Rice transcriptional repressor OsTIE1 controls anther dehiscence and male sterility by regulating JA biosynthesis.

Proper anther dehiscence is essential for successful pollination and reproduction in angiosperms, and jasmonic acid (JA) is crucial for the process. However, the mechanisms underlying the tight regulation of JA biosynthesis during anther development remain largely unknown. Here, we demonstrate that the rice (Oryza sativa L.) ethylene-response factor-associated amphiphilic repression (EAR) motif-containing protein TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTORS (TCP) INTERACTOR CONTAINING EAR MOTIF PROTEIN1 (OsTIE1) tightly regulates JA biosynthesis by repressing TCP transcription factor OsTCP1/PCF5 during anther development. The loss of OsTIE1 function in Ostie1 mutants causes male sterility. The Ostie1 mutants display inviable pollen, early stamen filament elongation, and precocious anther dehiscence. In addition, JA biosynthesis is activated earlier and JA abundance is precociously increased in Ostie1 anthers. OsTIE1 is expressed during anther development, and OsTIE1 is localized in nuclei and has transcriptional repression activity. OsTIE1 directly interacts with OsTCP1, and overexpression of OsTCP1 caused early anther dehiscence resembling that of Ostie1. JA biosynthesis genes including rice LIPOXYGENASE are regulated by the OsTIE1-OsTCP1 complex. Our findings reveal that the OsTIE1-OsTCP1 module plays a critical role in anther development by finely tuning JA biosynthesis and provide a foundation for the generation of male sterile plants for hybrid seed production.

GLUTAMYL-tRNA SYNTHETASE 1 deficiency confers thermosensitive male sterility in rice by affecting reactive oxygen species homeostasis.

Temperature is one of the key environmental factors influencing crop fertility and yield. Understanding how plants sense and respond to temperature changes is, therefore, crucial for improving agricultural production. In this study, we characterized a temperature-sensitive male sterile mutant in rice (Oryza sativa), glutamyl-tRNA synthetase 1-2 (ers1-2), that shows reduced fertility at high temperatures and restored fertility at low temperatures. Mutation of ERS1 resulted in severely delayed pollen development and meiotic progression at high temperatures, eventually leading to male sterility. Moreover, meiosis-specific events, including synapsis and crossover formation, were also delayed in ers1-2 compared with the wild type. However, these defects were all mitigated by growing ers1-2 at low temperatures. Transcriptome analysis and measurement of ascorbate, glutathione, and hydrogen peroxide (H2O2) contents revealed that the delayed meiotic progression and male sterility in ers1-2 were strongly associated with changes in reactive oxygen species (ROS) homeostasis. At high temperatures, ers1-2 exhibited decreased accumulation of ROS scavengers and overaccumulation of ROS. In contrast, at low temperatures, the antioxidant system of ROS was more active, and ROS contents were lower. These data suggest that ROS homeostasis in ers1-2 is disrupted at high temperatures but restored at low temperatures. We speculate that ERS1 dysfunction leads to changes in ROS homeostasis under different conditions, resulting in delayed or rescued meiotic progression and thermosensitive male fertility. ers1-2 may hold great potential as a thermosensitive material for crop heterosis breeding.

MutL homolog 1 participates in interference-sensitive meiotic crossover formation in soybean.

MutL homolog 1 (MLH1), a member of the MutL homolog family, is required for normal recombination in most organisms. However, its role in soybean (Glycine max) remains unclear to date. Here, we characterized the Glycine max female and male sterility 1 (Gmfms1) mutation that reduces pollen grain viability and increases embryo sac abortion in soybean. Map-based cloning revealed that the causal gene of Gmfms1 is Glycine max MutL homolog 1 (GmMLH1), and CRISPR/Cas9 knockout approach further validated that disruption of GmMLH1 confers the female-male sterility phenotype in soybean. Loss of GmMLH1 function disrupted bivalent formation, leading to univalent mis-segregation during meiosis and ultimately to female-male sterility. The Gmmlh1 mutant showed about a 78.16% decrease in meiotic crossover frequency compared to the wild type. The residual chiasmata followed a Poisson distribution, suggesting that interference-sensitive crossover formation was affected in the Gmmlh1 mutant. Furthermore, GmMLH1 could interact with GmMLH3A and GmMLH3B both in vivo and in vitro. Overall, our work demonstrates that GmMLH1 participates in interference-sensitive crossover formation in soybean, and provides additional information about the conserved functions of MLH1 across plant species.

