Identification of genome-wide variations among three elite restorer lines for hybrid-rice

Rice restorer lines play an important role in three-line hybrid rice production. Previous research based on molecular tagging has suggested that the restorer lines used widely today have narrow genetic backgrounds. However, patterns of genetic variation at a genome-wide scale in these restorer lines remain largely unknown. The present study performed re-sequencing and genome-wide variation analysis of three important representative restorer lines, namely, IR24, MH63, and SH527, using the Solexa sequencing technology. With the genomic sequence of the Indica cultivar 9311 as the reference, the following genetic features were identified: 267,383 single-nucleotide polymorphisms (SNPs), 52,847 insertion/deletion polymorphisms (InDels), and 3,286 structural variations (SVs) in the genome of IR24; 288,764 SNPs, 59,658 InDels, and 3,226 SVs in MH63; and 259,862 SNPs, 55,500 InDels, and 3,127 SVs in SH527. Variations between samples were also determined by comparative analysis of authentic collections of SNPs, InDels, and SVs, and were functionally annotated. Furthermore, variations in several important genes were also surveyed by alignment analysis in these lines. Our results suggest that genetic variations among these lines, although far lower than those reported in the landrace population, are greater than expected, indicating a complicated genetic basis for the phenotypic diversity of the restorer lines. Identification of genome-wide variation and pattern analysis among the restorer lines will facilitate future genetic studies and the molecular improvement of hybrid rice.     

Genome-wide discovery of DNA polymorphism in Brassica rapa

Single nucleotide polymorphisms (SNPs) and/or insertion/deletions (InDels) are frequent sequence variations in the plant genome, which can be developed as molecular markers for genetic studies on crop improvement. The ongoing Brassica rapa genome sequencing project has generated vast amounts of sequence data useful in genetic research. Here, we report a genome-wide survey of DNA polymorphisms in the B. rapa genome based on the 557 bacterial artificial clone sequences of B. rapa ssp. pekinensis cv. Chiifu. We identified and characterized 21,311 SNPs and 6,753 InDels in the gene space of the B. rapa genome by re-sequencing 1,398 sequence-tagged sites (STSs) in eight genotypes. Comparison of our findings with a B. rapa genetic linkage map confirmed that STS loci were distributed randomly over the B. rapa whole genome. In the 1.4 Mb of aligned sequences, mean nucleotide polymorphism and diversity were θ = 0.00890 and π = 0.00917, respectively. Additionally, the nucleotide diversity in introns was almost three times greater than that in exons, and the frequency of observed InDel was almost 17 times higher in introns than in exons. Information regarding SNPs/InDels obtained here will provide an important resource for genetic studies and breeding programs of B. rapa.     

Genome-wide DNA polymorphisms in elite indica rice inbreds discovered by whole-genome sequencing

Advances in next-generation sequencing technologies have aided discovery of millions of genome-wide DNA polymorphisms, single nucleotide polymorphisms (SNPs) and insertions-deletions (InDels), which are an invaluable resource for marker-assisted breeding. Whole-genome resequencing of six elite indica rice inbreds (three cytoplasmic male sterile and three restorer lines) resulted in the generation of 338?million 75-bp paired-end reads, which provided 85.4% coverage of the Nipponbare genome. A total of 2?819?086 nonredundant DNA polymorphisms including 2?495?052 SNPs, 160?478 insertions and 163?556 deletions were discovered between the inbreds and Nipponbare, providing an average of 6.8 SNPs/kb across the genome. Distribution of SNPs and InDels in the chromosome was nonrandom with SNP-rich and SNP-poor regions being evident across the genome. A contiguous 4.3-Mb region on chromosome 5 with extremely low SNP density was identified. Overall, 83?262 nonsynonymous SNPs spanning 16?379 genes and 3620 nonsynonymous InDels in 2625 genes have been discovered which provide valuable insights into the basis underlying performance of the inbreds and the hybrids between these inbred combinations. SNPs and InDels discovered from this diverse set of indica rice inbreds not only enrich SNP resources for molecular breeding but also enable the study of genome-wide variations on hybrid performance.     

