Utilization Of Heterosis Research Articles

Identification of S23 causing both interspecific hybrid male sterility and environment-conditioned male sterility in rice

BackgroundOryza glumaepatula represents an important resource of genetic diversity that can be used to improve rice production. However, hybrid sterility severely restricts gene flow between Oryza species, and hinders the utilization of distant heterosis in hybrid rice breeding.ResultsIn order to fully exploit the beneficial genes of O. glumaepatula and facilitate the conservation of these gene resources, a set of chromosome single-segment substitution lines (SSSLs) was developed using an indica variety HJX74 as the recurrent parent and an accession of O. glumaepatula as the donor parent. During the process of SSSLs development, S23, a locus conferring hybrid male sterility between O. sativa and O. glumaepatula, was identified and fine mapped to 11.54 kb and 7.08 kb genomic region in O. sativa and O. glumaepatula, respectively, encoding three and two candidate ORFs, respectively. qRT-PCR and sequence analysis excluded one common ORF as the candidate gene. In addition, hybrid male sterility caused by S23 was environment-sensitive, and could be observed only in natural short-day (NSD).ConclusionIdentification and candidate genes analysis of S23 in this study provides a valuable example to study the crosstalk between interspecific F1 hybrid male sterility and environment-conditioned male sterility in rice, facilitates reserving and utilizing favorable genes or alleles of wild Oryza species, and allows for a more efficient exploitation of distant heterosis in hybrid rice breeding.

An Overview on the Concept and Utilization of Heterosis in Livestock

Heterosis or hybrid vigour is the excellence of F1 cross beyond the average performance of the two parents and noticeable across species. Heterosis, coined by Professor G.H. Shull in 1914 is well known to exploit the benefits of crossbreeding. Heterosis is usually positive but negative heterosis does occur and is uncommon. Heterosis is widely accepted to occur due to non-additive gene action i.e. dominance, over-dominance and epistasis. The heterotic effects are usually expressed in percentage and always highest in F1 generation followed by a decline in later generations. This decline is mainly due to the recombination and segregation losses. Rotational crossbreeding systems are therefore followed to maintain levels of heterosis in later generations. Estimates of heterosis are high in low heritable traits followed by moderate in moderately heritable traits and negligible in high heritable traits. Besides improvement, there are some limitations to heterosis that shall overcome shortly.

The genetic mechanism of sex type, a complex quantitative trait, in Ricinus communis L.

Castor (Ricinus communis L.) is an important industrial crop. Castor oil is very important to the global special chemical industry as feedstock and biofuels. The global demand for castor oil is rising rapidly, however, the low-yield varieties has been the bottleneck of castor industry. Breeding high-yield hybrids using pistillate line has been the main approach of castor breeding, but it progressed slowly due to the limited knowledge to the genetic mechanism of pistillate character (PC). In this study, firstly, the experiments for male fertility restoration of 2 pistillate lines, YC1 and YC2, were conducted with 98 restoring lines. Secondly, the genetic analysis of these two pistillate lines were performed with 6 segregating populations derived from them. Thirdly, the QTLs conferring the PC were mapped with 3 different F2 populations under 2 environments with SSR markers, demonstrating that the PC was a complex quantitative trait controlled by major genes and polygenes. Totally, 16 QTLs were identified in 3 populations with a phenotypic variation explained (PVE) of 74.51%, 41.71% and 48.98% respectively, one of which was simultaneously detected in three populations and another in two populations. In addition, it was found that the epistasis effect was the important genetic component of PC, with a PVE of 29.78% and 26.24% in 2 populations respectively. Forthly, 5 QTLs underlying interspersed staminate flowers (ISF) were detected, proving that it was one of the sex types controlled by the same set of genes in castor. Conclusively, the PC was controlled by a number of recessive genes with both accumulative effect and overlapping effect, at least one pair of dominant epistatic genes and polygenes, that is, enough accumulated recessive genes was necessary for PC to express, if over, it still performed pistillate but extra more restoring genes would be needed to recover the reduntant pistillate genes. The presence of dominant epistatic genes were also necessary for the recessive genes to express the PC, otherwise the ISF would be possiple to happen. The ISF genes were also modified by polygene and the relative strength between the pistillate genes and the ISF genes determined the ISF expression. The conclusion revealed the genetic mechanism of castor sex type, providing not only a guidance for castor heterosis utilization but also a reference for genetic research of sex type in other unisexual flower plants.

