Using cultures synchronized by two independent procedures, alpha-factor arrest and centrifugal elutriation, we have investigated the expression of the Saccharomyces cerevisiae CDC6 gene through the cell cycle. Our results show that the CDC6 gene is periodically expressed in the yeast cell cycle. The level of CDC6 transcripts increases in late G1, reaching a peak (approximately 10-20-fold over the initial level) at about the G1/S phase boundary. The peak of CDC6 mRNA was observed to overlap or slightly precede that of the CDC8 message, and to obviously precede that of the histone H2A message by some 25 min. Unlike histone H2A mRNA, the CDC6 mRNA as well as CDC8 mRNA were not affected by hydroxyurea treatment. These results suggest that regulation of H2A mRNA is different from that of CDC6 or CDC8. We have studied the 5'-flanking regions of CDC6 and other cell cycle-regulated genes. DNA sequence analysis of the CDC6 promoter revealed two sequences, 5'-C/GACGCGNC/G-3' and 5'-PuGNAGAAA-3' (where Pu is a purine, and N is any nucleotide), which are repeated three times each. Similar sequence elements have also been found among several cell cycle-regulated genes, including the CDC8 gene, but are not found upstream of histone genes. The possible significance of these elements is discussed.
Chongqing Municipality, located in the superior citrus belt of the upper-middle Yangtze River, is one of the most important citrus-producing areas in China. A survey was performed to evaluate the occurrence and distribution of citrus viroids in this area, where Poncirus trifoliata is the main rootstock. From 2002 to 2006, 72 samples of sweet oranges (Citrus sinensis), lemons (C. jambhiri), mandarins (C. reticulata), and mandarin hybrids, which showed stunting, bark scaling, and cracking symptoms on the rootstock, were collected and graft inoculated into Arizona 861-S1 Etrog citron (C. medica) on rough lemon rootstock and maintained in a greenhouse at 28 to 32°C. Fifty-one of the seventy-two samples were cultivars imported from abroad, and the remaining samples were all local cultivars. Sixty samples induced symptoms typical of citrus viroids on the Etrog indicator plants. To identify the causal agent(s), a one-step reverse transcription (RT)-PCR protocol, using five primer pairs (1) targeting the complete genome sequences, was used to detect Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), Hop stunt viroid (HSVd), Citrus viroid III (CVd-III), and Citrus viroid IV (CVd-IV) (2). All 72 samples were infected by citrus viroids. Sixty-five and thirty-five of the seventy-two samples were positive for HSVd and CVd-III, respectively. CEVd and CBLVd were found, respectively, in 20 and 11 of 72 samples, whereas CVd-IV was not detected. Of 72 samples, 12 without typical symptoms on Etrog citrons were infected by HSVd and CBLVd. Nearly all (70 of 72) infected citrus plants harbored more than one viroid species, and two plants were both infected by CEVd, CBLVd, HSVd, and CVd-III. RT-PCR products were purified and ligated into pGEM T-Easy Vector (Promega, Madison, WI) and three clones for each of the four viroid species were sequenced and deposited in GenBank: CEVd (Accession Nos. EU382202, U382203, and EU382204); CBLVd (Accession Nos. EU382211, EU382212, and EU382213); HSVd (Accession Nos. EU382208, EU382209, and EU382210); and CVd-III (Accession Nos. EU382205, EU382206, and EU382207). BLAST analysis showed that these nucleotide sequences had greater than 94% nucleotide identity to the most similar genome sequences in GenBank. Sweet orange was more frequently infected by viroids than the other citrus cultivars. To our knowledge, this is the first report of CBLVd, HSVd, and CVd-III in Chongqing and the first report of CBLVd in China. The high incidence of citrus viroids in Chongqing necessitates rapid development of a system of propagation and testing to reduce the incidence of viroids and the associated loss of citrus production. References: (1) L. Bernard and N. Duran-Vila. Mol. Cell. Probes 20:105, 2006. (2) K. Z. Tang et al. Acta Hortic. Sin. 32:408, 2005.
