Elucidating Mitochondrial DNA Markers of Ogura-Based CMS Lines in Indian Cauliflowers (Brassica oleracea var. botrytis L.) and Their Floral Abnormalities Due to Diversity in Cytonuclear Interactions

Molecular advances in research and applications of male sterility systems in tomato

Tomato, belonging to the nightshade family, is globally considered as a model system for classical and molecular genetics, genomics, and reproductive developmental studies. In the current scenario of climate change, hybrid development is among the crucial elements in the genetic improvement of crop plants. The phenomenon of male sterility is a viable approach for ensuring hybrid seed purity and reducing the cost of hybrid seed production. This review aims to shed light on the use of neoteric genomics and genome editing tools in understanding the genetics and molecular regulation of male sterility in tomato. Plant male gametophyte development is highly susceptible to environmental stress. Abnormalities at any stage of male reproductive development, such as premature or delayed tapetal cell degradation triggered by oxidative stress and programmed cell death (PCD) leads to male sterility in tomato. In tomato, more than 55 sporogenous, structural, and functional male sterile mutants, which are mainly under the control of recessive nuclear genes, have been reported. Recently, the role of open reading frames (ORFs) in governing cytoplasmic male sterility in tomato has also been documented. This review highlights the genetic and genomic progress in the investigation of underlying molecular pathways and practical application of potential male sterile mutants in tomato breeding. The applications and future prospects of genome engineering with CRISPR/Cas9 and mitoTALEN in the generation of novel male sterile systems to expedite tomato breeding is discussed.

Integrated Transcriptomics and Metabolomics Analysis Reveals Convergent and Divergent Key Molecular Networks of Dominant Genic Male Sterility and Cytoplasmic Male Sterility in Cabbage

Cytoplasmic male sterility (CMS) and dominant genic male sterility (DGMS) both result in the inability to produce or release functional pollen, making them pivotal systems in the hybridization breeding programs of Brassica crops such as cabbage (B. oleracea var. capitata). However, the underling molecular mechanisms are still largely unexplored. This study integrated transcriptomic and metabolomic analyses of cabbage DGMS line, Ogura CMS line, and the maintainer line to uncover the molecular mechanisms underlying these sterility types. The joint analysis predominantly identified significantly enriched pathways, including carbohydrate metabolism, flavonoid biosynthesis, and phenylpropanoid pathways between the MS lines and the maintainer. Especially, the CMS line exhibited a broader range of metabolic perturbations, with a total of 3556 significantly differentially expressed genes (DEGs) and 439 differentially accumulated metabolites (DAMs) detected, particularly in the vitamin B6 metabolism pathway, which showed significant alterations. Given the differences in the inactivation period of microspores in CMS and DGMS lines, we found that DEGs unique to DGMS and maintainer line, such as BoGRPs and BoLTPs, primarily regulate fertility development before the unicellular stage. The DEGs shared between CMS_vs_maintainer and DGMS_vs_maintainer mainly govern microspore development after release from the tetrad, such as BoHXK1 and BoIDH. Additionally, the DEGs unique to CMS_vs_maintainer may contribute to other damage in floral organs beyond male fertility, potentially leading to severe bud abortion, such as BoPNPO. These findings provide a comprehensive framework for understanding the molecular mechanisms of male sterility and offer valuable insights into future breeding strategies in cruciferous vegetables.

Characterization of the complete mitogenome of Tiarella polyphylla, commonly known as Asian foamflower: insights into the multi-chromosomes structure and DNA transfers

BACKGROUND

Tiarella polyphylla D. Don has been traditionally used to cure asthma and skin eruptions. However, the sequence and the structure of the mitogenome of T. polyphylla remained elusive, limiting the genomic and evolution analysis based on the mitogenome.

RESULTS

Using a combination of Illumina and Nanopore sequencing reads, we de novo assembled the complete mitogenome of T. polyphylla. In addition to unveiling the major configuration of the T. polyphylla mitogenome was three circular chromosomes with lengths of 430,435 bp, 126,943 bp, and 55,269 bp, we revealed five (R01-R05) and one (R06) repetitive sequence could mediate the intra- and inter-chromosomal recombination, respectively. Furthermore, we identified 208 short and 25 long tandem segments, seven cp-derived mtDNAs, 106 segments of mtDNAs transferred to the nuclear genome, and 653 predicted RNA editing sites. Based on the sequence of the mitogenomes, we obtained the resolved phylogeny of the seven Saxifragales species.