A 163-bp insertion in the Capana10g000198 encoding a MYB transcription factor causes male sterility in pepper (Capsicum annuum L.).

Male sterility provides an efficient approach for commercial exploitation of heterosis. Despite more than 20 genic male sterile (GMS) mutants documented in pepper (Capsicum annuum L.), only two causal genes have been successfully identified. Here, a novel spontaneous recessive GMS mutant, designated msc-3, is identified and characterized at both phenotypic and histological levels. Pollen abortion of msc-3 mutant may be due to the delayed tapetum degradation, leading to the non-degeneration of tetrads callosic wall. Then, a modified MutMap method and molecular marker linkage analysis were employed to fine mapping the msc-3 locus, which was delimited to the ~139.91-kb region harboring 10 annotated genes. Gene expression and structure variation analyses indicate the Capana10g000198, encoding a R2R3-MYB transcription factor, is the best candidate gene for the msc-3 locus. Expression profiling analysis shows the Capana10g000198 is an anther-specific gene, and a 163-bp insertion in the Capana10g000198 is highly correlated with the male sterile (MS) phenotype. Additionally, downregulation of Capana10g000198 in male fertile plants through virus-induced gene silencing resulted in male sterility. Finally, possible regulatory relationships of the msc-3 gene with the other two reported pepper GMS genes, msc-1 and msc-2, have been studied, and comparative transcriptome analysis reveals the expression of 16 GMS homologs are significantly downregulated in the MS anthers. Overall, our results reveal that Capana10g000198 is the causal gene underlying the msc-3 locus, providing important theoretical clues and basis for further in-depth study on the regulatory mechanisms of pollen development in pepper.

Comparative transcriptome analysis reveals the impact of daily temperature difference on male sterility in photo-thermo-sensitive male sterile wheat.

BACKGROUND: Photo-thermo-sensitive male sterility (PTMS), which refers to the male sterility triggered by variations in photoperiod and temperature, is a crucial element in the wheat two-line hybrid system. The development of safe production and efficient propagation for male sterile lines holds utmost importance in two-line hybrid wheat. Under the stable photoperiod condition, PTMS is mainly induced by high or low temperatures in wheat, but the effect of daily temperature difference (DTD) on the fertility conversion of PTMS lines has not been reported. Here, three BS type PTMS lines including BS108, BS138, and BS366, as well as a control wheat variety J411 were used to analyze the correlation between fertility and DTD using differentially sowing tests, photo-thermo-control experiments, and transcriptome sequencing. RESULTS: The differentially sowing tests suggested that the optimal sowing time for safe seed production of the three PTMS lines was from October 5th to 25th in Dengzhou, China. Under the condition of 12 h 12 °C, the PTMS lines were greatly affected by DTD and exhibited complete male sterility at a temperature difference of 15 °C. Furthermore, under different temperature difference conditions, a total of 20,677 differentially expressed genes (DEGs) were obtained using RNA sequencing. Moreover, through weighted gene co-expression network analysis (WGCNA) and KEGG enrichment analysis, the identified DEGs had a close association with "starch and sucrose metabolism", "phenylpropanoid biosynthesis", "MAPK signaling pathway-plant", "flavonoid biosynthesis", and "cutin, and suberine and wax biosynthesis". qRT-PCR analysis showed the expression levels of core genes related to KEGG pathways significantly decreased at a temperature difference of 15 ° C. Finally, we constructed a transcriptome mediated network of temperature difference affecting male sterility. CONCLUSIONS: The findings provide important theoretical insights into the correlation between temperature difference and male sterility, providing guidance for the identification and selection of more secure and effective PTMS lines.

