Control of Grain Weight and Size in Rice (Oryza sativa L.) by OsPUB3 Encoding a U-Box E3 Ubiquitin Ligase

Grain weight and size, mostly determined by grain length, width and thickness, are crucial traits affecting grain quality and yield in rice. A quantitative trait locus controlling grain length and width in rice, qGS1-35.2, was previously fine-mapped in a 57.7-kb region on the long arm of chromosome 1. In this study, OsPUB3, a gene encoding a U-box E3 ubiquitin ligase, was validated as the causal gene for qGS1-35.2. The effects were confirmed firstly by using CRISPR/Cas9-based mutagenesis and then through transgenic complementation of a Cas9-free knock-out (KO) mutant. Two homozygous KO lines were produced, each having a 1-bp insertion in OsPUB3 which caused frameshift mutation and premature termination. Compared with the recipient and a transgenic-negative control, both mutants showed significant decreases in grain weight and size. In transgenic complementation populations derived from four independent T₀ plants, grain weight of transgenic-positive plants was significantly higher than transgenic-negative plants, coming with increased grain length and a less significant decrease in grain width. Based on data documented in RiceVarMap V2.0, eight haplotypes were classified according to six single-nucleotide polymorphisms (SNPs) found in the OsPUB3 coding region of 4695 rice accessions. Significant differences on grain size traits were detected between the three major haplotypes, Hap1, Hap2 and Hap3 that jointly occupy 98.6% of the accessions. Hap3 having the largest grain weight and grain length but intermediate grain width exhibits a potential for simultaneously improving grain yield and quality. In another set of 257 indica rice cultivars tested in our study, Hap1 and Hap2 remained to be the two largest groups. Their differences on grain weight and size were significant in the background of non-functional gse5, but non-significant in the background of functional GSE5, indicating a genetic interaction between OsPUB3 and GSE5. Cloning of OsPUB3 provides a new gene resource for investigating the regulation of grain weight and size.

Control of Grain Shape and Size in Rice by Two Functional Alleles of OsPUB3 in Varied Genetic Background

Grain shape and size are key determinants of grain appearance quality and yield in rice. In our previous study, a grain shape QTL, qGS1-35.2, was fine-mapped using near-isogenic lines (NILs) derived from a cross between Zhenshan 97 (ZS97) and Milyang 46 (MY46). One annotated gene, OsPUB3, was found to be the most likely candidate gene. Here, knockout and overexpression experiments were performed to investigate the effects of OsPUB3 on grain shape and size. Four traits were tested, including grain length, grain width, grain weight, and the ratio of grain length to width. Knockout of OsPUB3 in NIL^ZS97, NIL^MY46, and another rice cultivar carrying the OsPUB3^MY46 allele all caused decreases in grain width and weight and increases in the ratio of grain length to width. Results also showed that the magnitude of the mutational effects varied depending on the target allele and the genetic background. Moreover, it was found that NIL^ZS97 and NIL^MY46 carried different functional alleles of OsPUB3, causing differences in grain shape rather than grain weight. In the overexpression experiment, significant differences between transgenic-positive and transgenic-negative plants were detected in all four traits. These results indicate that OsPUB3 regulates grain shape and size through a complex mechanism and is a good target for deciphering the regulatory network of grain shape. This gene could be used to improve grain appearance quality through molecular breeding as well.

Control of Thousand-Grain Weight by OsMADS56 in Rice

Grain weight and size are important traits determining grain yield and influencing grain quality in rice. In a previous study, a quantitative trait locus controlling thousand-grain weight (TGW) in rice, qTGW10-20.8, was mapped in a 70.7 kb region on chromosome 10. Validation of the candidate gene for qTGW10-20.8, OsMADS56 encoding a MADS-box transcription factor, was performed in this study. In a near-isogenic line (NIL) population segregated only at the OsMADS56 locus, NILs carrying the OsMADS56 allele of IRBB52 were 1.9% and 2.9% lower in TGW than NILs carrying the OsMADS56 allele of Teqing in 2018 and 2020, respectively. Using OsMADS56 knock-out mutants and overexpression transgenic plants, OsMADS56 was validated as the causal gene for qTGW10-20.8. Compared with the recipients, the TGW of the knock-out mutants was reduced by 6.0-15.0%. In these populations, decreased grain weight and size were associated with a reduction in the expression of OsMADS56. In transgenic populations of OsMADS56 driven by a strong constitutive promoter, grain weight and size of the positive plants were significantly higher than those of the negative plants. Haplotype analysis showed that the Teqing-type allele of OsMADS56 is the major type presented in cultivated rice and used in variety improvement. Cloning of OsMADS56 provides a new gene resource to improve grain weight and size through molecular design breeding.

Identification through fine mapping and verification using CRISPR/Cas9-targeted mutagenesis for a minor QTL controlling grain weight in rice

A minor QTL for grain weight in rice, qTGW1.2b, was fine-mapped. Its casual gene OsVQ4 was confirmed through CRISPR/Cas9-targeted mutagenesis, exhibiting an effect that was larger than the original QTL effect. The CRISPR/Cas system exhibits a great potential for rice improvement, but the application was severely hindered due to insufficient target genes, especial the lack of validated genes underlying quantitative trait loci having small effects. In this study, a minor QTL for grain weight, qTGW1.2b, was fine-mapped into a 44.0 kb region using seven sets of near isogenic lines (NILs) developed from the indica rice cross (Zhenshan 97)³/Milyang 46, followed by validation of the causal gene using CRISPR/Cas9-targeted mutagenesis. In the NIL populations, 1000-grain weight of the Zhenshan 97 homozygous lines decreased by 0.9-2.0% compared with the Milyang 46 homozygous lines. A gene encoding VQ-motif protein, OsVQ4, was identified as the candidate gene based on parental sequence differences. The effect of OsVQ4 was confirmed by creating CRISPR/Cas9 knockout lines, whose 1000-grain weight decreased by 2.8-9.8% compared with the wild-type transgenic line and the recipient. These results indicate that applying genome editing system could create novel alleles with large phenotypic variation at minor QTLs, which is an effective way to validate causal genes of minor QTLs. Our study establishes a strategy for cloning minor QTLs, which could also be used to identify a large number of potential target genes for the application of CRISPR/Cas system.

[Follow-up and retrospective investigation of patients with pneumoconiosis in Jiangsu Province, China]

