Forces driving transposable element load variation during Arabidopsis range expansion.

Genetic load refers to the accumulated and potentially life-threatening deleterious mutations in populations. Understanding the mechanisms underlying genetic load variation of transposable element (TE) insertion, a major large-effect mutation, during range expansion is an intriguing question in biology. Here, we used 1,115 global natural accessions of Arabidopsis (Arabidopsis thaliana) to study the driving forces of TE load variation during its range expansion. TE load increased with range expansion, especially in the recently established Yangtze River basin population. Effective population size, which explains 62.0% of the variance in TE load, high transposition rate, and selective sweeps contributed to TE accumulation in the expanded populations. We genetically mapped and identified multiple candidate causal genes and TEs, and revealed the genetic architecture of TE load variation. Overall, this study reveals the variation in TE genetic load during Arabidopsis expansion and highlights the causes of TE load variation from the perspectives of both population genetics and quantitative genetics.

Arabidopsis EXECUTER1 interacts with WRKY transcription factors to mediate plastid-to-nucleus singlet oxygen signaling.

Chloroplasts produce singlet oxygen (1O2), which causes changes in nuclear gene expression through plastid-to-nucleus retrograde signaling to increase plant fitness. However, the identity of this 1O2-triggered pathway remains unclear. Here, we identify mutations in GENOMES UNCOUPLED4 (GUN4) and GUN5 as suppressors of phytochrome-interacting factor1 (pif1) pif3 in regulating the photo-oxidative response in Arabidopsis thaliana. GUN4 and GUN5 specifically interact with EXECUTER1 (EX1) and EX2 in plastids, and this interaction is alleviated by treatment with Rose Bengal (RB) or white light. Impaired expression of GUN4, GUN5, EX1, or EX2 leads to insensitivity to excess light and overexpression of EX1 triggers photo-oxidative responses. Strikingly, upon light irradiation or RB treatment, EX1 transiently accumulates in the nucleus and the nuclear fraction of EX1 shows a similar molecular weight as the plastid-located protein. Point mutagenesis analysis indicated that nuclear localization of EX1 is required for its function. EX1 acts as a transcriptional co-activator and interacts with the transcription factors WRKY18 and WRKY40 to promote the expression of 1O2-responsive genes. This study suggests that EX1 may act in plastid-to-nucleus signaling and establishes a 1O2-triggered retrograde signaling pathway that allows plants adapt to changing light environments during chloroplast development.

Signatures of Adaptation and Purifying Selection in Highland Populations of Dasiphora fruticosa.

High mountains harbor a considerable proportion of biodiversity, but we know little about how diverse plants adapt to the harsh environment. Here we finished a high-quality genome assembly for Dasiphora fruticosa, an ecologically important plant distributed in the Qinghai-Tibetan Plateau and lowland of the Northern Hemisphere, and resequenced 592 natural individuals to address how this horticulture plant adapts to highland. Demographic analysis revealed D. fruticosa underwent a bottleneck after Naynayxungla Glaciation. Selective sweep analysis of two pairs of lowland and highland populations identified 63 shared genes related to cell wall organization or biogenesis, cellular component organization, and dwarfism, suggesting parallel adaptation to highland habitats. Most importantly, we found that stronger purging of estimated genetic load due to inbreeding in highland populations apparently contributed to their adaptation to the highest mountain. Our results revealed how plants could tolerate the extreme plateau, which could provide potential insights for species conservation and crop breeding.

Transcriptional repression specifies the central cell for double fertilization.

Double fertilization is a key innovation for the evolutionary success of angiosperms by which the two fertilized female gametes, the egg cell and central cell, generate the embryo and endosperm, respectively. The female gametophyte (embryo sac) enclosed in the sporophyte is derived from a one-celled haploid cell lineage. It undergoes successive events of mitotic divisions, cellularization, and cell specification to give rise to the mature embryo sac, which contains the two female gametes accompanied by two types of accessory cells, namely synergids and antipodals. How the cell fate of the central cell is specified has long been equivocal and is further complicated by the structural diversity of female gametophyte across plant taxa. Here, MADS-box protein AGL80 was verified as a transcriptional repressor that directly suppresses the expression of accessory cell-specific genes to specify the central cell. Further genetic rescue and phylogenetic assay of the AGL80 orthologs revealed a possible conserved mechanism in the Brassicaceae family. Results from this study provide insight into the molecular determination of the second female gamete cell in Brassicaceae.

