Mapping five novel interspecific hybrid sterility loci between Oryza sativa and Oryza meridionalis.
ABSTRACT: Oryza meridionalis is a potential source for improving Asian cultivated rice O. sativa via direct hybridization and backcrossing. However, hybrid sterility between O. sativa and O. meridionalis is the main barrier of reproduction hindering the transfer of favorable genes from O. meridionalis to O. sativa. To investigate the nature of hybrid sterility between O. sativa and O. meridionalis, three accessions of O. meridionalis were used as male parents to cross Dianjingyou 1, an O. sativa subsp. japonica cultivar following the backcross with the recurrent parent of Dianjingyou 1. Twenty pollen sterility NILs (BC6F1) were obtained and genotyped by using simple sequence repeat (SSR) markers distributed across the 12 rice chromosomes. The heterozygous markers were employed to genotype the corresponding segregation populations for mapping sterility genes. As a result, five novel loci for pollen sterility between O. sativa and O. meridionalis were identified and designated as S51(t), S52(t), S53(t), S54(t) and S55(t), respectively. The genetic behavior of five novel loci followed one-locus allelic interaction model. The disharmonious interaction between Asian cultivated rice allele and wild relative allele led to the partial or full abortion of male gametes for one parent allele in the heterozygotes. These results will be useful for elucidating the mechanism of interspecific hybrid sterility and further utilizing favorable genes from O. meridionalis for enhancement of rice breeding.
Project description:Hybrid sterility between Oryza sativa and O. glaberrima is a main reproduction barrier when transferring the favorable alleles from O. glaberrima to O. sativa and it happens due to allelic interaction at sterility loci. Neutral alleles at each locus have the potential to overcome the sterility between the two cultivated rice species. In this study, an O. sativa cultivar Dianjingyou 1 (DJY1) and its near-isogenic lines (NILs) harboring the single sterility allele S1-glab, S19-glab, S20-glab, S37-glab, S38-glab and S39-glab as the tested lines were crossed with O. glaberrima, O. rufipogon, O. nivara, O. glumaepatula, O. barthii, O. meridionalis and O. sativa so as to detect the neutral alleles of these loci. Pollen fertility was investigated in the paired F1s based on two seasons' result and genotypic segregation was also analyzed in some F2 populations to confirm the results of pollen fertility investigation. The neutral alleles of S38-n and S39-n were identified based upon the pollen fertility and genotypic segregation analysis for the first time. The neutral alleles of sterility loci detected from present report have the potential to know of the nature of interspecific hybrid sterility, and to overcome the interspecific hybrid sterility between O. sativa and O. glaberrima.
Project description:Hybrid sterility hinders the transfer of useful traits between Oryza sativa and O. glaberrima. In order to further understand the nature of interspecific hybrid sterility between these two species, a strategy of multi-donors was used to elucidate the range of interspecific hybrid sterility in this study. Fifty-nine accessions of O. glaberrima were used as female parents for hybridization with japonica cultivar Dianjingyou 1, after several backcrossings using Dianjingyou 1 as the recurrent parent and 135 BC6F1 sterile plants were selected for genotyping and deducing hybrid sterility QTLs. BC6F1 plants containing heterozygous target markers were selected and used to raise BC7F1 mapping populations for QTL confirmation and as a result, one locus for gamete elimination on chromosome 1 and two loci for pollen sterility on chromosome 4 and 12, which were distinguished from previous reports, were confirmed and designated as S37(t), S38(t) and S39(t), respectively. These results will be valuable for understanding the range of interspecific hybrid sterility, cloning these genes and improving rice breeding through gene introgression.
Project description:Oryza glumaepatula originates from South America continent and contains many valuable traits, such as tolerance to abiotic stress, high yield and good cooking qualities. However, hybrid sterility severely hindered the utilization of favorable genes of O. glumaepatula by interspecific hybridization. In order to further understand the nature of hybrid sterility between O. sativa and O. glumaepatula, a near isogenic line (NIL) was developed using a japonica variety Dianjingyou 1 as the recurrent parent and an accession of O. glumaepatula as the donor parent. A novel gene S56(t) for pollen sterility was mapped into the region between RM20797 and RM1093 on the short arm of chromosome 7, the physical distance between the two markers was about 469 kb. The genetic behavior of S56(t) followed one-locus allelic interaction model, the male gametes carrying the alleles of O. sativa in the heterozygotes were aborted completely. These results would help us clone S56(t) gene and understand the role of S56(t) in interspecific sterility.
