Characterising resistance to Turnip mosaic virus (TuMV) in Turnip (Brassica rapa rapa)

A Brassica rapa rapa L. line has been identified with high resistance to seven isolates of Turnip mosaic virus (TuMV) (including UK 1, CHN 5, CZE 1, CDN 1, GBR 6, POL 1 and UK 4) representing the major pathotypes of the virus. Resistant plants showed no symptoms following mechanical inoculation with TuMV and no virus was detected in the plants by ELISA. A cross was made between the rapid-cycling Brassica rapa line R-o-18 (which has been found to be susceptible to all the TuMV isolates) and a plant from the resistant B. rapa rapa line. The small amount of the F1 generation seed available from this cross has been grown and inoculated with the seven TuMV isolates. F1 plants were uniformly resistant to the UK 1 isolate of TuMV, uniformly susceptible to the CHN 5 isolate (only 2 plants inoculated) and segregated for resistance and susceptibility to the other five TuMV isolates. This suggested that the parent B. rapa rapa plant used in the cross was probably homozygous for one, or more dominant resistance genes to the UK 1 isolate of TuMV and heterozygous for one, or more dominant resistance genes to the other TuMV isolates. When self seed (S1) from the parent plant from the resistant line was inoculated with the TuMV isolates GBR 6 and UK 4, the segregation for the former isolate was not significantly different from 3 resistant to 1 susceptible, whereas for the latter isolate, the segregation was 4 resistant to 9 susceptible, suggesting resistance to GBR 6 is controlled by a single dominant gene, whereas resistance to UK 4 is controlled by two or more dominant resistance genes. The putative resistance genes appear to confer hitherto unknown dominant TuMV resistance specificities, and in combination have the exciting potential of providing durable resistance to TuMV

A comparison of Olpidium isolates from a range of host plants using internal transcribed spacer sequence analysis and host range studies

Olpidium brassicae is a ubiquitous obligate root-infecting fungal pathogen. It is an important vector of a wide range of plant viruses. Olpidium isolates that infected brassica plants did not infect lettuce plants and vice-versa. Host range tests, PCR amplification and sequencing of the internal transcribed spacer (ITS) and 5.8S regions of 25 Olpidium isolates from brassica, carrot, cucumber and lettuce originating from four continents revealed differences between isolates. Based on their ability to infect lettuce and brassicas and the differences between their ITS1, 5.8S and ITS2 regions they could be separated into a number of distinct groups. Comparisons with other published sequences revealed two distinct genetic groups of brassica-infecting isolates, two distinct groups of lettuce-infecting isolates, one of which contained a carrot-infecting isolate and a distinct group comprising a cucumber-infecting isolate and a melon-infecting isolate. The possibility of the isolates belonging to three distinct species is discussed

Shifting Patterns of Nitrogen Excretion and Amino Acid Catabolism Capacity during the Life Cycle of the Sea Lamprey (\u3cem\u3ePetromyzon mariunus\u3c/em\u3e)

The jawless fish, the sea lamprey (Petromyzon marinus), spends part of its life as a burrow-dwelling, suspension-feeding larva (ammocoete) before undergoing a metamorphosis into a free swimming, parasitic juvenile that feeds on the blood of fishes. We predicted that animals in this juvenile, parasitic stage have a great capacity for catabolizing amino acids when large quantities of protein-rich blood are ingested. The sixfold to 20-fold greater ammonia excretion rates (JAmm) in postmetamorphic (nonfeeding) and parasitic lampreys compared with ammocoetes suggested that basal rates of amino acid catabolism increased following metamorphosis. This was likely due to a greater basal amino acid catabolizing capacity in which there was a sixfold higher hepatic glutamate dehydrogenase (GDH) activity in parasitic lampreys compared with ammocoetes. Immunoblotting also revealed that GDH quantity was 10-fold and threefold greater in parasitic lampreys than in ammocoetes and upstream migrant lampreys, respectively. Higher hepatic alanine and aspartate aminotransferase activities in the parasitic lampreys also suggested an enhanced amino acid catabolizing capacity in this life stage. In contrast to parasitic lampreys, the twofold larger free amino acid pool in the muscle of upstream migrant lampreys confirmed that this period of natural starvation is accompanied by a prominent proteolysis. Carbamoyl phosphate synthetase III was detected at low levels in the liver of parasitic and upstream migrant lampreys, but there was no evidence of extrahepatic (muscle, intestine) urea production via the ornithine urea cycle. However, detection of arginase activity and high concentrations of arginine in the liver at all life stages examined infers that arginine hydrolysis is an important source of urea. We conclude that metamorphosis is accompanied by a metabolic reorganization that increases the capacity of parasitic sea lampreys to catabolize intermittently large amino acid loads arising from the ingestion of protein rich blood from their prey/hosts. The subsequent generation of energy-rich carbon skeletons can then be oxidized or retained for glycogen and fatty acid synthesis, which are essential fuels for the upstream migratory and spawning phases of the sea lamprey’s life cycle