Scaling-up and proteomic analysis reveals photosynthetic and metabolic insights toward prolonged H2 photoproduction in Chlamydomonas hpm91 mutant lacking proton gradient regulation 5 (PGR5).

Clean and sustainable H2 production is crucial to a carbon-neutral world. H2 generation by Chlamydomonas reinhardtii is an attractive approach for solar-H2 from H2O. However, it is currently not large-scalable because of lacking desirable strains with both optimal H2 productivity and sufficient knowledge of underlying molecular mechanism. We hereby carried out extensive and in-depth investigations of H2 photoproduction of hpm91 mutant lacking PGR5 (Proton Gradient Regulation 5) toward its up-scaling and fundamental mechanism issues. We show that hpm91 is at least 100-fold scalable (up to 10 L) with continuous H2 collection of 7287 ml H2/10L-HPBR in averagely 26 days under sulfur deprivation. Also, we show that hpm91 is robust and active during sustained H2 photoproduction, most likely due to decreased intracellular ROS relative to wild type. Moreover, we obtained quantitative proteomic profiles of wild type and hpm91 at four representing time points of H2 evolution, leading to 2229 and 1350 differentially expressed proteins, respectively. Compared to wild type, major proteome alterations of hpm91 include not only core subunits of photosystems and those related to anti-oxidative responses but also essential proteins in photosynthetic antenna, C/N metabolic balance, and sulfur assimilation toward both cysteine biosynthesis and sulfation of metabolites during sulfur-deprived H2 production. These results reveal not only new insights of cellular and molecular basis of enhanced H2 production in hpm91 but also provide additional candidate gene targets and modules for further genetic modifications and/or in artificial photosynthesis mimics toward basic and applied research aiming at advancing solar-H2 technology.

Adaptation and Phenotypic Diversification in Arabidopsis through Loss-of-Function Mutations in Protein-Coding Genes.

According to the less-is-more hypothesis, gene loss is an engine for evolutionary change. Loss-of-function (LoF) mutations resulting in the natural knockout of protein-coding genes not only provide information about gene function but also play important roles in adaptation and phenotypic diversification. Although the less-is-more hypothesis was proposed two decades ago, it remains to be explored on a large scale. In this study, we identified 60,819 LoF variants in 1071 Arabidopsis (Arabidopsis thaliana) genomes and found that 34% of Arabidopsis protein-coding genes annotated in the Columbia-0 genome do not have any LoF variants. We found that nucleotide diversity, transposable element density, and gene family size are strongly correlated with the presence of LoF variants. Intriguingly, 0.9% of LoF variants with minor allele frequency larger than 0.5% are associated with climate change. In addition, in the Yangtze River basin population, 1% of genes with LoF mutations were under positive selection, providing important insights into the contribution of LoF mutations to adaptation. In particular, our results demonstrate that LoF mutations shape diverse phenotypic traits. Overall, our results highlight the importance of the LoF variants for the adaptation and phenotypic diversification of plants.

Transposable elements drive rapid phenotypic variation in Capsella rubella.

Rapid phenotypic changes in traits of adaptive significance are crucial for organisms to thrive in changing environments. How such phenotypic variation is achieved rapidly, despite limited genetic variation in species that experience a genetic bottleneck is unknown. Capsella rubella, an annual and inbreeding forb (Brassicaceae), is a great system for studying this basic question. Its distribution is wider than those of its congeneric species, despite an extreme genetic bottleneck event that severely diminished its genetic variation. Here, we demonstrate that transposable elements (TEs) are an important source of genetic variation that could account for its high phenotypic diversity. TEs are (i) highly enriched in C. rubella compared with its outcrossing sister species Capsella grandiflora, and (ii) 4.2% of polymorphic TEs in C. rubella are associated with variation in the expression levels of their adjacent genes. Furthermore, we show that frequent TE insertions at FLOWERING LOCUS C (FLC) in natural populations of C. rubella could explain 12.5% of the natural variation in flowering time, a key life history trait correlated with fitness and adaptation. In particular, we show that a recent TE insertion at the 3' UTR of FLC affects mRNA stability, which results in reducing its steady-state expression levels, to promote the onset of flowering. Our results highlight that TE insertions can drive rapid phenotypic variation, which could potentially help with adaptation to changing environments in a species with limited standing genetic variation.

