Cytoplasmic-nuclear genomic barriers in rice pollen development revealed by comparison of global gene expression profiles among five independent cytoplasmic male sterile lines

Unveiling the Genetic Basis Underlying Rice Anther Culturability via Segregation Distortion Analysis in Doubled Haploid Population

Anther culture (AC) is a valuable technique in rice breeding. However, the genetic mechanisms underlying anther culturability remain elusive, which has hindered its widespread adoption in rice breeding programs. During AC, microspores carrying favorable alleles for AC are selectively regenerated, leading to segregation distortion (SD) of chromosomal regions linked to these alleles in the doubled haploid (DH) population. Using the AC method, a DH population was generated from the japonica hybrid rice Shenyou 26. A genetic map consisting of 470 SNPs was constructed using this DH population, and SD analysis was performed at both the single- and two-locus levels to dissect the genetic basis underlying anther culturability. Five segregation distortion loci (SDLs) potentially linked to anther culturability were identified. Among these, SDL5 exhibited an overrepresentation of alleles from the female parent, while SDL1.1, SDL1.2, SDL2, and SDL7 displayed an overrepresentation of alleles from the male parent. Furthermore, six pairs of epistatic interactions (EPIs) that influenced two-locus SDs in the DH population were discovered. A cluster of genetic loci, associated with EPI-1, EPI-3, EPI-4, and EPI-5, overlapped with SDL1.1, indicating that the SDL1.1 locus may play a role in regulating anther culturability via both additive and epistatic mechanisms. These findings provide valuable insights into the genetic control of anther culturability in rice and lay the foundation for future research focused on identifying the causal genes associated with anther culturability.

Investigation of B-atp6-orfH79 distributing in Chinese populations of Oryza rufipogon and analysis of its chimeric structure

BACKGROUND

The cytoplasmic male sterility (CMS) of rice is caused by chimeric mitochondrial DNA (mtDNA) that is maternally inherited in the majority of multicellular organisms. Wild rice (Oryza rufipogon Griff.) has been regarded as the ancestral progenitor of Asian cultivated rice (Oryza sativa L.). To investigate the distribution of original CMS source, and explore the origin of gametophytic CMS gene, a total of 427 individuals with seventeen representative populations of O. rufipogon were collected in from Dongxiang of Jiangxi Province to Sanya of Hainan Province, China, for the PCR amplification of atp6, orfH79 and B-atp6-orfH79, respectively.

RESULTS

The B-atp6-orfH79 and its variants (B-atp6-GSV) were detected in five among seventeen populations (i.e. HK, GZ, PS, TL and YJ) through PCR amplification, which could be divided into three haplotypes, i.e., BH1, BH2, and BH3. The BH2 haplotype was identical to B-atp6-orfH79, while the BH1 and BH3 were the novel haplotypes of B-atp6-GSV. Combined with the high-homology sequences in GenBank, a total of eighteen haplotypes have been revealed, only with ten haplotypes in orfH79 and its variants (GSV) that belong to three species (i.e. O. rufipogon, Oryza nivara and Oryza sativa). Enough haplotypes clearly demonstrated the uniform structural characteristics of the B-atp6-orfH79 as follows: except for the conserved sequence (671 bp) composed of B-atp6 (619 bp) and the downstream followed the B-atp6 (52 bp, DS), and GSV sequence, a rich variable sequence (VS, 176 bp) lies between the DS and GSV with five insertion or deletion and more than 30 single nucleotide polymorphism. Maximum likelihood analysis showed that eighteen haplotypes formed three clades with high support rate. The hierarchical analysis of molecular variance (AMOVA) indicated the occurrence of variation among all populations (F_ST = 1; P < 0.001), which implied that the chimeric structure occurred independently. Three haplotypes (i.e., H1, H2 and H3) were detected by the primer of orfH79, which were identical to the GVS in B-atp6-GVS structure, respectively. All seventeen haplotypes of the orfH79, belonged to six species based on our results and the existing references. Seven existed single nucleotide polymorphism in GSV section can be translated into eleven various amino acid sequences.

