Genetics of amylose content in rice (Oryza sativa L)

Inheritance of amylose content was studied in crosses involving very low-, intermediate-, and high-amylose parents. The single-grain analysis of parents, F₁, F₂, B₁F₁, and B₂F₁ seed from a single-season harvest, showed that the parental mean difference of 14–17 % in IR37307-8/BPI 121-407 or IR37307-8/IR24632-34 and about 20% in the cross IR37307-8/IR8 were controlled by a single gene with major effect, along with some minor genes and/or modifiers. The appearance of segregants inbetween the two parents was attributed to gene dosage effects in the endosperm. The results indicate that selection for amylose level can effectively be done in early segregating generations. Selection for intermediary segregants would be ineffective because the dosage effects would dissipate in further generations.     

QTL detection and MAS selection efficiency for lipid content in brown rice (Oryza sativa L.)

Rice lipid content as one of important ingredients of functional food and industrial products has become an entirely new target in the rice breeding programs worldwide. A genetic linkage map spanning 12 rice chromosomes with an average interval of 10.51 cM between markers was created using 172 DNA markers, which intended to elucidate genetic basis of lipid content in brown rice by QTL detection. Eight QTLs related to lipid content with LOD from 2.52 to 7.86 were mapped on chromosome1, 2, 3, 5, 6, 7 and 9 using a doubled haploid (DH) population from a cross of ‘Samgang/Nagdong’ with field experiments for five years. Two QTLs of qLC5.1 and qLC6.1 in the intervals 5014-5024 and 6011-RM19696 were repeatedly detected over four years at average LOD scores of 4.85 and 4.21, respectively. Five of eight QTLs tend to increase the lipid content from ‘Samgang’ alleles. Epistatic and environmental effects played important roles and explained 42.20% of phenotype variations. Three QTLs of qLC6.1, qLC7.1 and qLC9.1 collectively explained much than 27% of phenotype variations and increased 0.25% of lipid content and, showed much than 85% of selection efficiency for the lines with high lipid contents in the F7 population from a cross of ‘Samgang/Nagdong’. Thus it provides the sufficient possibility to realize QTLs pyramiding and to promote process of rice breeding.     

QTL mapping for the paste viscosity characteristics in rice (Oryza sativa L.)

In order to understand the genetic basis of the paste viscosity characteristics (RVA profile, which is tested on the Rapid Visco Analyser) of the rice grain, we mapped QTLs for RVA profile parameters using a DH population derived from a cross between an indica variety, Zai-Ye-Qing 8 (ZYQ8), and a japonica variety, Jing-Xi 17 (JX17). Evidence of genotype-by-environment interaction was found by comparing the mapped QTLs between two locations, Hainan (HN) and Hangzhou (HZ). A total of 20 QTLs for six parameters of the RVA profiles were identified at least one location. Only the waxy locus (wx) located on chromosome 6 was detected significantly at both environments for five traits, i.e. hot paste viscosity (HPV), cool paste viscosity (CPV), breakdown viscosity (BDV), consistency viscosity (CSV) and setback viscosity (SBV). This locus explained 19.5%–63.7% of the total variations at both environments, suggesting that the RVA profiles were mainly controlled by the wx gene. HPV, CPV, BDV, CSV and SBV were also controlled by other QTLs whose effects on the respective parameter were detected only in one environment, while for the peak viscosity (PKV), only 2 QTLs, 1 at HN,the other at HZ, were identified. These results indicate that RVA profiles are obviously affected by environment. Received: 18 July 1999 / Accepted: 27 August 1999     

Mutants having a low content of 16-kDa allergenic protein in rice (Oryza sativa L.)

