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As the core of heterosis utilization, cytoplasmic male sterility (CMS) has been widely used in hybrid seed production. Previous studies have shown that CMS is always closely related to the altered programming of mitochondrial genes. To explore candidate CMS genes in cotton (Gossypium hirsutum), sequencing and de novo assembly were performed on the mitochondrial genome of the G. hirsutum CMS line SI3A, with G. harknessii CMS-D2 cytoplasm, and the corresponding G. hirsutum restorer line 0-613-2R. Remarkable variations in genome structure and gene transcripts were detected. The mitochondrial genome of SI3A has three circle molecules, including one main circle and two sub-circles, while 0-613-2R only has one. RNA-seq and RT-qPCR analysis proved that orf606a and orf109a, which have a chimeric structure and transmembrane domain, were highly expressed in abortive anthers of SI3A. In addition, comparative analysis of RNA-seq and full-length transcripts revealed the complex I gene nad4 to be expressed at a lower level in SI3A than in its restorer and that it featured an intron retention splicing pattern. These two novel chimeric ORFs and nad4 are potential candidates that confer CMS character in SI3A. This study provides new insight into the molecular basis of the nuclear–cytoplasmic interaction mechanism, and that putative CMS genes might be important sources for future precise design cross-breeding of cotton.

Hybrid breeding can help us to meet the challenge of feeding a growing world population with limited agricultural land. The demand for soybean is expected to grow; however, the hybrid soybean is still in the process of commercialization even though considerable progress has been made in soybean genome and genetic studies in recent years. Here, we summarize recent advances in male sterility-based breeding programs and the current status of hybrid soybean breeding. A number of male-sterile lines with cytoplasmic male sterility (CMS), genic-controlled photoperiod/thermo-sensitive male sterility, and stable nuclear male sterility (GMS) have been identified in soybean. More than 40 hybrid soybean varieties have been bred using the CMS three-line hybrid system and the cultivation of hybrid soybean is still under way. The key to accelerating hybrid soybean breeding is to increase the out-crossing rate in an economical way. This review outlines current problems with the hybrid soybean breeding systems and explores the current efforts to make the hybrid soybean a commercial success.

Cytoplasmic male sterility (CMS) is a widespread phenotype in plants, which present a defect in the production of functional pollen. The male sterilizing factors usually consist of unusual genes or open reading frames encoded by the mitochondrial genome. CMS can be suppressed by specific nuclear genes called restorers of fertility ( s). In the majority of cases, genes produce proteins that act directly on the CMS conferring mitochondrial transcripts by binding them specifically and promoting processing events. In this review, we explore the wide array of mechanisms guiding fertility restoration. PPR proteins represent the most frequent protein class among identified Rfs and they exhibit ideal characteristics to evolve into restorer of fertility when the mechanism of restoration implies a post-transcriptional action. Here, we review the literature that highlights those characteristics and help explain why PPR proteins are ideal for the roles they play as restorers of fertility.

Orobanchaceae have become a model group for studies on the evolution of parasitic flowering plants, and Aeginetia indica, a holoparasitic plant, is a member of this family. In this study, we assembled the complete chloroplast and mitochondrial genomes of A. indica. The chloroplast and mitochondrial genomes were 56,381 bp and 401,628 bp long, respectively. The chloroplast genome of A. indica shows massive plastid genes and the loss of one IR (inverted repeat). A comparison of the A. indica chloroplast genome sequence with that of a previous study demonstrated that the two chloroplast genomes encode a similar number of proteins (except atpH) but differ greatly in length. The A. indica mitochondrial genome has 53 genes, including 35 protein-coding genes (34 native mitochondrial genes and one chloroplast gene), 15 tRNA (11 native mitochondrial genes and four chloroplast genes) genes, and three rRNA genes. Evidence for intracellular gene transfer (IGT) and horizontal gene transfer (HGT) was obtained for plastid and mitochondrial genomes. ψndhB and ψcemA in the A. indica mitogenome were transferred from the plastid genome of A. indica. The atpH gene in the plastid of A. indica was transferred from another plastid angiosperm plastid and the atpI gene in mitogenome A. indica was transferred from a host plant like Miscanthus siensis. Cox2 (orf43) encodes proteins containing a membrane domain, making ORF (Open Reading Frame) the most likely candidate gene for CMS development in A. indica.

