Terrestrial orchid conservation in the age of extinction

Background

Conservation through reserves alone is now considered unlikely to achieve protection of plant species necessary to mitigate direct losses of habitat and the pervasive impact of global climate change. Assisted translocation/migration represent new challenges in the face of climate change; species, particularly orchids, will need artificial assistance to migrate from hostile environments, across ecological barriers (alienated lands such as farmlands and built infrastructure) to new climatically buffered sites. The technology and science to underpin assisted migration concepts are in their infancy for plants in general, and orchids, with their high degree of rarity, represent a particularly challenging group for which these principles need to be developed. It is likely that orchids, more than any other plant family, will be in the front-line of species to suffer large-scale extinction events as a result of climate change.

Scope

The South West Australian Floristic Region (SWAFR) is the only global biodiversity hotspot in Australia and represents an ideal test-bed for development of orchid conservation principles. Orchids comprise 6 % of all threatened vascular plants in the SWAFR, with 76 out of the 407 species known for the region having a high level of conservation risk. The situation in the SWAFR is a portent of the global crisis in terrestrial orchid conservation, and it is a region where innovative conservation solutions will be required if the impending wave of extinction is to be averted. Major threatening processes are varied, and include land clearance, salinity, burning, weed encroachment, disease and pests. This is compounded by highly specialized pollinators (locally endemic native invertebrates) and, in the most threatened groups such as hammer orchids (Drakaea) and spider orchids (Caladenia), high levels of mycorrhizal specialization. Management and development of effective conservation strategies for SWAFR orchids require a wide range of integrated scientific approaches to mitigate impacts that directly influence ecological traits critical for survival.

Conclusions

In response to threats to orchid species, integrated conservation approaches have been adopted (including ex situ and translocation principles) in the SWAFR with the result that a significant, multidisciplinary approach is under development to facilitate conservation of some of the most threatened taxa and build expertise to carry out assisted migration to new sites. Here the past two decades of orchid conservation research in the SWAFR and the role of research-based approaches for managing effective orchid conservation in a global biodiversity hotspot are reviewed.Key words: Orchids, pollination, mycorrhiza, integrated conservation, terrestrial, threats, ex situ conservation, in situ conservation     

Arabidopsis Separase Functions beyond the Removal of Sister Chromatid Cohesion during Meiosis