Genome-wide identification of CaWD40 proteins reveals the involvement of a novel complex (CaAN1-CaDYT1-CaWD40-91) in anthocyanin biosynthesis and genic male sterility in Capsicum annuum.

BACKGROUND: The WD40 domain, one of the most abundant in eukaryotic genomes, is widely involved in plant growth and development, secondary metabolic biosynthesis, and mediating responses to biotic and abiotic stresses. WD40 repeat (WD40) protein has been systematically studied in several model plants but has not been reported in the Capsicum annuum (pepper) genome. RESULTS: Herein, 269, 237, and 257 CaWD40 genes were identified in the Zunla, CM334, and Zhangshugang genomes, respectively. CaWD40 sequences from the Zunla genome were selected for subsequent analysis, including chromosomal localization, phylogenetic relationships, sequence characteristics, motif compositions, and expression profiling. CaWD40 proteins were unevenly distributed on 12 chromosomes, encompassing 19 tandem duplicate gene pairs. The 269 CaWD40s were divided into six main branches (A to F) with 17 different types of domain distribution. The CaWD40 gene family exhibited diverse expression patterns, and several genes were specifically expressed in flowers and seeds. Yeast two-hybrid (Y2H) and dual-luciferase assay indicated that CaWD40-91 could interact with CaAN1 and CaDYT1, suggesting its involvement in anthocyanin biosynthesis and male sterility in pepper. CONCLUSIONS: In summary, we systematically characterized the phylogeny, classification, structure, and expression of the CaWD40 gene family in pepper. Our findings provide a valuable foundation for further functional investigations on WD40 genes in pepper.

The Dark Side of the pollen: BSA-seq identified genomic regions linked to male sterility in globe artichoke.

Globe artichoke (Cynara cardunculus var. scolymus; 2n = 2x = 34) is a food crop consumed for its immature flower heads. Traditionally, globe artichoke varietal types are vegetatively propagated. However, seed propagation makes it possible to treat the crop as annual, increasing field uniformity and reducing farmers costs, as well as pathogens diffusion. Despite globe artichoke's significant agricultural value and the critical role of heterosis in the development of superior varieties, the production of hybrids remains challenging without a reliable system for large-scale industrial seed production. Male sterility (MS) presents a promising avenue for overcoming these challenges by simplifying the hybridization process and enabling cost-effective seed production. However, within the Cynara genus, genic male sterility has been linked to three recessive loci in globe artichoke, with no definitive genetic mechanism elucidated to date. A 250 offsprings F2 population, derived from a cross between a MS globe artichoke and a male fertile (MF) cultivated cardoon (C. cardunculus var. altilis) and fitting a monogenic segregation model (3:1), was analyzed through BSA-seq, aiming at the identification of genomic regions/genes affecting male sterility. Four QTL regions were identified on chromosomes 4, 12, and 14. By analyzing the sequence around the highest pick on chromosome 14, a cytochrome P450 (CYP703A2) was identified, carrying a deleterious substitution (R/Q) fixed in the male sterile parent. A single dCAPS marker was developed around this SNP, allowing the discrimination between MS and MF genotypes within the population, suitable for applications in plant breeding programs. A 3D model of the protein was generated by homology modeling, revealing that the mutated amino acid is part of a highly conserved motif crucial for protein folding.

Cytological analysis of flower development, insights into suitable growth area and genomic background: implications for Glehnia littoralis conservation and sustainable utilization.