Project description:Wild rice relatives having the same AA genome as domesticated rice (Oryza sativa) comprise the primary gene pool for rice genetic improvement. Among them, O. meridionalis and O. rufipogon are found in the northern part of Australia. Three Australian wild rice strains, Jpn1 (O. rufipogon), Jpn2, and W1297 (O. meridionalis), and one cultivated rice cultivar Taichung 65 (T65) were used in this study. A recurrent backcrossing strategy was adopted to produce chromosomal segment substitution lines (CSSLs) carrying chromosomal segments from wild relatives and used for trait evaluation and genetic analysis. The segregation of the DNA marker RM136 locus on chromosome 6 was found to be highly distorted, and a recessive lethal gene causing abortion at the seed developmental stage was shown to be located between two DNA markers, KGC6_10.09 and KGC6_22.19 on chromosome 6 of W1297. We name this gene as SEED DEVELOPMENT 1 (gene symbol: SDV1). O. sativa is thought to share the functional dominant allele Sdv1-s (s for sativa), and O. meridionalis is thought to share the recessive abortive allele sdv1-m (m for meridionalis). Though carrying the sdv1-m allele, the O. meridionalis accessions can self-fertilize and bear seeds. We speculate that the SDV1 gene may have been duplicated before the divergence between O. meridionalis and the other AA genome Oryza species, and that O. meridionalis has lost the function of the SDV1 gene and has kept the function of another putative gene named SDV2.
Project description:Sterility is common in hybrids between divergent populations, such as the indica and japonica subspecies of Asian cultivated rice (Oryza sativa). Although multiple loci for plant hybrid sterility have been identified, it remains unknown how alleles of the loci interact at the molecular level. Here we show that a locus for indica-japonica hybrid male sterility, Sa, comprises two adjacent genes, SaM and SaF, encoding a small ubiquitin-like modifier E3 ligase-like protein and an F-box protein, respectively. Most indica cultivars contain a haplotype SaM(+)SaF(+), whereas all japonica cultivars have SaM(-)SaF(-) that diverged by nucleotide variations in wild rice. Male semi-sterility in this heterozygous complex locus is caused by abortion of pollen carrying SaM(-). This allele-specific gamete elimination results from a selective interaction of SaF(+) with SaM(-), a truncated protein, but not with SaM(+) because of the presence of an inhibitory domain, although SaM(+) is required for this male sterility. Lack of any one of the three alleles in recombinant plants does not produce male sterility. We propose a two-gene/three-component interaction model for this hybrid male sterility system. The findings have implications for overcoming male sterility in inter-subspecific hybrid rice breeding.
Project description:Oryza longistaminata originates from African wild rice and contains valuable traits conferring tolerance to biotic and abiotic stress. However, interspecific crosses between O. longistaminata and Oryza sativa cultivars are hindered by reproductive barriers. To dissect the mechanism of interspecific hybrid sterility, we developed a near-isogenic line (NIL) using indica variety RD23 as the recipient parent and O. longistaminata as the donor parent. Both pollen and embryo sac semi-sterility were observed in F1 hybrids between RD23 and NIL. Cytological analysis demonstrated that pollen abortion in F1 hybrids occurred at the early bi-nucleate stage due to a failure of the first mitosis in microspores. Partial embryo sacs in the F1 hybrids were defective during the functional megaspore formation stage. Most notably, nearly half of the male or female gametes were aborted in heterozygotes S40iS40l, regardless of their genotypes. Thus, S40 was indicated as a one-locus sporophytic sterility gene controlling both male and female fertility in hybrids between RD23 and O. longistaminata. A population of 16?802 plants derived from the hybrid RD23/NIL-S40 was developed to fine-map S40. Finally, the S40 locus was delimited to an 80-kb region on the short arm of chromosome 1 in terms with reference sequences of cv. 93-11. Eight open reading frames (ORFs) were localized in this region. On the basis of gene expression and genomic sequence analysis, ORF5 and ORF8 were identified as candidate genes for the S40 locus. These results are helpful in cloning the S40 gene and marker-assisted transferring of the corresponding neutral allele in rice breeding programs.
