OsREC8 is essential for chromatid cohesion and metaphase I monopolar orientation in rice meiosis

The successful transmission of chromosomes during mitosis and meiosis relies on the establishment and subsequent release of cohesion between replicated chromatids. Cohesion is mediated by a four-subunit structural maintenance of chromosome complex, called cohesins. REC8 is a key component of this meiotic cohesion complex in most model organisms studied to date. Here, we isolated and dissected the functions of OsREC8, a rice (Oryza sativa) REC8 homolog, using two null Osrec8 mutants. We showed that OsREC8 encodes a protein that localized to meiotic chromosomes from approximately meiotic interphase to metaphase I. Homologous pairing and telomere bouquet formation were abnormal in Osrec8 meiocytes. Furthermore, fluorescent in situ hybridization experiments on Osrec8 meiocytes demonstrated that the mutation eliminated meiotic centromeric cohesion completely during prophase I and also led to the bipolar orientation of the kinetochores during the first meiotic division and accordingly resulted in premature separation of sister chromatid during meiosis I. Immunolocalization analyses revealed that the loading of PAIR2, PAIR3, OsMER3, and ZEP1 all depended on OsREC8. By contrast, the presence of the OsREC8 signal in pair2, pair3, Osmer3, and zep1 mutants indicated that the loading of OsREC8 did not rely on these four proteins. These results suggest that OsREC8 has several essential roles in the meiotic processes.

Introgression of qPE9-1 allele, conferring the panicle erectness, leads to the decrease of grain yield per plant in japonica rice (Oryza sativa L.)

Panicle architecture is closely related to yield formation. The qPE9-1 gene has been proved to be widely used in high-yield rice cultivar developments, conferring erect panicle character in japonica rice. Recently, qPE9-1 has been successfully cloned; however, the genetic effect on grain yield per plant of the erect panicle allele qPE9-1 is controversial yet. In the present study, a drooping panicle parent Nongken 57, carrying qpe9-1 allele, was used as recurrent parent to successively backcross to a typical erect panicle line from the double haploid (DH) population (Wuyunjing 8/Nongken 57), which was previously shown to carry qPE9-1 allele. Thus a pair of near-isogenic lines (NILs) was developed. The comparison of agronomic traits between the NILs showed that, when qpe9-1 was replaced by qPE9-1, the panicle architecture was changed from drooping to erect; moreover, the panicle length, plant height, 1000-grain weight and the tillers were significantly decreased, consequently resulting in the dramatic decrease of grain yield per plant by 30%. Therefore, we concluded that the qPE9-1 was a major factor controlling panicle architecture, and qPE9-1 had pleiotropic nature, with negative effects on grain yield per plant. This result strongly suggests that the erect panicle allele qPE9-1 should be used together with other favorable genes in the high-yield breeding practice. In addition, the effect of qPE9-1 on eating and cooking quality was also discussed in the present study.

Anatomical and chemical characteristics of culm of rice brittle mutant bc7(t)

Brittleness culm is an important agronomic trait that has a potential usefulness in agricultural activity as animal forage. In the present study, the anatomy of culm of rice (Oryza sativa L.) brittle mutant bc7(t) was investigated with light microscopy and electron microscopy. Findings showed bc7(t) exhibited higher area percentages of mechanical and conducting tissues, and lower cell wall thickness of sclerenchyma cells. Chemical analyses and 13C CP/MAS NMR spectra of cell walls indicated that the content of cellulose decreased, and the contents of hemicellulose, lignin and silicon was increased in bc7(t). Lignin histochemical staining and cytochemical localisation revealed that the higher lignin was localised in epidermal, sclerenchyma and vascular bundle cells in bc7(t). The energy dispersive X-ray microanalysis showed that the contents of silicon were higher in bc7(t) than in the wild type. These results indicate that cellulose, hemicellulose, lignin, silicon and the area percentages of mechanical and conducting tissues could be regulated in a compensatory fashion, possibly contributing to metabolic flexibility and a growth advantage to sustain the bc7(t) normal growth habit like the wild-type plant.

