in asexual populations. This model implies that the high mobility of AVR-Pita is a key mechanism accounting for the rapid adaptation toward Pita. Dynamic adaptation of some fungal plant pathogens may be achieved by deletion and recovery of avirulence genes using a population as a unit of adaptation.     

A retrospective analysis of germline competence in rat embryonic stem cell lines

The factors responsible for conferring germline competence in embryonic stem (ES) cell lines remain unidentified. In the present study, rat ES cell lines (n = 17) were established with 3i medium (SU5402, PD0325901, CHIR99021), 2i medium (PD0325901, CHIR99021) or 2iF medium (PD0325901, CHIR99021, forskolin), and their potential for germline transmission to the G1 generation was examined. Rat strains were divided into an albino group (F344, Wistar or CAG/Venus transgenic rats with the Wistar background) or a colored coat group (Brown-Norway, Dark-Agouti, or BLK rats selected from >F3 generations of Wistar × Dark-Agouti rats based on their black coat color). Successful germline transmission was observed in 57 % (4/7), 40 % (2/5) and 100 % (5/5) of the ES cells established with 3i, 2i and 2iF media, respectively. ES cell lines from the homozygous CAG/Venus transgenic rats were established in all three media, but only the lines established with the 2iF medium were germline-competent. Neither coat-color (albino: 64 %, 7/11; colored: 67 %, 4/6) nor gender of the ES cell lines (XX: 67 %, 2/3; XY: 64 %, 9/14) were likely to affect germline transmission.     

Influence of chloroplastic photo-oxidative stress on mitochondrial alternative oxidase capacity and respiratory properties: a case study with Arabidopsis yellow variegated 2

Mitochondrial alternative oxidase (AOX), the unique respiratory terminal oxidase in plants, catalyzes the energy-wasteful cyanide (CN)-resistant respiration. Although it has been demonstrated that leaf AOX is up-regulated under high-light (HL) conditions, the in vivo mechanism of AOX up-regulation by light is still unknown. In the present study, we examined whether the photo-oxidative stress in the chloroplast modulates mitochondrial respiratory properties, especially the AOX capacity, using Arabidopsis leaf-variegated mutant yellow variegated 2 (var2) and exposing plants to HL. var2 mutants lack FtsH2 metalloprotease required for the repair of damaged PSII. Indeed, var2-1 suffered from photo-oxidative stress even before the HL treatments. While the activities of tricarboxylic acid cycle enzymes and cytochrome c oxidase in var2-1 were almost identical to those in the wild type, the amount of AOX protein and the CN-resistant respiration rate were higher in var2-1. Real-time PCR analysis revealed that HL treatment induced the expression of some energy-dissipating respiratory genes, including AOX1a, NDB2 and UCP5, more strongly in var2-1. Western blotting using var2-1 leaf extracts specific to green or white sectors, containing functional or non-functional photosynthetic apparatus, respectively, revealed that more AOX protein was induced in the green sectors by the HL treatment. These results indicate that photo-oxidative stress by excess light is involved in the regulation of respiratory gene expression and the modulation of respiratory properties, especially the AOX up-regulation.     

IcsB,secreted via the type III secretion system,is chaperoned by IpgA and required at the post-invasion stage of Shigella pathogenicity

Shigella deliver a subset of effector proteins such as IpaA, IpaB and IpaC via the type III secretion system (TTSS) into host cells during the infection of colonic epithelial cells. Many bacterial effectors including some from Shigella require specific chaperones for protection from degradation and targeting to the TTSS. In this study, we have investigated the role of the icsB gene located upstream of the ipaBCDA operon in Shigella infection because the role of IcsB as a virulence factor remains unknown. Here, we found that the IcsB protein is secreted via the TTSS of Shigella in vitro and in vivo. We show that IpgA protein encoded by ipgA, the gene immediately downstream of icsB, serves as the chaperone required for the stabilization and secretion of IcsB. We have shown that IcsB binds to IpgA in bacterial cytosol and the binding site is in the middle of the IcsB protein. Intriguingly, although its significance in Shigella pathogenicity is as yet unclear, the icsB gene can be read-through into the ipgA gene to create a translational fusion protein. Furthermore, the contribution of IcsB to the pathogenicity of Shigella was demonstrated by plaque-forming assay and the Sereny test. The ability of the icsB mutant to form plaques was greatly reduced compared with that of the wild type in MDCK cell monolayers. Furthermore, when guinea pig eyes were infected with a non-polar icsB mutant, the bacteria failed to provoke keratoconjunctivitis. These results suggest that IcsB is secreted via the TTSS, chaperoned by IpgA, and required at the post-invasion stage of Shigella pathogenicity     

