Data Release of the AST3-2 Automatic Survey from Dome A, Antarctica

AST3-2 is the second of the three Antarctic Survey Telescopes, aimed at wide-field time-domain optical astronomy. It is located at Dome A, Antarctica, which is by many measures the best optical astronomy site on the Earth's surface. Here we present the data from the AST3-2 automatic survey in 2016 and the photometry results. The median 5$\sigma$ limiting magnitude in $i$-band is 17.8 mag and the light curve precision is 4 mmag for bright stars. The data release includes photometry for over 7~million stars, from which over 3,500 variable stars were detected, with 70 of them newly discovered. We classify these new variables into different types by combining their light curve features with stellar properties from surveys such as StarHorse.Comment: 16 pages, 20 figures, accepted for publication in MNRA

Exoplanets in the Antarctic Sky I. The first data release of AST3-II (CHESPA) and new found variables within the southern CVZ of TESS

Located at Dome A, the highest point of the Antarctic plateau, the Chinese Kunlun station is considered to be one of the best ground-based photometric sites because of its extremely cold, dry, and stable atmosphere. A target can be monitored from there for over 40 days without diurnal interruption during a polar winter. This makes Kunlun station a perfect site to search for short-period transiting exoplanets. Since 2008, an observatory has existed at Kunlun station, and three telescopes are working there. Using these telescopes, the AST3 project has been carried out over the last 6 yr with a search for transiting exoplanets as one of its key programs (CHESPA). In the austral winters of 2016 and 2017, a set of target fields in the southern continuous viewing zone (CVZ) of TESS were monitored by the AST3-II telescope. In this paper, we introduce the CHESPA and present the first data release containing photometry of 26,578 bright stars (m(i) <= 15). The best photometric precision at the optimum magnitude for the survey is around 2 mmag. To demonstrate the data quality, we also present a catalog of 221 variables with a brightness variation greater than 5 mmag from the 2016 data. Among these variables, 179 are newly identified periodic variables not listed in the AAVSO database (https://www.aavso.org/), and 67 are listed in the Candidate Target List. These variables will require careful attention to avoid false-positive signals when searching for transiting exoplanets. Dozens of new transiting exoplanet candidates will be released in a subsequent paper

Exoplanets in the Antarctic Sky. II. 116 Transiting Exoplanet Candidates Found by AST3-II (CHESPA) within the Southern CVZ of TESS

We report first results from the CHinese Exoplanet Searching Program from Antarctica (CHESPA)-a wide-field high-resolution photometric survey for transiting exoplanets carried out using telescopes of the AST3 (Antarctic Survey Telescopes times 3) project. There are now three telescopes (AST3-I, AST3-II, and CSTAR-II) operating at Dome A-the highest point on the Antarctic Plateau-in a fully automatic and remote mode to exploit the superb observing conditions of the site, and its long and uninterrupted polar nights. The search for transiting exoplanets is one of the key projects for AST3. During the austral winters of 2016 and 2017 we used the AST3-II telescope to survey a set of target fields near the southern ecliptic pole, falling within the continuous viewing zone of the TESS mission. The first data release of the 2016 data, including images, catalogs, and light curves of 26,578 bright stars (7.5 <= m(i) <= 15), was presented in Zhang et al. The best precision, as measured by the rms of the light curves at the optimum magnitude of the survey (m(i) = 10), is around 2 mmag. We detect 222 objects with plausible transit signals from these data, 116 of which are plausible transiting exoplanet candidates according to their stellar properties as given by the TESS Input Catalog, Gaia DR2, and TESS-HERMES spectroscopy. With the first data release from TESS expected in late 2018, this candidate list will be timely for improving the rejection of potential false-positives

Population Diversity of Rice Stripe Virus-Derived siRNAs in Three Different Hosts and RNAi-Based Antiviral Immunity in <em>Laodelphgax striatellus</em>