The history and prospect of rice genetic breeding in China

Rice breeding in China has experienced three major leaps of dwarf breeding, heterosis utilization and green super rice cultivation, accompanied by six important processes: dwarf breeding (the first green revolution), three-line hybrid rice cultivation, two-line hybrid rice cultivation, inter-subspecies heterosis utilization, ideal plant type breeding and green super rice cultivation. The breeding subject ranges from the unique trait of high yield to the complex traits of resistance, high quality and high yield. The breeding concept is gradually upgraded from high yield and quality to the second green revolution concept of "less investment, more output, and better environment". Rice functional genomics achievements have prepared many genes with important utilization values for the second green revolution, and rice breeding is moving towards a new era of design breeding. The genomic selection technology and transgenic technology will help to develop the green super rice for "less pesticides, less fertilizers, water saving and drought tolerance, superior quality and high yield". Here, we summarize the development process of rice genetics and breeding in China, point out advantages and disadvantages of various breeding methods and breeding techniques, systematically introduce the molecular mechanisms on cytoplasmic male sterility, photoperiod-sensitive male genic sterility and indica-japonica hybrid sterility, review the important functional genes related to rice plant architecture, panicle architecture, grain size and nutrient use efficiency, clarify the correlation between yield and heading date, and highlight the important position of China in the rice basic research in the world. In particular, we emphasize the fact that Chinese rice production styles have undergone or are undergoing tremendous changes in recent years, and the breeding concept must also keep pace with the changing production styles. In the future, the hybrid breeding technology should be closely integrated with modern breeding technologies to breed rice varieties that must not only meet the market demand, but also have the natural and healthy characteristics and adapt to the new farming system and methods.

Comparative analysis of circular RNAs between soybean cytoplasmic male-sterile line NJCMS1A and its maintainer NJCMS1B by high-throughput sequencing

BackgroundCytoplasmic male sterility (CMS) is a natural phenomenon of pollen abortion caused by the interaction between cytoplasmic genes and nuclear genes. CMS is a simple and effective pollination control system, and plays an important role in crop heterosis utilization. Circular RNAs (circRNAs) are a vital type of non-coding RNAs, which play crucial roles in microRNAs (miRNAs) function and post-transcription control. To explore the expression profile and possible functions of circRNAs in the soybean CMS line NJCMS1A and its maintainer NJCMS1B, high-throughput deep sequencing coupled with RNase R enrichment strategy was conducted.ResultsCircRNA libraries were constructed from flower buds of NJCMS1A and its maintainer NJCMS1B with three biological replicates. A total of 2867 circRNAs were identified, with 1009 circRNAs differentially expressed between NJCMS1A and NJCMS1B based on analysis of high-throughput sequencing. Of the 12 randomly selected circRNAs with different expression levels, 10 showed consistent expression patterns based on high-throughput sequencing and quantitative real-time PCR analyses. Tissue specific expression patterns were also verified with two circRNAs by quantitative real-time PCR. Most parental genes of differentially expressed circRNAs were mainly involved in biological processes such as metabolic process, biological regulation, and reproductive process. Moreover, 83 miRNAs were predicted from the differentially expressed circRNAs, some of which were strongly related to pollen development and male fertility; The functions of miRNA targets were analyzed using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG), and the target mRNAs were significantly enriched in signal transduction and programmed cell death. Furthermore, a total of 165 soybean circRNAs were predicted to contain at least one internal ribosome entry site (IRES) element and an open reading frame, indicating their potential to encode polypeptides or proteins.ConclusionsOur study indicated that the circRNAs might participate in the regulation of flower and pollen development, which could provide a new insight into the molecular mechanisms of CMS in soybean.