Summary Rice mutants containing low levels of the 16-kDa allergenic protein, which is the main allergen in the rice grain for patients of atopic dermatitis due to the intake of rice, were screened, and 4 independent mutant lines with small amounts of this protein were found by SDS gel electrophoresis and immunoblot analysis. These mutants were grouped into two types. Two mutant lines, 85KG-4 and 86RG-18, contained low levels of the 16k-Da and 26-kDa polypeptides and a high level of the 57-kDa polypeptide. The 16-kDa polypeptide content of these mutants was about half that of the original cultivars. Homozygous lines were developed, and these showed normal growth and seed set. The other 2 mutant lines, 87KG-970 and 89WPKE-149, showed traces of the 16-kDa and 26 kDa polypeptides and contained a high level of the 13 kDa polypeptide. The homozygous plants of this type were sterile. All of the mutant lines had floury endosperms. Genetic analysis suggested that low 16-kDa polypeptide content is controlled by a single recessive gene. Attempts to separate of the genes for low 16-kDa polypeptide content and floury endosperm by crossing with the original cultivar were unsuccessful, suggesting the tight linkage of these two genes or pleiotropism of a single mutated gene. The relationship between low 16-kDa polypeptide content and the floury character and the possible use of the mutant as a low allergen rice are discussed.     

Chromosomal location of genes conditioning low amylose content of endosperm starches in rice,Oryza sativa L.

Summary Eight dull mutants that lower the amylose content of rice endosperm as well as waxy mutant and a cultivar with common grains were crossed in a diallele manner. The amylose content of F₁ and F₂ seeds was determined on the basis of single grain analysis. It was concluded that the low amylose content of dull mutants is under monogenic recessive control. Alleles for low amylose content are located at five loci designated as du-1, du-2, du-3, du-4 and du-5. These loci are independent of wx locus located on chromosome 6. The five du loci have an additive effect in lowering the amylose content. Two loci, du-1 and du-4, were found to be located on chromosomes 7 and 4, respectively.     

High amylose mutants of rice,Oryza sativa L.

Summary Five mutant lines of rice with increased amylose content in starch granules were identified among floury endosperm mutants. The amylose contents of the mutants ranged from 29.4% to 35.4% and were about twice as high as that of the normal counterpart. Starch properties of the high amylose mutants were analyzed by column chromatography, X-ray diffractometry, photopastegraphy and scanning electron microscopy. The high amylose mutants produced longer unit chains of amylopectin than those of the normal counterpart as well as an increased amount of amylose. A X-ray diffractogram of starch in the mutant was characterized by a type B pattern, while that in the normal counterpart showed a type A pattern which is typical for starches of common cereals. The temperatures at the initiation of gelatinization of the mutants were much higher than that for the normal counterpart. The endosperm cells of the mutant were loosely packed with irregular round-shaped starch granules, whereas those of the normal counterpart were densely packed with polyhedral starch granules. Judging from the results obtained, it was concluded that starch properties of the high amylose mutants of rice were similar to those of the amylose-extender (ae) mutant of maize.     

A rice (Oryza sativa L.) mutant having a low content of glutelin and a high content of prolamine

Among the mutant lines of rice that have been selected for morphological characters, one line, NM67, was found to have a low content of glutelin and a higher content of prolamine in its seed protein than other Japanese cultivars. This mutant is a semi-dwarf and partially sterile line, and its leaves turn yellow before heading. Genetic analysis after backcross to the original cultivar, Nihonmasari, revealed the following: (1) the character of low glutelin content was always accompanied by the character of high prolamine content; (2) the low glutelin (and high prolamine) character seemed to be manifested by a single dominant gene; and (3) semi-dwarfness, low fertility and early yellowing leaf of the mutant, which might also be pleiotropy, were controlled by a single recessive gene independent of the gene for protein content. The protein character of NM67 was genetically separated from semi-dwarfness and low fertility, and a new line having low glutelin content and high prolamine content with normal morphological characters comparable to those of the original cultivar was obtained from the progenies of the cross. The possible use of this line as a low protein rice cultivar is discussed.     

Detection of allelic variation at the Wx locus with single-segment substitution lines in rice (Oryza sativa L.)

Apparent amylose content (AAC) is a key determinant of eating and cooking quality in rice and it is mainly controlled by the Wx gene which encodes a granule-bound starch synthase (GBSS). In this study, sixteen single-segment substitution lines harboring the Wx gene from 16 different donors and their recipient HJX74 were used to detect the naturally occurring allelic variation at the Wx locus. The AAC in the materials varied widely and could be grouped into glutinous, low, intermediate, and two high AAC sub-classes, high I (24.36?C25.20%) and high II (25.81?C26.19%), under different experimental environments, which showed a positive correlation with the enzymatic activity of GBSS. One insertion/deletion (InDel) and three single nucleotide polymorphisms in the Wx gene were detected and their combinations resulted in the variation of five classes of AAC. Based on the results of AAC phenotypes, GBSS activities and cDNA sequences, five Wx alleles, wx, Wx ^t, Wx ^g1, Wx ^g2, and Wx ^g3, were identified, two of which, Wx ^g2 and Wx ^g3, are separated for the first time in this study. Under different cropping seasons, the AAC differed significantly for the Wx ^t and Wx ^g1 alleles, with higher AAC in the fall season than in the spring season, but did not differ significantly for the wx, Wx ^g2, and Wx ^g3 alleles. In conclusion, the present results might contribute to our understanding of the naturally occurring allelic variation at the Wx locus and will facilitate the improvement of rice quality by marker-assisted selection.     