红莲型杂交稻(红莲2号)及其骨干亲本的RAPD分析与鉴定

利用RAPD技术,从248个随机寡核苷酸引物（10－mer）中筛出18个引物对红莲型杂交稻组合红莲2号及其亲本（T－07A、T－07B、YD6－05）,另6个红莲型胞质不育系的骨干恢复和汕优63及其亲本共14份水稻材料进行分析。共检测到173个多态性标记。聚类分析结果表明：不育系与保持系间因核背景相似,遗传差异很小;杂种（F1）的基因型更倾向于恢复系;恢复系与保持系间遗传距离的相对较大,但各恢复系之间的遗传距离较小。利用这些标记能有效地地区交组合中不育系,保持系、恢复系和杂种（F1）。     

Development of genome-wide DNA polymorphism database for map-based cloning of rice genes

DNA polymorphism is the basis to develop molecular markers that are widely used in genetic mapping today. A genome-wide rice (Oryza sativa) DNA polymorphism database has been constructed in this work using the genomes of Nipponbare, a cultivar of japonica, and 93-11, a cultivar of indica. This database contains 1,703,176 single nucleotide polymorphisms (SNPs) and 479,406 Insertion/Deletions (InDels), approximately one SNP every 268 bp and one InDel every 953 bp in rice genome. Both SNPs and InDels in the database were experimentally validated. Of 109 randomly selected SNPs, 107 SNPs (98.2%) are accurate. PCR analysis indicated that 90% (97 of 108) of InDels in the database could be used as molecular markers, and 68% to 89% of the 97 InDel markers have polymorphisms between other indica cultivars (Guang-lu-ai 4 and Long-te-pu B) and japonica cultivars (Zhong-hua 11 and 9522). This suggests that this database can be used not only for Nipponbare and 93-11, but also for other japonica and indica cultivars. While validating InDel polymorphisms in the database, a set of InDel markers with each chromosome 3 to 5 marker was developed. These markers are inexpensive and easy to use, and can be used for any combination of japonica and indica cultivars used in this work. This rice DNA polymorphism database will be a valuable resource and important tool for map-based cloning of rice gene, as well as in other various research on rice (http://shenghuan.shnu.edu.cn/ricemarker).     

Conversion of a rice CMS maintainer into a photo- or thermo-sensitive genetic male sterile line

A maintainer line of 3-line hybrid rice commonly presents a certain genetic distance to a 2-line restorer line, but in many cases, 2-line restorer lines present defects upon recovery of the object cytoplasmic male sterile (CMS) line of the maintainer line, which impedes the utilization of their heterosis. Here, we report a strategy and an example of converting a maintainer into a photoperiod/temperature-sensitive genic male sterile (P/TGMS) line with an almost identical genetic background, thus maximizing the heterosis. Firstly, through treatment of maintainer line T98B with ⁶⁰C_O-γ irradiation, we identified the TGMS line T98S, which is sterile at higher temperatures and fertile at lower temperatures. Secondly, the T98S line was proven to be identical to T98B with regard to genetic background via an examination of 48 parental polymorphous SSR markers and exhibited excellent blossom traits similar to those of T98B, with an extensive forenoon flowering rate of 75.92% and a high exertion rate of 64.59%. Thirdly, in a combination test, three out of six hybrids from T98S crossed with 2-line restorer lines showed a yield increase of 6.70–15.69% for 2 consecutive years. These results demonstrated that the strategy can generate a new P/TGMS line with strong general combining ability (converted from a maintainer line), thus helping to increase the genetic diversity of male sterile heterotic groups.     