Identification of long noncoding natural antisense transcripts (lncNATs) correlated with drought stress response in wild rice (Oryza nivara).

BACKGROUND: Wild rice, including Oryza nivara and Oryza rufipogon, which are considered as the ancestors of Asian cultivated rice (Oryza sativa), possess high genetic diversity and serve as a crucial resource for breeding novel cultivars of cultivated rice. Although rice domestication related traits, such as seed shattering and plant architecture, have been intensively studied at the phenotypic and genomic levels, further investigation is needed to understand the molecular basis of phenotypic differences between cultivated and wild rice. Drought stress is one of the most severe abiotic stresses affecting rice growth and production. Adaptation to drought stress involves a cascade of genes and regulatory factors that form complex networks. O. nivara inhabits swampy areas with a seasonally dry climate, which is an ideal material to discover drought tolerance alleles. Long noncoding natural antisense transcripts (lncNATs), a class of long noncoding RNAs (lncRNAs), regulate the corresponding sense transcripts and play an important role in plant growth and development. However, the contribution of lncNATs to drought stress response in wild rice remains largely unknown. RESULTS: Here, we conducted strand-specific RNA sequencing (ssRNA-seq) analysis of Nipponbare (O. sativa) and two O. nivara accessions (BJ89 and BJ278) to determine the role of lncNATs in drought stress response in wild rice. A total of 1246 lncRNAs were identified, including 1091 coding-noncoding NAT pairs, of which 50 were expressed only in Nipponbare, and 77 were expressed only in BJ89 and/or BJ278. Of the 1091 coding-noncoding NAT pairs, 240 were differentially expressed between control and drought stress conditions. Among these 240 NAT pairs, 12 were detected only in Nipponbare, and 187 were detected uniquely in O. nivara. Furthermore, 10 of the 240 coding-noncoding NAT pairs were correlated with genes enriched in stress responsive GO terms; among these, nine pairs were uniquely found in O. nivara, and one pair was shared between O. nivara and Nipponbare. CONCLUSION: We identified lncNATs associated with drought stress response in cultivated rice and O. nivara. These results will improve our understanding of the function of lncNATs in drought tolerance and accelerate rice breeding.

Rice FLUORESCENT1 Is Involved in the Regulation of Chlorophyll.

Chlorophyll biosynthesis plays essential roles in photosynthesis and plant growth in response to environmental conditions. The accumulation of excess chlorophyll biosynthesis intermediates under light results in the production of reactive oxygen species and oxidative stress. In this study, we identified a rice (Oryza sativa) mutant, oxidation under photoperiod (oxp), that displayed photobleached lesions on its leaves, reduced growth and decreased chlorophyll content during light/dark cycles or following a dark-to-light transition. The oxp mutant accumulated more chlorophyll precursors (5-aminolevulinic acid and protochlorophyllide) than the wild type in the dark, and more singlet oxygen following light exposure. Several singlet-oxygen-responsive genes were greatly upregulated in oxp, whereas the expression patterns of OsPORA and OsPORB, two genes encoding the chlorophyll biosynthesis enzyme NADPH:protochlorop hyllide oxidoreductase, were altered in de-etiolated oxp seedlings. Molecular and complementation studies revealed that oxp is a loss-of-function mutant in LOC_Os01g32730, a homolog of FLUORESCENT (FLU) in Arabidopsis thaliana. Rice PHYTOCHROME-INTERACTING FACTOR-LIKE14 (OsPIL14) transcription factor directly bound to the OsFLU1 promoter and activated its expression. Dark-grown transgenic rice seedlings overexpressing OsPIL14 accumulated more chlorophyll and turned green faster than the wild type upon light illumination. Thus, OsFLU1 is an important regulator of chlorophyll biosynthesis in rice.

[Common types of massive intraoperative haemorrhage, treatment philosophy and operating skills in pelvic cancer surgery].