Circular dichroism in biological photonic crystals and cubic chiral nets

Nature provides impressive examples of chiral photonic crystals, with the notable example of the cubic so-called srs network (the label for the chiral degree-three network modeled on SrSi2) or gyroid structure realized in wing scales of several butterfly species. By a circular polarization analysis of the band structure of such networks, we demonstrate strong circular dichroism effects: The butterfly srs microstructure, of cubic I4(1)32 symmetry, shows significant circular dichroism for blue to ultraviolet light, that warrants a search for biological receptors sensitive to circular polarization. A derived synthetic structure based on four like-handed silicon srs nets exhibits a large circular polarization stop band of a width exceeding 30%. These findings offer design principles for chiral photonic devices.

Fine mapping and candidate gene analysis of ptgms2-1, the photoperiod-thermo-sensitive genic male sterile gene in rice (Oryza sativa L.)

Photoperiod-thermo-sensitive genic male sterile (PTGMS) rice exhibits a number of desirable traits for hybrid rice production. The cloning genes responsible for PTGMS and those elucidating male sterility mechanisms and reversibility to fertility would be of great significance to provide a foundation to develop new male sterile lines. Guangzhan63S, a PTGMS line, is one of the most widely used indica two-line hybrid rice breeding systems in China. In this study, genetic analysis based on F(2) and BC(1)F(2) populations derived from a cross between Guangzhan63S and 1587, determined a single recessive gene controls male sterility in Guangzhan63S. Molecular marker techniques combined with bulked-segregant analysis (BSA) were used and located the target gene (named ptgms2-1) between two SSR markers RM12521 and RM12823. Fine mapping of the ptgms2-1 locus was conducted with 45 new Insertion-Deletion (InDel) markers developed between the RM12521 and RM12823 region, using 634 sterile individuals from F(2) and BC(1)F(2) populations. Ptgms2-1 was further mapped to a 50.4 kb DNA fragment between two InDel markers, S2-40 and S2-44, with genetic distances of 0.08 and 0.16 cM, respectively, which cosegregated with S2-43 located on the AP004039 BAC clone. Ten genes were identified in this region based on annotation results from the RiceGAAS system. A nuclear ribonuclease Z gene was identified as the candidate for the ptgms2-1 gene. This result will facilitate cloning the ptgms2-1 gene. The tightly linked markers for the ptgms2-1 gene locus will further provide a useful tool for marker-assisted selection of this gene in rice breeding programs.

Interplay of cAMP and MAPK pathways in hCG secretion and fusogenic gene expression in a trophoblast cell line

Differentiation of human placental mononuclear trophoblasts into a multinucleate syncytium involves up-regulation of key proteins promoting cell fusion and increased capacity for placental hormonogenesis. It is well established that the activation of adenylyl cyclase leads to increased expression of trophoblast fusogenic gene machinery and human chorionic gonadotropin (hCG) secretion. We used the forskolin-induced syncytialisation of BeWo choriocarcinoma cells as a model to characterise in detail the signalling pathway downstream of adenylyl cyclase. Forskolin treatment induced a rapid and potent ERK1/2 and p38MAPK phosphorylation; this cascade required PKA-AKAP interactions and led to downstream CREB-1/ATF-1 phosphorylation via ERK1/2-dependent but p38MAPK-independent mechanisms. Interestingly both p38MAPK and ERK1/2 were involved in forskolin-induced hCG-secretion, suggesting the presence of additional p38MAPK-dependent but CREB-1/ATF-1-independent pathways. Forskolin treatment of BeWo cells significantly up-regulated the expression of various fusogenic gene mRNAs, including syncytin-1 and -2 (by 3- and 10-fold, respectively) the transcription factors old astrocyte specifically induced substance (OASIS) and glial cells missing a (GCMa) (by 3- and 6-fold, respectively) and the syncytin-2 receptor, major facilitator superfamily domain containing 2 (MFSD2) (by 2-fold). Up-regulation of AKAP79 and AKAP250 (by 2.5- and 4-fold, respectively) was also identified in forskolin-treated BeWo cells. Forskolin effects on all these genes were suppressed by chemical inhibition of p38MAPK whereas only specific genes were sensitive to ERK1/2 inhibition. This data provide novel insights into the signalling molecules and mechanisms regulating fusogenic gene expression by the adenylyl cyclase pathway.