Male Sterility of an AHAS-Mutant Induced by Tribenuron-Methyl Solution Correlated With the Decrease of AHAS Activity in Brassica napus L.

Tribenuron-methyl (TBM), an acetohydroxyacid synthase (AHAS)-inhibiting herbicide, can be used as an efficient chemical hybridization agent to induce male sterility for practical utilization of heterosis in rapeseed (Brassica napus L.). Utilization of rapeseed mutants harboring herbicide-resistant AHAS alleles as the male parent can simplify the hybrid seed production protocol. Here we characterized a novel TBM-resistant mutant K5 derived from an elite rapeseed variety, Zhongshuang No. 9 (ZS9), by ethyl methyl sulfonate mutagenesis. Comparative analysis of three BnAHAS genes (BnAHAS1, BnAHAS2, and BnAHAS3) between the mutant K5 and ZS9 identified a C-to-T transition at 544 from the translation start site in BnAHAS1 in K5 (This resistant allele is referred to as BnAHAS1544T), which resulted in a substitution of proline with serine at 182 in BnAHAS1. Both ZS9 and K5 plants could be induced complete male sterility under TBM treatment (with 0.10 and 20 mg⋅L-1 of TBM, respectively). The relationship between TBM-induced male sterility (Y) and the relative AHAS activity of inflorescences (X) could be described as a modified logistic function, Y = 100-A/(1+Be(-KX)) for the both genotypes, although the obtained constants A, B, and K were different in the functions of ZS9 and K5. Transgenic Arabidopsis plants expressing BnAHAS1544T exhibited a higher TBM resistance of male reproductive organ than wild type, which confirmed that the Pro-182-Ser substitution in BnAHAS1 was responsible for higher TBM-resistance of male reproductive organs. Taken together, our findings provide a novel valuable rapeseed mutant for hybrid breeding by chemical hybridization agents and support the hypothesis that AHAS should be the target of the AHAS-inhibiting herbicide TBM when it is used as chemical hybridization agent in rapeseed.

Genetic investigation and cytological comparison of two genic male sterile lines 9012A and MSL in Brassica napus L.

Genic male sterility (GMS) is one of the effective pollination control systems in hybrid rapeseed (Brassica napus L.) breeding. The recessive GMS lines 9012A and Lembke (MSL) have made a great contribution to the utilization of heterosis in rapeseed. Cytological observation and genetic investigation were employed to reveal anther abortion characters and genetic relationship of 9012A and MSL. Cytological and transmission electron microscopy observation revealed that anther abortion of 9012A and MSL initiated at the microsporocyte stage, both lines showed premature or retarded degradation of tapetum. Some anthers in 9012A developed to the microspore stage since their tapetal cells changed to the secretory type. However, MSL anthers did not progress to the tetrad stage, since the tapetum did not change to the secretory type. Genetic investigation revealed that MSL and 9012A had the same temporary maintainer system, while their cytoplasm types were different. The cytoplasm of MSL was similar to Cam while 9012A was similar to Nap type. The results laid a solid foundation for utilization of the two male sterile lines in rapeseed hybrid breeding.

Oxidative Stress and Aberrant Programmed Cell Death Are Associated With Pollen Abortion in Isonuclear Alloplasmic Male-Sterile Wheat.