Objective: To investigate the features, changing trend, and rules of pneumoconiosis in Jiangsu Province, China, as well as the health status of patients with pneumoconiosis. Methods: From July to October 2019, the patients with pneumoconiosis, reported up to the end of 2018 in Jiangsu Province, were enrolled as respondents, and follow-up and retrospective investigation were performed. A total of 24405 patients with pneumoconiosis were investigated, and related data were collected from the monitoring system of cause of death for residents, pneumoconiosis network reporting system, occupational disease diagnosis institution, management institutions for the reporting of occupational diseases, and related residents' committee or village committee. The patients with pneumoconiosis, who had been reported, were followed up by telephone or on-site visit to obtain the information on their conditions. A descriptive analysis was performed for age of onset, working years, sex, category of industry, type of pneumoconiosis, annual disease onset, geographic distribution, and medical security. Results: Among the 24405 patients, a male/female ratio was 16.81∶1. Of all 24405 patients, 15948 (65.35%) had stage 1 pneumoconiosis, 5289 (21.67%) had stage 2 pneumoconiosis, and 1637 (6.71%) had stage 3 pneumoconiosis. The mean working years for dust exposure was 16.25±9.95 years for all patients, and the mean working years for dust exposure was 15.80±9.95 years for patients with stage 1 pneumoconiosis, 17.82±9.80 years for patients with stage 2 pneumoconiosis, and 16.31±9.90 years for patients with stage 3 pneumoconiosis. The highest number of cases of pneumoconiosis was reported in Wuxi (5744 cases, accounting for 23.54%) , followed by Zhenjiang (4160 cases, accounting for 17.05%) , Xuzhou (3851 cases, accounting for 15.78%) , Yancheng (3340 cases, accounting for 13.69%) , and Suzhou (2948 cases, accounting for 12.08%) . Major types of pneumoconiosis included silicosis (15392 cases, accounting for 63.07%) and coal workers' pneumoconiosis (5253 cases, accounting for 21.52%) . In this survey, 21115 completed follow-up, among whom 15924 survived and 5191 died, 15924 patients with pneumoconiosis survived, among whom 7461 (46.85%) had an age of ≥70 years and 2515 (15.79%) were exposed to dust for 5-9 years. The industries involved were mainly coal mining and washing industry (5687 cases, accounting for 35.71%) and public management, social security, and social organization (3349 cases, accounting for 21.03%) ; in terms of security, 7999 patients (50.23%) were covered by occupational injury insurance, 946 (5.94%) were compensated by employers, 4537 (28.49%) were covered by basic medical insurance for urban and rural residents, 1590 (9.98%) were covered by critical illness insurance, and 5458 (34.28%) were covered by other types of social security, such as medical assistance and poverty relief. Conclusion: Silicosis and coal worker's pneumoconiosis are the key points for the prevention and treatment of pneumoconiosis in Jiangsu Province, and supervision should be strengthened for industries and regions with serious dust hazards.

Fine-mapping of qTGW2, a quantitative trait locus for grain weight in rice (Oryza sativa L.)

Background

Grain weight is a grain yield component, which is an integrated index of grain length, width and thickness. They are controlled by a large number of quantitative trait loci (QTLs). Besides major QTLs, minor QTLs play an essential role. In our previous studies, QTL analysis for grain length and width was performed using a recombinant inbred line population derived from rice cross TQ/IRBB lines. Two major QTLs were detected, which were located in proximity to GS3 and GW5 that have been cloned. In the present study, QTLs for grain weight and shape were identified using rice populations that were homozygous at GS3 and GW5.

Method

Nine populations derived from the indica rice cross TQ/IRBB52 were used. An F_10:11population named W1, consisting of 250 families and covering 16 segregating regions, was developed from one residual heterozygote (RH) in the F₇generation of Teqing/IRBB52. Three near isogenic line (NIL)-F₂ populations, ZH1, ZH2 and ZH3 that comprised 205, 239 and 234 plants, respectively, were derived from three RHs in F_10:11. They segregated the target QTL region in an isogenic background. Two NIL populations, HY2 and HY3, were respectively produced from homozygous progeny of the ZH2 and ZH3 populations. Three other NIL-F₂ populations, Z1, Z2 and Z3, were established using three RHs having smaller heterozygous segments. QTL analysis for 1000-grain weight (TGW), grain length (GL), grain width (GW), and length/width ratio (LWR) was conducted using QTL IciMapping and SAS procedure with GLM model.

Result

A total of 27 QTLs distributed on 12 chromosomes were identified. One QTL cluster, qTGW2/qGL2/qGW2 located in the terminal region of chromosome 2, were selected for further analysis. Two linked QTLs were separated in region Tw31911−RM266. qGL2 was located in Tw31911−Tw32437 and mainly controlled GL and GW. The effects were larger on GL than on GW and the allelic directions were opposite. qTGW2 was located in Tw35293−RM266 and affected TGW, GL and GW with the same allelic direction. Finally, qTGW2 was delimited within a 103-kb region flanked by Tw35293 and Tw35395.

Conclusion

qTGW2 with significant effects on TGW, GL and GW was validated and fine-mapped using NIL and NIL-F₂ populations. These results provide a basis for map-based cloning of qTGW2 and utilization of qTGW2 in the breeding of high-yielding rice varieties.

Pleiotropic Effects of Rice Florigen Gene RFT1 on the Amino Acid Content of Unmilled Rice

In rice, the contents of protein and amino acids are the major parameters of nutritional quality. Co-localization of quantitative trait loci (QTLs) for heading date and protein content were reported, but pleiotropism of heading-date genes on protein contents has not been investigated. Here, we reported that rice florigen gene RFT1 plays an important role in controlling amino acid contents of rice grain. Firstly, 73 QTLs for the contents of 17 amino acids in unmilled rice were detected using recombinant inbred lines (RILs) of the indica rice cross Zhenshan 97 (ZS97)/Milyang 46 (MY46). Then, the effect of the largest cluster consisting of 14 QTLs, located in proximity to the rice florigen genes RFT1 and Hd3a, was validated using three populations consisting of near isogenic lines (NILs) that only segregated a region covering the target QTL. The first and second NIL populations were derived from a residual heterozygote identified from the ZS97/MY46 RIL population, consisting of homozygous lines that were only segregated in a 29.9-kb region covering the two florigen genes and a 1.7-kb region for RFT1, respectively. The third NIL population was segregated for the RFT1^ZS97 transgene in the background of japonica rice cultivar Zhonghua 11. In all the three NIL populations, RFT1 was shown to have a strong effect on the contents of most amino acids, with the ZS97 allele always having the reducing effects. By comparing QTLs for amino acid contents detected in the ZS97/MY46 RIL population and genes/QTLs previously identified for heading date difference between ZS97 and MY46, possible pleiotropism on amino acid contents was also shown for other key heading-date genes including Hd1, Ghd7, and OsGI.

Genetic mapping of ionomic quantitative trait loci in rice grain and straw reveals OsMOT1;1 as the putative causal gene for a molybdenum QTL qMo8

Rice is a major dietary source of essential mineral nutrients and toxic elements (aka ionome) for humans. However, the genetic basis underlying the variation in ionome is still largely unknown. Here, we mapped 51 and 61 quantitative trait loci (QTLs) controlling the concentrations of 13 and 15 elements in rice (Oryza sativa L.) grain and straw, respectively, using a recombinant inbred lines (RILs) that were grown at three different field sites in 3 years. Several QTLs were repeatedly detected in both grain and straw or in multiple years; the resulting 87 unique QTLs with 17 of them (20%) were co-localized with previously reported corresponding QTLs and 70 were novel ionomic QTLs. At least, 14 genomic clusters that controlled the concentrations of multiple elements were identified. Furthermore, we identified a molybdate transporter gene OsMOT1;1 as the putative causal gene for a QTL controlling molybdenum concentration in both straw and grain. QTL analyses based on the concentrations of multiple elements in both grain and straw of RIL population grown in three field sites in 3 years allow us to identify tissue common QTLs and reproducible QTLs that were validated in multiple years. The identification of ionomic QTLs will be useful in revealing the molecular mechanisms underlying the accumulation of elements in rice and providing the opportunity to reduce the accumulation of toxic elements and enrich the accumulation of beneficial elements in rice grain.

Dissection of three quantitative trait loci for grain size on the long arm of chromosome 10 in rice (Oryza sativa L.)

Background

Thousand grain weight is a key component of grain yield in rice, and a trait closely related to grain length (GL) and grain width (GW) that are important traits for grain quality. Causal genes for 16 quantitative trait loci (QTL) affecting these traits have been cloned, but more QTL remain to be characterized for establishing a genetic regulating network. A QTL controlling grain size in rice, qGS10, was previously mapped in the interval RM6100–RM228 on chromosome 10. This study aimed to delimitate this QTL to a more precise location.