Granule structure and distribution of allomorphs in C-type high-amylose rice starch granule modified by antisense RNA inhibition of starch branching enzyme

C-type starch, which is a combination of both A-type and B-type crystal starch, is usually found in legumes and rhizomes. We have developed a high-amylose transgenic line of rice (TRS) by antisense RNA inhibition of starch branching enzymes. The starch in the endosperm of this TRS was identified as typical C-type crystalline starch, but its fine granular structure and allomorph distribution remained unclear. In this study, we conducted morphological and spectroscopic studies on this TRS starch during acid hydrolysis to determine the distribution of A- and B-type allomorphs. The morphology of starch granules after various durations of acid hydrolysis was compared by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results showed that amorphous regions were located at the center part of TRS starch subgranules. During acid hydrolysis, starch was degraded from the interior of the subgranule to the outer surface, while the peripheral part of the subgranules and the surrounding band of the starch granule were highly resistant to acid hydrolysis. The spectroscopic changes detected by X-ray powder diffraction, 13C cross-polarization magic-angle spinning NMR, and attenuated total reflectance Fourier transform infrared showed that the A-type allomorph was hydrolyzed more rapidly than the B-type, and that the X-ray diffraction profile gradually changed from a native C-type to a CB-type with increasing hydrolysis time. Our results showed that, in TRS starch, the A-type allomorph was located around the amorphous region, and was surrounded by the B-type allomorph located in the peripheral region of the subgranules and the surrounding band of the starch granule. Thus, the positions of A- and B-type allomorphs in the TRS C-type starch granule differ markedly from those in C-type legume and rhizome starch.

Developing high throughput genotyped chromosome segment substitution lines based on population whole-genome re-sequencing in rice (Oryza sativa L.)

BACKGROUND

Genetic populations provide the basis for a wide range of genetic and genomic studies and have been widely used in genetic mapping, gene discovery and genomics-assisted breeding. Chromosome segment substitution lines (CSSLs) are the most powerful tools for the detection and precise mapping of quantitative trait loci (QTLs), for the analysis of complex traits in plant molecular genetics.

RESULTS

In this study, a wide population consisting of 128 CSSLs was developed, derived from the crossing and back-crossing of two sequenced rice cultivars: 9311, an elite indica cultivar as the recipient and Nipponbare, a japonica cultivar as the donor. First, a physical map of the 128 CSSLs was constructed on the basis of estimates of the lengths and locations of the substituted chromosome segments using 254 PCR-based molecular markers. From this map, the total size of the 142 substituted segments in the population was 882.2 Mb, was 2.37 times that of the rice genome. Second, every CSSL underwent high-throughput genotyping by whole-genome re-sequencing with a 0.13× genome sequence, and an ultrahigh-quality physical map was constructed. This sequencing-based physical map indicated that 117 new segments were detected; almost all were shorter than 3 Mb and were not apparent in the molecular marker map. Furthermore, relative to the molecular marker-based map, the sequencing-based map yielded more precise recombination breakpoint determination and greater accuracy of the lengths of the substituted segments, and provided more accurate background information. Third, using the 128 CSSLs combined with the bin-map converted from the sequencing-based physical map, a multiple linear regression QTL analysis mapped nine QTLs, which explained 89.50% of the phenotypic variance for culm length. A large-effect QTL was located in a 791,655 bp region that contained the rice 'green revolution' gene.

CONCLUSIONS

The present results demonstrated that high throughput genotyped CSSLs combine the advantages of an ultrahigh-quality physical map with high mapping accuracy, thus being of great potential value for gene discovery and genetic mapping. These CSSLs may provide powerful tools for future whole genome large-scale gene discovery in rice and offer foundations enabling the development of superior rice varieties.

