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Vernalization, the acceleration of flowering by the prolonged cold of winter, ensures that plants flower in favorable spring conditions. During vernalization in Arabidopsis, cold temperatures repress FLOWERING LOCUS C (FLC) expression in a mechanism involving VERNALIZATION INSENSITIVE 3 (VIN3), and this repression is epigenetically maintained by a Polycomb-like chromatin regulation involving VERNALIZATION 2 (VRN2), a Su(z)12 homolog, VERNALIZATION 1 (VRN1), and LIKE-HETEROCHROMATIN PROTEIN 1. In order to further elaborate how cold repression triggers epigenetic silencing, we have targeted mutations that result in FLC misexpression both at the end of the prolonged cold and after subsequent development. This identified VERNALIZATION 5 (VRN5), a PHD finger protein and homolog of VIN3. Our results suggest that during the prolonged cold, VRN5 and VIN3 form a heterodimer necessary for establishing the vernalization-induced chromatin modifications, histone deacetylation, and H3 lysine 27 trimethylation required for the epigenetic silencing of FLC. Double mutant and FLC misexpression analyses reveal additional VRN5 functions, both FLC-dependent and -independent, and indicate a spatial complexity to FLC epigenetic silencing with VRN5 acting as a common component in multiple pathways.

The determinants that specify the genomic targets of Polycomb silencing complexes are still unclear. Polycomb silencing of Arabidopsis FLOWERING LOCUS C (FLC) accelerates flowering and involves a cold-dependent epigenetic switch. Here we identify a single point mutation at an intragenic nucleation site within FLC that prevents this epigenetic switch from taking place. The mutation blocks nucleation of plant homeodomain-Polycomb repressive complex 2 (PHD-PRC2) and indicates a role for the transcriptional repressor VAL1 in the silencing mechanism. VAL1 localizes to the nucleation region in vivo, promoting histone deacetylation and FLC transcriptional silencing, and interacts with components of the conserved apoptosis- and splicing-associated protein (ASAP) complex. Sequence-specific targeting of transcriptional repressors thus recruits the machinery for PHD-PRC2 nucleation and epigenetic silencing.

Drought and high salinity are two major environmental factors that significantly limit the productivity of agricultural crops worldwide. WRKY transcription factors play essential roles in the adaptation of plants to abiotic stresses. However, WRKY genes involved in drought and salt tolerance in cotton (Gossypium hirsutum) are largely unknown. Here, a group IId WRKY gene, GhWRKY17, was isolated and characterized. GhWRKY17 was found to be induced after exposure to drought, salt, H2O2 and ABA. The constitutive expression of GhWRKY17 in Nicotiana benthamiana remarkably reduced plant tolerance to drought and salt stress, as determined through physiological analyses of the germination rate, root growth, survival rate, leaf water loss and Chl content. GhWRKY17 transgenic plants were observed to be more sensitive to ABA-mediated seed germination and root growth. However, overexpressing GhWRKY17 in N. benthamiana impaired ABA-induced stomatal closure. Furthermore, we found that GhWRKY17 modulated the increased sensitivity of plants to drought by reducing the level of ABA, and transcript levels of ABA-inducible genes, including AREB, DREB, NCED, ERD and LEA, were clearly repressed under drought and salt stress conditions. Consistent with the accumulation of reactive oxygen species (ROS), reduced proline contents and enzyme activities, elevated electrolyte leakage and malondialdehyde, and lower expression of ROS-scavenging genes, including APX, CAT and SOD, the GhWRKY17 transgenic plants exhibited reduced tolerance to oxidative stress compared with wild-type plants. These results therefore indicate that GhWRKY17 responds to drought and salt stress through ABA signaling and the regulation of cellular ROS production in plants.