Method

A total of 12 populations were used. The ZC9 population comprised 203 S_1:2 families derived from a residual heterozygous (RH) plant in the F₉ generation of the indica rice cross Teqing (TQ)/IRBB52, segregating the upper region of RM6100–RM228 and three more regions on chromosomes 1, 9, and 11. The Ti52-1 population comprised 171 S₁ plants derived from one RH plant in F₇ of TQ/IRBB52, segregating a single interval that was in the lower portion of RM6100–RM228. The other ten populations were all derived from Ti52-1, including five S₁ populations with sequential segregating regions covering the target region and five near isogenic line (NIL) populations maintaining the same segregating pattern. QTL analysis for 1,000-grain weight, GL, and GW was performed using QTL IciMapping and SAS procedure GLM.

Result

Three QTL were separated in the original qGS10 region. The qGL10.1 was located in the upper region RM6704–RM3773, shown to affect GL only. The qGS10.1 was located within a 207.1-kb interval flanked by InDel markers Te20811 and Te21018, having a stable and relatively high effect on all the three traits analyzed. The qGS10.2 was located within a 1.2-Mb interval flanked by simple sequence repeat markers RM3123 and RM6673. This QTL also affected all the three traits but the effect was inconsistent across different experiments. QTL for grain size were also detected in all the other three segregating regions.

Conclusion

Three QTL for grain size that were tightly linked on the long arm of chromosome 10 of rice were separated using NIL populations with sequential segregating regions. One of them, qGS10.1, had a stable and relatively high effect on grain weight, GL, and GW, providing a good candidate for gene cloning. Another QTL, qGS10.2, had a significant effect on all the three traits but the effect was inconsistent across different experiments, providing an example of genotype-by-environmental interaction.

Importance of the Interaction between Heading Date Genes Hd1 and Ghd7 for Controlling Yield Traits in Rice

Appropriate flowering time is crucial for successful grain production, which relies on not only the action of individual heading date genes, but also the gene-by-gene interactions. In this study, influences of interaction between Hd1 and Ghd7 on flowering time and yield traits were analyzed using near isogenic lines derived from a cross between indica rice cultivars ZS97 and MY46. In the non-functional ghd7^ZS97 background, the functional Hd1^ZS97 allele promoted flowering under both the natural short-day (NSD) conditions and natural long-day (NLD) conditions. In the functional Ghd7^MY46 background, Hd1^ZS97 remained to promote flowering under NSD conditions, but repressed flowering under NLD conditions. For Ghd7, the functional Ghd7^MY46 allele repressed flowering under both conditions, which was enhanced in the functional Hd1^ZS97 background under NLD conditions. With delayed flowering, spikelet number and grain weight increased under both conditions, but spikelet fertility and panicle number fluctuated. Rice lines carrying non-functional hd1^MY46 and functional Ghd7^MY46 alleles had the highest grain yield under both conditions. These results indicate that longer growth duration for a larger use of available temperature and light does not always result in higher grain production. An optimum heading date gene combination needs to be carefully selected for maximizing grain yield in rice.

Dissection and fine-mapping of two QTL for grain size linked in a 460-kb region on chromosome 1 of rice

BACKGROUND

Grain size is a key determinant of grain weight and a trait having critical influence on grain quality in rice. While increasing evidences are shown for the importance of minor-effect QTL in controlling complex traits, the attention has not been given to grain size until recently. In previous studies, five QTL having small effects for grain size were resolved on the long arm of chromosome 1 using populations derived from indica rice cross Zhenshan 97///Zhenshan 97//Zhenshan 97/Milyang 46. One of them, qTGW1.2c that was located in a 2.1-Mb region, was targeted for fine-mapping in the present study.

RESULTS

Firstly, the qTGW1.2c region was narrowed down into 1.1 Mb by determining genotypes of the cross-over regions using polymorphic markers newly developed. Then, one BC₂F₉ plant that was only heterozygous in the updated QTL region was identified. A total of 12 populations in generations from BC₂F_11:12 to BC₂F_15:16 were derived and used for QTL mapping. Two QTL linked in a 460-kb region were separated. The qGS1-35.2 was delimited into a 57.7-kb region, containing six annotated genes of which five showed nucleotide polymorphisms between the two parental lines. Quantitative real-time PCR detected expression differences between near isogenic lines for qGS1-35.2 at three of the six annotated genes. This QTL affected grain length and width with opposite allelic directions, exhibiting significant effect on ratio of grain length to width but showing little influence on yield traits. The other QTL, qGW1-35.5, was located within a 125.5-kb region and found to primarily control grain width and consequently affect grain weight.

CONCLUSIONS

Our work lays a foundation for cloning of two minor QTL for grain size that have potential application in rice breeding. The qGS1-35.2 could be used to modify grain appearance quality without yield penalty because it affects grain shape but hardly influences grain yield, while qGW1-35.5 offers a new gene recourse for enhancing grain yield since it contributes to grain size and grain weight simultaneously.

Natural variation at qHd1 affects heading date acceleration at high temperatures with pleiotropism for yield traits in rice

BACKGROUND

Rice is highly sensitive to temperature fluctuations. Recently, the frequent occurrence of high temperature stress has heavily influenced rice production. Proper heading date in specific environmental conditions could ensure high grain yield. Rice heading greatly depends on the accurate measurement of environmental changes, particularly in day length and temperature. In contrary to the detailed understanding of the photoperiod pathway, little has been known about how temperature regulates the genetic control of rice heading.

RESULTS

Near isogenic lines that were segregated for qHd1, were developed from a cross between indica rice varieties Zhenshan 97 (ZS97) and Milyang 46 (MY46). Using a five sowing-date experiment in the paddy field, we observed the involvement of qHd1 in temperature responses. With the gradual increase of temperature from Trial I to V, heading date of MY46 homozygotes continued to decrease for about 5 d per trial from 76 to 58 d, while that of ZS97 homozygotes was promoted at the same rate from Trial I to III and then stabilized at 69 d. This thermal response was confirmed in a temperature-gradient experiment conducted in the phytotron. It is also found that tolerance of the ZS97 allele to heading acceleration at high temperature was associated with higher grain weight that resulted in higher grain yield. Then, by qRT-PCR and RNA-seq, we found the pathway OsMADS51-Ehd1-RFT1/Hd3a underlying the qHd1-mediated floral response to temperature. By sequence comparison, OsMADS51 for qHd1 displayed a 9.5-kb insertion in the 1st intron of the ZS97 allele compared to the MY46 allele. Furthermore, this large insertion is commonly found in major early-season indica rice varieties, but not in the middle- and late-season ones, which corresponds to the requirement for high-temperature tolerance during the heading and grain-filling stages of early-season rice.

CONCLUSIONS

Beneficial alleles at qHd1 confer tolerance to high temperatures at the heading and grain-filling stages, playing a significant role in the eco-geographical adaptation of early-season indica rice during modern breeding. These results, together with the underlying OsMADS51-Ehd1-RFT1/Hd3a floral pathway, provide valuable information for better understanding the molecular mechanism of temperature responsive regulation of heading date and yield traits in rice.