CONCLUSIONS

Generally, this study, indicating that orfH79 was always accompanied by the B-atp6, not only provide two original CMS sources for rice breeding, but also confirm the uniform structure of B-atp-orfH79, which contribute to revealing the origin of rice gametophytic CMS genes, and the reason about frequent recombination of mitochondrial DNA.

Induction of Male Sterility by Targeted Mutation of a Restorer-of-Fertility Gene with CRISPR/Cas9-Mediated Genome Editing in Brassica napus L

Brassica napus L. (canola, oil seed rape) is one of the world's most important oil seed crops. In the last four decades, the discovery of cytoplasmic male-sterility (CMS) systems and the restoration of fertility (Rf) genes in B. napus has improved the crop traits by heterosis. The homologs of Rf genes, known as the restoration of fertility-like (RFL) genes, have also gained importance because of their similarities with Rf genes. Such as a high non-synonymous/synonymous codon replacement ratio (dN/dS), autonomous gene duplications, and a possible engrossment in fertility restoration. B. napus contains 53 RFL genes on chromosomes A9 and C8. Our research aims to study the function of BnaRFL11 in fertility restoration using the CRISPR/Cas9 genome editing technique. A total of 88/108 (81.48%) T₀ lines, and for T₁, 110/145 (75%) lines carried T-DNA insertions. Stable mutations were detected in the T₀ and T₁ generations, with an average allelic mutation transmission rate of 81%. We used CRISPR-P software to detect off-target 50 plants sequenced from the T₀ generation that showed no off-target mutation, signifying that if the designed sgRNA is specific for the target, the off-target effects are negligible. We also concluded that the mutagenic competence of the designed sgRNAs mediated by U6-26 and U6-29 ranged widely from 31% to 96%. The phenotypic analysis of bnarfl11 revealed defects in the floral structure, leaf size, branch number, and seed production. We discovered a significant difference between the sterile line and fertile line flower development after using a stereomicroscope and scanning electron microscope. The pollen visibility test showed that the pollen grain had utterly degenerated. The cytological observations of homozygous mutant plants showed an anther abortion stage similar to nap-CMS, with a Orf222, Orf139, Ap3, and nad5c gene upregulation. The bnarfl11 shows vegetative defects, including fewer branches and a reduced leaf size, suggesting that PPR-encoding genes are essential for the plants' vegetative and reproductive growth. Our results demonstrated that BnaRFL11 has a possible role in fertility restoration. The current study's findings suggest that CRISPR/Cas9 mutations may divulge the functions of genes in polyploid species and provide agronomically desirable traits through a targeted mutation.

Mechanism and Utilization of Ogura Cytoplasmic Male Sterility in Cruciferae Crops

Hybrid production using lines with cytoplasmic male sterility (CMS) has become an important way to utilize heterosis in vegetables. Ogura CMS, with the advantages of complete pollen abortion, ease of transfer and a progeny sterility rate reaching 100%, is widely used in cruciferous crop breeding. The mapping, cloning, mechanism and application of Ogura CMS and fertility restorer genes in Brassica napus, Brassica rapa, Brassica oleracea and other cruciferous crops are reviewed herein, and the existing problems and future research directions in the application of Ogura CMS are discussed.

Effect of sterile cytoplasms on content of absolutely dry matter in the grain sorghum hybrids

Analysis of absolutely dry matter (ADM) accumulation is important indicator of productivity of crop plants. For three seasons, we investigated the effect of sterile cytoplasms on content of ADM in the F1 hybrids of grain sorghum obtained on the basis of two series of alloplasmic iso-nuclear CMS-lines: (1) with A3, A4, and 9E cytoplasms and (2) with 9E and M35-1A cytoplasms. For the first time, the effect of the type of sterile cytoplasm on content of ADM in the F1 sorghum hybrids was shown. In each season, A3 cytoplasm reduced ADM in the F1 hybrids at the “tillering – heading” stage, whereas 9E cytoplasm increased ADM at the “heading – complete maturity” stage. The most significant differences were observed under drought conditions. These data indicate the genetic influence of cytoplasm on assimilation capacity of sorghum hybrids and tolerance to drought stress.