Cytoplasmic male sterility is crucial for the utilization of hybrid heterosis and it possibly occurs in parallel with tapetal programmed cell death (PCD) and oxidative metabolism responses. However, little is known about the mechanisms that underlie pollen abortion in wheat. Therefore, we obtained two isonuclear alloplasmic male sterile lines (IAMSLs) with Aegilops kotschyi and Ae. juvenalis cytoplasm. Compared with the maintainer line, cytochemical analyses of the anthers demonstrated that the IAMSLs exhibited anomalous tapetal PCD and organelles, with premature PCD in K87B1-706A and delayed PCD in Ju87B1-706A. We also found that the dynamic trends in reactive oxygen species (ROS) were consistent in these two IAMSLs during anther development and they were potentially associated with the initiation of tapetal PCD. In addition, the activities of ROS-scavenging enzymes increased rapidly, whereas non-enzymatic antioxidants were downregulated together with excess ROS production in IAMSLs. Real-time PCR analysis showed that the expression levels of superoxide dismutase, catalase, and ascorbate peroxidase genes, which encode important antioxidant enzymes, were significantly upregulated during early pollen development. Thus, we inferred that excessive ROS and the abnormal transcript levels of antioxidant enzyme genes disrupted the balance of the antioxidant system and the presence of excess ROS may have been related to aberrant tapetal PCD progression, thereby affecting the development of microspores and ultimately causing male sterility. These relationships between the mechanism of PCD and ROS metabolism provide new insights into the mechanisms responsible for abortive pollen in wheat.

Transcriptomic analysis reveals overdominance playing a critical role in nicotine heterosis in Nicotiana tabacum L.

BackgroundAs a unique biological phenomenon, heterosis has been concerned with the superior performance of the heterosis than either parents. Despite several F1 hybrids, containing supernal nicotine content, had been discovered and applied to heterosis utilization in Nicotiana tabacum L., nevertheless, the potential molecular mechanism revealing nicotine heterosis has not been illustrated clearly.ResultPhenotypically, the F1 hybrids (Vall6 × Basma) show prominent heterosis in nicotine content by 3 years of field experiments. Transcriptome analysis revealed that genes participating in nicotine anabolism (ADC, PMT, MPO, QPT, AO, QS, QPT, A622, BBLs) and nicotine transport (JAT2, MATE1 and 2, NUP1 and 2) showed an upregulated expression in the hybrid, a majority of which demonstrated an overdominant performance. RT-PCR confirmed that nicotine anabolism was induced in the hybrid.ConclusionsThese findings strongly suggest that nicotine synthesis and transport efficiency improved in hybrid and overdominance at gene-expression level played a critical role in heterosis of nicotine metabolism.

Pervasive interactions of Sa and Sb loci cause high pollen sterility and abrupt changes in gene expression during meiosis that could be overcome by double neutral genes in autotetraploid rice

BackgroundIntersubspecific autotetraploid rice hybrids possess high hybrid vigor; however, low pollen fertility is a critical hindrance in its commercial utilization. Our previous study demonstrated that polyploidy could increase the multi-loci interaction and cause high pollen abortion in autotetraploid rice hybrids. However, there is little known about the critical role of pollen sterility locus or loci in the intersubspecific hybrids. We developed autotetraploid rice hybrids harboring heterozygous genotypes (SiSiSjSj) at different pollen sterility loci by using the near isogenic lines of Taichung65-4×. Moreover, autotetraploid lines carrying double neutral genes, San and Sbn, were used to assess their effect on fertility restoration.ResultsCytological studies showed that the deleterious genetic interactions at Sa and Sb pollen sterility loci resulted in higher pollen sterility (76.83%) and abnormal chromosome behavior (24.59%) at metaphase I of meiosis in autotetraploid rice hybrids. Transcriptome analysis revealed 1092 differentially expressed genes (DEG) in a hybrid with the pervasive interactions at Sa and Sb pollen sterility loci, and most of the genes (about 83%) exhibited down regulation. Of the DEG, 60 were associated with transcription regulation and 18 genes were annotated as meiosis-related genes. Analysis on the hybrids developed by using autotetraploid rice harboring double neutral genes, San and Sbn, revealed normal pollen fertility, and transcriptome analysis showed non-significant difference in number of DEG among different hybrids.ConclusionsOur finding revealed that pervasive interactions at Sa and Sb pollen sterility loci cause high sterility in the autotetraploid hybrids that lead to the down-regulation of important meiosis-related genes and transcription regulation factors. Moreover, we also found that the hybrids sterility could be overcome by double neutral genes, San and Sbn, in autotetraploid rice hybrids. The present study provided a strong evidence for the utilization of heterosis in autotetraploid rice hybrids.