Assessment and genetic analysis of heavy metal content in rice grain using an Oryza sativa × O. rufipogon backcross inbred line population

BACKGROUND

Heavy metal accumulation in rice is a growing concern for public health. Backcross inbred lines derived from an interspecific cross of Oryza sativa × O. rufipogon were grown in two distinct ecological locations (Hangzhou and Lingshui, China). The objective of this study was to characterise the contents of heavy metal in rice grains, and to identify quantitative trait loci (QTLs) for heavy metal contents.

RESULTS

The contents of Ni, As, Pb, Cr and Hg in milled rice showed a significant decline as compared with those in brown rice, whereas the content of Cd showed little change. The concentration of heavy metal in rice grain varied greatly between the two environments. A total of 24 QTLs responsible for heavy metal contents were detected, including two for both the brown and milled rice, 13 for brown rice only, and nine for milled rice only. All the QTLs except two had the enhancing alleles derived from O. rufipogon. Sixteen QTLs were clustered in six chromosomal regions.

CONCLUSION

Environmental variation plays an important role in the heavy metal contents in rice grain. QTLs detected in this study might be useful for breeding rice varieties with low heavy metal content. © 2017 Society of Chemical Industry.

Effects of Hd2 in the presence of the photoperiod-insensitive functional allele of Hd1 in rice

The role of photoperiod sensitivity (PS) of flowering genes have become well recognized in rice, whereas little attention has been drawn to the non-PS component of these genes, especially to their influence on gene-by-gene interactions. Rice populations in which the photoperiod-sensitive allele at Hd1 has become insensitive to photoperiod but continued to affect heading date (HD) were used in this study to fine-map a quantitative trait locus (QTL) for HD and analyze its genetic relationship to Hd1. The QTL was delimitated to a 96.3-kb region on the distal end of the long arm of chromosome 7. Sequence comparison revealed that this QTL is identical to Hd2. In the near-isogenic line (NIL) populations analyzed, Hd1 and Hd2 were shown to be photoperiod insensitive and have pleiotropic effects for HD, plant height and yield traits. The two genes were found to largely act additively in regulating HD and yield traits. The results indicate that non-PS components of flowering genes involved in photoperiod response play an important role in controlling flowering time and grain yield in rice, which should allow breeders to better manipulate pleiotropic genes for balancing adaptability and high-yielding accumulation.

Summary: We show that photoperiod-insensitive components of alleles of Hd1 and Hd2 play an important role in balancing ecological adaptability and high-yield accumulation in rice.

Dissection of the qTGW1.1 region into two tightly-linked minor QTLs having stable effects for grain weight in rice

BACKGROUND

Most agronomical traits of crop species are complex traits controlled by multiple genes and affected by environmental factors. While considerable efforts have been made to fine-map and clone major quantitative trait loci (QTLs) for yield-related traits in rice, it is not until recently that the attention has been paid to minor QTLs. Following previous dissection of QTLs for grain weight and grain size in a 12-Mb interval on the long arm of chromosome 1 in rice, this study targeted at one putative QTL region for a more precise mapping and for analyzing the genotype-by-environment interaction of minor QTLs.

RESULTS

Four BC2F10 plants of the indica rice cross ZS97///ZS97//ZS97/MY46 were selected. They carried overlapped heterozygous segments that jointly covered the entire putative region for qTGW1.1 detected previously. Four sets of near isogenic lines (NILs) were developed from selfing progenies of the four plants. Each NIL set consisted of 32 ZS97 homozygous lines and 32 MY46 homozygous lines that differed in the corresponding heterozygous region. They were grown in two locations having distinct ecological conditions and measured for 1000-grain weight, grain length and grain width. Two QTLs were separated in an 835.2-kb interval flanked by DNA markers Wn28447 and RM11569. They both showed consistent effects across the two environments. The qTGW1.1a located within the 120.4-kb interval Wn28447 - RM11543 significantly affect all the three traits with the enhancing allele derived from ZS97, showing a stronger influence on grain weight than on grain length and width. The qTGW1.1b located in the 521.8-kb interval RM11554 - RM11569 significantly affect grain weight and length with the enhancing allele derived from MY46, having a stronger influence on grain length than on grain weight. Consistent performance of the two QTLs was confirmed in a validation experiment using five NIL-F2 populations segregated for either qTGW1.1a or qTGW1.1b.

CONCLUSION

Separation of closely-linked QTLs having small effects is achievable in the absence of major-QTL segregation. Minor QTLs for complex traits could act consistently in diverse environments, offering the potential of pyramiding beneficial alleles of multiple minor QTLs through marker-assisted selection.

Mapping of Quantitative Trait Loci for Contents of Macro- and Microelements in Milled Rice (Oryza sativa L.)

Macro- and microelement contents are important traits for nutritional quality in rice. In this study, quantitative trait loci (QTLs) for the contents of seven mineral elements in milled rice were detected using recombinant inbred lines (RILs) of the indica rice cross Zhenshan 97/Milyang 46, followed by the validation and fine mapping of a QTL region on the short arm of chromosome 6. A total of 20 QTLs distributed on chromosomes 1, 3, 5, 6, 10, and 11 were detected in the RIL population. Co-localizations of QTLs for multiple traits were observed, of which the qP3/qMg3/qZn3 region was shown to have the largest effects for the contents of phosphorus, magnesium, and zinc, and the qK6.1/qCa6/qZn6/qMn6/qCu6 region was found to be responsible for five of the seven traits. Using near isogenic lines having sequential segregating region, the target QTL on chromosome 6 was delimitated to a 29.9 kb region flanked by RM19410 and Si2944. This QTL showed major effects for all seven traits, with the enhancing alleles derived from the male parent Milyang 46.

Genome-wide polymorphisms between the parents of an elite hybrid rice and the development of a novel set of PCR-based InDel markers

Genome-wide re-sequencing of the Zhenshan 97 (ZS97) and Milyang 46 (MY46) parents of an elite three-line hybrid rice developed in China resulted in the generation of 9.91 G bases of data with an effective sequencing depth of 11.66x and 11.51x, respectively. Detection of genome-wide DNA polymorphisms, single nucleotide polymorphisms (SNPs), short insertions/deletions (InDels; 1-5 bp), and structural variations (SVs), which is an invaluable variation resource for genetic research and molecular marker-assisted breeding, was conducted by comparing whole-genome re-sequencing data. A total of 364,488 SNPs, 61,181 InDels and 6298 SVs were detected in ZS97 and 364,179 SNPs, 61,984 InDels and 6408 SVs were detected in MY46 compared to the 9311 reference sequence. Synteny analysis of the variation revealed a total of 77,013 identical and 181,737 different SNPs and 15,021 identical and 1205 different InDels between ZS97 and MY46, respectively. A total of 180 InDels 3-8 bp in length between ZS97 and MY46 were selected for experimental validation; 160 polymerase chain reaction products were efficiently separated on 6% non-denaturing polyacrylamide gels. Identification of genome-wide variation among the parents of the elite hybrid as well as the set of 160 polymerase chain reaction-based InDel markers will facilitate future genetic studies and the molecular breeding of hybrid rice.

Fine mapping of qHd1, a minor heading date QTL with pleiotropism for yield traits in rice (Oryza sativa L.)