Unraveling the Genetic Basis of Fertility Restoration for Cytoplasmic Male Sterile Line WNJ01A Originated From Brassica juncea in Brassica napus

Crosses that lead to heterosis have been widely used in the rapeseed (Brassica napus L.) industry. Cytoplasmic male sterility (CMS)/restorer-of-fertility (Rf) systems represent one of the most useful tools for rapeseed production. Several CMS types and their restorer lines have been identified in rapeseed, but there are few studies on the mechanisms underlying fertility restoration. Here, we performed morphological observation, map-based cloning, and transcriptomic analysis of the F₂ population developed by crossing the CMS line WNJ01A with its restorer line Hui01. Paraffin-embedded sections showed that the sporogenous cell stage was the critical pollen degeneration period, with major sporogenous cells displaying loose and irregular arrangement in sterile anthers. Most mitochondrial electron transport chain (mtETC) complex genes were upregulated in fertile compared to sterile buds. Using bulked segregant analysis (BSA)-seq to analyze mixed DNA pools from sterile and fertile F₂ buds, respectively, we identified a 6.25 Mb candidate interval where Rfw is located. Using map-based cloning experiments combined with bacterial artificial chromosome (BAC) clone sequencing, the candidate interval was reduced to 99.75 kb and two pentatricopeptide repeat (PPR) genes were found among 28 predicted genes in this interval. Transcriptome sequencing showed that there were 1679 DEGs (1023 upregulated and 656 downregulated) in fertile compared to sterile F₂ buds. The upregulated differentially expressed genes (DEGs) were enriched in the Kyoto Encyclopedia of Genes and Genomes (KEGG) lysine degradation pathway and phenylalanine metabolism, and the downregulated DEGs were enriched in cutin, suberine, and wax biosynthesis. Furthermore, 44 DEGs were involved in pollen and anther development, such as tapetum, microspores, and pollen wall development. All of them were upregulated except a few such as POE1 genes (which encode Pollen Ole e I allergen and extensin family proteins). There were 261 specifically expressed DEGs (9 and 252 in sterile and fertile buds, respectively). Regarding the fertile bud-specific upregulated DEGs, the ubiquitin-proteasome pathway was enriched. The top four hub genes in the protein-protein interaction network (BnaA09g56400D, BnaA10g18210D, BnaA10g18220D, and BnaC09g41740D) encode RAD23d proteins, which deliver ubiquitinated substrates to the 26S proteasome. These findings provide evidence on the pathways regulated by Rfw and improve our understanding of fertility restoration.

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

BACKGROUND

Cytoplasmic 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.

RESULTS

CircRNA 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.

CONCLUSIONS

Our 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.

Different lengths, copies and expression levels of the mitochondrial atp6 gene in male sterile and fertile lines of carrot (Daucus carota L.)

The male-sterile carrot is an effective material for carrot breeding. The atp6 gene is involved in carrot fertility. However, the differences in lengths, copies, and expression profiles of the atp6 gene in fertile and male-sterile lines of carrot are unclear. In this study, one copy atp6 gene was found in the mtDNAs of 'Kuroda' (fertility, 954 bp) and 'Wuye-BY' (male sterility, 819 bp) carrot lines, while two copies atp6 genes (Wuye-L and Wuye-D, 954 bp and 819 bp, respectively) were found in the mtDNA of 'Wuye' (fertility). Two putative conserved domains have been detected in the carrot atp6 protein. Evolutionary analysis showed that the atp6 protein sequences of Wuye-L and Kuroda were clustered in the same branch, while Wuye-D and Wuye-BY were clustered in the same branch. The atp6 gene was higher expressed in the flowers of 'Kuroda' and 'Wuye' (Wuye-L), while lower expressed in 'Wuye-BY' and 'Wuye' (Wuye-D).

Comparative transcript profiling of alloplasmic male-sterile lines revealed altered gene expression related to pollen development in rice (Oryza sativa L.)

BACKGROUND

Cytoplasmic male sterility (CMS) is an ideal model for investigating the mitochondrial-nuclear interaction and down-regulated genes in CMS lines which might be the candidate genes for pollen development in rice. In this study, a set of rice alloplasmic sporophytic CMS lines was obtained by successive backcrossing of Meixiang B, with three different cytoplasmic types: D62A (D type), ZS97A (WA type) and XQZ-A (DA type).