BACKGROUND: Glehnia littoralis F. Schmidt ex Miq., an endangered plant species with significant medicinal, edible, and ecological value, is now a central concern for conservation and sustainable utilization. Investigating the physiological and ecological mechanisms leading to its endangerment and elucidating its genetic background constitutes the foundation for conducting in-depth research on G. littoralis. RESULTS: Our observations have revealed a significant degree of floral sterility in wild populations of G. littoralis. The inflorescences of G. littoralis are classified into three types: completely fertile, completely sterile, and partially fertile compound umbels. Moreover, the flowers of G. littoralis can be categorized into fertile and sterile types. Sterile flowers exhibited abnormalities in the stigma, ovary, and ovules. This study is the first to discover that the presence or absence of a giant cell at the funiculus during the initiation of ovule primordium determines whether the flower can develop normally, providing cytological evidence for female sterility in G. littoralis. Conversely, both fertile and sterile flowers produced normally developed pollen. Field observations have suggested that robust plants bear more fertile umbels, while weaker ones have fewer or even no fertile umbels, indicating a close relationship between flower fertility and plant nutritional status. Our model correctly predicted that the eastern coastal regions of China, as well as prospective areas in Neimenggu and Sichuan, are suitable environments for its cultivation. Additionally, Using flow cytometry and genome survey, we estimated the genome size of G. littoralis to be 3.06 Gb and the heterozygosity to be 4.58%. CONCLUSION: The observations and findings presented in this study were expected to provide valuable insights for further conserving its genetic resources and sustainable utilization of G. littoralis.

Integrated transcriptomic and metabolomic analysis provides insight into the pollen development of CMS-D1 rice.

BACKGROUND: Cytoplasmic male sterility (CMS) has greatly improved the utilization of heterosis in crops due to the absence of functional male gametophyte. The newly developed sporophytic D1 type CMS (CMS-D1) rice exhibits unique characteristics compared to the well-known sporophytic CMS-WA line, making it a valuable resource for rice breeding. RESULTS: In this research, a novel CMS-D1 line named Xingye A (XYA) was established, characterized by small, transparent, and shriveled anthers. Histological and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assays conducted on anthers from XYA and its maintainer line XYB revealed that male sterility in XYA is a result of delayed degradation of tapetal cells and abnormal programmed cell death (PCD) of microspores. Transcriptome analysis of young panicles revealed that differentially expressed genes (DEGs) in XYA, compared to XYB, were significantly enriched in processes related to chromatin structure and nucleosomes during the microspore mother cell (MMC) stage. Conversely, processes associated with sporopollenin biosynthesis, pollen exine formation, chitinase activity, and pollen wall assembly were enriched during the meiosis stage. Metabolome analysis identified 176 specific differentially accumulated metabolites (DAMs) during the meiosis stage, enriched in pathways such as α-linoleic acid metabolism, flavone and flavonol biosynthesis, and linolenic acid metabolism. Integration of transcriptomic and metabolomic data underscored the jasmonic acid (JA) biosynthesis pathway was significant enriched in XYA during the meiosis stage compared to XYB. Furthermore, levels of JA, MeJA, OPC4, OPDA, and JA-Ile were all higher in XYA than in XYB at the meiosis stage. CONCLUSIONS: These findings emphasize the involvement of the JA biosynthetic pathway in pollen development in the CMS-D1 line, providing a foundation for further exploration of the molecular mechanisms involved in CMS-D1 sterility.

Genetic manipulation of the genes for clonal seeds results in sterility in cotton.

BACKGROUND: Heterosis is a common phenomenon in plants and has been extensively applied in crop breeding. However, the superior traits in the hybrids can only be maintained in the first generation but segregate in the following generations. Maintaining heterosis in generations has been challenging but highly desirable in crop breeding. Recent study showed that maternally produced diploid seeds could be achieved in rice by knocking out three meiosis related genes, namely REC8, PAIR1, OSD1 to create MiMe in combination with egg cell specific expression of BBM transcription factor, a technology called clonal seeds. Interestingly, there has been very limited reports indicating the feasibility of this approach in other crops. RESULTS: In this study, we aimed to test whether clonal seeds could be created in cotton. We identified the homologs of the three meiosis related genes in cotton and used the multiplex CRISPR/Cas9 gene editing system to simultaneously knock out these three genes in both A and D sub-genomes. More than 50 transgenic cotton plants were generated, and fragment analysis indicated that multiple gene knockouts occurred in the transgenic plants. However, all the transgenic plants were sterile apparently due to the lack of pollen. Pollination of the flowers of the transgenic plants using the wild type pollens could not generate seeds, an indication of defects in the formation of female sexual cells in the transgenic plants. In addition, we generated transgenic cotton plants expressing the cotton BBM gene driven by the Arabidopsis egg cell specific promoter pDD45. Two transgenic plants were obtained, and both showed severely reduced fertility. CONCLUSIONS: Overall, our results indicate that knockout of the clonal seeds related genes in cotton causes sterility and how to manipulate genes to create clonal seeds in cotton requires further research.