Formation of semi-compound C-type starch granule in high-amylose rice developed by antisense RNA inhibition of starch-branching enzyme

Cereal starch granules with high-amylose and resistant starch (RS) always show irregular morphology and special crystalline structure, but their formation during grain development is not yet clear. In our previous studies, we had generated a transgenic rice line (TRS) enriched with amylose and RS, which contained semi-compound starch showing a C-type crystalline structure. In this study, the formation of semi-compound C-type starch granule during TRS endosperm development was carefully investigated with light, scanning electron, and transmission electron microscopes and X-ray powder diffraction. The results showed that the TRS starch subgranules, each with a central hilum, were individually initiated in amyloplast and showed an A-type crystal at the early stage of starch granule development, which was similar to that in its wild type. However, with the endosperm development, the amylose content in TRS endosperm starch increased and the B-type starch crystal was deposited in the periphery of subgranules; then, the adjacent subgranules fused together and finally formed a continuous outer layer band surrounding the entire circumference of the starch granule. Accordingly, a mechanistic model for the formation of semi-compound C-type starch granules is proposed.

Calculation of the Johann error for spherically bent x-ray imaging crystal spectrometers

New x-ray imaging crystal spectrometers, currently operating on Alcator C-Mod, NSTX, EAST, and KSTAR, record spectral lines of highly charged ions, such as Ar(16+), from multiple sightlines to obtain profiles of ion temperature and of toroidal plasma rotation velocity from Doppler measurements. In the present work, we describe a new data analysis routine, which accounts for the specific geometry of the sightlines of a curved-crystal spectrometer and includes corrections for the Johann error to facilitate the tomographic inversion. Such corrections are important to distinguish velocity induced Doppler shifts from instrumental line shifts caused by the Johann error. The importance of this correction is demonstrated using data from Alcator C-Mod.

C-type starch from high-amylose rice resistant starch granules modified by antisense RNA inhibition of starch branching enzyme

High-amylose starch is a source of resistant starch (RS) which has a great benefit on human health. A transgenic rice line (TRS) enriched amylose and RS had been developed by antisense RNA inhibition of starch branching enzymes. In this study, the native starch granules were isolated from TRS grains as well as the wild type, and their crystalline type was carefully investigated before and after acid hydrolysis. In high-amylose TRS rice, the C-type starch, which might result from the combination of both A-type and B-type starch, was observed and subsequently confirmed by multiple physical techniques, including X-ray powder diffraction, solid-state nuclear magnetic resonance, and Fourier transform infrared. Moreover, the change of starch crystalline structure from C- to B-type during acid hydrolysis was also observed in this RS-rich rice. These data could add to our understanding of not only the polymorph structure of cereal starch but also why high-amylose starch is more resistant to digestion.

The central element protein ZEP1 of the synaptonemal complex regulates the number of crossovers during meiosis in rice

ZEP1, a transverse filament (TF) protein, is the rice (Oryza sativa) homolog of Arabidopsis thaliana ZYP1. In the Tos17-insertional zep1 mutants, homologous chromosomes align along the entire length of the chromosome, but the synaptonemal complex is not assembled in early prophase I. Crossovers are well formed, and 12 bivalents could be detected from diakinesis to metaphase I, which leads to equal chromosomal segregation in anaphase I. Moreover, the number of crossovers has a tendency to be increased compared with that in the wild type. These phenomena are different from the TF mutants identified so far in other organisms. Chiasma terminalization of the bivalent, which occurs frequently in the wild type, seldom occurred in zep1. Transmission electron micrographs and immunodetection using an antibody against ZEP1 showed that ZEP1 is the central element of the synaptonemal complex. Although PAIR2 and MER3 were loaded normally in zep1, their dissociation was delayed severely compared with the wild type. In addition, ZEP1 is reloaded onto chromosomes in early microspores as the chromosome decondense, suggesting that ZEP1 might have other biological functions during this process.

Microstructure and ultrastructure of high-amylose rice resistant starch granules modified by antisense RNA inhibition of starch branching enzyme

A high-amylose transgenic rice line (TRS) modified by antisense RNA inhibition of starch branching enzymes revealed a resistant starch-rich quality. Compound starch granules in whole grains of the regular rice cultivar Teqing (TQ) were readily split during fracturing, whereas the starch granules in TRS were structurally intact and showed large voluminous, non-angular rounded bodies and elongated, filamentous structures tolerant of fracturing. In isolated preparation, TQ starch granules broke up into separate polygonal granules, whereas TRS starch granules kept their intactness. TRS starch granules consisted of packed smaller subgranules, some of which located at the periphery of starch granules were fused to each other with adjacent ones forming a thick band or wall encircling the entire circumference of the granules. TQ starch granules had a high concentration of amylose in the concentric hilum, whereas TRS starch granules showed a relatively even distribution of amylose with intense amylose in both hilum and band.