RESULTS

Using microarray, the anther transcript profiles of the three indica rice CMS lines revealed 622 differentially expressed genes (DEGs) in each of the three CMS lines compared with the maintainer line Meixiang B. GO and MapMan analysis indicated that these DEGs were mainly involved in lipid metabolism and cell wall organization. Compared with the gene expression of sporophytic and gametophytic CMS lines, 303 DEGs were identified and 56 of them were down-regulated in all the CMS lines of rice. These down-regulated DEGs in the CMS lines were found to be involved in tapetum or cell wall formation and their suppressed expression might be related to male sterility. Weighted gene co-expression network analysis (WGCNA) revealed that two modules were significantly associated with male sterility and many hub genes that were differentially expressed in the CMS lines.

CONCLUSION

A large set of putative genes involved in anther development was identified in the present study. The results will give some information for the nuclear gene regulation by different cytoplasmic genotypes and provide a rich resource for further functional research on the pollen development in rice.

Involvement of a universal amino acid synthesis impediment in cytoplasmic male sterility in pepper

To explore the mechanisms of pepper (Capsicum annuum L.) cytoplasmic male sterility (CMS), we studied the different maturation processes of sterile and fertile pepper anthers. A paraffin section analysis of the sterile anthers indicated an abnormality of the tapetal layer and an over-vacuolization of the cells. The quantitative proteomics results showed that the expression of histidinol dehydrogenase (HDH), dihydroxy-acid dehydratase (DAD), aspartate aminotransferase (ATAAT), cysteine synthase (CS), delta-1-pyrroline-5-carboxylate synthase (P5CS), and glutamate synthetase (GS) in the amino acid synthesis pathway decreased by more than 1.5-fold. Furthermore, the mRNA and protein expression levels of DAD, ATAAT, CS and P5CS showed a 2- to 16-fold increase in the maintainer line anthers. We also found that most of the amino acid content levels decreased to varying degrees during the anther tapetum period of the sterile line, whereas these levels increased in the maintainer line. The results of our study indicate that during pepper anther development, changes in amino acid synthesis are significant and accompany abnormal tapetum maturity, which is most likely an important cause of male sterility in pepper.

Mitochondrial ORF79 levels determine pollen abortion in cytoplasmic male sterile rice

Cytoplasmic male sterility (CMS) is an important agricultural trait characterized by lack of functional pollen, and caused by ectopic and defective mitochondrial gene expression. The pollen function in CMS plants is restored by the presence of nuclear-encoded restorer of fertility (Rf) genes. Previously, we cloned Rf2, which restores the fertility of Lead Rice (LD)-type CMS rice. However, neither the function of Rf2 nor the identity of the mitochondrial gene causing CMS has been determined in LD-CMS rice. Here, we show that the mitochondrial gene orf79 acts as a CMS-associated gene in LD-CMS rice, similar to its role in BT-CMS rice originating from Chinsurah Boro II, and Rf2 weakly restores fertility in BT-CMS rice. We also show that RF2 promotes degradation of atp6-orf79 RNA in a different manner from that of RF1, which is the Rf gene product in BT-CMS rice. The amount of ORF79 protein in LD-CMS rice was one-twentieth of the amount in BT-CMS rice. The difference in ORF79 protein levels probably accounts for the mild and severe pollen defects in LD-CMS and BT-CMS rice, respectively. In the presence of Rf2, accumulation of ORF79 was reduced to almost zero and 25% in LD-CMS and BT-CMS rice, respectively, which probably accounts for the complete and weak fertility restoration abilities of Rf2 in LD-CMS and BT-CMS rice, respectively. These observations indicate that the amount of ORF79 influences the pollen fertility in two strains of rice in which CMS is induced by orf79.

UNCLES: method for the identification of genes differentially consistently co-expressed in a specific subset of datasets

Background

Collective analysis of the increasingly emerging gene expression datasets are required. The recently proposed binarisation of consensus partition matrices (Bi-CoPaM) method can combine clustering results from multiple datasets to identify the subsets of genes which are consistently co-expressed in all of the provided datasets in a tuneable manner. However, results validation and parameter setting are issues that complicate the design of such methods. Moreover, although it is a common practice to test methods by application to synthetic datasets, the mathematical models used to synthesise such datasets are usually based on approximations which may not always be sufficiently representative of real datasets.