<div><h3>Background</h3><p>Small RNA-mediated gene silencing plays evolutionarily conserved roles in gene regulation and defense against invasive nucleic acids. Virus-derived small interfering RNAs (vsiRNAs) are one of the key elements involved in RNA silencing-based antiviral activities in plant and insect. vsiRNAs produced after viruses infecting hosts from a single kingdom (i.e., plant or animal) are well described. In contrast, vsiRNAs derived from viruses capable of infecting both plants and their insect vectors have not been characterized.</p> <h3>Methodology/Principal Findings</h3><p>We examined Rice stripe virus (RSV)-derived small interfering RNAs in three different hosts, <em>Oryza sativa</em>, <em>Nicotiana benthamiana</em> and a natural RSV transmitting vector <em>Laodelphgax striatellus</em>, through deep sequencing. Our results show that large amounts of vsiRNAs generated in these hosts after RSV infection. The vsiRNAs from <em>N. benthamiana</em> and <em>L. striatellus</em> mapped equally to the genomic- and antigenomic-strand of RSV RNAs. They showed, however, a significant bias in those from <em>O. sativa</em>. Furthermore, our results demonstrate that the number and size distributions of vsiRNAs in the three hosts were very different. In <em>O. sativa</em> and <em>N. benthamiana</em>, most vsiRNAs were mapped to the discrete regions in the RSV genome sequence, and most of the vsiRNAs from these two hosts were generated from RSV genomic RNAs 3 and 4. In contrast, the vsiRNAs identified in <em>L. striatellus</em> distributed uniformly along the whole genome of RSV. We have also shown that silencing Agronaute 2 in <em>L. striatellus</em> enhanced RSV accumulation in this host.</p> <h3>Conclusions/Significance</h3><p>Our study demonstrates that the core RNA-induced gene silencing (RNAi) machinery is present in <em>L. striatellus</em>. We also provide evidence that the RNAi-mediated immunity against RSV is present in <em>L. striatellus</em>. We propose that a common small RNA-mediated virus defense mechanism exists in both helipterum insects and plants, but the vsiRNAs are generated differentially in different hosts.</p> </div

Profile of RSV-derived vsiRNAs from <i>O.sativa</i> (A), <i>N. benthamiana</i> (B) and <i>L. striatellus</i> (C) along the RSV genome.

<p>The horizontal axis represents four RSV genomes which are banded together. Numbers on the y axis correspond to the frequencies of vsiRNAs mapped to the RSV genomic (−) or antigenomic (+) sequences. D, Schematic genome organization of RSV.</p

Relative frequency of 5′ terminal nucleotide of vsiRNAs.

<p>The vsiRNAs derived from RSV-infected generated in <i>O. sativa</i>, <i>N. benthamiana</i> and <i>L. striatellus</i> are shown in blue, red and green, respectively.</p

Sequence alignment of Argonaute 2 from <i>L. striatellus</i> and other insect species (A), and structure of the partial Argonaute proteins predicted using the NCBI Conserved Domains Server (B).

<p>Conserved PAZ and Piwi domains were identified in the assembled <i>L. striatellus</i> AGO2. Abbreviation and accession number of Argonaute 2 proteins of different species are as follows: <i>Laodelphax striatellus</i> (Lstratell, JX023533), <i>Sogatella furcifera</i> (Sfurcifera, JX023535), <i>Nilaparvata lugens</i> (Nlugens, JX023534), <i>Acyrthosiphon pisum</i> (Apisum_XPO, XP_003240621), <i>Tribolium castaneum</i> (Tcastaneum, NP_001107828), <i>Aedes aegypti</i> (Aaegypti_A, ACR56327), <i>Homo sapiens</i> (Hsapiens_A, NP_001158095), <i>Rattus norvegicus</i> (Rnorvegicu, NP_067608), <i>Drosophila sechellia</i> (Dsechellia, XP_002045323).</p

RNAi controlled RSV infection in <i>L. striatellus</i>.

<p>A: Relative expression level of Ago2 in <i>L. striatellus</i> at 6 days post injection with dsRNAs. The experiments were repeated three times. B: Detection of RSV genomic RNA accumulation after silencing <i>Ago</i>2 gene. Lane 1, non-treated viruferious <i>L. striatellus</i>; lane 2, <i>L. striatellus</i> injected with dsGFP; lane 3, <i>L. striatellus</i> injected with dsAgo2.</p

Statistical analysis of vsiRNAs mapped to the RSV genomic (−) or antigenomic (+) sequences.

<p>In each species, red color represents the (−) sRNA, and blue color represents the (+) sRNA.</p

Summary of Illumia deep sequencing data.

<p>Summary of Illumia deep sequencing data.</p