Citrus yellow vein clearing virus (CYVCV) is a new citrus virus that has become an important factor restricting the development of China'scitrus industry, and the CYVCV coat protein (CP) is associated with viral pathogenicity. In this study, the Eureka lemon zinc finger protein (ZFP) ClDOF3.4 was shown to interact with CYVCV CP in vivo and in vitro. Transient expression of ClDOF3.4in Eureka lemon induced the expression of salicylic acid (SA)-related and hypersensitive response marker genes, and triggered a reactive oxygen species burst, ion leakage necrosis, and the accumulation of free SA. Furthermore, the CYVCV titer in ClDOF3.4 transgenic Eureka lemon plants was approximately 69.4% that in control plants 6 months after inoculation, withonly mild leaf chlorotic spots observed in those transgenic plants. Taken together, the results indicate that ClDOF3.4 not only interacts with CP but also induces an immune response in Eureka lemon by inducing the SA pathways. This is the first report that ZFP is involved in the immune response of a citrus viral disease, which provides a basis for further study of the molecular mechanism of CYVCV infection.
Abstract Tiny, pelagic arthropods from the Anisian Luoping Biota exposed in two quarries near Luoping, Yunnan Province, China, represent the numerically most abundant organisms in the assemblage. They form the basis for definition of two, and possibly three, species referred to the order Lophogastrida, family Eucopiidae. Yunnanocopia grandis new genus new species and Y . longicauda n. gen. new species represent the oldest occurrence of mysidaceans in the fossil record. Their anatomy allies them with the Ladinian species Schimperella acanthocercus Taylor, Schram, and Shen, 2001, from Guizhou Province, China, which previously was thought to be the oldest lophogastrid, and with extant species of Eucopiidae. Their appearance in the Anisian represents one additional element of the early faunal radiation within the Luoping Biota following the end-Permian extinction event. Presence of well-preserved oostegites, along with other morphological features, documents a conservative bauplan expressed in Eucopiidae.
Abstract Background Citrus yellow vein clearing virus (CYVCV) is the causative agent of citrus yellow vein clearing disease, and poses a serious threat to the lemon industry in Asia. The common symptoms of CYVCV-infected lemon plants are leaf crinkling, leaf chlorotic mottling, and yellow vein clearing. However, the molecular mechanisms underlying CYVCV-citrus interaction that responsible for symptom occurrence is still unclarified. In this study, RNA-seq was performed to analyze the gene expression patterns of ‘Eureka’ lemon ( Citrus limon Burm. f.) plants in response to CYVCV infection. Results There were 3691 differentially expressed genes (DEGs) identified by comparison between mock and CYVCV-infected lemon plants through RNA-seq. Bioinformatics analyses revealed that these DEGs were components of different pathways involved in phenylpropanoid biosynthesis, brassinosteroid biosynthesis, flavonoid biosynthesis and photosynthesis. Among these, the DEGs related to phytohormone metabolism and photosynthesis pathways were further enriched and analyzed. This study showed that different phytohormone-related genes had different responses toward CYVCV infection, however almost all of the photosynthesis-related DEGs were down-regulated in the CYVCV-infected lemon plants. The obtained RNA-seq data were validated by RT-qPCR using 12 randomly chosen genes, and the results of mRNA expression analysis were consistent with those of RNA-seq. Conclusions The phytohormone biosynthesis, signaling and photosynthesis-related genes of lemon plants were probably involved in systemic infection and symptom occurrence of CYVCV. Notably, CYVCV infection had regulatory effects on the biosynthesis and signaling of phytohormone, which likely improve systemic infection of CYVCV. Additionally, CYVCV infection could cause structural changes in chloroplast and inhibition of photosynthesis pathway, which probably contribute to the appearance of leaf chlorotic mottling and yellow vein clearing in CYVCV-infected lemon plants. This study illustrates the dynamic nature of the citrus-CYVCV interaction at the transcriptome level and provides new insights into the molecular mechanism underlying the pathogenesis of CYVCV in lemon plants.
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