Results

Here, we propose an unsupervised method for the unification of clustering results from multiple datasets using external specifications (UNCLES). This method has the ability to identify the subsets of genes consistently co-expressed in a subset of datasets while being poorly co-expressed in another subset of datasets, and to identify the subsets of genes consistently co-expressed in all given datasets. We also propose the M-N scatter plots validation technique and adopt it to set the parameters of UNCLES, such as the number of clusters, automatically. Additionally, we propose an approach for the synthesis of gene expression datasets using real data profiles in a way which combines the ground-truth-knowledge of synthetic data and the realistic expression values of real data, and therefore overcomes the problem of faithfulness of synthetic expression data modelling. By application to those datasets, we validate UNCLES while comparing it with other conventional clustering methods, and of particular relevance, biclustering methods. We further validate UNCLES by application to a set of 14 real genome-wide yeast datasets as it produces focused clusters that conform well to known biological facts. Furthermore, in-silico-based hypotheses regarding the function of a few previously unknown genes in those focused clusters are drawn.

Conclusions

The UNCLES method, the M-N scatter plots technique, and the expression data synthesis approach will have wide application for the comprehensive analysis of genomic and other sources of multiple complex biological datasets. Moreover, the derived in-silico-based biological hypotheses represent subjects for future functional studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-015-0614-0) contains supplementary material, which is available to authorized users.

Identification of tapetum-specific genes by comparing global gene expression of four different male sterile lines in Brassica oleracea

The tapetum plays an important role in anther development by providing necessary enzymes and nutrients for pollen development. However, it is difficult to identify tapetum-specific genes on a large-scale because of the difficulty of separating tapetum cells from other anther tissues. Here, we reported the identification of tapetum-specific genes by comparing the gene expression patterns of four male sterile (MS) lines of Brassica oleracea. The abortive phenotypes of the four MS lines revealed different defects in tapetum and pollen development but normal anther wall development when observed by transmission electron microscopy. These tapetum displayed continuous defective characteristics throughout the anther developmental stages. The transcriptome from flower buds, covering all anther developmental stages, was analyzed and bioinformatics analyses exploring tapetum development-related genes were performed. We identified 1,005 genes differentially expressed in at least one of the MS lines and 104 were non-pollen expressed genes (NPGs). Most of the identified NPGs were tapetum-specific genes considering that anther walls were normally developed in all four MS lines. Among the 104 NPGs, 22 genes were previously reported as being involved in tapetum development. We further separated the expressed NPGs into different developmental stages based on the MS defects. The data obtained in this study are not only informative for research on tapetum development in B. oleracea, but are also useful for genetic pathway research in other related species.

Workable male sterility systems for hybrid rice: Genetics, biochemistry, molecular biology, and utilization

The exploitation of male sterility systems has enabled the commercialization of heterosis in rice, with greatly increased yield and total production of this major staple food crop. Hybrid rice, which was adopted in the 1970s, now covers nearly 13.6 million hectares each year in China alone. Various types of cytoplasmic male sterility (CMS) and environment-conditioned genic male sterility (EGMS) systems have been applied in hybrid rice production. In this paper, recent advances in genetics, biochemistry, and molecular biology are reviewed with an emphasis on major male sterility systems in rice: five CMS systems, i.e., BT-, HL-, WA-, LD- and CW- CMS, and two EGMS systems, i.e., photoperiod- and temperature-sensitive genic male sterility (P/TGMS). The interaction of chimeric mitochondrial genes with nuclear genes causes CMS, which may be restored by restorer of fertility (Rf) genes. The PGMS, on the other hand, is conditioned by a non-coding RNA gene. A survey of the various CMS and EGMS lines used in hybrid rice production over the past three decades shows that the two-line system utilizing EGMS lines is playing a steadily larger role and TGMS lines predominate the current two-line system for hybrid rice production. The findings and experience gained during development and application of, and research on male sterility in rice not only advanced our understanding but also shed light on applications to other crops.