Mapping and candidate-gene screening of the novel Turnip mosaic virus resistance gene retr02 in Chinese cabbage (Brassica rapa L.)

The extreme resistance to Turnip mosaic virus observed in the Chinese cabbage (Brassica rapa) line, BP8407, is monogenic and recessive. Bulked segregant analysis was carried out to identify simple sequence repeat and Indel markers linked to this recessive resistance gene, termed recessive Turnip mosaic virus resistance 02 (retr02). Mapping of PCR-specific Indel markers on 239 individuals of a BP8407 × Ji Zao Chun F 2 population, located this resistance gene to a 0.9-cM interval between two Indel markers (BrID10694 and BrID101309) and in scaffold000060 or scaffold000104 on chromosome A04 of the B. rapa genome. Eleven eukaryotic initiation factor 4E (eIF4E) and 14 eukaryotic initiation factor 4G (eIF4G) genes are predicted in the B. rapa genome. A candidate gene, Bra035393 on scaffold000104, was predicted within the mapped resistance locus. The gene encodes the eIF(iso)4E protein. Bra035393 was sequenced in BP8407 and Ji Zao Chun. A polymorphism (A/G) was found in exon 3 between BP8407 and Ji Zao Chun. This gene was analysed in four resistant and three susceptible lines. A correlation was observed between the amino acid substitution (Gly/Asp) in the eIF(iso)4E protein and resistance/susceptibility. eIF(iso)4E has been shown previously to interact with the TuMV genome-linked protein, VPg

Nucleotide bias of DCL and AGO in plant anti-virus gene silencing

Plant Dicer-like (DCL) and Argonaute (AGO) are the key enzymes involved in anti-virus post-transcriptional gene silencing (AV-PTGS). Here we show that AV-PTGS exhibited nucleotide preference by calculating a relative AV-PTGS efficiency on processing viral RNA substrates. In comparison with genome sequences of dicot-infecting Turnip mosaic virus (TuMV) and monocot-infecting Cocksfoot streak virus (CSV), viral-derived small interfering RNAs (vsiRNAs) displayed positive correlations between AV-PTGS efficiency and G+C content (GC%). Further investigations on nucleotide contents revealed that the vsiRNA populations had G-biases. This finding was further supported by our analyses of previously reported vsiRNA populations in diverse plant-virus associations, and AGO associated Arabidopsis endogenous siRNA populations, indicating that plant AGOs operated with G-preference. We further propose a hypothesis that AV-PTGS imposes selection pressure(s) on the evolution of plant viruses. This hypothesis was supported when potyvirus genomes were analysed for evidence of GC elimination, suggesting that plant virus evolution to have low GC% genomes would have a unique function, which is to reduce the host AV-PTGS attack during infections

Development of a scoring method to identify important areas of plant diversity in Ireland

peer-reviewedIn the face of accelerating biodiversity loss it is more important than ever to identify important areas of biodiversity and target limited resources for conservation. We developed a method to identify areas of important plant diversity using known species’ distributions and evaluations of the species importance. We collated distribution records of vascular plants and developed a scoring method of spatial prioritisation to assign conservation value to the island of Ireland at the hectad scale (10 km × 10 km) and at the tetrad scale (2 km × 2 km) for two counties where sufficient data were available. Each plant species was assigned a species conservation value based on both its conservation status and distribution in Ireland. For each cell, the species conservation values within the cell were summed, thereby differentiating between areas of high and low conservation value across the landscape. Areas with high conservation value represent the most important areas for plant conservation. The protected area cover and the number of species present in these important areas were also examined by first defining threshold values using two different criteria. Species representation was high in the important areas; the identified important areas of plant diversity maintained high representation of species of conservation concern and achieved high species representation overall, requiring a low number of sites (<8%) to do so. The coincidence of protected areas and important areas for plant diversity was found to be low and while some important areas of plant diversity might benefit from the general protection afforded by these areas, our research highlights the need for conservation outside of protected areas