A minor QTL for heading date located on the long arm of rice chromosome 1 was delimitated to a 95.0-kb region using near isogenic lines with sequential segregating regions. Heading date and grain yield are two key factors determining the commercial potential of a rice variety. In this study, rice populations with sequential segregating regions were developed and used for mapping a minor QTL for heading date, qHd1. A total of 18 populations in six advanced generations through BC2F6 to BC2F11 were derived from a single BC2F3 plant of the indica rice cross Zhenshan 97 (ZS97)///ZS97//ZS97/Milyang 46. The QTL was delimitated to a 95.0-kb region flanked by RM12102 and RM12108 in the terminal region of the long arm of chromosome 1. Results also showed that qHd1 was not involved in the photoperiodic response, having an additive effect ranging from 2.4 d to 2.9 d observed in near isogenic lines grown in the paddy field and under the controlled conditions of either short day or long day. The QTL had pleiotropic effects on yield traits, with the ZS97 allele delaying heading and increasing the number of spikelets per panicle, the number of grains per panicle and grain yield per plant. The candidate region contains ten annotated genes including two genes with functional information related to the control of heading date. These results lay a foundation for the cloning of qHd1. In addition, this kind of minor QTLs could be of great significance in rice breeding for allowing minor adjustment of heading date and yield traits.

Pleiotropism of the photoperiod-insensitive allele of Hd1 on heading date, plant height and yield traits in rice

Five populations segregated in isogenic backgrounds and three sets of near isogenic lines (NILs) overlapping in a 362.3-kb region covering heading date gene Hd1 were developed from the indica rice cross Zhenshan97 (ZS97)/Milyang 46 (MY46). They were used to analyze the effects of Hd1 on heading date, plant height and yield traits. In a background of the parental mixtures, the photoperiod-sensitive allele derived from ZS97 functioned in promoting and delaying flowering in the natural short-day and long-day conditions, respectively. In the background of ZS97, no response to the photoperiod was observed, whereas the photoperiod-insensitive allele derived from MY46 functioned in delaying flowering, increasing plant height, and enhancing grain productivity. The additive effects estimated in two NIL sets were 6.14 and 6.14 d for heading date, 4.46 and 5.55 cm for plant height, 10.82 and 11.54 for the number of spikelets per panicle, 6.82 and 8.00 for the number of grains per panicle, and 2.16 and 2.23 g for grain yield per plant, which explained 94.1% and 96.3%, 70.5% and 84.8%, 52.4% and 55.2%, 28.9% and 39.2%, and 36.5% and 26.9% of the phenotypic variances, respectively. Since the photoperiod-insensitive allele of Hd1 confers a long vegetative phase, it is a good candidate for breeding rice varieties with high yielding potential for low latitudes.

Validation and dissection of quantitative trait loci for leaf traits in interval RM4923-RM402 on the short arm of rice chromosome 6

Validation and dissection of a QTL region for leaf traits in rice which has been reported in a number of independent studies were conducted. Three sets of near isogenic lines (NILs) were originated from a residual heterozygous line derived the indica cross Zhenshan 97B/Milyang 46. They were overlapping and totally covered a 4.2-Mb heterogenous region extending from RM4923 to RM402 on the short arm of rice chromosome 6. Each NIL set consisted of 10 maternal lines and 10 paternal lines. They were measured for the length, width, perimeter and area of the top three leaves and the number of spikelets per panicle, number of grains per panicle and grain weight per panicle. In NIL sets 6-4 and 6-7, differing in intervals RM4923-RM225 and RM19410-RM6119, respectively, significant variations with the enhancing alleles from the female parent ZS97 were shown for the length, perimeter and area except for the area of the third leaf from top in 6-4, but the effects were lower in 6-4 than in 6-7. No significant effects were detected for the three traits in the remaining NIL set. It was shown that flag leaf length (FLL) is the primary target of the QTLs detected. Two QTLs for FLL linked in repulsion phase were resolved, of which qFLL6.2 located in the 1.19-Mb interval RM3414-RM6917 had a major effect with the enhancing allele from Zhenshan 97B, and qFLL6.1 located in the 946.8-kb interval RM19350-RM19410 had a smaller effect with the enhancing allele from Milyang 46. The two QTLs also exerted pleiotropic effects on the yield traits.

Progress in research and development on hybrid rice: a super-domesticate in China

BACKGROUND

China has been successful in breeding hybrid rice strains, but is now facing challenges to develop new hybrids with high-yielding potential, better grain quality, and tolerance to biotic and abiotic stresses. This paper reviews the most significant advances in hybrid rice breeding in China, and presents a recent study on fine-mapping quantitative trait loci (QTLs) for yield traits.

SCOPE

By exploiting new types of male sterility, hybrid rice production in China has become more diversified. The use of inter-subspecies crosses has made an additional contribution to broadening the genetic diversity of hybrid rice and played an important role in the breeding of super rice hybrids in China. With the development and application of indica-inclined and japonica-inclined parental lines, new rice hybrids with super high-yielding potential have been developed and are being grown on a large scale. DNA markers for subspecies differentiation have been identified and applied, and marker-assisted selection performed for the development of restorer lines carrying disease resistance genes. The genetic basis of heterosis in highly heterotic hybrids has been studied, but data from these studies are insufficient to draw sound conclusions. In a QTL study using stepwise residual heterozygous lines, two linked intervals harbouring QTLs for yield traits were resolved, one of which was delimited to a 125-kb region.

CONCLUSIONS

Advances in rice genomic research have shed new light on the genetic study and germplasm utilization in rice. Molecular marker-assisted selection is a powerful tool to increase breeding efficiency, but much work remains to be done before this technique can be extended from major genes to QTLs.

Isolation and Characterization of Defense Response Genes Involved in Neck Blast Resistance of Rice

Two cDNA libraries enriched for transcripts differentially expressed in plants of two rice lines with similar genetic backgrounds and same leaf blast resistance but different responses to neck blast using suppression subtractive hybridization (SSH). After differential screening and sequence analysis of the selected clones, 90 unique cDNA clones were found, of which 74 clones were with known functions according to the putative functions of their homologous genes in the database. They may be involved in pathogen response, signal transduction, transcription, etc. Expression differences of 17 out of the 26 selected cDNA clones in resistant and susceptible lines were confirmed by RT-PCR. Expression profilings of the 26 cDNA clones at the early stages after inoculation were also revealed by RT-PCR. This is the first report on the rice neck blast resistance at mRNA level and will facilitate the further study of genetic mechanism of neck blast resistance.

[Genetic analysis of starch branching enzyme activity in rice grain]

To make an genetic analysis of starch branching enzyme (Q enzyme) inheritance, which is important in catalyzing the formation of amylopectin and thereby raising the amylopectin/amylose ratio of starch in rice grains, a linkage map of 207 DNA markers were constructed by using 247 recombinant inbred lines derived from an indica-indica rice cross Zhenshan 97B/Milyang46. In 2002 and 2003, the activities of starch branching enzyme of the parents and 247 RILs were measured 10 d and 20 d respectively after flowering (Table 1). A total of 3 quantitative trait loci (QTLs) were detected to have significant additive effects on Q enzyme activities 10 d after flowering with 10% phenotypic variations explained for the three QTLs (Table 2, Fig.1). Meanwhile, qQ10-6 with significant QTL x environment interaction was detected. Epistasis analysis detected 5 and 2 significant additive-by-additive interactions for Q enzyme 10 d and 20 d respectively after flowering (Table 3), and three pairs of QTLs 10 d after flowering with significant epistasis x environment interactions were detected, explaining 3% to 12% of the phenotypic variation. The results showed that the environmental factors had obvious effect on the gene expression of Q enzyme activity in rice grain. Meanwhile, the location of qQ10-6 in relation to that of QTLs for gelatinization temperature, gene loci involved in ADPG pyrophosphorylase and soluble starch synthase were discussed with the help of a genetic map.

[QTL mapping and interaction analysis of genotype x environment (Fe2+ -concentrations ) for mesocotyl length in rice (Oryza sativa L.)]