Comparative transcript profiling of the fertile and sterile flower buds of pol CMS in B. napus

BACKGROUND

The Polima (pol) system of cytoplasmic male sterility (CMS) and its fertility restoration gene Rfp have been used in hybrid breeding in Brassica napus, which has greatly improved the yield of rapeseed. However, the mechanism of the male sterility transition in pol CMS remains to be determined.

RESULTS

To investigate the transcriptome during the male sterility transition in pol CMS, a near-isogenic line (NIL) of pol CMS was constructed. The phenotypic features and sterility stage were confirmed by anatomical analysis. Subsequently, we compared the genomic expression profiles of fertile and sterile young flower buds by RNA-Seq. A total of 105,481,136 sequences were successfully obtained. These reads were assembled into 112,770 unigenes, which composed the transcriptome of the bud. Among these unigenes, 72,408 (64.21%) were annotated using public protein databases and classified into functional clusters. In addition, we investigated the changes in expression of the fertile and sterile buds; the RNA-seq data showed 1,148 unigenes had significantly different expression and they were mainly distributed in metabolic and protein synthesis pathways. Additionally, some unigenes controlling anther development were dramatically down-regulated in sterile buds.

CONCLUSIONS

These results suggested that an energy deficiency caused by orf224/atp6 may inhibit a series of genes that regulate pollen development through nuclear-mitochondrial interaction. This results in the sterility of pol CMS by leading to the failure of sporogenous cell differentiation. This study may provide assistance for detailed molecular analysis and a better understanding of pol CMS in B. napus.

Mitochondria and cytoplasmic male sterility in plants

Mitochondria are essential organelles in cells not only because they supply over 90% of the cell's energy but also because their dysfunction is associated with disease. Owing to the importance of mitochondria, there are many questions about mitochondria that must be answered. Cytoplasmic male sterility (CMS) is a mysterious natural phenomenon, and the mechanism of the origin of CMS is unknown. Despite successful utilization of CMS and restoration of fertility (Rf) in practice, the underlying mechanisms of these processes remain elusive. This review summarizes the genes involved in CMS and Rf, with a special focus on recent studies reporting the mechanisms of the CMS and Rf pathways, and concludes with potential working models.

Cytoplasmic genome substitution in wheat affects the nuclear-cytoplasmic cross-talk leading to transcript and metabolite alterations

Background

Alloplasmic lines provide a unique tool to study nuclear-cytoplasmic interactions. Three alloplasmic lines, with nuclear genomes from Triticum aestivum and harboring cytoplasm from Aegilops uniaristata, Aegilops tauschii and Hordeum chilense, were investigated by transcript and metabolite profiling to identify the effects of cytoplasmic substitution on nuclear-cytoplasmic signaling mechanisms.

Results

In combining the wheat nuclear genome with a cytoplasm of H. chilense, 540 genes were significantly altered, whereas 11 and 28 genes were significantly changed in the alloplasmic lines carrying the cytoplasm of Ae. uniaristata or Ae. tauschii, respectively. We identified the RNA maturation-related process as one of the most sensitive to a perturbation of the nuclear-cytoplasmic interaction. Several key components of the ROS chloroplast retrograde signaling, together with the up-regulation of the ROS scavenging system, showed that changes in the chloroplast genome have a direct impact on nuclear-cytoplasmic cross-talk. Remarkably, the H. chilense alloplasmic line down-regulated some genes involved in the determination of cytoplasmic male sterility without expressing the male sterility phenotype. Metabolic profiling showed a comparable response of the central metabolism of the alloplasmic and euplasmic lines to light, while exposing larger metabolite alterations in the H. chilense alloplasmic line as compared with the Aegilops lines, in agreement with the transcriptomic data. Several stress-related metabolites, remarkably raffinose, were altered in content in the H. chilense alloplasmic line when exposed to high light, while amino acids, as well as organic acids were significantly decreased. Alterations in the levels of transcript, related to raffinose, and the photorespiration-related metabolisms were associated with changes in the level of related metabolites.