CONCLUSIONS

These results presented the mitogenome features and expanded its potential applications in phylogenetics, species identification, and cytoplasmic male sterility (CMS) in the future.

Insights into structure, codon usage, repeats, and RNA editing of the complete mitochondrial genome of Perilla frutescens (Lamiaceae)

Perilla frutescens (L.) Britton, a member of the Lamiaceae family, stands out as a versatile plant highly valued for its unique aroma and medicinal properties. Additionally, P. frutescens seeds are rich in Îś-linolenic acid, holding substantial economic importance. While the nuclear and chloroplast genomes of P. frutescens have already been documented, the complete mitochondrial genome sequence remains unreported. To this end, the sequencing, annotation, and assembly of the entire Mitochondrial genome of P. frutescens were hereby conducted using a combination of Illumina and PacBio data. The assembled P. frutescens mitochondrial genome spanned 299,551 bp and exhibited a typical circular structure, involving a GC content of 45.23%. Within the genome, a total of 59 unique genes were identified, encompassing 37 protein-coding genes, 20 tRNA genes, and 2 rRNA genes. Additionally, 18 introns were observed in 8 protein-coding genes. Notably, the codons of the P. frutescens mitochondrial genome displayed a notable A/T bias. The analysis also revealed 293 dispersed repeat sequences, 77 simple sequence repeats (SSRs), and 6 tandem repeat sequences. Moreover, RNA editing sites preferentially produced leucine at amino acid editing sites. Furthermore, 70 sequence fragments (12,680 bp) having been transferred from the chloroplast to the mitochondrial genome were identified, accounting for 4.23% of the entire mitochondrial genome. Phylogenetic analysis indicated that among Lamiaceae plants, P. frutescens is most closely related to Salvia miltiorrhiza and Platostoma chinense. Meanwhile, inter-species Ka/Ks results suggested that Ka/Ks < 1 for 28 PCGs, indicating that these genes were evolving under purifying selection. Overall, this study enriches the mitochondrial genome data for P. frutescens and forges a theoretical foundation for future molecular breeding research.

Commercial suitability and characterization of newly developed Erucastrum canariense (Can) sterile cytoplasm based cytoplasmic male sterile (CMS) lines in Indian cauliflower

The study presents the first to characterize novel Erucastrum canarianse Webb and Berthel (or Can) sterile cytoplasm-based CMS lines in Indian cauliflower (Brassica oleracea var. botrytis L.) and investigating their commercial suitability. Eleven Can-based CMS lines were examined for 12 agro-morphological and yield traits,18 floral traits, four seed yield traits together with three each of the Ogura (source: wild Japanese Radish) and Tour (Source: Brassica tournefortii) cytoplasms. All of the recorded floral and seed traits showed significant (P > 0.05) differences between the CMS lines of each group. Agro-morphological and yield traits in CMS lines and their maintainers, however, were non-significantly different. All the Can- and Ogura-based CMS lines showed flowering and appropriate seed formation by natural cross-pollination. Only two Tour cytoplasm-based CMS lines, Tour (DC-41-5) and Tour (DC-67), produced the smallest malformed flowers and stigma. The highest seed yield per plant in CMS lines was in Ogu (DC-98-4) and the lowest in Tour (DC-67). P14 and P15, two polymorphic mtDNA markers, were discovered for the Can CMS system for early detection. Five primers (ITS5a-ITS4, atpF-atpH, P16, rbeL and trnL), along with their maintainers, were sequenced and aligned to detect nucleotide changes including as additions and or deletions at different positions. The newly introduced E. canariense sterile cytoplasm-based CMS system in cauliflower is the subject of the first comprehensive report, which emphasises their potential as a further stable and reliable genetic mechanism for hybrid breeding.

Mitochondrial genome comparison and phylogenetic analysis of Dendrobium (Orchidaceae) based on whole mitogenomes

BACKGROUND

Mitochondrial genomes are essential for deciphering the unique evolutionary history of seed plants. However, the rules of their extreme variation in genomic size, multi-chromosomal structure, and foreign sequences remain unresolved in most plant lineages, which further hindered the application of mitogenomes in phylogenetic analyses.

