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Summary Genic‐cytoplasmic male sterility (CMS) due to interactions between nuclear and cytoplasmic genomes is a well‐known phenomenon in some Solanum spp. hybrids, but genes involved are not known. In this study, the chondriomes of two isonuclear male‐fertile and sterile somatic hybrids (SH9A and SH9B, respectively) between the common potato (S. tuberosum Group Tuberosum, tbr) and the wild species S. commersonii were sequenced and compared to those of parental species to identify mitochondrial genes involved in the expression of male sterility. A putative novel gene (orf125) was found only in tbr and in male‐sterile hybrids. Physical or functional deletion of orf125 by mtDNA editing in SH9B and its allotopic expression in SH9A clearly demonstrated that orf125 affects male fertility. Besides knockout mutants induced by mitoTALEN and DddA‐derived cytosine base editing, specific orf125 missense mutations generated by the latter approach also induced reversion to male fertility in edited SH9B plants, prompting further studies on ORF125 structure–function relationship. The organization of the mitochondrial genome region implicated in CMS was found to be conserved across all common potato accessions, while an identical copy of tbr orf125 was detected in accessions belonging to the S. berthaultii species complex (ber). Such findings corroborate the hypothesis that ber accessions with T/β cytoplasm outcrossed as female with Andean potato, giving rise to the differentiation of the Chilean potato, and highlight the origin of mitochondrial factors contributing to genic‐cytoplasmic male sterility in some tuber‐bearing Solanum hybrids. Our results contribute to the development of innovative breeding approaches in potato.

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.

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.

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.

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.

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.

Cytoplasmic male sterility (CMS) observed in many plants leads defect in the production of functional pollen, while the expression of CMS is suppressed by a fertility restorer gene in the nuclear genome. Ogura CMS of radish is induced by a mitochondrial orf138, and a fertility restorer gene, Rfo, encodes a P-type PPR protein, ORF687, acting at the translational level. But, the exact function of ORF687 is still unclear. We found a Japanese variety showing male sterility even in the presence of Rfo. We examined the pollen fertility, Rfo expression, and orf138 mRNA in progenies of this variety. The progeny with Type H orf138 and Rfo showed male sterility when their orf138 mRNA was unprocessed within the coding region. By contrast, all progeny with Type A orf138 were fertile though orf138 mRNA remained unprocessed in the coding region, demonstrating that ORF687 functions on Type A but not on Type H. In silico analysis suggested a specific binding site of ORF687 in the coding region, not the 5′ untranslated region estimated previously, of Type A. A single nucleotide substitution in the putative binding site diminishes affinity of ORF687 in Type H and is most likely the cause of the ineffectiveness of ORF687. Furthermore, fertility restoration by RNA processing at a novel site in some progeny plants indicated a new and the third fertility restorer gene, Rfs, for orf138. This study clarified that direct ORF687 binding to the coding region of orf138 is essential for fertility restoration by Rfo.

In angiosperms, mitochondrial-encoded genes can cause cytoplasmic male sterility (CMS), resulting in the coexistence of female and hermaphroditic individuals (gynodioecy). We compared four complete mitochondrial genomes from the gynodioecious species Silene vulgaris and found unprecedented amounts of intraspecific diversity for plant mitochondrial DNA (mtDNA). Remarkably, only about half of overall sequence content is shared between any pair of genomes. The four mtDNAs range in size from 361 to 429 kb and differ in gene complement, with rpl5 and rps13 being intact in some genomes but absent or pseudogenized in others. The genomes exhibit essentially no conservation of synteny and are highly repetitive, with evidence of reciprocal recombination occurring even across short repeats (< 250 bp). Some mitochondrial genes exhibit atypically high degrees of nucleotide polymorphism, while others are invariant. The genomes also contain a variable number of small autonomously mapping chromosomes, which have only recently been identified in angiosperm mtDNA. Southern blot analysis of one of these chromosomes indicated a complex in vivo structure consisting of both monomeric circles and multimeric forms. We conclude that S. vulgaris harbors an unusually large degree of variation in mtDNA sequence and structure and discuss the extent to which this variation might be related to CMS.