A recombinant inbred lines (RILs) population derived from a cross between Zhenshan97B and Miyang46 was used for detecting QTLs with additive effects and additive-by-additive epistasis for rice mesocotyl length. A linkage map consisting of 207 DNA markers,distributing on the 12 chromosomes of rice,was employed for QTL mapping by using software QTL Mapper 1.6 of mixed linear model. Rice mesocotyl length under germination conditions with 4 different FeSO4 concentrations (0, 1.79, 7.16, 14.32 mmol/L) was measured 7 days after planting. A total of 6 QTLs with significant additive effects on chromosome 1, 5 and 9, with variance explained of 3.5%-11.4%, eleven QTLs with significant additive x additive epistatic effects on chromosome 1, 2, 3, 4, 5, 8 were detected, with variance explained of 4.5%-8.1%. In addition, one QTL for environmental interaction (Fe2+ -concentrations) was detected.

Genetic dissections of partial resistances to leaf and neck blast in rice (Oryza sativa L.)

In a recombinant inbred line (RIL) population of indica rice, two subpopulations composed of susceptible lines were selected for mapping of partial resistance to leaf blast with two isolates of the pathogen. A third subpopulation composed of susceptible lines with similar heading time was used for mapping of partial resistance to neck blast with a third isolate. The traits measured for partial resistance included diseased leaf area (DLA), lesion size (LS) and lesion number (LN) for leaf blast and lesion length (LL) and conidium amount (CA) for neck blast. A linkage map consisting of 168 DNA markers was constructed by using the whole RIL population. Quantitative trait loci (QTLs) conditioning these traits were determined at one-locus and two-locus levels. Eleven main-effect QTLs and 28 digenic interactions were detected by QTLMapper 1.01 b. Only three QTLs showing main effects were also involved in digenic interactions for the same trait. General contributions of epistatic QTLs of each trait ranged from 16.0% to 51.7%, while those of main-effect QTLs of each trait ranged from 4.7% to 38.8%. The general contributions of main-effect QTLs of most traits were smaller than those of epistatic QTLs, confirming the importance of epistasis as the genetic basis for complex traits. The general contributions of the main and epistatic effects of all QTLs detected for the two traits LL and CA of the partial resistance to neck blast reached 70.6% and 82.6% respectively, which obviously represented a major part of the genetic basis controlling partial resistance to neck blast. The results indicated the necessity for partial resistance mapping to use susceptible subpopulations where the interference of major resistance genes is avoided.

QTL x environment interactions in rice. I. heading date and plant height

One hundred twenty six doubled-haploid (DH) rice lines were evaluated in nine diverse Asian environments to reveal the genetic basis of genotype x environment interactions (GEI) for plant height (PH) and heading date (HD). A subset of lines was also evaluated in four water-limited environments, where the environmental basis of G x E could be more precisely defined. Responses to the environments were resolved into individual QTL x environment interactions using replicated phenotyping and the mixed linear-model approach. A total of 37 main-effect QTLs and 29 epistatic QTLs were identified. On average, these QTLs were detectable in 56% of the environments. When detected in multiple environments, the main effects of most QTLs were consistent in direction but varied considerably in magnitude across environments. Some QTLs had opposite effects in different environments, particularly in water-limited environments, indicating that they responded to the environments differently. Inconsistent QTL detection across environments was due primarily to non- or weak-expression of the QTL, and in part to significant QTL x environment interaction effects in the opposite direction to QTL main effects, and to pronounced epistasis. QTL x environment interactions were trait- and gene-specific. The greater GEI for HD than for PH in rice were reflected by more environment-specific QTLs, greater frequency and magnitude of QTL x environment interaction effects, and more pronounced epistasis for HD than for PH. Our results demonstrated that QTL x environment interaction is an important property of many QTLs, even for highly heritable traits such as height and maturity. Information about QTL x environment interaction is essential if marker-assisted selection is to be applied to the manipulation of quantitative traits.

[QTLs mapping of leaf traits and root vitality in a recombinant inbred line population of rice]

By employing a recombinant inbred line (RIL) population of 247 lines derived from an inidca-indica cross Zhenshan 97B x Milyang 46, a linkage map consisting of 158 DNA markers was constructed and used for the determination of QTLs conditioning five leaf traits and root exudates. The leaf traits analyzed were leaf area, leaf length, leaf width, leaf perimeter and leaf length/width ratio measured on top first leaf, top second and top third leaves. The RIL population showed transgressive segregation on each trait, and highly significant or significant positive correlations were observed between all traits except between leaf length and width, and between leaf perimeter and length/width ratio. A total of 24 QTLs located in 9 intervals were detected to have significant additive effects for leaf traits analyzed, with LOD scores ranging 2.9-11.8 and 4.0%-32.5% phenotypic variation explained for a single QTL. Clustering of QTLs for leaf traits was evident. In interval RM197-RZ516 on chromosome 6, 2 QTLs for leaf length, 2 QTLs for leaf width and 3 QTLs for leaf length/width ratio of different leaves were detected, among which the alleles for increasing trait values were from Zhenshan 97B for leaf length and leaf length/width ratio, and from Milyang 46 for leaf width. In interval RM1-RG532 on chromosome 1,2 QTLs for leaf length and 2 QTLs for leaf perimeter were detected on top first leaf and top second leaf, respectively, and all the alleles for increasing trait values were from Milyang 46. In this interval, larger additive effects were observed for QTLs detected on top first leaf than at top second leaf. In interval RZ667-B10B on chromosome 6, a QTL for leaf perimeter of top second leaf was detected, accounting for 8.0% phenotypic variation. In intervals RZ66-RM264 and RG81-RM313 on chromosome 8 and 12, each QTL was detected for leaf length of top third leaf and explained for 9.0% and 15.3% phenotypic variation, respectively. Epistasis analysis detected 56 and 4 significant additive-by-additive interactions for leaf traits and root vitality, explaining 2.7% to 13.7% and 6.8% to 14.9% of the total phenotypic variation, respectively. On comparison with QTLs for yield traits detected in the same population previously, it was found that the majority of QTLs for leaf traits and root vitality and those for yield traits were located in similar intervals. Fine mapping of QTLs for both leaf and yield traits in these chromosomal regions would facilitate investigations of the source-sink relationship in rice.

Genetic differentiation of wild relatives of rice as assessed by RFLP analysis

To study genetic diversity and relationships of wild relatives of rice, 58 accessions of Oryza rufipogon, Oryza nivara, Oryza sativa f. spontanea and the cultivated Oryza sativa, representing a wide range of their distribution, were analyzed using the restriction fragment length polymorphism (RFLP) technique. All 30-used RFLP probes detected polymorphisms among the Oryza accessions, with an average of 3.8 polymorphic fragments per probe. Considerable genetic diversity was scored among the Oryza accessions with a similarity coefficient ranging from 0.28 to 0.93; but the cluster analysis of the accessions did not show an apparent grouping based on the species classification, instead they were scattered randomly in different groups. Noticeably, the Oryza accessions from the same geographic region, or near-by geographic regions, tended to be clustered in the same groups. The indica rice varieties showed relatively high genetic diversity and were scattered in different groups of their wild relatives, but the japonica varieties showed a relatively low variation and formed an independent group. It is concluded from the molecular analytical result that: (1) the four Oryza taxa have a remarkably close relationship and their independent species status need to be carefully reviewed; (2) geographic isolation has played a significant role in the differentiation of the Oryza accessions; therefore, a wide geographic range needs to be covered in collecting wild rice germplasm for ex situ conservation; and (3) the conventional conclusion of indica rice being directly domesticated from its ancestral wild species, and japonica rice being derived from indica, gains support from our data.