Genetic analysis and molecular mapping of low amylose gene du12(t) in rice (Oryza sativa L.)

Key message

We obtained interesting results for genetic analysis and molecular mapping of the du12(t) gene.

Abstract

Control of the amylose content in rice is the major strategy for breeding rice with improved quality. In this study, we conducted genetic analysis and molecular mapping to identify the dull gene in the dull rice, Milyang262. A single recessive gene, tentatively designated as du12(t), was identified as the dull gene that leads to the low amylose character of Milyang262. To investigate the inheritance of du12(t), genetic analysis on an F₂ population derived from a cross between the gene carrier, Milyang262, and a moderate amylose content variety, Junam, was conducted. A segregation ratio of 3:1 (χ ² = 1.71, p = 0.19) was observed, suggesting that du12(t) is a single recessive factor that controls the dull character in Milyang262. Allelism tests confirmed that du12(t) is not allelic to other low amylose controlling genes, wx or du1. Recessive class analysis was performed to localize the du12(t) locus. Mapping of du12(t) was conducted on F₂ and F₃ populations of Baegokchal/Milyang262 cross. Linkage analysis of 120 F₂ plants revealed that RM6926 and RM3509 flank du12(t) at a 2.38-Mb region. To refine the du12(t) locus position, 986 F₂ and 289 F₃ additional normal plants were screened by the flanking markers. Twenty-six recombinant plants were identified and later genotyped with four additional adjacent markers located between RM6926 and RM3509. Finally, du12(t) was mapped to an 840-kb region on the distal region of the long arm of chromosome 6, delimited by SSR markers RM20662 and RM412, and co-segregated by RM3765 and RM176.     

Fine mapping of the grain chalkiness QTL qPGWC-7 in rice (Oryza sativa L.)

Chalkiness of rice grain is an important quality component of rice, as it has a profound influence on eating and milling qualities. We has determined the inheritance of percentage of grain with chalkiness (PGWC) using a set of chromosome segment substitution lines, made from a cross between cv. PA64s and cv. 9311. Two loci controlling PGWC, designated as qPGWC-6 and qPGWC-7, were located on, respectively, chromosomes 6 and 7. Comparisons were made between C-51 (a CSSL harbouring qPGWC-7 and having a chalky endosperm) and the recurrent parent 9311 (translucent endosperm) to characterize the physical and chemical differences between translucent and chalky endosperm. Unlike the translucent endosperm, the chalky endosperm contains loosely packed starch granules, and there were significant difference between C-51 and 9311 for amylopectin structure and degree of crystallinity, but not for either amylose content or starch viscosity. Segregation analysis of the F₂ population from the cross between C-51 and 9311 showed PGWC is a semi-dominant trait, controlled by single nuclear gene. A large F₂ population was constructed from the cross C51 × 9311, and used for the fine mapping of qPGWC-7, which was located to a 44-kb DNA fragment, containing thirteen predicted genes. This result provides a springboard for the map-based cloning of qPGWC-7 and allowed for marker-assisted selection for endosperm texture.     

Heterosis breeding in rice (Oryza sativa L.)