Genome-wide DNA polymorphism and transcriptome analysis of an early-maturing rice mutant

In order to develop a rice population with improved important traits such as flowering time, we developed 2,911 M₂ targeting-induced local lesions in genomes (TILLING) lines by irradiating rice seeds with γ-rays. In all, 15 M₃ lines were obtained from 3 different M₂ lines that exhibited an early-maturing phenotype: these plants matured approximately 25 days faster than wild-type (WT) plants. To identify genome-wide DNA polymorphisms, we performed whole-genome resequencing of both the plant types, i.e., WT and early-maturing TILLING 1 (EMT1), and obtained mapped reads of 118,488,245 bp (99.53 %) and 128,489,860 bp (99.72 %), respectively; Nipponbare was used as the reference genome. We obtained 63,648 and 147,728 single nucleotide polymorphisms (SNPs) and 33,474 and 31,082 insertions and deletions (InDels) for the WT and EMT1, respectively. Interestingly, there was a higher number of SNPs (2.6-fold) and slightly lower number of InDels (0.9-fold) in EMT1 than in WT. The expression of at least 202 structurally altered genes was changed in EMT1, and functional enrichment analysis of these genes revealed that their molecular functions were related to flower development. These results might provide a critical insight into the regulatory pathways of rice flowering.     

The Organelle Genomes of Hassawi Rice (Oryza sativa L.) and Its Hybrid in Saudi Arabia: Genome Variation, Rearrangement, and Origins

Hassawi rice (Oryza sativa L.) is a landrace adapted to the climate of Saudi Arabia, characterized by its strong resistance to soil salinity and drought. Using high quality sequencing reads extracted from raw data of a whole genome sequencing project, we assembled both chloroplast (cp) and mitochondrial (mt) genomes of the wild-type Hassawi rice (Hassawi-1) and its dwarf hybrid (Hassawi-2). We discovered 16 InDels (insertions and deletions) but no SNP (single nucleotide polymorphism) is present between the two Hassawi cp genomes. We identified 48 InDels and 26 SNPs in the two Hassawi mt genomes and a new type of sequence variation, termed reverse complementary variation (RCV) in the rice cp genomes. There are two and four RCVs identified in Hassawi-1 when compared to 93-11 (indica) and Nipponbare (japonica), respectively. Microsatellite sequence analysis showed there are more SSRs in the genic regions of both cp and mt genomes in the Hassawi rice than in the other rice varieties. There are also large repeats in the Hassawi mt genomes, with the longest length of 96,168 bp and 96,165 bp in Hassawi-1 and Hassawi-2, respectively. We believe that frequent DNA rearrangement in the Hassawi mt and cp genomes indicate ongoing dynamic processes to reach genetic stability under strong environmental pressures. Based on sequence variation analysis and the breeding history, we suggest that both Hassawi-1 and Hassawi-2 originated from the Indonesian variety Peta since genetic diversity between the two Hassawi cultivars is very low albeit an unknown historic origin of the wild-type Hassawi rice.     

Genome-wide single nucleotide polymorphisms and insertion–deletions of Oryza sativa L. subsp. japonica cultivars grown near the northern limit of rice cultivation

Single nucleotide polymorphisms (SNPs) and insertions–deletions (InDels) are valuable molecular markers for molecular breeding among genetically closely related cultivars. Rice (Oryza sativa L. subsp. japonica) cultivars grown in Hokkaido (45–42°N), the northernmost region of rice paddy cultivation in Japan, have been bred for over 100 years for adaptation to low summer temperatures together with high yield and good eating quality. In this study, for 10 closely related rice cultivars released in Hokkaido and cultivar Koshihikari, we identified genome-wide SNPs and InDels by next-generation sequencing. More than 29 million reads from the Hokkaido cultivars, each 101 nucleotides long, were uniquely mapped to the Nipponbare reference genome. The average of the total nucleotide length of all uniquely mapped reads corresponded to 10.9 times (3,978 Mb with genome coverage of 90.7 %) the Nipponbare reference genome. An average of 99,955 putative SNPs (1.8 times the number in Koshihikari) and 14,617 putative InDels (also 1.8 times the number in Koshihikari) were detected in Hokkaido cultivars relative to the Nipponbare genome, which enabled analyses of the inheritance of pedigree haplotypes of four cultivars, SNPs and InDels among closely related Hokkaido cultivars, and haplotype blocks unique to Hokkaido cultivars. The comprehensive SNP and InDel data provide DNA marker resources and will facilitate quantitative trait locus analysis of biparental mapping of very closely related Hokkaido cultivars. Furthermore, the haplotype blocks unique to Hokkaido cultivars represent ideal genetic regions for improvement of cultivars to be grown near the northern and southern limits of rice cultivation.     