[Analysis of gene expression profiles during host-Magnaporthe grisea interactions in a pair of near isogenic lines of rice]

A pair of near isogenic lines G205 and G71 were selected from recombinant inbred lines (RIL) of Zhong156 x Gumei2. On the resistance locus Pi-25(t), G205 had the resistant allele that was from Gumei 2 while G71 had the susceptible allele that was from Zhong156. For the genetic background, different alleles were detected on only 24 loci out of the 672 RFLP or SSLP loci surveyed. The expression profiles of G205 and G71 in response to Magnaporthe grisea were investigated using cDNA microarray containing 2200 Expression Sequence Tags (ESTs). The leaves were inoculated with the pathogen for 12 hours at 4-leaf stage and 998 genes were identified in total. Three genes were up-regulated significantly by the fungus in G205 only. The functions of two genes were known but that of the third gene were unknown. The two genes encoded casein kinase II alpha subunit and retrotransponson TOS17 insertion element respectively. Other thirty-five genes had similar expression patterns between NILs. Among them, 17 genes were up-regulated while 18 genes were down-regulated by the inoculation. The functions of 33 out of the 35 genes were known. BLAST analysis showed that all thirty-five. BLAST analysis showed that all thirty-five genes with known functions were relative to defense reactions, signal transduction, stress response, photosynthesis and sugar metabolism. Northern blot confirmed that four of five differentially displayed genes randomly selected had the same expression patterns as those detected in cDNA microarray. Two of them were up-regulated genes encoding casein kinase II alpha subunit and glycine-rich protein (Grp), and the other two down-regulated genes encoding nitrilase-associated protein and 18S small subnit ribosomal RNA gene respectively. Northern blot also revealed that the expression of Grp was consistently up-regulated from 0 to 36 h after the inoculation of the fungus. These results showed that cDNA microarray was a useful tool to study the molecular mechanisms of disease resistance in plants.

[Mapping of fertility-restoring genes with main effects and epistatic effects for CMS-DA in rice]

A test-cross population was established for mapping genes conditioning fertility restoration for dwarf-wild-abortive cytoplasmic male sterility(CMS-DA) in rice. A recombinant inbred line(RIL) population consisting of 210 lines was derived from the cross Xieqingzao B/Miyang 46, in which Xieqingzao B is the maintainer line of CMS-DA Xieqingzao A, and Miyang 46 is the restorer line. Each of the RILs was crossed to Xieqingzao A, and the resulting F1s were used for phenotyping of the spikelet fertility in 1999 and 2000. A linkage map consisting of 129 RFLP and SSLP markers was constructed. QTLs having significant main effects and/or epistatic effects for spikelet fertility were determined with QTLMAPPER 1.0 of mixed linear model. Background genetic variation due to main and epistatic effects of important markers was controlled. Four QTLs having significant main effects for fertility restoration were detected. A major gene qRf-10-2 was located in interval RM258-RZ811 on the long arm of chromosome 10, and QTL qRf-1 displaying a moderate main effect was located in a position close to RG532 on chromosome 1. Two other QTLs were located on chromosome 5 (qRF-5) and the short arm of chromosome 10 (qRf-10-1), in which the main effect of qRf-5 bacame significant only in the absence of qRf-10-2. A significant digenic interaction was detected, which occurred between QTLs qRf-1 and qRf-5. No significant QTL by environmental interactions and epistasis by environmental interactions were detected. Analyses on the gene effects based on markers closest to the Rf genes were made, and multi-locus interactions were implied. The present results were also compared to a previous study on mapping fertility restoration genes in Milyang 46 for wild-abortive CMS Zhenshan 97A, and to other published reports. It was indicated that differences on the genetic control of fertility restoration among different rice populations were mainly attributed to variations on genes with minor main effects and epistatic effects.

[Propagation of hepatitis E virus in several cell lines including human embryo lung diploid cell KMB17]

OBJECTIVE

To investigate the hepatitis E virus (HEV) sensitive cells and its tissue culture conditions.

METHODS

The HEV from dejecta supernatant of patients with acute hepatitis E was amplified and activated by passaged in Rhesus. Then, the positive dejecta samples of infected monkeys were dealt with super-centrifugation and virus for culture was obtained. Various human-derived (including KMB17, A549, BEL7402, and Hela) and non-human primates derived cells (Vero) were inoculated with HEV. Sensitivity of cells to HEV was measured by CPE (cytopathic effect), RT-PCR and immunofluorescence.

RESULTS

CPE in KMB17, A549 and BEL7402 cells appeared during 7-9 days, meanwhile, cells shelled during 11-13 days on the first filial generation. The existence of HEV genome +RNA and replicated -RNA was still detectable by RT-PCR after the tenth filial generation. Neither CPE nor amplification of HEV genome RNA could be detected in Hela and Vero cells after the second to fourth filial generation. HEV could also be detected from inoculated KMB17 cells by immunofluorescence and RT-PCR.

CONCLUSIONS

It indicates that KMB17, A549 and BEL7402 cells are sensitive to HEV under the experimental culture conditions, while Hela and Vero cells are insensitive. Tissue culture system of HEV in certain filial generation is established.

[Purification and immunological characterization of hepatitis E virus recombinant chimeric antigen encoded by ORF2 fragments and ORF3]

OBJECTIVE

To study immunological characteristics of recombinant chimeric HEV antigen.

METHODS

Constructed recombinant plasmids pThioHisORF(2.1 + 2.2 + 3), which contains three HEV antigen gene fragments (ORF2.1:6287-6403nt, ORF2.2:6743-7126nt, ORF3), was transformed into E. coli and induced with IPTG. Expressed product P(2.1 + 2.2 + 3) existed in inclusion bodies, was purified by denature SP Sepharose FF cation exchange chromatography. Rabbits and rats were immunized with renatured P(2.1 + 2.2 + 3). The level of IgG in sera from experimental animals and clinical patients were examined with P(2.1 + 2.2 + 3) by ELISA. The characteristics of IgG of immunized animals interacted with recombinant antigen expressed by baculovirus system as well as recombinant chimeric antigen interacted with clinical patients sera were evaluated by Western-blotting.

RESULTS

High titer of IgG antibodies, 1:25,600 in rabbits and 1:12,800 in rats, were detected after immunized with P(2.1 + 2.2 + 3). Furthermore, recombinant antigen expressed by baculovirus system was specifically recognized by IgG of experimental animal immunized with P(2.1 + 2.2 + 3), and the purified recombinant chimeric antigen P(2.1 + 2.2 + 3) was specifically reacted with the IgG of clinical patients.

CONCLUSIONS

Recombinant chimeric antigen appears a promising strategy for detection of and prevention from HEV infection.

[Expression of hepatitis E virus ORF3 gene fragment in baculovirus system and its immunological character]

OBJECTIVE

To express hepatitis E virus (HEV) ORF3 protein by baculovirus system and provide basis for immunological character research.

METHODS

Hepatitis E Virus ORF3 gene fragment was obtained by RT-PCR, ligated with vector pThioHisA for sequencing and then inserted into transfected vector pVL1393 to construct recombinant plasmid. Mediated by Lipofectin Reagent, the recombinant vector and baculovirus linearized DNA (BaculoGold) co-transfected insect cell Sf9 to make recombinant baculovirus. Expressed ORF3 was analyzed for its immunological character by Western blotting, and immunized Kunming Mice.