Summary Studies conducted at the International Rice Research Institute (IRRI) during 1980 and 1981 have shown up to 73% heterosis, 59% heterobeltiosis and 34% standard heterosis for yield in rice. The latter was estimated in comparison to commercial varieties: IR36 and IR42 (yield 4–5 t/ha in wet season trials and 7–8 t/ha in dry season trials). Generally speaking, absolute yield was lower and extent of standard heterosis was higher in wet season than in dry season with some exception. Yields up to 5.9 t/ha (22% standard heterosis) in the wet season and 10.4 t/ha (34% standard heterosis) in the dry season were obtained. Most of the hybrids performed better in some season while some performed better in both seasons. Hybrids showed better lodging resistance although they were 5–10 cm taller. F₁ hybrids had significant positive correlations with the parental traits viz., yield (r = 0.446), tillering (r = 0.746), height (r = 0.810) and flowering (r = 0.843). Selection of parents among elite breeding lines on the basis of their per se yield performance, diverse origin and resistance to insects and diseases should give heterotic combination. Yield advantage of hybrids was due primarily to increase in number of spikelets per unit area even though tiller number was reduced. Grain weight was either the same or slightly higher. High yielding hybrids also showed significant heterosis and heterobeltiosis for total dry matter and harvest index. For commercial utilization of heterosis in rice, effective male sterility and fertility restoration systems are available and up to 45% natural outcrossing on male sterile lines has been observed. Consequently, F₁ rice hybrid have been successfully developed and used in China. Prospects of developing hybrid rice varieties elsewhere appear bright especially in countries that have organized seed production, certification and distribution programs and where hybrid seed can be produced at a reasonable cost.     

Clustered QTL for source leaf size and yield traits in rice (Oryza sativa L.)

Improvement of plant type plays an important role in super-high yield breeding in rice (Oryza sativa L.). In the present study, a set of backcross recombinant inbred lines derived from a cross of 9311 and Zhenshan97, both elite indica hybrid parents, were developed to identify quantitative trait loci (QTL) for flag leaf size, panicle and yield traits. Forty-seven QTL for 14 traits were detected in common in the two environmental trials, of which nine genomic regions contained clustered QTL affecting plant type traits and yield traits. Four co-localized QTL on chromosomes 1, 6, 7 and 8 involving QTL for flag leaf size (flag leaf length, width and area) contained the QTL for yield traits such as panicle weight (PW) and secondary branch number (SBN), and in all cases alleles from 9311 increased source leaf size and were associated with increased sink size and yield (SBN and PW). Using a subset of overlapping substitution lines for the QTL region on chromosome 1, the QTL were validated and narrowed into a 990?kbp interval (RM3746?CRM10435) with pleiotropic effects on flag leaf size, PW, SBN and spikelet number per panicle. These QTL clusters with large effects on source leaf size and yield-related traits provide good targets for marker-assisted breeding for plant type improvement and high-yield potential in rice.     

Heredity, physiology and mapping of a chlorophyll content gene of rice (Oryza sativa L.)

A single dominant gene Gc controls the trait of high chlorophyll (Chl) content in rice (cultivar (cv.) Zhenshan 97B). The contents of Chl b and total Chl increased 100% and 25%, respectively, when Gc was introduced. In addition, photosynthetic rate, biomass and grain yield also increased by 20%, 17% and 16%, respectively. Three simple sequence repeats (SSR) markers (rm462, rm6340 and rm6464) that are linked to Gc were identified by amplification of DNA samples from near-isogenic lines using two hundred pairs of primers. The genetic distances on the short arm of rice chromosome 1 between Gc and rm6464, rm6340 and rm462 were 0, 0.588 and 1.18 cM, respectively.     

Modulation of amylose content by structure‐based modification of OsGBSS1 activity in rice (Oryza sativa L.)

The rice Waxy (Wx) gene encodes granule‐bound starch synthase 1 (EC 2.4.1.242), OsGBSS1, which is responsible for amylose synthesis in rice seed endosperm. In this study, we determined the functional contribution of eight amino acids on the activity of OsGBSS1 by introducing site‐directed mutated Wx gene constructs into the wx mutant glutinous rice. The eight amino acid residues are suspected to play roles in OsGBSS1 structure maintenance or function based on homologous enzyme sequence alignment and homology modelling. Both OsGBSS1 activity and amylose content were analysed in homozygous transgenic lines carrying the mutated OsGBSS1 (Wx) genes. Our results indicate that mutations at diverse sites in OsGBSS1 reduces its activity by affecting its starch‐binding capacity, its ADP‐glucose‐binding capability or its protein stability. Our results shed new light on the structural basis of OsGBSS1 activity and the mechanisms of OsGBSS1 activity on amylose synthesis in vivo. This study also demonstrates that it is feasible to finely modulate amylose content in rice grains by modifying the OsGBSS1 activity.     