Hybridization improved bacteria resistance in abalone: Evidence from physiological and molecular responses

Hybridization is an effective way of improving germplasm in abalone, as it often generates benign traits in the hybrids. The hybrids of Haliotis discus hannai and H. gigantea have shown heterosis in terms of disease resistance than one or both parental species. In the present study, to elucidate the physiological and molecular mechanism of this heterosis, we analyzed the dynamic changes of several immune indexes including survival rate, total circulating haemocyte count (THC), phagocytic activity, reactive oxygen species level (ROS) and phenoloxidase activity (PO) in two parental species, H. discus hannai (DD) and H. gigantea (GG), and their reciprocal hybrids H. discus hannai ♀ × H. gigantea ♂ (DG), H. gigantea ♀ × H. discus hannai ♂ (GD) challenged with a mixture of Vibrio harveyi, V. alginolyticus and V. parahaemolyticus (which have been demonstrated to be pathogenic to abalone). Besides, we cloned and analyzed three important immune genes: heat shock protein 70 (hsp70), ferritin and cold shock domain protein (csdp) in H. discus hannai and H. gigantea, then further investigated their mRNA level changes in the four abalone genotypes after bacterial challenge. Results showed that these physiological and molecular parameters were significantly induced by bacterial exposure, and their changing patterns were obviously different between the four genotypes: (1) Survival rates of the two hybrids were higher than both parental species after bacterial exposure; (2) DG had higher THC than the other three genotypes; (3) Phagocytosis responded slower in the hybrids than in the parental species; (4) DD's ROS level was lower than the other three genotypes at 48 h post infection; (5) Phenoloxidase activity was lower in DD during the infection compared to the other genotypes; (6) mRNA levels of hsp70 and csdp, were always lower in at least one parental species (DD) than in the hybrids after the bacterial exposure. Results from this study indicate that the hybrids are more active or efficient in immune system function, hence they could effectively defense against a bacterial invasion, leading to higher survival rates after challenge. This study provides physiological and molecular evidences for interpreting the disease resistant heterosis in this abalone hybrid system, which could help us in a better understanding and utilization of heterosis in abalone aquaculture.

Breeding and study of two new photoperiod- and thermo-sensitive genic male sterile lines of polyploid rice (Oryza sativa L.)

Male sterile lines play an important role in the utilization of heterosis. To explore and exploit the heterosis of polyploid hybrid rice, two photoperiod- and thermo-sensitive genic male sterile lines of polyploid rice, PS006 and PS012, were bred via chromosome doubling, complex hybridization and self-breeding. The characteristics of these two lines, including the agronomic traits, growth, development, fertility transformation and combining ability, were investigated. Both lines had good agronomic characteristics and flowering habits, a high outcrossing rate, obvious fertility alterations and good combining abilities. Their hybrids showed strong heterosis and great potential for increasing rice productivity and quality. The new polyploid rice photoperiod- and thermo-sensitive genic male sterile lines will provide material for further research into polyploidy and hybrid vigour in rice and promote the exploitation of polyploid hybrid rice.

Advances in understanding the molecular mechanisms of cytoplasmic male sterility and restoration in rice.

Cytoplasmic male sterility (CMS) in plants is a male reproductive defect determined by mitochondrial genes and inherited maternally. CMS can be suppressed by nuclear restorer of fertility (Rf) genes. Therefore, CMS/Rf systems provide a classic model for the study of mitochondrial-nuclear interactions in plants. Moreover, CMS/Rf systems are economical, effective tools for the production of hybrid seeds. For example, CMS/Rf systems have been applied in over forty countries to breed hybrid rice (Oryza sativa L.) with improved yields due to hybrid vigor. The production of hybrid rice mainly depends on three types of CMS systems, namely Wild-Abortive type CMS (CMS-WA), Hong-Lian type CMS (CMS-HL) and Boro II type CMS (CMS-BT). Understanding the molecular mechanisms underlying these CMS/Rf systems will help us to understand mitochondrial-nuclear interactions, and accelerate the utilization of heterosis for improvement in yield. In the past decades, research benefitting from the availability of the high-quality, annotated mitochondrial and nuclear genome sequences of rice has isolated many CMS genes, identified the cognate nuclear Rf genes and studied the molecular mechanisms underlying CMS and restoration in rice. Here, we focus on recent advances in studies of the three major CMS/Rf systems in rice and discuss the key issues facing basic research and application of CMS/Rf systems in the future.