Confirmation of Radish Isolate of Turnip mosaic virus in India through biological and serological evidences

Background and Objective: Oilseed brassica are one of the most exploited agricultural commodities in International trade with diversified use in human and animal consumption besides their potential use in producing green energy in the form of biofuels. Turnip mosaic virus is one of the limiting factors for declining oil content in brassica. The present studies were therefore conducted to confirm the presence of this important virus in brassica through biological and serological assays. Materials and Methods: A total of 518 samples collected from 84 locations spanning across 5 states and 1 union territory from symptomatic plants were collected and assayed in DAS-ELISA using Turnip mosaic virus (TuMV) specific polyclonal antiserum. Biological and serological host range of the virus isolate was established and different varieties/breeding lines of oilseed brassica were screened for developing a resistance panel against TuMV. Results: Turnip mosaic virus incidence ranged between 0.6-8.3% in oilseed brassica and 0.2-17.6% in crucifer vegetables. Turnip mosaic virus was recorded in very high concentration from radish as indicated by the optical density values. Mustard variety Tender Green was established as the best propagative host of Indian radish isolate of Turnip mosaic virus. Out of 32 varieties/breeding lines of oilseed brassica collected from different sources in India, 25 varieties/lines were found to be susceptible to Turnip mosaic virus under glasshouse conditions and DAS-ELISA further confirmed these findings. Conclusion: A radish isolate of Turnip mosaic virus has been identified on the basis of biological and serological assays and results obtained for screening of brassica germplasm against Turnip mosaic virus are expected to help in ascertaining the sources of resistance against this virus

Microbial Selection and Survival in Subseafloor Sediment

Many studies have examined relationships of microorganisms to geochemical zones in subseafloor sediment. However, responses to selective pressure and patterns of community succession with sediment depth have rarely been examined. Here we use 16S rDNA sequencing to examine the succession of microbial communities at sites in the Indian Ocean and the Bering Sea. The sediment ranges in depth from 0.16 to 332 m below seafloor and in age from 660 to 1,300,000 years. The majority of subseafloor taxonomic diversity is present in the shallowest depth sampled. The best predictor of sequence presence or absence in the oldest sediment is relative abundance in the near-seafloor sediment. This relationship suggests that perseverance of specific taxa into deep, old sediment is primarily controlled by the taxonomic abundance that existed when the sediment was near the seafloor. The operational taxonomic units that dominate at depth comprise a subset of the local seafloor community at each site, rather than a grown-in group of geographically widespread subseafloor specialists. At both sites, most taxa classified as abundant decrease in relative frequency with increasing sediment depth and age. Comparison of community composition to cell counts at the Bering Sea site indicates that the rise of the few dominant taxa in the deep subseafloor community does not require net replication, but might simply result from lower mortality relative to competing taxa on the long timescale of community burial

Spontaneous transient outward currents arise from microdomains where BK channels are exposed to a mean Ca(2+) concentration on the order of 10 microM during a Ca(2+) spark

Ca(2+) sparks are small, localized cytosolic Ca(2+) transients due to Ca(2+) release from sarcoplasmic reticulum through ryanodine receptors. In smooth muscle, Ca(2+) sparks activate large conductance Ca(2+)-activated K(+) channels (BK channels) in the spark microdomain, thus generating spontaneous transient outward currents (STOCs). The purpose of the present study is to determine experimentally the level of Ca(2+) to which the BK channels are exposed during a spark. Using tight seal, whole-cell recording, we have analyzed the voltage-dependence of the STOC conductance (g((STOC))), and compared it to the voltage-dependence of BK channel activation in excised patches in the presence of different [Ca(2+)]s. The Ca(2+) sparks did not change in amplitude over the range of potentials of interest. In contrast, the magnitude of g((STOC)) remained roughly constant from 20 to -40 mV and then declined steeply at more negative potentials. From this and the voltage dependence of BK channel activation, we conclude that the BK channels underlying STOCs are exposed to a mean [Ca(2+)] on the order of 10 microM during a Ca(2+) spark. The membrane area over which a concentration \u3e or =10 microM is reached has an estimated radius of 150-300 nm, corresponding to an area which is a fraction of one square micron. Moreover, given the constraints imposed by the estimated channel density and the Ca(2+) current during a spark, the BK channels do not appear to be uniformly distributed over the membrane but instead are found at higher density at the spark site