Project description:Cytoplasmic male sterility (CMS) is a widely used genetic tool in modern hybrid rice breeding. Most genes conferring rice gametophytic CMS are homologous to orf79 and co-transcribe with atp6. However, the origin, differentiation and flow of these mitochondrial genes in wild and cultivated rice species remain unclear. In this study, we performed de novo assembly of the mitochondrial genomes of 221 common wild rice (Oryza rufipogon Griff.) and 369 Asian cultivated rice (Oryza sativa L.) accessions, and identified 16 haplotypes of atp6-orf79-like structures and 11 orf79 alleles. These homologous structures were classified into 4 distinct groups (AO-I, AO-II, AO-III and AO-IV), all of which were observed in O. rufipogon but only AO-I was detected in O. sativa, causing a decrease in the frequency of atp6-orf79-like structures from 19.9% to 8.1%. Phylogenetic and biogeographic analyses revealed that the different groups of these gametophytic CMS-related genes in O. rufipogon evolved in a multicentric pattern. The geographical origin of the atp6-orf79-like structures was further traced back, and a candidate region in north-east of Gangetic Plain on the Indian Peninsula (South Asia) was identified as the origin centre of AO-I. The orf79 alleles were detected in all three cytoplasmic types (Or-CT0, Or-CT1 and Or-CT2) of O. rufipogon, but only two alleles (orf79a and orf79b) were observed in Or-CT0 type of O. sativa, while no orf79 allele was found in other types of O. sativa. Our results also revealed that the orf79 alleles in cultivated rice originated from the wild rice population in South and South-East Asia. In addition, strong positive selection pressure was detected on the sequence variations of orf79 alleles, and a special evolutionary strategy was noted in these gametophytic CMS-related genes, suggesting that their divergence could be beneficial to their survival in evolution.
Project description:Reproductive barriers are commonly observed in both animals and plants, in which they maintain species integrity and contribute to speciation. This report shows that a combination of loss-of-function alleles at two duplicated loci, DUPLICATED GAMETOPHYTIC STERILITY 1 (DGS1) on chromosome 4 and DGS2 on chromosome 7, causes pollen sterility in hybrid progeny derived from an interspecific cross between cultivated rice, Oryza sativa, and an Asian annual wild rice, O. nivara Male gametes carrying the DGS1 allele from O. nivara (DGS1-nivaras ) and the DGS2 allele from O. sativa (DGS2-T65s ) were sterile, but female gametes carrying the same genotype were fertile. We isolated the causal gene, which encodes a protein homologous to DNA-dependent RNA polymerase (RNAP) III subunit C4 (RPC4). RPC4 facilitates the transcription of 5S rRNAs and tRNAs. The loss-of-function alleles at DGS1-nivaras and DGS2-T65s were caused by weak or nonexpression of RPC4 and an absence of RPC4, respectively. Phylogenetic analysis demonstrated that gene duplication of RPC4 at DGS1 and DGS2 was a recent event that occurred after divergence of the ancestral population of Oryza from other Poaceae or during diversification of AA-genome species.
Project description:Hybrid incompatibility in F(1) hybrids or later generations is often observed as sterility or inviability. This incompatibility acts as postzygotic reproductive isolation, which results in the irreversible divergence of species. Here, we show that the reciprocal loss of duplicated genes encoding mitochondrial ribosomal protein L27 causes hybrid pollen sterility in F(1) hybrids of the cultivated rice Oryza sativa and its wild relative O. glumaepatula. Functional analysis revealed that this gene is essential for the later stage of pollen development, and distribution analysis suggests that the gene duplication occurred before the divergence of the AA genome species. On the basis of these results, we discuss the possible contribution of the "founder effect" in establishing this reproductive barrier.
Project description:Hybrids between divergent populations commonly show hybrid sterility; this reproductive barrier hinders hybrid breeding of the japonica and indica rice (Oryza sativa L.) subspecies. Here we show that structural changes and copy number variation at the Sc locus confer japonica-indica hybrid male sterility. The japonica allele, Sc-j, contains a pollen-essential gene encoding a DUF1618-domain protein; the indica allele, Sc-i, contains two or three tandem-duplicated ~?28-kb segments, each carrying an Sc-j-homolog with a distinct promoter. In Sc-j/Sc-i hybrids, the high-expression of Sc-i in sporophytic cells causes suppression of Sc-j expression in pollen and selective abortion of Sc-j-pollen, leading to transmission ratio distortion. Knocking out one or two of the three Sc-i copies by CRISPR/Cas9 rescues Sc-j expression and male fertility. Our results reveal the gene dosage-dependent allelic suppression as a mechanism of hybrid incompatibility, and provide an effective approach to overcome the reproductive barrier for hybrid breeding.