Conclusion

The replacement of a wheat cytoplasm with the cytoplasm of a related species affects the nuclear-cytoplasmic cross-talk leading to transcript and metabolite alterations. The extent of these modifications was limited in the alloplasmic lines with Aegilops cytoplasm, and more evident in the alloplasmic line with H. chilense cytoplasm. We consider that, this finding might be linked to the phylogenetic distance of the genomes.

Mitochondrial DNA genetic polymorphism in thirteen rice cytoplasmic male sterile lines

Thirteen rice CMS lines derived from different cytoplasms were classified into eight groups by PCR amplification on mtDNA. The orf79 gene, which causes Boro II CMS, possibly results in Dian1-CMS. Thirteen rice cytoplasmic male sterile (CMS) lines derived from different cytoplasms are widely used for hybrid rice breeding. Based on 27 loci on mitochondrial DNA, including single nucleotide polymorphisms and segmental sequence variations between typical indica and japonica as well as high-polymorphism segmental sequence variations and single nucleotide polymorphisms among rice CMS lines, the 13 rice CMS lines were classified into eight groups: (I) wild-abortive CMS, Indonesian Shuitiangu CMS, K-CMS, Gang CMS, D-CMS and dwarf abortive CMS; (II) Maxie-CMS; (III) Honglian CMS; (IV) Boro II CMS; (V) Dian1-CMS; (VI) Liao-CMS; (VII) Lead CMS; and (VIII) Chinese wild rice CMS. According to their pollen abortion phenotypes, groups I and II (including 7 CMS lines) were classified as sporophytic CMS lines, the cytoplasmic genetic relationships among which were very close. They could have originated from similar, or even the same, cytoplasm donors. Groups III-VIII (including 6 CMS lines) were categorized as gametophytic CMS lines, the cytoplasms of which differed from one another, with some having relatively far genetic relationships. Dian1-CMS was found to harbor the orf79 gene, which causes Boro II CMS, whereas Liao-CMS had an orf79 structure that does not result in Lead CMS. Therefore, we speculated that orf79 is associated with Dian1-CMS but not with Liao-CMS. The atp6-orf79 structure related to sterility was also found to experience multiple evolutionary turnovers. All sporophytic CMS lines were indica-like. Except the Honglian CMS line, which was indica-like, all gametophytic CMS lines were japonica-like.

Ogura-CMS in Chinese cabbage (Brassica rapa ssp. pekinensis) causes delayed expression of many nuclear genes

We investigated the mechanism regulating cytoplasmic male sterility (CMS) in Brassica rapa ssp. pekinensis using floral bud transcriptome analyses of Ogura-CMS Chinese cabbage and its maintainer line in B. rapa 300-K oligomeric probe (Br300K) microarrays. Ogura-CMS Chinese cabbage produced few and infertile pollen grains on indehiscent anthers. Compared to the maintainer line, CMS plants had shorter filaments and plant growth, and delayed flowering and pollen development. In microarray analysis, 4646 genes showed different expression, depending on floral bud size, between Ogura-CMS and its maintainer line. We found 108 and 62 genes specifically expressed in Ogura-CMS and its maintainer line, respectively. Ogura-CMS line-specific genes included stress-related, redox-related, and B. rapa novel genes. In the maintainer line, genes related to pollen coat and germination were specifically expressed in floral buds longer than 3mm, suggesting insufficient expression of these genes in Ogura-CMS is directly related to dysfunctional pollen. In addition, many nuclear genes associated with auxin response, ATP synthesis, pollen development and stress response had delayed expression in Ogura-CMS plants compared to the maintainer line, which is consistent with the delay in growth and development of Ogura-CMS plants. Delayed expression may reduce pollen grain production and/or cause sterility, implying that mitochondrial, retrograde signaling delays nuclear gene expression.

The Rice Oligonucleotide Array Database: an atlas of rice gene expression

BACKGROUND

Microarray technologies facilitate high-throughput gene expression analysis. However, the diversity of platforms for rice gene expression analysis hinders efficient analysis. Tools to broadly integrate microarray data from different platforms are needed.