Field Performance of Transgenic indica Hybrid Rice with Improved Cooking and Eating Quality by Down-regulation of Wx Gene Expression

High amylose content (AC) in rice endosperm is correlated with poor grain quality, particularly in indica hybrid rice. We have generated several homozygous transgenic parent lines of indica hybrid rice carrying an antisense Waxy (Wx) gene and demonstrated that the AC in seeds of these lines decreased dramatically. Two transgenic maintainer lines (L25B and L18B), derived from one of the key maintainer parents of an indica hybrid rice in China, Long-te-fu B (LTF-B), were selected and the antisense Wx gene was subsequently introgressed into the male-sterile counterpart, LTF-A, with the aim to generate improved indica hybrids. The indica hybrids derived from the selected transgenic male-sterile lines and restorer lines were tested for quality and agronomic performance under normal field conditions. Our results demonstrated that the reduction of AC in the homozygous transgenic maintainer lines stably passed down in five successive generations and the improved quality was also found in their relevant transgenic hybrids produced. The other two key characters of rice cooking and eating quality, the gel consistence (GC) and gelatinization temperature (GT), were also improved in the grains of both the transgenic maintainer lines and their relevant hybrids. In addition, no change was observed for most of the agronomic characters of the transgenic maintainer lines and the relevant transgenic hybrids. Although the grain weight of the transgenic line was reduced, the grain yield of the homozygous transgenic parent lines and the transgenic hybrids was similar when compared with that of the wild-type controls. These results suggest that transgenic approaches are an effective way to obtain rice lines with both improved qualities and high yield, especially for indica hybrid rice.     

Identification and characterization of nucleotide variations in the genome of Ziziphus jujuba (Rhamnaceae) by next generation sequencing

In this study, single-nucleotide polymorphisms (SNPs) and insertions/deletions (InDels) in the genome of Ziziphus jujuba were identified using sequences generated by the Roche 454 GS-FLX sequencer. A total of, 573,141 reads were produced with an average read length of 360 bp. After quality control, 258,754 of the filtered reads were assembled into 23,864 contigs, and 293,458 remained as singletons. Using the contig assemblies as a reference, 17,160 SNPs and 478 InDels were identified. Among the SNPs, transitions occurred three times more frequently than transversions. In transitions, the number of C/T and G/A transitions was similar. Among the transversions, A/T was the most abundant, and C/G was much rarer than any of the other types of transversions, accounting for only about half the numbers of A/C, A/T and G/T transversions. For the InDels, mononucleotide changes amounted to 64.4 % of the total number of InDels. In general, the frequency of detected InDels decreased as the length of the InDels increased. This study provides valuable marker resources for future genetic studies of Ziziphus spp.     

Evaluation of genetic diversity of parental lines for development of heterotic groups in hybrid rice (Oryza sativa L.)

Knowledge of genetic diversity and potential heterotic relationships among parental lines is of significant importance in hybrid rice breeding programs. In the present study, in order to understand the genetic diversity among 96 parental lines, they were characterized for their diversity with respect to their morphological traits (n?=?12) and molecular markers using a set of 50 SSR markers. Morphological diversity was estimated using Mahalanobis D² statistics in terms of generalized group distance. Based on morphological diversity analysis, the 96 lines were grouped into 5 major and 13 monogenotypic clusters. In molecular marker analysis, the parental lines were consistently clustered into B (Maintainer group) and R (Restorer group) groups based on distance and model based approaches. Strong correspondence was observed between the pedigree of parental lines with molecular genotyping based grouping than morphological trait based grouping. From the results of the present investigation, it is evident that the available diversity among the two groups i.e., maintainer group (B) and restorer group (R) is sufficient for developing heterotic hybrids, but within the maintainer and restorer groups, the diversity is limited, the diversity among restorers was moderate, while it was low among the maintainers and hence efforts are needed for broadening their genetic base of parental lines for development and adoption of high-yielding hybrids.