Transcriptome analysis reveals the potential lncRNA-mRNA modules involved in genetic male sterility and fertility of Chinese cabbage (brassica rapa L. ssp. pekinensis).

BACKGROUND: Long non-coding RNAs (lncRNAs) play a crucial role in regulating gene expression vital for the growth and development of plants. Despite this, the role of lncRNAs in Chinese cabbage (Brassica rapa L. ssp. pekinensis) pollen development and male fertility remains poorly understood. RESULTS: In this study, we characterized a recessive genic male sterile mutant (366-2 S), where the delayed degradation of tapetum and the failure of tetrad separation primarily led to the inability to form single microspores, resulting in male sterility. To analyze the role of lncRNAs in pollen development, we conducted a comparative lncRNA sequencing using anthers from the male sterile mutant line (366-2 S) and the wild-type male fertile line (366-2 F). We identified 385 differentially expressed lncRNAs between the 366-2 F and 366-2 S lines, with 172 of them potentially associated with target genes. To further understand the alterations in mRNA expression and explore potential lncRNA-target genes (mRNAs), we performed comparative mRNA transcriptome analysis in the anthers of 366-2 S and 366-2 F at two stages. We identified 1,176 differentially expressed mRNAs. Remarkably, GO analysis revealed significant enrichment in five GO terms, most notably involving mRNAs annotated as pectinesterase and polygalacturonase, which play roles in cell wall degradation. The considerable downregulation of these genes might contribute to the delayed degradation of tapetum in 366-2 S. Furthermore, we identified 15 lncRNA-mRNA modules through Venn diagram analysis. Among them, MSTRG.9997-BraA04g004630.3 C (ß-1,3-glucanase) is associated with callose degradation and tetrad separation. Additionally, MSTRG.5212-BraA02g040020.3 C (pectinesterase) and MSTRG.13,532-BraA05g030320.3 C (pectinesterase) are associated with cell wall degradation of the tapetum, indicating that these three candidate lncRNA-mRNA modules potentially regulate pollen development. CONCLUSION: This study lays the foundation for understanding the roles of lncRNAs in pollen development and for elucidating their molecular mechanisms in regulating male sterility in Chinese cabbage.

The characteristic analysis of TaTDF1 reveals its function related to male sterility in wheat (Triticum aestivum L.).

BACKGROUND: The male sterile lines are an important foundation for heterosis utilization in wheat (Triticum aestivum L.). Thereinto, pollen development is one of the indispensable processes of wheat reproductive development, and its fertility plays an important role in wheat heterosis utilization, and are usually influencing by genes. However, these key genes and their regulatory networks during pollen abortion are poorly understood in wheat. RESULTS: DEFECTIVE IN TAPETAL DEVELOPMENT AND FUNCTION 1 (TDF1) is a member of the R2R3-MYB family and has been shown to be essential for early tapetal layer development and pollen grain fertility in rice (Oryza sativa L.) and Arabidopsis thaliana. In order to clarify the function of TDF1 in wheat anthers development, we used OsTDF1 gene as a reference sequence and homologous cloned wheat TaTDF1 gene. TaTDF1 is localized in the nucleus. The average bolting time of Arabidopsis thaliana overexpressed strain (TaTDF1-OE) was 33 d, and its anther could be colored normally by Alexander staining solution, showing red. The dominant Mosaic suppression silence-line (TaTDF1-EAR) was blue-green in color, and the anthers were shrimpy and thin. The TaTDF1 interacting protein (TaMAP65) was confirmed using Yeast Two-Hybrid Assay (Y2H) and Bimolecular-Fluorescence Complementation (BiFC) experiments. The results showed that downregulated expression of TaTDF1 and TaMAP65 could cause anthers to be smaller and shrunken, leading to pollen abortion in TaTDF1 wheat plants induced by virus-induced gene-silencing technology. The expression pattern of TaTDF1 was influenced by TaMAP65. CONCLUSIONS: Thus, systematically revealing the regulatory mechanism of wheat TaTDF1 during anther and pollen grain development may provide new information on the molecular mechanism of pollen abortion in wheat.