RESULTS

Here, we took Dendrobium (Orchidaceae) which shows the great divergence of morphology and difficulty in species taxonomy as the study focus. We first de novo assembled two complete mitogenomes of Dendrobium wilsonii and Dendrobium henanense that were 763,005 bp and 807,551 bp long with multichromosomal structures. To understand the evolution of Dendrobium mitogenomes, we compared them with those of four other orchid species. The results showed great variations of repetitive and chloroplast-derived sequences in Dendrobium mitogenomes. Moreover, the intergenic content of Dendrobium mitogenomes has undergone expansion during evolution. We also newly sequenced mitogenomes of 26 Dendrobium species and reconstructed phylogenetic relationships of Dendrobium based on genomic mitochondrial and plastid data. The results indicated that the existence of chloroplast-derived sequences made the mitochondrial phylogeny display partial characteristics of the plastid phylogeny. Additionally, the mitochondrial phylogeny provided new insights into the phylogenetic relationships of Dendrobium species.

CONCLUSIONS

Our study revealed the evolution of Dendrobium mitogenomes and the potential of mitogenomes in deciphering phylogenetic relationships at low taxonomic levels.

Targeted knockout of a conserved plant mitochondrial gene by genome editing

Fusion proteins derived from transcription activator-like effectors (TALEs) have emerged as genome editing tools for mitochondria. TALE nucleases (TALENs) have been applied to delete chimaeric reading frames and duplicated (redundant) genes but produced complex genomic rearrangements due to the absence of non-homologous end-joining. Here we report the targeted deletion of a conserved mitochondrial gene, nad9, encoding a subunit of respiratory complex I. By generating a large number of TALEN-mediated mitochondrial deletion lines, we isolated, in addition to mutants with rearranged genomes, homochondriomic mutants harbouring clean nad9 deletions. Characterization of the knockout plants revealed impaired complex I biogenesis, male sterility and defects in leaf and flower development. We show that these defects can be restored by expressing a functional Nad9 protein from the nuclear genome, thus creating a synthetic cytoplasmic male sterility system. Our data (1) demonstrate the feasibility of using genome editing to study mitochondrial gene functions by reverse genetics, (2) highlight the role of complex I in plant development and (3) provide proof-of-concept for the construction of synthetic cytoplasmic male sterility systems for hybrid breeding by genome editing.

A natural mutation in the promoter of Ms-cd1 causes dominant male sterility in Brassica oleracea

Male sterility has been used for crop hybrid breeding for a long time. It has contributed greatly to crop yield increase. However, the genetic basis of male sterility has not been fully elucidated. Here, we report map-based cloning of the cabbage (Brassica oleracea) dominant male-sterile gene Ms-cd1 and reveal that it encodes a PHD-finger motif transcription factor. A natural allele Ms-cd1PΔ-597, resulting from a 1-bp deletion in the promoter, confers dominant genic male sterility (DGMS), whereas loss-of-function ms-cd1 mutant shows recessive male sterility. We also show that the ethylene response factor BoERF1L represses the expression of Ms-cd1 by directly binding to its promoter; however, the 1-bp deletion in Ms-cd1PΔ-597 affects the binding. Furthermore, ectopic expression of Ms-cd1PΔ-597 confers DGMS in both dicotyledonous and monocotyledonous plant species. We thus propose that the DGMS system could be useful for breeding hybrids of multiple crop species.

Comparative analysis of mitochondrial genomes provides insights into the mechanisms underlying an S-type cytoplasmic male sterility (CMS) system in wheat (Triticum aestivum L.)

Cytoplasmic male sterility (CMS) has been widely used in crop cross breeding. There has been much research on wheat CMS. However, the correlation between S-type CMS and mitochondrial genome remains elusive. Herein, we sequenced the mitochondrial genome of wheat CMS line and compared it with the maintainer line. The results showed that the mitochondrial genome of CMS line encoded 26 tRNAs, 8 rRNAs, and 35 protein-coding genes, and the cob encoding complex III in which the protein coding gene is mutated. This protein is known to affect reactive oxygen (ROS) production. The analysis of ROS metabolism in developing anthers showed that the deficiency of antioxidants and antioxidant enzymes in the sterile system aggravated membrane lipid oxidation, resulting in ROS accumulation, and influencing the anther development. Herein, cob is considered as a candidate causative gene sequence for CMS.