RESULTS

In this study, we developed the Rice Oligonucleotide Array Database (ROAD, http://www.ricearray.org) to explore gene expression across 1,867 publicly available rice microarray hybridizations. The ROAD's user-friendly web interface and variety of visualization tools facilitate the extraction of gene expression profiles using gene and microarray element identifications. The ROAD supports meta-analysis of genes expressed in different tissues and at developmental stages. Co-expression analysis tool provides information on co-regulation between genes under general, abiotic and biotic stress conditions. Additionally, functional analysis tools, such as Gene Ontology and KEGG (Kyoto Encyclopedia of Genes and Genomes) Orthology, are embedded in the ROAD. These tools facilitate the identification of meaningful biological patterns in a list of query genes.

CONCLUSIONS

The Rice Oligonucleotide Array Database provides comprehensive gene expression profiles for all rice genes, and will be a useful resource for researchers of rice and other grass species.

Molecular genetics, physiology and biology of self-incompatibility in Brassicaceae

Self-incompatibility (SI) is defined as the inability to produce zygotes after self-pollination in a fertile hermaphrodite plant, which has stamens and pistils in the same flower. This structural organization of the hermaphrodite flower increases the risk of self-pollination, leading to low genetic diversity. To avoid this problem plants have established several pollination systems, among which the most elegant system is surely SI. The SI trait can be observed in Brassica crops, including cabbage, broccoli, turnip and radish. To produce hybrid seed of these crops efficiently, the SI trait has been employed in an agricultural context. From another point of view, the recognition reaction of SI during pollen-stigma interaction is an excellent model system for cell-cell communication and signal transduction in higher plants. In this review, we describe the molecular mechanisms of SI in Brassicaceae, which have been dissected by genetic, physiological, and biological approaches, and we discuss the future prospects in relation to associated scientific fields and new technologies.

The fertility restorer gene, Rf2, for Lead Rice-type cytoplasmic male sterility of rice encodes a mitochondrial glycine-rich protein

Cytoplasmic male sterility (CMS) is associated with a mitochondrial mutation that causes an inability to produce fertile pollen. The fertility of CMS plants is restored in the presence of a nuclear-encoded fertility restorer (Rf) gene. In Lead Rice-type CMS, discovered in the indica variety 'Lead Rice', fertility of the CMS plant is restored by the single nuclear-encoded gene Rf2 in a gametophytic manner. We performed map-based cloning of Rf2, and proved that it encodes a protein consisting of 152 amino acids with a glycine-rich domain. Expression of Rf2 mRNA was detected in developing and mature anthers. An RF2-GFP fusion was shown to be targeted to mitochondria. Replacement of isoleucine by threonine at amino acid 78 of the RF2 protein was considered to be the cause of functional loss in the rf2 allele. As Rf2 does not encode a pentatricopeptide repeat protein, unlike a majority of previously identified Rf genes, the data from this study provide new insights into the mechanism for restoring fertility in CMS.

OryzaExpress: an integrated database of gene expression networks and omics annotations in rice

Similarity of gene expression profiles provides important clues for understanding the biological functions of genes, biological processes and metabolic pathways related to genes. A gene expression network (GEN) is an ideal choice to grasp such expression profile similarities among genes simultaneously. For GEN construction, the Pearson correlation coefficient (PCC) has been widely used as an index to evaluate the similarities of expression profiles for gene pairs. However, calculation of PCCs for all gene pairs requires large amounts of both time and computer resources. Based on correspondence analysis, we developed a new method for GEN construction, which takes minimal time even for large-scale expression data with general computational circumstances. Moreover, our method requires no prior parameters to remove sample redundancies in the data set. Using the new method, we constructed rice GENs from large-scale microarray data stored in a public database. We then collected and integrated various principal rice omics annotations in public and distinct databases. The integrated information contains annotations of genome, transcriptome and metabolic pathways. We thus developed the integrated database OryzaExpress for browsing GENs with an interactive and graphical viewer and principal omics annotations (http://riceball.lab.nig.ac.jp/oryzaexpress/). With integration of Arabidopsis GEN data from ATTED-II, OryzaExpress also allows us to compare GENs between rice and Arabidopsis. Thus, OryzaExpress is a comprehensive rice database that exploits powerful omics approaches from all perspectives in plant science and leads to systems biology.