Celery (Apium graveolens L.) is an important leafy vegetable worldwide. The development of F1 hybrids in celery is highly dependent on cytoplasmic male sterility (CMS) because emasculation is difficult. In this study, we first report a celery CMS, which was found in a high-generation inbred line population of the Chinese celery “tanzhixiangqin”. Comparative analysis, following sequencing and assembly of the complete mitochondrial genome sequences for this celery CMS line and its maintainer line, revealed that there are 21 unique regions in the celery CMS line and these unique regions contain 15 ORFs. Among these ORFs, only orf768a is a chimeric gene, consisting of 1497 bp sequences of the cox1 gene and 810 bp unidentified sequences located in the unique region, and the predicted protein product of orf768a possesses 11 transmembrane domains. In summary, the results of this study indicate that orf768a is likely to be a strong candidate gene for CMS induction in celery. In addition, orf768a can be a co-segregate marker, which can be used to screen CMS in celery.

Background Sugarcane is a crucial crop for both sugar and bioethanol production. The nobilization breeding and utilization of wild germplasm have significantly enhanced its productivity. However, the pollen sterility in Saccharum officinarum restricts its role to being a female parent in crosses with Saccharum spontaneum during nobilization breeding, resulting in a narrow genetic basis for modern sugarcane cultivars. Mitochondria, often referred to as the intracellular “energy factories”, provide energy for plant life activities, and are also implicated in cytoplasmic male sterility (CMS). Results We performed mitochondrial genome assembly and structural analysis of two Saccharum founding species. We discovered that the proportions of repeat sequences are the primary factor contributing to the variations in mitochondrial genome structure and size between the two Saccharum species. Heterologous expression of the mitochondrial chimeric gene ORF113 , which is highly expressed in male-sterile S. officinarum flowers, significantly inhibits growth and ATP synthesis in yeast cells, making it a key candidate CMS-related gene in sugarcane. Furthermore, we developed two co-dominant simple sequence repeat (SSR) markers based on the mitochondrial genome, which can effectively distinguish the cytoplasmic types of the two Saccharum species. Conclusion In this study, we identified structural variants and developed SSR molecular markers in the mitochondrial genomes of both S. officinarum and S. spontaneum . We also identified a novel mitochondrial chimeric ORF as a key candidate CMS-related gene. These findings offer valuable insights into variety identification, genetic resource development, and cross-breeding strategies in sugarcane.

Background Wheat plays a pivotal role in global food and nutritional security. To meet the growing demand for food, increasing wheat production through hybrid development remains an untapped avenue. However, the autogamy of wheat causes a significant challenge for hybrid development. Results The present study aimed to convert the elite bread wheat cultivars HD3086 and HD2932 into a cytoplasmic male-sterile (CMS) lines using the CMS donor parent (A-GW365) through a backcross breeding approach. Background analysis using 152 and 145 SSR markers confirmed ˃95% recovery of recurrent parent genomes (RPG) of the HD3086 and HD2932, respectively. The newly developed CMS lines were evaluated for pollen sterility and phenotypic similarity in comparison to recurrent parents. The cytological study and DUS characterisation of the converted A lines revealed complete sterility and similarity with the recurrent parent for morphological and agronomic traits. Further, two converted A lines, A-HD3086 and A-HD2932 and donor A line A-GW365 were crossed with six newly developed fertility restorer lines (R lines) in a line × tester breeding design. Combining ability analysis revealed positive general combining ability (GCA) for A-HD3086 and 955R across the three trials, and they were identified as the best tester and line, respectively, for grain yield. Furthermore, the genotype × environment interaction analysed through GGE biplot revealed that hybrids G1 (A-HD3086 × 908-3R), G2 (A-HD3086 × 917R), G4 (A-HD3086 × 955R), and G12 (A-GW365 × 1752R) were high-yielding and stable performers. Based on combining ability estimates, grain yield performance, and stability analysis, hybrids G4 (A-HD3086 × 955R) and G12 (A-GW365 × 1752R) were identified as the best-performing hybrids across the environmental trials. Conclusions The present study reported the conversion of agronomically superior cultivars to CMS lines and their practical utilization for the development of CMS-based hybrids.