     

Construction of a genetic map based on high-throughput SNP genotyping and genetic mapping of a TuMV resistance locus in Brassica rapa

Brassica rapa is a member of the Brassicaceae family and includes vegetables and oil crops that are cultivated worldwide. The introduction of durable resistance against turnip mosaic virus (TuMV) into agronomically important cultivars has been a significant challenge for genetic and horticultural breeding studies of B. rapa. Based on our previous genome-wide analysis of DNA polymorphisms between the TuMV-resistant doubled haploid (DH) line VC40 and the TuMV-susceptible DH line SR5, we constructed a core genetic map of the VCS-13M DH population, which is composed of 83 individuals derived from microspore cultures of a F₁ cross between VC40 and SR5, by analyzing the segregation of 314 sequence-characterized genetic markers. The genetic markers correspond to 221 SNPs and 31 InDels of genes as well as 62 SSRs, covering 1,115.9 cM with an average distance of 3.6 cM between the adjacent marker loci. The alignment and orientation of the constructed map showed good agreement with the draft genome sequence of Chiifu, thus providing an efficient strategy to map genic sequences. Using the genetic map, a novel dominant TuMV resistance locus (TuMV-R) in the VCS-13M DH population was identified as a 0.34 Mb region in the short arm of chromosome A6 in which four CC–NBS–LRR resistance genes and two pathogenesis-related-1 genes reside. The genetic map developed in this study can play an important role in the genetic study of TuMV resistance and the molecular breeding of B. rapa.     

Genome-Wide Analysis of Genetic Variations and the Detection of Rich Variants of NBS-LRR Encoding Genes in Common Wild Rice Lines

Common wild rice (Oryza rufipogon Griff.) is invaluable genetic resource for rice resistance breeding. Whole-genome re-sequencing was conducted to systematically analyze the variations in two new inbred lines (Huaye 3 and Huaye 4) developed from a common wild rice. A total of 4,841,127 SNPs, 1,170,479 InDels, 24,080 structural variations (SVs), and 298 copy number variations (CNVs) were identified in three materials. Approximately 16.24 and 5.64% of the total SNPs and InDels of Huaye 3 and Huaye 4 were located in genic regions, respectively. Together, 12,486 and 15,925 large-effect SNPs, and 12,417 and 14,513 large-effect InDels, which affect the integrity of the encoded protein, were identified in Huaye 3 and Huaye 4, respectively. The distribution map of 194 and 245 NBS-LRR encoding homologs was constructed across 12 rice chromosomes. Further, GO enrichment analysis of the homologs with identical genotype variations in Huaye 3 and Huaye 4 revealed 67, 82, and 58 homologs involved in cell death, response to stress, and both terms, respectively. Comparative analysis displayed that 550 out of 652 SNPs and 129 out of 147 InDels were present in a widely used blast-susceptible rice variety (LTH). Protein-protein interaction analysis revealed a strong interaction between NBS-LRR candidates and several known R genes. One homolog of disease resistance protein (RPM1) was involved in the plant-pathogen interaction pathway. Artificial inoculation of disease/insect displayed resistance phenotypes against rice blast and brown planthopper in two lines. The results will provide allele-specific markers for rice molecular breeding.     

Analysis of chloroplast differences in leaves of rice isonuclear alloplasmic lines

The chloroplast being an important organelle of plant cells could possibly be associated with plant cytoplasmic male sterility (CMS). To better understand the correlation between (CMS) and chloroplast, we presented a comprehensive analysis based on the changes of photosynthetic parameters, chloroplasts ultrastructure, soluble sugar and starch content, the relative expression of sugar and starch metabolism genes, and chloroplast genome in rice isonuclear alloplasmic CMS lines at the flowering stage. Leaf gas exchange parameters did not affect by CMS lines (M2BS and M2A), although intercellular CO₂ concentration (C _i) was influenced in both M2BS and M2A. Ultrastructural observation results indicated that many starch granules were observed in the chloroplast of CMS lines, especially bigger size in M2BS, while few ones in M2B. Only the chloroplasts of M2A contained some additional number of lipoids compared with those of the other two lines (M2B and M2BS). Soluble sugar and starch contents in CMS lines (M2BS and M2A) were significantly higher than those in maintainer line (M2B) (p?<?0.01). The relative expression of sugar and starch metabolism genes indicated the imbalance of starch and sugar synthesis and decomposition may lead to accumulation of starch granules and demonstrated the presence of cytoplasmic effects. Moreover, chloroplast genome sequencing results showed similarity in both CMS lines, which revealed different single nucleotide polymorphisms (SNPs) and insertion/deletion (InDels) models compared with their maintainer line. Those models were located in psbD, rpoC2, rpl33, psbB, ndhA, ndhH, and intergenic regions. These findings, aligned with the possible association of CMS characteristics with cpDNA and genetically close relationship among both CMS lines, may contribute for future research.     