OBJECTIVE: To explore the common types of massive intraoperative bleeding, clinical characteristics, treatment philosophy and operating skills in pelvic cancer surgery. METHODS: We treated massive intraoperative bleeding in 19 patients with pelvic cancer in our department from January 2003 to March 2012. Their clinical data were retrospectively analyzed. The clinical features of massive intraoperative bleeding were analyzed, the treatment experience and lessons were summed up, and the operating skills to manage this serious issue were analyzed. RESULTS: In this group of 19 patients, 7 cases were of presacral venous plexus bleeding, 5 cases of internal iliac vein bleeding, 6 cases of anterior sacral venous plexus and internal iliac vein bleeding, and one cases of internal and external iliac vein bleeding. Six cases of anterior sacral plexus bleeding and 4 cases of internal iliac vein bleeding were treated with suture ligation to stop the bleeding. Six cases of anterior sacral and internal iliac vein bleeding, one cases of anterior sacral vein bleeding, and one case of internal iliac vein bleeding were managed with transabdominal perineal incision or transabdominal cotton pad compression hemostasis. One case of internal and external iliac vein bleeding was treated with direct ligation of the external iliac vein and compression hemostasis of the internal iliac vein. Among the 19 patients, 18 cases had effective hemostasis. Their blood loss was 400-1500 ml, and they had a fair postoperative recovery. One patient died due to massive intraoperative bleeding of ca. 4500 ml. CONCLUSIONS: Most of the massive intraoperative bleeding during pelvic cancer surgery is from the presacral venous plexus and internal iliac vein. The operator should go along with the treatment philosophy to save the life of the patient above all, and to properly perform suture ligation or compression hemostasis according to the actual situation, and with mastered crucial operating hemostatic skills.

Less Is More, Natural Loss-of-Function Mutation Is a Strategy for Adaptation.

Gene gain and loss are crucial factors that shape the evolutionary success of diverse organisms. In the past two decades, more attention has been paid to the significance of gene gain through gene duplication or de novo genes. However, gene loss through natural loss-of-function (LoF) mutations, which is prevalent in the genomes of diverse organisms, has been largely ignored. With the development of sequencing techniques, many genomes have been sequenced across diverse species and can be used to study the evolutionary patterns of gene loss. In this review, we summarize recent advances in research on various aspects of LoF mutations, including their identification, evolutionary dynamics in natural populations, and functional effects. In particular, we discuss how LoF mutations can provide insights into the minimum gene set (or the essential gene set) of an organism. Furthermore, we emphasize their potential impact on adaptation. At the genome level, although most LoF mutations are neutral or deleterious, at least some of them are under positive selection and may contribute to biodiversity and adaptation. Overall, we highlight the importance of natural LoF mutations as a robust framework for understanding biological questions in general.

Cysteine-rich peptides promote interspecific genetic isolation in Arabidopsis.

Reproductive isolation is a prerequisite for speciation. Failure of communication between female tissues of the pistil and paternal pollen tubes imposes hybridization barriers in flowering plants. Arabidopsis thaliana LURE1 (AtLURE1) peptides and their male receptor PRK6 aid attraction of the growing pollen tube to the ovule. Here, we report that the knockout of the entire AtLURE1 gene family did not affect fertility, indicating that AtLURE1-PRK6-mediated signaling is not required for successful fertilization within one Arabidopsis species. AtLURE1s instead function as pollen tube emergence accelerators that favor conspecific pollen over pollen from other species and thus promote reproductive isolation. We also identified maternal peptides XIUQIU1 to -4, which attract pollen tubes regardless of species. Cooperation between ovule attraction and pollen tube growth acceleration favors conspecific fertilization and promotes reproductive isolation.

Transposable Elements Contribute to the Adaptation of Arabidopsis thaliana.

Transposable elements (TEs) are mobile genetic elements with very high mutation rates that play important roles in shaping genome architecture and regulating phenotypic variation. However, the extent to which TEs influence the adaptation of organisms in their natural habitats is largely unknown. Here, we scanned 201 representative resequenced genomes from the model plant Arabidopsis thaliana and identified 2,311 polymorphic TEs from noncentromeric regions. We found expansion and contraction of different types of TEs in different A. thaliana populations. More importantly, we identified two TE insertions that are likely candidates to play a role in adaptive evolution. Our results highlight the importance of variations in TEs for the adaptation of plants in general in the context of rapid global climate change.