Cytoplasmic Male Sterility, a maternally inherited trait which suppresses the production of viable pollen, eliminates the need for detasseling of females in hybrid maize seed production. A set of 88 diverse elite CIMMYT Asia maize inbred lines converted to CMS-C using a temperate donor, were evaluated for stable p er se performance for grain yield, male sterility and Turcicum Leaf Blight resistance. Performances of CMS maize hybrids of varied genetic backgrounds across diverse environments -- seasons, years, agroecologies, countries, abiotic- and biotic stresses -- established a stable and robust diversification process which included the identification of potential maintainers and restorers that will benefit researchers, the seed industry and farmers. While multiple CMS hybrids showed a range of yield performances comparable to non-CMS checks, we report on a distinct 9.9% yield advantage of a CMS hybrid compared to its isogenic non-CMS counterpart through a head-to-head analysis. From implications in enhancing global genetic gains to addressing issues of labour availability and rising wages, the technology offers opportunities for intellectual property protection and region-wide taming of tropical Asian maize germplasm diversity by imposing a heterotic discipline.

Pentatricopeptide repeat ( PPR ) gene family is one of the largest gene families in higher plants. The Restoration of fertility like ( RFL ) clade of the family plays a crucial role in restoring fertility of cytoplasmic male sterility (CMS) lines in plants. Common tobacco ( Nicotiana tabacum L.) is an important economic crop of which the CMS hybrids have been widely used in commercial cultivation. However, the restorer line of tobacco and the regulatory mechanism of fertility restoration remain elusive. In addition, PPR and RFL genes have not been illustrated in common tobacco. In this study, a total of 1002 NtPPR genes were identified, of which 27 NtRFLs belonging to P subfamily were demonstrated. The collinearity analysis showed that a total of 15 pairs of NtRFL genes had collinear relationship and unevenly distributed in 9 linkage groups. Cis-element analysis revealed that a large number of environmental stress and phytohormone response elements were located in the promoter of NtRFLs . By combining the RNA-seq and qPCR analysis, NtRFL3 was further selected as the candidate gene due to its significantly higher expression at early anther development in the fertile line MF1. NtRFL3 was predicted to be localized in mitochondria and shared high sequence similarity with the known fertility-restorer PPR592 in petunia. Our results provided new gene targets for molecular breeding of tobacco restorer lines and for illustration of molecular mechanism on fertility restoration of plant CMS lines.

Background Cytoplasmic male sterility (CMS) has been widely used for commercial F1 hybrid seeds production. CMS is primarily caused by chimeric genes in mitochondrial genomes. However, which specific stages of anther development in cabbage are affected by the chimeric genes remain unclear. Results In the present study, the complete mitochondrial genomes were sequenced and assembled for the maintainer and Ogura CMS cabbage lines. The genome size of the maintainer and Ogura CMS cabbage are 219,962 bp and 236,648 bp, respectively. There are 67 and 69 unknown function ORFs identified in the maintainer and Ogura CMS cabbage mitochondrial genomes, respectively. Four orfs , orf102a , orf 122b, orf 138a and orf 154a were specifically identified in the Ogura CMS mitochondrial genome, which were likely generated by recombination with Ogura type radish during breeding process. Among them, ORF138a and ORF154a possessed a transmembrane structure, and orf138a was co-transcribed with the atp8 and trnfM genes. orf154a is partially homologous to the ATP synthase subunit 1 ( atpA ) gene. Both these genes were likely responsible for the CMS phenotype. In addition, cytological sections showed that the abnormal proliferation of tapetal cells might be the immediate cause of cytoplasmic male-sterility in Ogura CMS cabbage lines. RNA-seq results showed that orf138a and orf154a in Ogura CMS might influence transcript levels of genes in energy metabolic pathways. Conclusions The presence of orf138a and orf154a lead to increased of ATPase activity and ATP content by affecting the transcript levels of genes in energy metabolic pathways, which could provide more energy for the abnormal proliferation of tapetal cells. Our data provides new insights into cytoplasmic male-sterility from whole mitochondrial genomes, cytology of anther development and transcriptome data.