Understanding the role of P-type ATPases in regulating pollen fertility and development in pigeonpea.

The P-type ATPase superfamily genes are the cation and phospholipid pumps that transport ions across the membranes by hydrolyzing ATP. They are involved in a diverse range of functions, including fundamental cellular events that occur during the growth of plants, especially in the reproductive organs. The present work has been undertaken to understand and characterize the P-type ATPases in the pigeonpea genome and their potential role in anther development and pollen fertility. A total of 59 P-type ATPases were predicted in the pigeonpea genome. The phylogenetic analysis classified the ATPases into five subfamilies: eleven P1B, eighteen P2A/B, fourteen P3A, fifteen P4, and one P5. Twenty-three pairs of P-type ATPases were tandemly duplicated, resulting in their expansion in the pigeonpea genome during evolution. The orthologs of the reported anther development-related genes were searched in the pigeonpea genome, and the expression profiling studies of specific genes via qRT-PCR in the pre- and post-meiotic anther stages of AKCMS11A (male sterile), AKCMS11B (maintainer) and AKPR303 (fertility restorer) lines of pigeonpea was done. Compared to the restorer and maintainer lines, the down-regulation of CcP-typeATPase22 in the post-meiotic anthers of the male sterile line might have played a role in pollen sterility. Furthermore, the strong expression of CcP-typeATPase2 in the post-meiotic anthers of restorer line and CcP-typeATPase46, CcP-typeATPase51, and CcP-typeATPase52 in the maintainer lines, respectively, compared to the male sterile line, clearly indicates their potential role in developing male reproductive organs in pigeonpea.

Cytoplasmic male sterility-based hybrids: mechanistic insights.

MAIN CONCLUSION: A comprehensive understanding of the nucleocytoplasmic interactions that occur between genes related to the restoration of fertility and cytoplasmic male sterility (CMS) provides insight into the development of hybrids of important crop species. Modern biotechnological techniques allow this to be achieved in an efficient and quick manner. Heterosis is paramount for increasing the yield and quality of a crop. The development of hybrids for achieving heterosis has been well-studied and proven to be robust and efficient. Cytoplasmic male sterility (CMS) has been explored extensively in the production of hybrids. The underlying mechanisms of CMS include the role of cytotoxic proteins, PCD of tapetal cells, and improper RNA editing of restoration factors. On the other hand, the restoration of fertility is caused by the presence of restorer-of-fertility (Rf) genes or restorer genes, which inhibit the effects of sterility-causing genes. The interaction between mitochondria and the nuclear genome is crucial for several regulatory pathways, as observed in the CMS-Rf system and occurs at the genomic, transcriptional, post-transcriptional, translational, and post-translational levels. These CMS-Rf mechanisms have been validated in several crop systems. This review aims to summarize the nucleo-mitochondrial interaction mechanism of the CMS-Rf system. It also sheds light on biotechnological interventions, such as genetic engineering and genome editing, to achieve CMS-based hybrids.

Characterization and validation of TaAGL66, a gene related to fertility conversion of wheat in the presence of Aegilops kotschyi cytoplasm.