Separase is a capase family protease that is required for the release of sister chromatid cohesion during meiosis and mitosis. Proteolytic cleavage of the α-kleisin subunit of the cohesin complex at the metaphase-to-anaphase transition is essential for the proper segregation of chromosomes. In addition to its highly conserved role in cleaving the α-kleisin subunit, separase appears to have acquired additional diverse activities in some organisms, including involvement in mitotic and meiotic anaphase spindle assembly and elongation, interphase spindle pole body positioning, and epithelial cell reorganization. Results from the characterization of Arabidopsis (Arabidopsis thaliana) separase (ESP) demonstrated that meiotic expression of ESP RNA interference blocked the proper removal of cohesin from chromosomes and resulted in the presence of a mixture of fragmented chromosomes and intact bivalents. The presence of large numbers of intact bivalents raised the possibility that separase may also have multiple roles in Arabidopsis. In this report, we show that meiotic expression of ESP RNA interference blocks the removal of cohesin during both meiosis I and II, results in alterations in nonhomologous centromere association, disrupts the radial microtubule system after telophase II, and affects the proper establishment of nuclear cytoplasmic domains, resulting in the formation of multinucleate microspores.The proper segregation of chromosomes during mitosis and meiosis is dependent on the systematic formation and subsequent removal of sister chromatid cohesion, which is required for homologous chromosome pairing, recombination, and repair (for review, see Onn et al., 2008; Peters et al., 2008). It is also required for the pairwise alignment of chromosomes on the metaphase I spindle and for the generation of tension across centromeres, thereby ensuring their bipolar attachment. In mitosis, cohesion is maintained by the cohesin complex, which consists of four evolutionally conserved proteins: Sister Chromatid Cohesion1 (SCC1), SCC3, Structural Maintenance of Chromosome1 (SMC1), and SMC3 (for review, see Nasmyth and Haering, 2005). During meiosis, SCC1 is largely replaced by its meiotic homolog REC8.The establishment of sister chromatid cohesion in yeast involves a multistep process (Milutinovich et al., 2007) that begins during telophase of the previous cell cycle when cohesin subunits associate with the chromatin, ultimately becoming enriched at discrete loci termed cohesin-associated regions (Blat and Kleckner, 1999; Laloraya et al., 2000). Cohesion is established during S-phase in a process that requires the Chromosome Transmission Fidelity protein (Ctf7), which is also known as Eco1 (Skibbens et al., 1999; Toth et al., 1999) and involves the replication fork (Kenna and Skibbens, 2003; Lengronne et al., 2006). In budding yeast (Saccharomyces cerevisiae) and fission yeast (Schizosaccharomyces pombe), cohesin complexes remain on the chromosomes until mitotic anaphase (Uhlmann et al., 1999, 2000; Tomonaga et al., 2000). In contrast, in vertebrates, most cohesin complexes are released from the chromosomes during prophase in a separase-independent process (Waizenegger et al., 2000; Losada et al., 2002). The small fraction of cohesin that remains primarily in centromeric regions is released to start anaphase (Sumara et al., 2000). The release of chromosome cohesion at the metaphase-to-anaphase transition is triggered by the Cys protease, separase (ESP1), which specifically cleaves the α-kleisin subunit (Ciosk et al., 1998; Uhlmann et al., 1999, 2000; Buonomo et al., 2000; Hauf et al., 2001). Prior to the metaphase-to-anaphase transition, securin inhibits the protease activity of separase. At the onset of anaphase, securin is degraded by the anaphase-promoting complex/cyclosome freeing separase, which cleaves SCC1, facilitating the release of cohesion and chromosome separation (Cohen-Fix et al., 1996; Ciosk et al., 1998).Studies on the distribution of cohesin proteins during meiosis in a number of organisms, including yeast, Caenorhabditis elegans, mammals, and Arabidopsis (Arabidopsis thaliana), have shown that similar to the situation during mitosis in animal cells, a significant amount of cohesin is either removed from or redistributed on prophase chromosomes in a separase-independent process (Pasierbek et al., 2001; Cai et al., 2003; Eijpe et al., 2003; Lee et al., 2003; Yu and Koshland, 2005). The final resolution of chiasmata, formed as the result of homologous chromosome recombination, and the separation of homologous chromosomes depends on separase cleavage of the meiotic α-kleisin subunit, REC8, along chromosome arms at anaphase I (Buonomo et al., 2000; Kitajima et al., 2003). Centromeric cohesion is protected by the conserved SGO family of proteins until anaphase II when separase cleavage of REC8 facilitates the separation of sister chromatids (Rabitsch et al., 2003; Katis et al., 2004; McGuinness et al., 2005).In addition to its highly conserved role in cleaving the α-kleisin subunit, separase appears to have acquired additional diverse activities in different organisms (Queralt and Uhlmann, 2005). For example, separase plays a role in DNA repair by promoting the redistribution of cohesin complexes to sites of DNA damage during mitotic interphase in budding and fission yeast (Nagao et al., 2004; Strom et al., 2004). Separase is also important for mitotic anaphase spindle assembly and elongation (Jensen et al., 2001; Papi et al., 2005; Baskerville et al., 2008), interphase spindle pole body positioning (Nakamura et al., 2002), and spindle formation during meiosis in yeast (Buonomo et al., 2003). It is also important for the proper positioning of the centrosomes during the first asymmetric mitotic division, eggshell development in C. elegans (Siomos et al., 2001; Rappleye et al., 2002), and for epithelial cell reorganization and dynamics in Drosophila melanogaster (Pandey et al., 2005). In zebra fish, a separase mutation causes genome instability and increased susceptibility to epithelial cancer (Shepard et al., 2007).Results from the characterization of Arabidopsis separase suggested that the protein also has multiple roles in plants (Liu and Makaroff, 2006). Seeds homozygous for a T-DNA insert in Arabidopsis ESP exhibited embryo arrest at the globular stage with the endosperm exhibiting a weak titan-like phenotype. Furthermore, expression of ESP RNA interference (RNAi) from the meiosis-specific DMC1 promoter disrupted the proper removal of the SYN1 cohesin protein from chromosomes during meiosis and resulted in the presence of a mixture of fragmented chromosomes and intact bivalents. The presence of large numbers of intact bivalents led the authors to suggest that in addition to its requirement for the removal of cohesin, ESP may also be required for either the proper attachment of the kinetochores to the spindle or spindle function. These findings, along with the observations that separase appears to have multiple roles in other organisms, led us to conduct a detailed characterization of meiosis in ESP RNAi plants.In this report, we show that meiotic expression of ESP RNAi blocks the release of sister chromatid cohesion during both meiosis I and II, results in nonhomologous centromere association, disrupts the radial microtubule system (RMS) after telophase II, and affects the proper establishment of nuclear cytoplasmic domains. Unlike the large majority of plant meiotic mutants that have been characterized to date, reduction of ESP levels during meiosis leads to the formation of multinucleate microspores.     