Long-term balancing selection contributes to adaptation in Arabidopsis and its relatives.

BACKGROUND: In contrast to positive selection, which reduces genetic variation by fixing beneficial alleles, balancing selection maintains genetic variation within a population or species and plays crucial roles in adaptation in diverse organisms. However, which genes, genome-wide, are under balancing selection and the extent to which these genes are involved in adaptation are largely unknown. RESULTS: We performed a genome-wide scan for genes under balancing selection across two plant species, Arabidopsis thaliana and its relative Capsella rubella, which diverged about 8 million generations ago. Among hundreds of genes with shared coding-region polymorphisms, we find evidence for long-term balancing selection in five genes: AT1G35220, AT2G16570, AT4G29360, AT5G38460, and AT5G44000. These genes are involved in the response to biotic and abiotic stress and other fundamental biochemical processes. More intriguingly, for these genes, we detected significant ecological diversification between the two haplotype groups, suggesting that balancing selection has been very important for adaptation. CONCLUSIONS: Our results indicate that beyond the well-known S-locus genes and resistance genes, many loci are under balancing selection. These genes are mostly correlated with resistance to stress or other fundamental functions and likely play a more important role in adaptation to diverse habitats than previously thought.

Adaptation of Arabidopsis thaliana to the Yangtze River basin.

BACKGROUND: Organisms need to adapt to keep pace with a changing environment. Examining recent range expansion aids our understanding of how organisms evolve to overcome environmental constraints. However, how organisms adapt to climate changes is a crucial biological question that is still largely unanswered. The plant Arabidopsis thaliana is an excellent system to study this fundamental question. Its origin is in the Iberian Peninsula and North Africa, but it has spread to the Far East, including the most south-eastern edge of its native habitats, the Yangtze River basin, where the climate is very different. RESULTS: We sequenced 118 A. thaliana strains from the region surrounding the Yangtze River basin. We found that the Yangtze River basin population is a unique population and diverged about 61,409 years ago, with gene flows occurring at two different time points, followed by a population dispersion into the Yangtze River basin in the last few thousands of years. Positive selection analyses revealed that biological regulation processes, such as flowering time, immune and defense response processes could be correlated with the adaptation event. In particular, we found that the flowering time gene SVP has contributed to A. thaliana adaptation to the Yangtze River basin based on genetic mapping. CONCLUSIONS: A. thaliana adapted to the Yangtze River basin habitat by promoting the onset of flowering, a finding that sheds light on how a species can adapt to locales with very different climates.

Association of long non-coding RNA HOTTIP with progression and prognosis in colorectal cancer.

Long non-coding RNA (lncRNA) has an important role in carcinoma progression and prognosis. However, little is known about the pathological role of lncRNA HOTTIP (HOXA transcript at the distal tip) in colorectal cancer (CRC) patients. This study attempted to investigate the association of lncRNA HOTTIP expression with progression and prognosis in CRC patients. LncRNA HOTTIP expression was measured in 156 CRC tissues and 21 adjacent non-malignant tissues using qRT-PCR. In present study, our results indicated that lncRNA HOTTIP was highly expressed in CRC compared with adjacent non-malignant tissues (P<0.001), and positively correlated with T stage (T1-2 vs. T3-4, P = 0.001), clinical stage (I-II stages vs. III-IV stages, P = 0.003), and distant metastasis (absent vs. present, P = 0.014) in CRC patients. Furthermore, we also observed that increased lncRNA HOTTIP expression was an unfavorable prognostic factor in CRC patients (P = 0.001), regardless of T stage, distant metastasis and clinical stage. Finally, overexpression of lncRNA HOTTIP was supposed to be an independent poor prognostic factor for CRC patients through multivariate analysis (P = 0.017). In conclusion, lncRNA HOTTIP overexpression maybe serves as an unfavorable prognosis predictor for CRC patients. However, a further larger sample size investigation is needed to support our results.

Transcriptional analyses of natural leaf senescence in maize.