Defense response of a pepper cultivar cv. Sy-2 is induced at temperatures below 24°C

Temperature is one of the most important environmental factors that influence plant growth and development. Recent studies imply that plants show various responses to non-extreme ambient temperatures. Previously, we have found that a pepper cultivar cv. Sy-2 (Capsicum chinense) shows developmental defects at temperatures below 24°C. In this study, to gain new insights into the temperature sensitivity of cv. Sy-2, temperature-sensitive genes were screened using microarray techniques. At restrictive temperature of 20°C, almost one-fourth of the 411 up-regulated genes were defense related or predicted to be defense related. Further expression analyses of several defense-related genes showed that defense-related genes in cv. Sy-2 were constitutively expressed at temperatures below 24°C. Moreover, accumulation of high level of salicylic acid (SA) in cv. Sy-2 grown at 20°C suggests that the defense response is activated in the absence of pathogens. To confirm that the defense response is induced in cv. Sy-2 below 24°C, we evaluated the resistance to biotrophic bacterial pathogen Xanthomonas campestris pv. vesicatoria and necrotrophic fungal pathogen Cercospora capsici. Cv. Sy-2 showed enhanced resistance to X. campestris pv. vesicatoria, but not to C. capsici.     

DNA Methylation Occurred around Lowly Expressed Genes of Plastid DNA during Tomato Fruit Development

We have analyzed DNA methylation of plastid DNA from fully ripened red fruits, green mature fruits, and green leaves of tomato (Lycopersicon esculentum var. Firstmore). Essentially identical restriction profiles were obtained between chromoplast and chloroplast DNAs by EcoRI digestion. BstNI/EcoRII and HpaII/MspI are pairs of isoschizomers that can discriminate between methylated and unmethylated DNAs. These endonucleases produced different restriction patterns of plastid DNAs from tomato fruits compared to tomato leaves. Moreover, we have found from Southern blots that methylation was not detected in DNA fragments containing certain genes that are actively expressed in chromoplasts, whereas DNA fragments bearing genes that are barely transcribed in chromoplasts are methylated.     

Ribosylation of the Base Residue of Inosine Derivatives by Phase-Transfer Catalysis

Abstract

Reaction of 2′,3′,5′-O-silylated inosine derivative 1 with 2, 3-O-isopropylidene-5-O-tritylribosyl chloride (3) in a two-phase (CH₂Cl₂-aq. NaOH) system in the presence of Bu₄NBr gave three products, i. e., 6-O-α-, 6-O-β-, and N ¹-β-isomers of glycosides 4, 5a, and 5b. A similar PTC reaction of 1 with 2, 3, 5-tri-O-benzylribosyl bromide (9) gave four regio- and stereo-isomers involving the N¹-β-glycoside 10. Reaction of 1 with 2, 3, 5-tri-O-benzoylribosyl bromide (11) afforded three products involving the desired N¹-β-glycoside 12b, which could be deprotected to give N ¹-ribosylinosine (15b) as a useful intermediate for the synthesis of cIDPR.

     

Importance of sandy bottoms in coral reefs to the oscillation of daily rhythms in the tropical wrasse Halichoeres trimaculatus

Most wrasse species swim during the day and bury themselves in the sandy bottoms of shallow reefs at night. This study aimed to evaluate the importance of sandy bottoms to the day-active/night-inactive rhythmicity of the tropical wrasse Halichoeres trimaculatus. Actogram analysis revealed that fish were active during the photophase and inactive during the scotophase in aquariums with both sandy and bare bottoms. When fish were kept in aquariums with bare bottoms, rhythmicity was maintained under constant dark conditions (DD) but became obscured under constant light conditions (LL), suggesting that a day-active/night-inactive rhythmicity is regulated by the circadian system. Robust fluctuations in Period1 (wPer1) and Period2 (wPer2) expression were observed in the pectoral fin tissue under light–dark conditions (LD). Similar fluctuations in wPer1 expression persisted under DD. When fish were kept under LD conditions for 7 days and then DD for 20 days, the emergence of fish from the sandy bottom was delayed gradually. At the same time, the peak time of wPer1 expression under DD was retarded from 06:00 to 10:00. Although wPer2 expression was dampened under DD, it increased after exposing fish to light. These results suggest that wPer1 and wPer2 are differentially involved in the day-active/night-inactive rhythmicity, and that blocking light with a sandy bed at night and exposing fish to light during emergence in the morning play important roles in maintaining consistent activities in wrasse species.