Test of agronomic characteristics and amplified fragment length polymorphism analysis of new rice germplasm developed from transformation of genomic DNA of distant relatives

New rice lines, restorer line RB207 and maintainer line Yewei B, with better agronomic traits were separately developed from variant progeny of R207 (rice restorer line) and V20B (rice maintainer line) through transformation of genomic DNA ofEchinochloa crusgalli (C₄ plant) andOryza minuta, respectively. The phenotypes of the variant lines were apparently different from those of the receptors. Yewei B had stronger tolerance to high temperature than did V20B. The number of spikelets per panicle and the 1000-grain weight of RB207 increased by 40% over those of R207. The results of amplified fragment length polymorphism (AFLP) analysis indicated that the polymorphism rates were both 4.4% between genomes of the variant lines and their receptors. Results demonstrated that special DNA segments fromE. crusgalli andO. minuta might integrate into the genome of cultivated rice and could be stably passed on. The study further shows that transformation of genomic DNA of distant relatives is an effective approach for creating new rice germ plasm. These authors contributed equally to this work.     

Genome-wide single nucleotide polymorphism discovery and validation in adzuki bean

Adzuki bean, also known as red bean (Vigna angularis), with 2n = 22 chromosomes, is an important legume crop in East Asian countries, including China, Japan, and Korea. For single nucleotide polymorphism (SNP) discovery, we used Vigna accessions, V. angularis IT213134 and its wild relative V. nakashimae IT178530, because of the lack of DNA sequence polymorphism in the cultivated species. Short read sequences of IT213134 and IT178530 of approximately 37 billion and 35 billion bp were produced using the Illumina HiSeq 2000 system to a sequencing depth of 61.5× and 57.7×, respectively. After de novo assembly was carried out with trimmed HiSeq reads from IT213134, 98,441 contigs of various sizes were produced with N50 of 13,755 bp. Using Burrows–Wheeler Aligner software, trimmed short reads of V. nakashimae IT178530 were successfully mapped to IT213134 contigs. All sequence variations at the whole-genome level were examined between the two Vigna species. Of the 1,565,699 SNPs, 59.4 % were transitions and 40.6 % were transversions. A total of 213,758 SNPs, consisting of 122,327 non-synonymous and 91,431 synonymous SNPs, were identified in coding sequences. For SNP validation, 96 SNPs in the genic region were chosen from among IT213134 contigs longer than 10 kb. Of these 96 SNPs, 88 were confirmed by Sanger sequencing of 10 adzuki bean genotypes from various geographic origins as well as IT213134 and its wild relative IT178530. These genome-wide SNP markers will enrich the existing Vigna resources and, specifically, could be of value for constructing a genetic map and evaluating the genetic diversity of adzuki bean.     