Laryngeal epithelial thickness: a comparison between optical coherence tomography and histology

OBJECTIVES

Optical coherence tomography, an imaging modality using near-infrared light, produces cross-sectional tissue images with a lateral pixel resolution of 10 microm. However, normative data is first needed on epithelial thickness for lesion characterisation, and, to date, little exists. The purpose of our study is to measure normal laryngeal epithelial thickness by in vivo optical coherence tomography, and compare these values to those obtained from fixed ex-vivo laryngectomy specimens.

DESIGN AND SETTING

Prospective at a single medical center in California, United States.

PARTICIPANTS

A total of 116 patients undergoing operative endoscopy.

MAIN OUTCOME MEASURES

Optical coherence tomography images of clinically normal laryngeal subsites were selected. Calibrated measurements of epithelial thickness at various laryngeal subsites were recorded. Measurements of epithelial thickness from corresponding areas were obtained using optical micrometry on histologically normal regions of 15 total laryngectomy specimens. Descriptive statistics were performed.

RESULTS

Mean epithelial optical coherence tomography thicknesses were: true vocal cords (81 microm), false vocal cords (78 microm), subglottis (61 microm), aryepiglottic folds (111 microm), laryngeal epiglottis (116 microm) and lingual epiglottis (170 microm). Epithelial thicknesses in fixed tissues were: true vocal cords (103 microm), false vocal cords (79 microm), aryepiglottic folds (205 microm) subglottis (61 microm), laryngeal epiglottis (38 microm) and lingual epiglottis (130 microm).

CONCLUSIONS

Optical coherence tomography does not have the artifacts associated with conventional histologic techniques. The inevitable development of office-based optical coherence tomography devices will increase the precision of laryngeal measurements and contribute to the clinical application of this technology in diagnosing laryngeal disease.

DEP and AFO regulate reproductive habit in rice

Sexual reproduction is essential for the life cycle of most angiosperms. However, pseudovivipary is an important reproductive strategy in some grasses. In this mode of reproduction, asexual propagules are produced in place of sexual reproductive structures. However, the molecular mechanism of pseudovivipary still remains a mystery. In this work, we found three naturally occurring mutants in rice, namely, phoenix (pho), degenerative palea (dep), and abnormal floral organs (afo). Genetic analysis of them indicated that the stable pseudovivipary mutant pho was a double mutant containing both a Mendelian mutation in DEP and a non-Mendelian mutation in AFO. Further map-based cloning and microarray analysis revealed that dep mutant was caused by a genetic alteration in OsMADS15 while afo was caused by an epigenetic mutation in OsMADS1. Thus, OsMADS1 and OsMADS15 are both required to ensure sexual reproduction in rice and mutations of them lead to the switch of reproductive habit from sexual to asexual in rice. For the first time, our results reveal two regulators for sexual and asexual reproduction modes in flowering plants. In addition, our findings also make it possible to manipulate the reproductive strategy of plants, at least in rice.

Sexual reproduction is essential for the life cycle of most flowering plants. However, pseudovivipary, in which floral organs are replaced by bulbils or plantlets, provides an asexual means for many grasses to reproduce in extreme environments. Although the molecular mechanism of pseudovivipary is still unknown, the high-frequency occurrence of pseudovivipary in extreme environments indicates that only a few key regulators are responsible for the switch of reproductive habit. Here, by analyzing three naturally occurring mutants in rice, we show that mutations in DEP and AFO lead to the transformation of rice flowers/spikelets into juvenile plantlets and subsequently the switch of reproductive strategy from sexual to asexual, suggesting that DEP and AFO might work cooperatively to regulate reproductive habit in rice. Thus, we reveal a critical mechanism of the switch of reproductive habit in plants. In addition, our results also make it possible to manipulate the reproductive habit of plants, at least in rice.