Three representative inter and intra-subspecific crosses reveal the genetic architecture of reproductive isolation in rice.

Systematic characterization of genetic and molecular mechanisms in the formation of hybrid sterility is of fundamental importance in understanding reproductive isolation and speciation. Using ultra-high-density genetic maps, 43 single-locus quantitative trait loci (QTLs) and 223 digenic interactions for embryo-sac, pollen, and spikelet fertility are depicted from three crosses between representative varieties of japonica and two varietal groups of indica, which provide an extensive archive for investigating the genetic basis of reproductive isolation in rice. Ten newly detected single-locus QTLs for inter- and intra-subspecific fertility are identified. Three loci for embryo-sac fertility are detected in both Nip×ZS97 and Nip×MH63 crosses, whereas QTLs for pollen fertility are not in common between the two crosses thus leading to fertility variation. Five loci responsible for fertility and segregation distortion are observed in the ZS97×MH63 cross. The importance of two-locus interactions on fertility are quantified in the whole genome, which identify that three types of interaction contribute to fertility reduction in the hybrid. These results construct the genetic architecture with respect to various forms of reproductive barriers in rice, which have significant implications in utilization of inter-subspecific heterosis along with improvement in the fertility of indica-indica hybrids at single- and multi-locus level.

Heterosis, combining ability and genetic effect, and relationship with genetic distance based on a diallel of hybrids from five diverse Gossypium barbadense cotton genotypes

The cultivated tetraploid Gossypium barbadense L. cotton produces superior natural fibers for the textile industry in the world. However, the possibility in utilization of heterosis to further increase its lint yield has not been extensively explored. In this study, two commercial US Pima cotton cultivars and three exotic G. barbadense lines, together with all of their possible hybrids in F1 and F2 progeny without reciprocals, were tested for lint yield, yield components, and fiber quality traits in four environments in 2005–2007. With a few exceptions, genotype (G), environment (E), and G × E were all significant or highly significant for all the traits studied. General combining ability (GCA) variances for all the traits in both F1 and F2 were also significant, while specific combining ability (SCA) variances were detected only for lint yield, fiber length, and micronaire in both generations and boll weight in F1. GCA × E was also detected for lint percent, seed index, and fiber length in both F1 and F2, and boll weight in F1, but none of the traits had significant SCA × E. As a group, F1 and F2 out-yielded the parent group by 20–40% and 6–10%, respectively. Mid-parent heterosis (MPH) for lint yield in F1 was generally positive, ranging from −4.7 to 116.4% with an average of 21.2–48.7%, while lint yield MPH in F2 ranged from −23.3 to 69.4% with an average of 6.4–12.4%. However, useful heterosis in lint yield was only detected in the hybrid between the two US commercial cultivars Pima S-7 and DP 340. MPH for other traits was low or not detected. MPH in F2 was lower than that in F1 but they were generally positively correlated. The genetic distances (GD) of the parents (based on 467 polymorphic RAPD and AFLP markers) between the five parents was not consistently correlated with MPH and SCA of their hybrids and dominant effects for lint yield and other traits. However, significant and positive correlations between GD of parents and the performance of their hybrids were detected for lint yield, lint percentage, and lint index in both F1 and F2 in most of the tests. GD of parents was also correlated with their GCA and additive effects in lint yield, lint percent, lint index, micronaire, plant height, and elongation. The results suggest that the close correlation between GD and hybrid performance per se was mainly due to the existence of GCA and additive effects from parents.