MAIN CONCLUSION: TaAGL66, a MADS-box transcription factor highly expressed in fertile anthers of KTM3315A, regulates anther and/or pollen development, as well as male fertility in wheat with Aegilops kotschyi cytoplasm. Male sterility, as a string of sophisticated biological processes in higher plants, is commonly regulated by transcription factors (TFs). Among them, MADS-box TFs are mainly participated in the processes of floral organ formation and pollen development, which are tightly related to male sterility, but they have been little studied in the reproductive development in wheat. In our study, TaAGL66, a gene that was specifically expressed in spikes and highly expressed in fertile anthers, was identified by RNA sequencing and the expression profiles data of these genes, and qRT-PCR analyses, which was localized to the nucleus. Silencing of TaAGL66 under fertility condition in KTM3315A, a thermo-sensitive male sterile line with Ae. kotschyi cytoplasm, displayed severe fertility reduction, abnormal anther dehiscence, defective pollen development, decreased viability, and low seed-setting. It can be concluded that TaAGL66 plays an important role in wheat pollen development in the presence of Ae. kotschyi cytoplasm, providing new insights into the utilization of male sterility.

A P-type pentatricopeptide repeat protein ZmRF5 promotes 5' region partial cleavages of atp6c transcripts to restore the fertility of CMS-C maize by recruiting a splicing factor.

A fast evolution within mitochondria genome(s) often generates discords between nuclear and mitochondria, which is manifested as cytoplasmic male sterility (CMS) and fertility restoration (Rf) system. The maize CMS-C trait is regulated by the chimeric mitochondrial gene, atp6c, and can be recovered by the restorer gene ZmRf5. Through positional cloning in this study, we identified the nuclear restorer gene, ZmRf5, which encodes a P-type pentatricopeptide repeat (PPR) family protein. The over-expression of ZmRf5 brought back the fertility to CMS-C plants, whereas its genomic editing by CRISPR/Cas9 induced abortive pollens in the restorer line. ZmRF5 is sorted to mitochondria, and recruited RS31A, a splicing factor, through MORF8 to form a cleaving/restoring complex, which promoted the cleaving of the CMS-associated transcripts atp6c by shifting the major cleavage site from 480th nt to 344 th nt for fast degradation, and preserved just right amount of atp6c RNA for protein translation, providing adequate ATP6C to assembly complex V, thus restoring male fertility. Interestingly, ATP6C in the sterile line CMo17A, with similar cytology and physiology changes to YU87-1A, was accumulated much less than it in NMo17B, exhibiting a contrary trend in the YU87-1 nuclear genome previously reported, and was restored to normal level in the presence of ZmRF5. Collectively these findings unveil a new molecular mechanism underlying fertility restoration by which ZmRF5 cooperates with MORF8 and RS31A to restore CMS-C fertility in maize, complemented and perfected the sterility mechanism, and enrich the perspectives on communications between nucleus and mitochondria.

Editing of ORF138 restores fertility of Ogura cytoplasmic male sterile broccoli via mitoTALENs.

Cytoplasmic male sterility (CMS), encoded by the mitochondrial open reading frames (ORFs), has long been used to economically produce crop hybrids. However, the utilization of CMS also hinders the exploitation of sterility and fertility variation in the absence of a restorer line, which in turn narrows the genetic background and reduces biodiversity. Here, we used a mitochondrial targeted transcription activator-like effector nuclease (mitoTALENs) to knock out ORF138 from the Ogura CMS broccoli hybrid. The knockout was confirmed by the amplification and re-sequencing read mapping to the mitochondrial genome. As a result, knockout of ORF138 restored the fertility of the CMS hybrid, and simultaneously manifested a cold-sensitive male sterility. ORF138 depletion is stably inherited to the next generation, allowing for direct use in the breeding process. In addition, we proposed a highly reliable and cost-effective toolkit to accelerate the life cycle of fertile lines from CMS-derived broccoli hybrids. By applying the k-mean clustering and interaction network analysis, we identified the central gene networks involved in the fertility restoration and cold-sensitive male sterility. Our study enables mitochondrial genome editing via mitoTALENs in Brassicaceae vegetable crops and provides evidence that the sex production machinery and its temperature-responsive ability are regulated by the mitochondria.

OsALKBH9-mediated m6A demethylation regulates tapetal PCD and pollen exine accumulation in rice.