Placental expression of 2,3 bisphosphoglycerate mutase in IGF-II knock out mouse: correlation of circulating maternal 2,3 bisphosphoglycerate and fetal growth

Bisphosphoglycerate mutase (BPGM) catalyses the formation of 2,3 bisphosphoglycerate (BPG) a ligand of haemoglobin. BPG facilitates liberation of oxygen from haemoglobin at low oxygen tension enabling efficient delivery of oxygen to tissues. We describe expression of BPGM in mouse labyrinthine trophoblasts, located at the maternal-placental interface. Expression is lower in placentae of igf2(+/-) knockout mice, a widely used model of growth restriction, compared to wild type placentae. Circulating maternal BPG increased throughout gestation but this increase was less in wt mothers carrying igf2(+/-) pups than in those carrying exclusively wt pups. This reduction was observed well before term and may contribute to the low birth weight of igf2(+/-) pups. Strikingly, we also measured reductions of fetal and placental weight in wt littermates of igf2(+/-) pups compared to pups developing in an exclusively wt environment. These data suggest that placental expression of BPGM can influence maternal BPG concentrations and supports a hypothesis under which BPG synthesized in the placenta may act on maternal haemoglobin to enhance delivery of oxygen to the developing fetus.

MER3 is required for normal meiotic crossover formation, but not for presynaptic alignment in rice

MER3, a ZMM protein, is required for the formation of crossovers in Saccharomyces cerevisiae and Arabidopsis. Here, MER3, the first identified ZMM gene in a monocot, is characterized by map-based cloning in rice (Oryza sativa). The null mutation of MER3 results in complete sterility without any vegetative defects. Cytological analyses show that chiasma frequency is reduced dramatically in mer3 mutants and the remaining chiasmata distribute randomly among different pollen mother cells, implying possible coexistence of two kinds of crossover in rice. Immunocytological analyses reveal that MER3 only exists as foci in prophase I meiocytes. In addition, MER3 does not colocalize with PAIR2 at the beginning of prophase I, but locates on one end of PAIR2 fragments at later stages, whereas MER3 foci merely locate on one end of REC8 fragments when signals start to be seen in early prophase I. The normal loading of PAIR2 and REC8 in mer3 implies that their loading is independent of MER3. On the contrary, the absence of MER3 signal in pair2 mutants indicates that PAIR2 is essential for the loading and further function of MER3.

Physiological and biochemical responses of in vitro Fusarium oxysporum f.sp. niveum to benzoic acid

The allelopathic potential of an artificially applied allelochemical, benzoic acid, on in vitro Fusarium oxysporum f.sp. niveum (a soil-borne pathogen causing watermelon wilt) was evaluated. Benzoic acid strongly inhibited its growth, sporulation and conidia germination, whereas it stimulated virulence factors of this pathogen. The biomass was reduced by 83-96 % and the conidia germinating rate and conidia production rate were decreased by 100 % at a concentration of >200 mg/L. However, phytopathogenic enzyme activities and mycotoxin production were stimulated with an increase of 10.2-1250 % for enzyme activities and 610-2630 % for mycotoxin yield.

Fine mapping and isolation of Bc7(t), allelic to OsCesA4

Several brittle culm mutants of rice were identified and characterized. In this study, we characterized a brittle mutant (bc7(t)) identified from japonica variety Zhonghua 11 by means of 60Co-gamma radiation. This mutant displays normal phenotype similar to its wild type plants except for the fragility of all plant body, with approximately 10% decrease in the cellulose content. The genetic analysis and gene fine mapping showed that the bc7(t) mutant was controlled by a recessive gene, residing on an 8.4 kb region of the long arm of chromosome 1. The gene annotation indicated that there was only one putative gene encoding cellulose synthase catalytic subunit (CesA) in this region, which was allelic to OsCesA4. Furthermore, the sequence analysis was carried out and 7 bases deletion in the junction of exon 10 and intron 10 was done in bc7(t) mutant, resulting in the change of reading frame and the consequent failure to generate functional protein. In addition, the result of RNA interference experiment showed that when the Bc7(t) was knocked down, the transplants exhibited fragility, similar to bc7(t) mutant. The finding of novel allele of OsCesA4 locus will facilitate the understanding of the mechanism of cell wall biosynthesis. The potential utilization of the bc7(t) mutant in animal food was discussed as well.