RESULTS

Recombinant ORF3 protein could be recognized by the known positive serum and promoted organism to produce HEV-specific antibody.

CONCLUSIONS

Recombinant baculovirus can express effectively HEV ORF3, which has HEV specific immunogenic character.

[Comparison of the detection of QTL for yield traits in different generations of a rice cross using two mapping approaches]

In the F2 and recombinant inbred populations of Zhenshan 97B/Milyang 46, RFLP linkage maps were constructed to detect QTL for yield and its component traits. Results indicated that QTL having substantial additive effects were generally detected in both F2 and recombinant inbred populations. In addition, the trait performances were measured either based on a single plant or on replicated trials in the recombinant inbred population hardly affected the detection of QTL of higher effects.

[Mapping genes for rice CMS-WA fertility restoration]

In a population consisting of 227 test-crosses of Zhenshan 97A x (Zhenshan 97B x Milyang 46) F6, a linkage map of 115 RFLP markers was constructed and employed to detect QTL for rice CMS-WA (wild abortive cytoplasmic male sterility) fertility restoration. One QTL having major effect, qRf-10, and 3 QTL having minor effects, qRf-1, qRf-7 and qRf-11, were detected. The four genes mainly acted additively with each other, but epistasis was also evident. Two minor QTL, qRf-1 and qRf-11, were significantly interacted with the major gene qRf-10. It was also found that interaction effects among minor QTL varied greatly depending on whether qRf-10 was present. Two other QTL, qSF-1 and qSF-7, were detected, which did not display any effects on fertility restoration. Instead, they showed effects for increasing SF when qRf-10 was present.

Identifying different types of de-differentiated microspores from indica-japonica F(1) hybrids with subspecies-differentiating RFLP probes in rice

The indica, japonica and intermediary types of de-differentiated microspores from indica-japonica F(1) hybrids were identified with 11 subspecies-differentiating RELP probes in rice (Oryza sativa L.). The results showed that the distribution of indica, japonica and intermediary types of de-differentiated microspores could be easily detected in a simple and quick way using the RFLP method. Moreover, the microspores from the same F(1) hybrid but inoculated onto different media, or microspores from different F(1) hybrids when inoculated onto the same medium, often displayed distinctive distribution curves of de-differentiated microspores types, indicating that the media employed in this experiment had high selectivity for the de-differentiation of certain types of microspores. The application of the RELP method to de-differentiated microspore identification is of great theoretical and practical significance in rice doubled-haploid breeding.

RFLP mapping of QTLs for yield and related characters in rice (Oryza sativa L.)

Quantitative triat loci (QTLs) for yield and related traits in rice were mapped based on RFLP maps from two indica/indica F2 populations, Tesanai 2/CB and Waiyin 2/CB. In Tesanai 2/CB, 14 intervals carrying QTLs for eight traits were detected, including 3 for grain weight per plant (GWT), 2 for number of panicles per plant (NP), 2 for number of grains per panicle (NG), 1 for total number of spikelets per panicle (TNS), 1 for spikelet fertility (SF), 3 for 1000-grain weight (TGWT), 1 for spikelet density (SD), and 1 for number of first branches per main panicle. The 3 QTLs for GWT were located on chromosomes 1, 2, and 4, with 1 in each chromosome. The additive effect of the single locus ranged from 2.0 g to 9.1 g. A major gene (np4) for NP was detected on chromosome 4 within the interval of RG143-RG214, about 4cM for RG143, and this locus explained 26.1% of the observed phenotypic variance for NP. The paternal allele of this locus was responsible for reduced panicles per plant (3 panicles per plant). In another population, Waiyin 2/CB, 12 intervals containing QTLs for six of the above-mentioned traits were detected, including 3 for GWT, 2 for each of NP, TNS, TGWT and SD, 1 for SF. Three QTLs for GWT were located on chromosome 1, 4, and 5, respectively. The additive effect of the single locus for GWT ranged from 6.7 g to 8.8 g, while the dominance effect was 1.7-11.5 g. QTL mapping in two populations with a common male parent is compared and discussed.

Identification of a set of RFLP probes for subspecies differentiation in Oryza sativa L

Sixty-eight indica-japonica tester-differentiating RFLP probes were tested in seven indica and seven japonica varieties of rice (Oryza sativa L.) with four enzyme digestions (EcoRI, EcoRV, HindIII and DraI). Twenty-one DNA clones were isolated as indica-japonica subspecies-differentiating probes. A set of 13 probes was established as core probes for subspecies differentiation and a pooled blotting analysis was carried out to facilitate the application of RFLP in rice genetics and breeding practice. A dendrogram of 12 wide-compatibility varieties was constructed based on RFLPs detected by 13 core probes with single enzyme digestions. It was speculated that most RFLPs of indica-japonica differentiating probes were generated by insertions/deletions, which may be of great significance for the origin and differentiation of subspecies in Oryza sativa L.

Gerchberg-Saxton and Yang-Gu algorithms for phase retrieval in a nonunitary transform system: a comparison

A detailed comparison of the original Gerchberg-Saxton and the Yang-Gu algorithms for the reconstruction of model images from two intensity measurements in a nonunitary transform system is presented. The Yang-Gu algorithm is a generalization of the Gerchberg-Saxton algorithm and is effective in solving the general amplitude-phase-retrieval problem in any linear unitary or nonunitary transform system. For a unitary transform system the Yang-Gu algorithm is identical to the Gerchberg-Saxton algorithm. The reconstruction of images from data corrupted with random noise is also investigated. The simulation results show that the Yang-Gu algorithm is relatively insensitive to the presence of noise in data. In all cases studied the Yang-Gu algorithm always resulted in a highly accurate recovered phase.

Iterative interlacing approach for synthesis of computer-generated holograms

An approach for optimizing computer-generated holograms is discussed. The approach can be summarized most generally as hierarchically designing a number of holograms to add up coherently to a single desired reconstruction. In the case of binary holograms, this approach results in the interlacing technique (IT) and the iterative interlacing technique (IIT). In the IT, a number of subholograms are designed and interlaced together to generate the total binary hologram. The first subhologram is designed to reconstruct the desired image. The succeeding subholograms are designed to correct the remaining error image. In the IIT, the remaining error image after the last subhologram is circulated back to the first subhologram, and the process is continued a number of sweeps until convergence. Both techniques can be used together with most computer-generated-hologram synthesis algorithms and result in a substantial reduction in reconstruction error as well as an increased speed of convergence in the case of iterative algorithms.

Preliminary studies on antigenic variation of poliovirus using neutralizing monoclonal antibodies

Cross-neutralization assays were done using 85 strains of poliovirus type 1 with five groups of monoclonal antibodies. These strains were classified into 10 subgroups which had marked differences in antigenicity. Subgroups P1-2 (28%) and P1-5 (43%) were dominant and have been epidemic in China in recent years. These two subgroups were antigenically different from the Sabin-1 strain, but according to their responses to one group of monoclonal antibodies they had antigenic epitopes in common with the Mahoney and Brunhilde strains. Similarly, 91 strains of type 3 poliovirus were classified into six subgroups with another five groups of monoclonal antibodies. The results showed that strain P3/Yunnan/2/84, which was isolated from cases of poliomyelitis in a local epidemic in the Yunnan province of China in 1984, and strain P3/Finland/23127/84, which was isolated in Finland in 1984, were both antigenically different from the Sabin-3 strain and the reference virulent strain.