The N6-methyladenosine (m6A) mRNA modification is crucial for plant development and stress responses. In rice, the male sterility resulting from the deficiency of OsFIP37, a core component of m6A methyltransferase complex, emphasizes the significant role of m6A in male fertility. m6A is reversible and can be removed by m6A demethylases. However, whether mRNA m6A demethylase regulates male fertility in rice has remained unknown. Here, we identify the mRNA m6A demethylase OsALKBH9 and demonstrate its involvement in male fertility regulation. Knockout of OsALKBH9 causes male sterility, dependent on its m6A demethylation activity. Cytological analysis reveals defective tapetal programmed cell death (PCD) and excessive accumulation of microspores exine in Osalkbh9-1. Transcriptome analysis of anthers shows up-regulation of genes involved in tapetum development, sporopollenin synthesis, and transport pathways in Osalkbh9-1. Additionally, we demonstrate that OsALKBH9 demethylates the m6A modification in TDR and GAMYB transcripts, which affects the stability of these mRNAs and ultimately leads to excessive accumulation of pollen exine. Our findings highlight the precise control of mRNA m6A modification and reveal the pivotal roles played by OsALKBH9-mediated m6A demethylation in tapetal PCD and pollen exine accumulation in rice.

Temperature and light reverse the fertility of rice P/TGMS line ostms19 via reactive oxygen species homeostasis.

P/TGMS (Photo/thermo-sensitive genic male sterile) lines are crucial resources for two-line hybrid rice breeding. Previous studies revealed that slow development is a general mechanism for sterility-fertility conversion of P/TGMS in Arabidopsis. However, the difference in P/TGMS genes between rice and Arabidopsis suggests the presence of a distinct P/TGMS mechanism in rice. In this study, we isolated a novel P/TGMS line, ostms19, which shows sterility under high-temperature conditions and fertility under low-temperature conditions. OsTMS19 encodes a novel pentatricopeptide repeat (PPR) protein essential for pollen formation, in which a point mutation GTA(Val) to GCA(Ala) leads to ostms19 P/TGMS phenotype. It is highly expressed in the tapetum and localized to mitochondria. Under high temperature or long-day photoperiod conditions, excessive ROS accumulation in ostms19 anthers during pollen mitosis disrupts gene expression and intine formation, causing male sterility. Conversely, under low temperature or short-day photoperiod conditions, ROS can be effectively scavenged in anthers, resulting in fertility restoration. This indicates that ROS homeostasis is critical for fertility conversion. This relationship between ROS homeostasis and fertility conversion has also been observed in other tested rice P/TGMS lines. Therefore, we propose that ROS homeostasis is a general mechanism for the sterility-fertility conversion of rice P/TGMS lines.

An E3 ubiquitin ligase CSIT2 controls critical sterility-inducing temperature of thermo-sensitive genic male sterile rice.

Thermo-sensitive genic male sterile (TGMS) lines are the core of two-line hybrid rice (Oryza sativa). However, elevated or unstable critical sterility-inducing temperatures (CSITs) of TGMS lines are bottlenecks that restrict the development of two-line hybrid rice. However, the genes and molecular mechanisms controlling CSIT remain unknown. Here, we report the CRITICAL STERILITY-INDUCING TEMPERATURE 2 (CSIT2) that encodes a really interesting new gene (RING) type E3 ligase, controlling the CSIT of thermo-sensitive male sterility 5 (tms5)-based TGMS lines through ribosome-associated protein quality control (RQC). CSIT2 binds to the large and small ribosomal subunits and ubiquitinates 80S ribosomes for dissociation, and may also ubiquitinate misfolded proteins for degradation. Mutation of CSIT2 inhibits the possible damage to ubiquitin system and protein translation, which allows more proteins such as catalases to accumulate for anther development and inhibits abnormal accumulation of reactive oxygen species (ROS) and premature programmed cell death (PCD) in anthers, partly rescuing male sterility and raised the CSIT of tms5-based TGMS lines. These findings reveal a mechanism controlling CSIT and provide a strategy for solving the elevated or unstable CSITs of tms5-based TGMS lines in two-line hybrid rice.