The molecular epidemiology of CVA16 in China between 1999 and 2008 reflects a pattern of endemic cocirculation of clusters B1a and B1b within subgenotype B1 viruses. The annual evolution rate of CVA16 was estimated as approximately 0.91 ؋ 10 ؊2 substitutions per synonymous nucleotide/year and is slightly lower than that of HEV71.Coxsackievirus A16 (CVA16) and human enterovirus 71 (HEV71) are the two major causative agents of hand, foot, and mouth disease (HFMD) (12,17). In recent years, numerous large outbreaks of HEV71-associated HFMD, which were often accompanied by severe complications, including death, increased research interest in HEV71 strains (1,14,16). In contrast, little interest was paid to CVA16 strains because CVA16-associated HFMD was usually mild and benign (2, 12). Although CVA16 is genetically most closely related to HEV71, the genetic diversity and molecular evolution of CVA16, unlike those of HEV71, have not been fully described (5,7,12,13). Cocirculation of CVA16 and HEV71 has been proven to have contributed to the serious outbreaks of HFMD that have occurred in China since 2007 (17); therefore, the genetic variability and the evolution of CVA16 were determined in this study.The 42 CVA16 strains evaluated in this study were isolated from HFMD patients from different geographical locations in the Shandong, Gansu, Inner Mongolia, and Qinghai provinces of China between 2007 and 2008 (see supplemental data). To investigate the molecular epidemiology of CVA16 in mainland China, 24 additional Chinese CVA16 sequences found in Beijing and Guangdong provinces between 1999 and 2005 and 35 international CVA16 sequences (obtained from the GenBank database) were also analyzed.The complete VP1/capsid sequences of the CVA16 strains were obtained as previously described, using in-house primers that flanked the VP1 region (13, 17): CVA16-VP1-S, 5Ј-ATTGGTG CTCCCACTACAGC-3Ј (nucleotides 2335 to 2354, relative to strain CVA16/G-10), and CVA16-VP1-A, 5Ј-GCTGTCCTCCC ACACAAGAT-3Ј (nucleotides 3426 to 3445, relative to strain CVA16/G-10).A total of 66 Chinese CVA16 sequences were divided into three lineages on the basis of phylogenetic analysis (Fig. 1). A 6.5 to 8.1% nucleotide divergence was found among these three lineages, suggesting that the CVA16-associated HFMD outbreaks in China were a result of the coincident circulation of three genetically distinct viruses.To determine the molecular epidemiology of Chinese CVA16 strains associated with HFMD epidemics, a phylogenetic dendrogram was constructed with 21 Chinese CVA16 sequences (randomly selected on the basis of their genetic relationships) that circulated during the period 1999-2008 in addition to the 35 international CVA16 sequences that represented two known genotypes (A and B) (13) (Fig. 2).As in a previous study (13), all CVA16 strains could be grouped into genotypes A and B. The prototype G-10 strain differed from the other strains by 27.5 to 30.2% and clustered separately from all other CVA16 strains, including Chinese CVA16 strains, which clearly belo...

Emerging epidemics of hand-foot-and-mouth disease (HFMD) associated with enterovirus 71 (EV71) has become a serious concern in mainland China. It caused 126 and 353 fatalities in 2008 and 2009, respectively. The epidemiologic and pathogenic data of the outbreak collected from national laboratory network and notifiable disease surveillance system. To understand the virological evolution of this emerging outbreak, 326 VP1 gene sequences of EV71 detected in China from 1987 to 2009 were collected for genetic analyses. Evidence from both traditional and molecular epidemiology confirmed that the recent HFMD outbreak was an emerging one caused by EV71 of subgenotype C4. This emerging HFMD outbreak is associated with EV71 of subgenotype C4, circulating persistently in mainland China since 1998, but not attributed to the importation of new genotype. Originating from 1992, subgenotype C4 has been the predominant genotype since 1998 in mainland China, with an evolutionary rate of 4.6∼4.8×10−3 nucleotide substitutions/site/year. The phylogenetic analysis revealed that the majority of the virus during this epidemic was the most recent descendant of subgenotype C4 (clade C4a). It suggests that the evolution might be one of the potential reasons for this native virus to cause the emerging outbreak in China. However, strong negative selective pressure on VP1 protein of EV71 suggested that immune escape might not be the evolving strategy of EV71, predicting a light future for vaccine development. Nonetheless, long-term antigenic and genetic surveillance is still necessary for further understanding.

BackgroundLarge-scale outbreaks of hand, foot, and mouth disease (HFMD) occurred repeatedly in the Central Plain of China (Shandong, Anhui, and Henan provinces) from 2007 until now. These epidemics have increased in size and severity each year and are a major public health concern in mainland China.Principal FindingsPhylogenetic analysis was performed and a Bayesian Markov chain Monte Carlo tree was constructed based on the complete VP1 sequences of HEV71 isolates. These analyses showed that the HFMD epidemic in the Central Plain of China was caused by at least 5 chains of HEV71 transmission and that the virus continued to circulate and evolve over the winter seasons between outbreaks. Between 1998 and 2010, there were 2 stages of HEV71 circulation in mainland China, with a shift from evolutionary branch C4b to C4a in 2003–2004. The evolution rate of C4a HEV71 was 4.99×10-3 substitutions per site per year, faster than the mean of all HEV71 genotypes. The most recent common ancestor estimates for the Chinese clusters dated to October 1994 and November 1993 for the C4a and C4b evolutionary branches, respectively. Compared with all C4a HEV71 strains, a nucleotide substitution in all C4b HEV71 genome (A to C reversion at nt2503 in the VP1 coding region, which caused amino acid substitution of VP1–10: Gln to His) had reverted.ConclusionsThe data suggest that C4a HEV71 strains introduced into the Central Plain of China are responsible for the recent outbreaks. The relationships among HEV71 isolates determined from the combined sequence and epidemiological data reveal the underlying seasonal dynamics of HEV71 circulation. At least 5 HEV71 lineages circulated in the Central Plain of China from 2007 to 2009, and the Shandong and Anhui lineages were found to have passed through a genetic bottleneck during the low-transmission winter season.