Leaf senescence is an important biological process that contributes to grain yield in crops. To study the molecular mechanisms underlying natural leaf senescence, we harvested three different developmental ear leaves of maize, mature leaves (ML), early senescent leaves (ESL), and later senescent leaves (LSL), and analyzed transcriptional changes using RNA-sequencing. Three sets of data, ESL vs. ML, LSL vs. ML, and LSL vs. ESL, were compared, respectively. In total, 4,552 genes were identified as differentially expressed. Functional classification placed these genes into 18 categories including protein metabolism, transporters, and signal transduction. At the early stage of leaf senescence, genes involved in aromatic amino acids (AAAs) biosynthetic process and transport, cellular polysaccharide biosynthetic process, and the cell wall macromolecule catabolic process, were up-regulated. Whereas, genes involved in amino acid metabolism, transport, apoptosis, and response to stimulus were up-regulated at the late stage of leaf senescence. Further analyses reveals that the transport-related genes at the early stage of leaf senescence potentially take part in enzyme and amino acid transport and the genes upregulated at the late stage are involved in sugar transport, indicating nutrient recycling mainly takes place at the late stage of leaf senescence. Comparison between the data of natural leaf senescence in this study and previously reported data for Arabidopsis implies that the mechanisms of leaf senescence in maize are basically similar to those in Arabidopsis. A comparison of natural and induced leaf senescence in maize was performed. Athough many basic biological processes involved in senescence occur in both types of leaf senescence, 78.07% of differentially expressed genes in natural leaf senescence were not identifiable in induced leaf senescence, suggesting that differences in gene regulatory network may exist between these two leaf senescence programs. Thus, this study provides important information for understanding the mechanism of leaf senescence in maize.

[Efficacy observation of paralleled clipping of rectal ligament in resection of rectal cancer in obese male patients].

OBJECTIVE: To investigate the approach and efficacy of dealing the rectal ligament in resection of rectal cancer in obese male patients. METHODS: A total of 92 patients (BMI>25 kg/m(2)) undergoing resection of rectal cancer from December 2008 to December 2010 in Henan Tumor hospital were assigned into 2 groups according to the surgical technique, the modified group (paralleled clipping of rectal ligament, 48 patients) and traditional group (44 patients). Operative time, intra-operational bleeding, rectal ulceration, ureteral injury, mesorectal integrity, and positive rate of lateral margin of pelvic wall were compared between two groups. RESULTS: The operative time was (66.9±99.8) min in modified group, which was significantly shorter than that in traditional group [(125.4±12.2) min, P=0.000]. Intra-operative bleeding was (160.3±27.2) ml in modified group and (150.5±28.5) ml in traditional group (P=0.093). Rectal ulceration rated were 0 and 18.2% (8/44), mesorectal disintegrity rates were 6.2% and 22.7%, pelvic infection rates were 2.1% (1/48) and 20.4 (9/44) in modified and traditional groups respectively, whose differences were all significant (all P<0.05). No ureteral injury and positive margin were found in both two groups. CONCLUSION: The approach of paralleled clipping of rectal ligament around the rectum meets the principle of TME, which is simple, safe and effective.

[Association of early diarrhea after the low anterior resection of rectal cancer and anastomotic leakage].

OBJECTIVE: To evaluate the association of early diarrhea(postoperative day 1 to 7) and anastomotic leakage after low anterior resection for rectal cancer. METHODS: Clinical data of 192 cases (group A, tumor from the anal verge 4-7 cm) from May 2004 to May 2007 and 236 cases(group B) from July 2007 to May 2010 in our hospital who received low anterior resection of rectal cancer were analyzed retrospectively. RESULTS: In group A, the incidence of early postoperative diarrhea was 19.3%(37/192), of which 9 cases were treated with anti-diarrhea drugs. The morbidity of anastomotic leakage in patients with diarrhea was significantly higher than those without early diarrhea(16.2% vs. 5.2%, P<0.05). In group B, the incidence of early postoperative diarrhea was 16.5%(39/236). All the patients were treated with anti-diarrhea drugs. There was no difference in the morbidity of anastomotic leakage between patients with diarrhea and those without early diarrhea(16.2% vs. 5.2%, P<0.05). There was no difference in early diarrhea between groups A and B(P>0.05). However, the incidence of anastomotic leakage in patients with early diarrhea was lower in group B(P<0.05). CONCLUSIONS: Early diarrhea after the low anterior resection of rectal cancer may indicate anastomotic leakage. Treatment of early postoperative diarrhea may reduce the risk of anastomotic leakage.