Reactive Oxygen Species Accumulation Strongly Allied with Genetic Male Sterility Convertible to Cytoplasmic Male Sterility in Kenaf

Disruption of recombination machinery alters the mutational landscape in plant organellar genomes

Land plant organellar genomes have extremely low rates of point mutation yet also experience high rates of recombination and genome instability. Characterizing the molecular machinery responsible for these patterns is critical for understanding the evolution of these genomes. While much progress has been made towards understanding recombination activity in land plant organellar genomes, the relationship between recombination pathways and point mutation rates remains uncertain. The organellar targeted mutS homolog MSH1 has previously been shown to suppress point mutations as well as non-allelic recombination between short repeats in Arabidopsis thaliana. We therefore implemented high-fidelity Duplex Sequencing to test if other genes that function in recombination and maintenance of genome stability also affect point mutation rates. We found small to moderate increases in the frequency of single nucleotide variants (SNVs) and indels in mitochondrial and/or plastid genomes of A. thaliana mutant lines lacking radA, recA1, or recA3. In contrast, osb2 and why2 mutants did not exhibit an increase in point mutations compared to wild type (WT) controls. In addition, we analyzed the distribution of SNVs in previously generated Duplex Sequencing data from A. thaliana organellar genomes and found unexpected strand asymmetries and large effects of flanking nucleotides on mutation rates in WT plants and msh1 mutants. Finally, using long-read Oxford Nanopore sequencing, we characterized structural variants in organellar genomes of the mutant lines and show that different short repeat sequences become recombinationally active in different mutant backgrounds. Together, these complementary sequencing approaches shed light on how recombination may impact the extraordinarily low point mutation rates in plant organellar genomes.

Transcriptomics reveals a core transcriptional network of K-type cytoplasmic male sterility microspore abortion in wheat (Triticum aestivum L.)

BACKGROUND

Cytoplasmic male sterility (CMS) plays a crucial role in hybrid production. K-type CMS, a cytoplasmic male sterile line of wheat with the cytoplasms of Aegilops kotschyi, is widely used due to its excellent characteristics of agronomic performance, easy maintenance and easy restoration. However, the mechanism of its pollen abortion is not yet clear.

RESULTS

In this study, wheat K-type CMS MS(KOTS)-90-110 (MS line) and it's fertile near-isogenic line MR (KOTS)-90-110 (MR line) were investigated. Cytological analysis indicated that the anthers of MS line microspore nucleus failed to divide normally into two sperm nucleus and lacked starch in mature pollen grains, and the key abortive period was the uninucleate stage to dinuclear stage. Then, we compared the transcriptome of MS line and MR line anthers at these two stages. 11,360 and 5182 differentially expressed genes (DEGs) were identified between the MS and MR lines in the early uninucleate and binucleate stages, respectively. Based on GO enrichment and KEGG pathways analysis, it was evident that significant transcriptomic differences were "plant hormone signal transduction", "MAPK signaling pathway" and "spliceosome". We identified 17 and 10 DEGs associated with the IAA and ABA signal transduction pathways, respectively. DEGs related to IAA signal transduction pathway were downregulated in the early uninucleate stage of MS line. The expression level of DEGs related to ABA pathway was significantly upregulated in MS line at the binucleate stage compared to MR line. The determination of plant hormone content and qRT-PCR further confirmed that hormone imbalance in MS lines. Meanwhile, 1 and 2 DEGs involved in ABA and Ethylene metabolism were also identified in the MAPK cascade pathway, respectively; the significant up regulation of spliceosome related genes in MS line may be another important factor leading to pollen abortion.

CONCLUSIONS

We proposed a transcriptome-mediated pollen abortion network for K-type CMS in wheat. The main idea is hormone imbalance may be the primary factor, MAPK cascade pathway and alternative splicing (AS) may also play important regulatory roles in this process. These findings provided intriguing insights for the molecular mechanism of microspore abortion in K-type CMS, and also give useful clues to identify the crucial genes of CMS in wheat.

Transcriptomic and Proteomic Analyses of Celery Cytoplasmic Male Sterile Line and Its Maintainer Line

Male sterility is a common phenomenon in the plant kingdom and based on the organelles harboring the male-sterility genes, it can be classified into the genic male sterility (GMS) and the cytoplasmic male sterility (CMS). In every generation, CMS can generate 100% male-sterile population, which is very important for the breeders to take advantage of the heterosis and for the seed producers to guarantee the seed purity. Celery is a cross-pollinated plant with the compound umbel type of inflorescence which carries hundreds of small flowers. These characteristics make CMS the only option to produce the commercial hybrid celery seeds. In this study, transcriptomic and proteomic analyses were performed to identify genes and proteins that are associated with celery CMS. A total of 1255 differentially expressed genes (DEGs) and 89 differentially expressed proteins (DEPs) were identified between the CMS and its maintainer line, then 25 genes were found to differentially expressed at both the transcript and protein levels. Ten DEGs involved in the fleece layer and outer pollen wall development were identified by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses, most of which were down-regulated in the sterile line W99A. These DEGs and DEPs were mainly enriched in the pathways of "phenylpropanoid/sporopollenin synthesis/metabolism", "energy metabolism", "redox enzyme activity" and "redox processes". Results obtained in this study laid a foundation for the future investigation of mechanisms of pollen development as well as the reasons for the CMS in celery.

Integrative Analysis of Transcriptomic and Proteomic Changes Related to Cytoplasmic Male Sterility in Spring Stem Mustard (Brassica juncea var. tumida Tsen et Lee)

The development of flower and pollen is a complex biological process that involves multiple metabolic pathways in plants. In revealing novel insights into flower and pollen development underlying male sterility (MS), we conducted an integrated profiling of gene and protein activities in developing buds in cytoplasmic male sterile (CMS) mutants of mustard (Brassica juncea). Using RNA-Seq and label-free quantitative proteomics, 11,832 transcripts and 1780 protein species were identified with significant differential abundance between the male sterile line 09-05A and its maintainer line 09-05B at the tetrad stage and bi-nucleate stage of B. juncea. A large number of differentially expressed genes (DEGs) and differentially abundant proteins (DAPs) involved in carbohydrate and energy metabolism, including starch and sucrose metabolism, tricarboxylic acid (TCA) cycle, glycolysis, and oxidoreductase activity pathways, were significantly downregulated in 09-05A buds. The low expression of these DEGs or functional loss of DAPs, which can lead to an insufficient supply of critical substrates and ATP, could be associated with flower development, pollen development, and changes in fertility in B. juncea. Therefore, this study provided transcriptomic and proteomic information of pollen abortion for B. juncea and a basis for further research on the molecular regulatory mechanism of MS in plants.