Heterosexual and Homosexual Partners Practising Unprotected Sex May Develop Allogeneic Immunity and to a Lesser Extent Tolerance

Background

Epidemiological studies suggest that allogeneic immunity may inhibit HIV-1 transmission from mother to baby and is less frequent in multiparous than uniparous women. Alloimmune responses may also be elicited during unprotected heterosexual intercourse, which is associated ex vivo with resistance to HIV infection.

Methodology/Principal Findings

The investigation was carried out in well-defined heterosexual and homosexual monogamous partners, practising unprotected sex and a heterosexual cohort practising protected sex. Allogeneic CD4⁺ and CD8⁺ T cell proliferative responses were elicited by stimulating PBMC with the partners'' irradiated monocytes and compared with 3^rd party unrelated monocytes, using the CFSE method. Significant increase in allogeneic proliferative responses was found in the CD4⁺ and CD8⁺ T cells to the partners'' irradiated monocytes, as compared with 3^rd party unrelated monocytes (p≤0.001). However, a significant decrease in proliferative responses, especially of CD8⁺ T cells to the partners'' compared with 3^rd party monocytes was consistent with tolerization, in both the heterosexual and homosexual partners (p<0.01). Examination of CD4⁺CD25⁺FoxP3⁺ regulatory T cells by flow cytometry revealed a significantly greater proportion of these cells in the homosexual than heterosexual partners practising unprotected sex (p<0.05). Ex vivo studies of infectivity of PBMC with HIV-1 showed significantly greater inhibition of infectivity of PBMC from heterosexual subjects practising unprotected compared with those practising protected sex (p = 0.02).

Conclusions/Significance

Both heterosexual and homosexual monogamous partners practising unprotected sex develop allogeneic CD4⁺ and CD8⁺ T cell proliferative responses to the partners'' unmatched cells and a minority may be tolerized. However, a greater proportion of homosexual rather than heterosexual partners developed CD4⁺CD25FoxP3⁺ regulatory T cells. These results, in addition to finding greater inhibition of HIV-1 infectivity in PBMC ex vivo in heterosexual partners practising unprotected, compared with those practising protected sex, suggest that allogeneic immunity may play a significant role in the immuno-pathogenesis of HIV-1 infection.     