基于CSSL的水稻穗颈长度QTL的代换作图

水稻穗颈长度是影响杂交水稻制种产量提高的重要农艺性状之一。文章利用94个以籼稻品种9311为遗传背景、粳稻品种日本晴为染色体片段供体的覆盖全基因组的染色体片段置换系(Chromosome segment substi-tution lines, CSSL)为材料, 调查和分析CSSL群体及双亲的穗颈长度。结果表明: 在17个置换系中检测到8个控制水稻穗颈长度的数量性状位点(Quantitative trait loci, QTL), 分别位于第2、3、7、8、9和第11染色体; 利用代换作图法, 定位了其中的7个穗颈长度QTL; 其加性效应值介于0.10~3.20之间, 其中qPE-9和qPE-11的加性效应值较大, 平均效应值分别为3.15和2.95, 表现为主效基因特征; qPE-2-2、qPE-3-1、qPE-3-2、qPE-7和qPE-8等5个QTL被定位在小于10.0 cM的区段内。利用CSSL可以有效地鉴定水稻穗颈长度QTL, 这些QTL为分子标记辅助选育穗颈长度适中的水稻品系及其进一步的精细定位奠定了基础。     

Generation and characterization of low phytic acid germplasm in rice (Oryza sativa L.)

Phytic acid (PA, myo-inositol 1,2,3,4,5,6-hexakisphosphate), or its salt form, phytate, is commonly regarded as the major anti-nutritional component in cereal and legume grains. Breeding of low phytic acid (lpa) crops has recently been considered as a potential way to increase nutritional quality of crop products. In this study, eight independent lpa rice mutant lines from both indica and japonica subspecies were developed through physical and chemical mutagenesis. Among them, five are non-lethal while the other three are homozygous lethal. None of the lethal lines could produce homozygous lpa plants through seed germination and growth under field conditions, but two of them could be rescued through in vitro culture of mature embryos. The non-lethal lpa mutants had lower PA content ranging from 34 to 64% that of their corresponding parent and four of them had an unchanged total P level. All the lpa mutations were inherited in a single recessive gene model and at least four lpa mutations were identified mutually non-allelic, while the other two remain to be verified. One mutation was mapped on chromosome 2 between microsatellite locus RM3542 and RM482, falling in the same region as the previously mapped lpa1-1 locus did; another lpa mutation was mapped on chromosome 3, tightly linked to RM3199 with a genetic distance of 1.198 cM. The latter mutation was very likely to have happened to the LOC_Os03g52760, a homolog of the maize myo-inositol kinase (EC 2.7.1.64) gene. The present work greatly expands the number of loci that could influence the biosynthesis of PA in rice, making rice an excellent model system for research in this area.     

Genetic analysis and QTL mapping for grain chalkiness characteristics of brown rice (Oryza sativa L.)

Grain chalkiness is one of the important appearance qualities in rice marketing. But it is a complex trait, controlled by polygenes and easily influenced by the environment. Genetic analysis and QTL detection was carried out on six characteristics of grain chalkiness consisting of the percentage of chalkiness (PGC), white belly (PWB) and white core grains (PWC), and the area of chalkiness (CA), white belly (WBA) and white core (WCA) in brown rice. A total of 16 main-effect QTLs associated with chalkiness characteristics of brown rice were mapped on seven chromosomes over two years. Among them,qPGC7.1 andqPWB7.2 were simultaneously located on chromosome 7 flanked by 7038 and 7042 at LOD scores 4.34 and 3.76, whileqPWC2.1 andqWCA2.1 were simultaneously located on chromosome 2 flanked by RM492 and RM324 with LOD scores of 2.50 and 3.39. Twelve epistatic combinations were detected for five chalkiness characteristics except for CA. Results indicated that WBA was mainly influenced by the additive effects of main-effect QTLs. PGC and PWC were affected by the effects of epistatic QTLs and the interactions between additive-by-additive effects and the environment. The effects of epistatic QTLs and the main-effect QTLs played important roles on CA, PWB and WCA. For the genetic improvement of grain chalkiness in breeding system, more attention should be paid to epistatic effects and the additive effects of main-effect QTLs.