QTL mapping of general combining abilities of four traits in maize using a high-density genetic map

AbstractGeneral combining abilities (GCAs) are very important in utilization of heterosis in maize breeding. However, its genetic basis is unclear. In the present study, a set of 118 doubled haploid (DH) lines were induced from F1 generations produced from the cross between the inbred line Zheng 58 and the inbred line W499 belonging to the Reid subgroup. Using the MaizeSNP50 BeadChip, a high-density genetic map was constructed based on the DH population which included 1 147 bin markers with an average interval length of 2.00 cM. Meanwhile, the DH population was crossed with three testers including W16-5, HD568, and W556, which belong to the Sipingtou subgroup. The GCAs of the ear height (EH), the kernel moisture content (KMC), the kernel ratio (KR), and the yield per plant (YPP) were estimated using these hybrids in three environments. Combining the high-density genetic map and the GCAs, a total of 14 QTLs were detected for the GCAs of the four traits. Especially, one pleiotropic QTL was identified on chromosome 1 between the SNP SYN16067 and the SNP PZE-101169244 which was simultaneously associated with the GCAs of the EH, the KR, and the YPP. These QTLs pave the way for further dissecting the genetic architecture underlying GCAs of the traits, and they may be used to enhance GCAs of inbred lines under the fixed heterotic pattern Reid×Sipingtou in China through a marker-assisted selection approach.

Cloning and Functional Analysis of MADS-box Genes, TaAG-A and TaAG-B, from a Wheat K-type Cytoplasmic Male Sterile Line

Wheat (Triticum aestivum L.) is a major crop worldwide. The utilization of heterosis is a promising approach to improve the yield and quality of wheat. Although there have been many studies on wheat cytoplasmic male sterility, its mechanism remains unclear. In this study, we identified two MADS-box genes from a wheat K-type cytoplasmic male sterile (CMS) line using homology-based cloning. These genes were localized on wheat chromosomes 3A and 3B and named TaAG-A and TaAG-B, respectively. Analysis of TaAG-A and TaAG-B expression patterns in leaves, spikes, roots, and stems of Chinese Spring wheat determined using quantitative RT-PCR revealed different expression levels in different tissues. TaAG-A had relatively high expression levels in leaves and spikes, but low levels in roots, while TaAG-B had relatively high expression levels in spikes and lower expression in roots, stems, and leaves. Both genes showed downregulation during the mononucleate to trinucleate stages of pollen development in the maintainer line. In contrast, upregulation of TaAG-B was observed in the CMS line. The transcript levels of the two genes were clearly higher in the CMS line compared to the maintainer line at the trinucleate stage. Overexpression of TaAG-A and TaAG-B in Arabidopsis resulted in phenotypes with earlier reproductive development, premature mortality, and abnormal buds, stamens, and stigmas. Overexpression of TaAG-A and TaAG-B gives rise to mutants with many deformities. Silencing TaAG-A and TaAG-B in a fertile wheat line using the virus-induced gene silencing (VIGS) method resulted in plants with green and yellow striped leaves, emaciated spikes, and decreased selfing seed set rates. These results demonstrate that TaAG-A and TaAG-B may play a role in male sterility in the wheat CMS line.