Synonymous codon usage pattern among the S,M, and L segments in Crimean-congo hemorrhagic fever virus

Crimean-Congo hemorrhagic fever (CCHF) virus is one among the major zoonosis viral diseases that use the Hyalomma ticks as their transmission vector to cause viral infection to the human and mammalian community. The fatality of infectious is high across the world especially in Africa, Asia, Middle East, and Europe. This study regarding codon usage bias of S, M, and L segments of the CCHF virus pertaining to the host Homo sapiens, reveals in-depth information about the evolutionary characteristics of CCHFV. Relative Synonymous Codon Usage (RSCU), Effective number of codons (ENC) were calculated, to determine the codon usage pattern in each segment. Correlation analysis between Codon adaptation index (CAI), GRAVY (Hydrophobicity), AROMO (Aromaticity), and nucleotide composition revealed bias in the codon usage pattern. There was no strong codon bias found among any segments of the CCHF virus, indicating both the factors i.e., natural selection and mutational pressure shapes the codon usage bias.     

Spatio‐temporal water dynamics in mature Banksia menziesii trees during drought

Southwest Australian Banksia woodlands are highly diverse plant communities that are threatened by drought‐ or temperature‐induced mortality due to the region's changing climate. We examined water relations in dominant Banksia menziesii R. Br. trees using magnetic leaf patch clamp pressure (ZIM‐) probes that allow continuous, real‐time monitoring of leaf water status. Multiple ZIM‐probes across the crown were complemented by traditional ecophysiological measurements. During summer, early stomatal downregulation of transpiration prevented midday balancing pressures from exceeding 2.5 MPa. Diurnal patterns of ZIM‐probe and pressure chamber readings agreed reasonably well, however, ZIM‐probes recorded short‐term dynamics, which are impossible to capture using a pressure chamber. Simultaneous recordings of three ZIM‐probes evenly spaced along leaf laminas revealed intrafoliar turgor gradients, which, however, did not develop in a strictly basi‐ or acropetal fashion and varied with cardinal direction. Drought stress manifested as increasing daily signal amplitude (low leaf water status) and occasionally as rising baseline at night (delayed rehydration). These symptoms occurred more often locally than across the entire crown. Microclimate effects on leaf water status were strongest in crown regions experiencing peak morning radiation (East and North). Extreme spring temperatures preceded the sudden death of B. menziesii trees, suggesting a temperature‐ or humidity‐related tipping point causing rapid hydraulic failure as evidenced by collapsing ZIM‐probe readings from an affected tree. In a warmer and drier future, increased frequency of B. menziesii mortality will result in significantly altered community structure and ecosystem function.     

Strigolactone Hormones and Their Stereoisomers Signal through Two Related Receptor Proteins to Induce Different Physiological Responses in Arabidopsis

We speculate that multicopy transposons, carrying both fitness and unfitness genes, can provide new positive and negative selection options to intractable weed problems. Multicopy transposons rapidly disseminate through populations, appearing in approximately 100% of progeny, unlike nuclear transgenes, which appear in a proportion of segregating populations. Different unfitness transgenes and modes of propagation will be appropriate for different cases: (1) outcrossing Amaranthus spp. (that evolved resistances to major herbicides); (2) Lolium spp., important pasture grasses, yet herbicide-resistant weeds in crops; (3) rice (Oryza sativa), often infested with feral weedy rice, which interbreeds with the crop; and (4) self-compatible sorghum (Sorghum bicolor), which readily crosses with conspecific shattercane and with allotetraploid johnsongrass (Sorghum halepense). The speculated outcome of these scenarios is to generate weed populations that contain the unfitness gene and thus are easily controllable. Unfitness genes can be under chemically or environmentally inducible promoters, activated after gene dissemination, or under constitutive promoters where the gene function is utilized only at special times (e.g. sensitivity to an herbicide). The transposons can be vectored to the weeds by introgression from the crop (in rice, sorghum, and Lolium spp.) or from planted engineered weed (Amaranthus spp.) using a gene conferring the degradation of a no longer widely used herbicide, especially in tandem with an herbicide-resistant gene that kills all nonhybrids, facilitating the rapid dissemination of the multicopy transposons in a weedy population.