Genome-Wide SNP Identification and Characterization in Two Soybean Cultivars with Contrasting Mungbean Yellow Mosaic India Virus Disease Resistance Traits

Mungbean yellow mosaic India virus (MYMIV) is a bipartite Geminivirus, which causes severe yield loss in soybean (Glycine max). Considering this, the present study was conducted to develop large-scale genome-wide single nucleotide polymorphism (SNP) markers and identify potential markers linked with known disease resistance loci for their effective use in genomics-assisted breeding to impart durable MYMIV tolerance. The whole-genome re-sequencing of MYMIV resistant cultivar ‘UPSM-534’ and susceptible Indian cultivar ‘JS-335’ was performed to identify high-quality SNPs and InDels (insertion and deletions). Approximately 234 and 255 million of 100-bp paired-end reads were generated from UPSM-534 and JS-335, respectively, which provided ~98% coverage of reference soybean genome. A total of 3083987 SNPs (1559556 in UPSM-534 and 1524431 in JS-335) and 562858 InDels (281958 in UPSM-534 and 280900 in JS-335) were identified. Of these, 1514 SNPs were found to be present in 564 candidate disease resistance genes. Among these, 829 non-synonymous and 671 synonymous SNPs were detected in 266 and 286 defence-related genes, respectively. Noteworthy, a non-synonymous SNP (in chromosome 18, named 18-1861613) at the 149^th base-pair of LEUCINE-RICH REPEAT RECEPTOR-LIKE PROTEIN KINASE gene responsible for a G/C transversion [proline (CCC) to alanine(GCC)] was identified and validated in a set of 12 soybean cultivars. Taken together, the present study generated a large-scale genomic resource such as, SNPs and InDels at a genome-wide scale that will facilitate the dissection of various complex traits through construction of high-density linkage maps and fine mapping. In the present scenario, these markers can be effectively used to design high-density SNP arrays for their large-scale validation and high-throughput genotyping in diverse natural and mapping populations, which could accelerate genomics-assisted MYMIV disease resistance breeding in soybean.     

Transgenic insect-resistant maintainer line (IR68899B) for improvement of hybrid rice

Heterosis has helped to increase rice yield in F₁ hybrids by 15–20% beyond the level of inbred semidwarf varieties. For stable yield performance rice hybrids must also possess genetic resistance to biotic stresses. One of these, stem borer, reduces the expected yield of hybrid rice. The truncated synthetic cryIA(b) gene from Bacillus thuringiensis is known to be effective in controlling stem borer. The development of transformation techniques has provided the technology for incorporating this bacterial gene into the rice genome, which has not been possible by conventional breeding methods. We have introduced a new approach of using a transgenic maintainer line for developing an insect-resistant hybrid rice. An elite IRRI maintainer line (IR68899B) has been transformed with the cryIA(b) gene driven by the 35S constitutive promoter using the biolistic method. The integration and expression of the cryIA(b) gene could be demonstrated through Southern and Western blot analyses that have been carried out so far up to the T₂ generations. Insect bioassay data showed an enhanced resistance to yellow stem borer in the Bt ⁺ transgenic plants. This is the first report of the development of a transgenic maintainer line for use in hybrid rice improvement. Received: 17 December 1997 / Revision received: 23 June 1998 / Accepted: 25 September 1998     

Genomic analysis of polycarpellary rice (Oryza sativa L.) through whole genome resequencing

There is a natural floral organ mutant of rice (var. Jugal) where the florets, popularly known as spikelet bear multiple carpels and produce multiple kernels in most of its grain. In our earlier work a detailed study has been done on its morpho-anatomical structure with allelic diversity and expression study of the major genetic loci associated with floral organ development. In present study high throughput whole genome sequencing was done which generated about of 3.7 million base pair genomic data for downstream analysis. The reads were about 101 bases long and mapped to the Oryza sativa var. Nipponbare as reference genome. Genome wide variant analysis detected 1,096,419 variants which included 943,033 SNPs and 153,386 InDels. A total of 24,920 non-synonymous SNPs were identified for 11,529 identified genes. Chromosome-wise distribution of uniquely mapped reads onto reference genome showed that maximum reads were mapped to 1st chromosome and least to 9th chromosome. 10th chromosome showed highest density of variations (about 325.6 per 100 kb genome sequence). Detailed sequence analysis of 23 floral organ developmental genes detected 419 potent variants where DL (Drooping Leaf) and OSH1 (Oryza sativa Homeobox1) genes showed highest number (32) of variants; whereas, MADS21 (Minichromosome Agamous Deficient Serum Factor 21) gene have lowest number (5) of variants. The information generated in this study will enrich the genomics of floral organ development in indica rice and cereal crops in general.