Development and prospect of hybrid <italic>japonica</italic> rice in China

The extension of hybrid japonica rice is of great significance to increase rice production and ensure grain security in China. The low productivity of parental materials and the narrow genetic distance between parents resulted in the insufficient superiority of hybrid japonica rice in China, and the yield of japonica rice cannot be improved significantly compared with that of conventional japonica rice. The low yield of hybrid seed production and few super japonica hybrid combinations directly limited the widely extension of hybrid japonica rice. In this paper, the history of development of japonica hybrid rice breeding in China was reviewed, including the discovery and utilization of sterile lines such as Dian type and BT type, as well as the breeding of hybrid japonica restorer lines (C57 and C418) with high combining ability via “ indica - japonica bridge” method. In addition, the key technology advances of increasing hybrid seed production of japonica rice and utilization of heterosis were summarized as following: (1) The increase of stigma exsertion rate and enhancement of stigma viability lead to high probability of successful fertilization, thus resulting in the increase of hybrid rice seed production. Significant correlations were showed between stigma exsertion rate and the ratio of floret length and width, stigma exsertion rate and column length, stigma exsertion rate and angle. Great progresses on stigma exsertion have been achieved from the studies on the genetic and molecular level (i.e marker-assisted selection). (2) To further increase the utilization of heterosis in hybrid japonica rice, the studies on heterotic groups and patterns for making hybrid combinations from the selection of superior parents in japonica rice were conducted. Based on the different heterotic groups of parental lines of japonica rice, several models for making hybrid combinations were proposed, including the model of heterosis complementation of indica and japonica rice, the model of the interactions of thermo-sensitive and photo-period-sensitive genes, and the model of grain structure complementation. These models emphasize comprehensive characteristics in rice breeding, including the utilization of indica - japonica intersubspecific heterosis, the applications of wide compatibility genes and restorer genes in rice, the anti-senility of leaves and roots, the applications of plant type such as large panicles and good grain-filling characteristics, and resistance for abiotic stress such as lodging resistance. Therefore, this study provides technical suggestions and strategies for further breeding and application of japonica hybrid rice.

Progress of super hybrid rice research in China

To meet the growing food demands in China, a program of super rice breeding was set up by the Chinese Ministry of Agriculture in 1996. The goals of this program is to achieve rice yield targets to 10.5, 12.0, 13.5, and 15.0 t/ha in single season rice growing area through four research phases. A proposed model of combining morphological improvement with the utilization of inter-subspecific ( indica / japonica ) heterosis, by Prof. Yuan LongPing in 1997, played a leading contribution for the program of super hybrid rice breeding. Until now, all yield targets of four phases have been achieved. The pioneer super hybrid rice variety, Liangyoupeijiu, met the Phase I yield target in 2000. The Phase II super hybrids were successfully developed in 2004. Y Liangyou No.1 (YLY1), the typical Phase II super hybrid rice variety, has a largest annual planting area among all hybrid rice varieties in China since 2010 and has been extended to more than 4 million hectare so far. Y Liangyou No.2 (YLY2) met the standard of phase III super rice with a yield record of 926.6 kg/mu (13.9 t/ha) in 2011. The breeding target of Phase IV super hybrid was achieved in 2014. The new variety, Y Liangyou 900 (YLY900), created a new yield record of 15.4 t/ha, which doubled the average rice yield in China. Up to now, 125 super rice varieties have been certificated by the Ministry of Agriculture with a total planting area of approximate 80 million hectare in China. However, how to further break the yield ceiling and realize the yield potential of elite varieties in diverse range of target environments remains to be the major challenges for super hybrid rice breeding. Herein, we proposed that utilization of ideotype and inter-subspecific heterosis, assisted with molecular design breeding, is still being the vital way to increase yield ceiling.

A Major QTL, Which Is Co-located with cly1, and Two Minor QTLs Are Associated with Glume Opening Angle in Barley (Hordeum vulgare L.).

Cleistogamous and chasmogamous are two opposing phenomena for flowering in barley. Cleistogamy limits the rate of outcrossing, and increases the cost of producing hybrid barley seeds. Selecting chasmogamous lines with a large glume opening angle (GOA) is essential for the utilization of barley heterosis. In the current study, 247 DH lines derived from a cross between Yangnongpi7 and Yang0187 were used to identify and validate quantitative trait loci (QTLs) associated with the GOA in different environments using SSR markers. Three QTLs associated with barley GOA were mapped on chromosomes 2H and 7H. The major QTL QGOA-2H-2 was mapped on chromosome 2H with the flanking markers of KDH and GBM1498, explaining 63.92% of the phenotypic variation. The marker KDH was developed from the gene Cly1, which was the candidate gene for QGOA-2H-2. This new marker can be used to identify barley chasmogamous lines with a large GOA. The two minor QTLs were validated at all three locations across two seasons after removing DH lines carrying the candidate gene Cly1 of QGOA-2H-2.