Development and utilization of an InDel marker linked to the fertility restorer genes of CMS-D8 and CMS-D2 in cotton

Heat-responsive microRNAs participate in regulating the pollen fertility stability of CMS-D2 restorer line under high-temperature stress

Anther development and pollen fertility of cytoplasmic male sterility (CMS) conditioned by Gossypium harknessii cytoplasm (CMS-D2) restorer lines are susceptible to continuous high-temperature (HT) stress in summer, which seriously hinders the large-scale application of "three-line" hybrids in production. Here, integrated small RNA, transcriptome, degradome, and hormone profiling was performed to explore the roles of microRNAs (miRNAs) in regulating fertility stability in mature pollens of isonuclear alloplasmic near-isogenic restorer lines NH and SH under HT stress at two environments. A total of 211 known and 248 novel miRNAs were identified, of which 159 were differentially expressed miRNAs (DEMs). Additionally, 45 DEMs in 39 miRNA clusters (PmCs) were also identified, and most highly expressed miRNAs were significantly induced in SH under extreme HT, especially four MIR482 and six MIR6300 family miRNAs. PmC28 was located in the fine-mapped interval of the Rf1 gene and contained two DEMs, gra-miR482_L-2R + 2 and gma-miR2118a-3p_R + 1_1ss18TG. Transcriptome sequencing identified 6281 differentially expressed genes, of which heat shock protein (HSP)-related genes, such as HSP70, HSP22, HSP18.5-C, HSP18.2 and HSP17.3-B, presented significantly reduced expression levels in SH under HT stress. Through integrating multi-omics data, we constructed a comprehensive molecular network of miRNA-mRNA-gene-KEGG containing 35 pairs of miRNA/target genes involved in regulating the pollen development in response to HT, among which the mtr-miR167a_R + 1, tcc-miR167c and ghr-miR390a, tcc-miR396c_L-1 and ghr-MIR169b-p3_1ss6AG regulated the pollen fertility by influencing ARF8 responsible for the auxin signal transduction, ascorbate and aldarate metabolism, and the sugar and lipid metabolism and transport pathways, respectively. Further combination with hormone analysis revealed that HT-induced jasmonic acid signaling could activate the expression of downstream auxin synthesis-related genes and cause excessive auxin accumulation, followed by a cascade of auxin signal transduction, ultimately resulting in pollen abortion. The results provide a new understanding of how heat-responsive miRNAs regulate the stability of fertility restoration for CMS-D2 cotton under heat stress.

Development of Omni InDel and supporting database for maize

Insertions-deletions (InDels) are the second most abundant molecular marker in the genome and have been widely used in molecular biology research along with simple sequence repeats (SSR) and single-nucleotide polymorphisms (SNP). However, InDel variant mining and marker development usually focuses on a single type of dimorphic InDel, which does not reflect the overall InDel diversity across the genome. Here, we developed Omni InDels for maize, soybean, and rice based on sequencing data and genome assembly that included InDel variants with base lengths from 1 bp to several Mb, and we conducted a detailed classification of Omni InDels. Moreover, we screened a set of InDels that are easily detected and typed (Perfect InDels) from the Omni InDels, verified the site authenticity using 3,587 germplasm resources from 11 groups, and analyzed the germplasm resources. Furthermore, we developed a Multi-InDel set based on the Omni InDels; each Multi-InDel contains multiple InDels, which greatly increases site polymorphism, they can be detected in multiple platforms such as fluorescent capillary electrophoresis and sequencing. Finally, we developed an online database website to make Omni InDels easy to use and share and developed a visual browsing function called "Variant viewer" for all Omni InDel sites to better display the variant distribution.

Comparative Transcriptome Profiling of CMS-D2 and CMS-D8 Systems Characterizes Fertility Restoration Genes Network in Upland Cotton

Resolving the genetic basis of fertility restoration for cytoplasmic male sterility (CMS) can improve the efficiency of three-line hybrid breeding. However, the genetic determinants of male fertility restoration in cotton are still largely unknown. This study comprehensively compared the full-length transcripts of CMS-D2 and CMS-D8 systems to identify potential genes linked with fertility restorer genes Rf₁ or Rf₂. Target comparative analysis revealed a higher percentage of differential genes in each restorer line as compared to their corresponding sterile and maintainer lines. An array of genes with specific expression in the restorer line of CMS-D2 had functional annotations related to floral development and pathway enrichments in various secondary metabolites, while specifically expressed genes in the CMS-D8 restorer line showed functional annotations related to anther development and pathway enrichment in the biosynthesis of secondary metabolites. Further analysis identified potentially key genes located in the target region of fertility restorer genes Rf₁ or Rf₂. In particular, Ghir_D05G032450 can be the candidate gene related to restorer gene Rf₁, and Ghir_D05G035690 can be the candidate gene associated with restorer gene Rf₂. Further gene expression validation with qRT-PCR confirmed the accuracy of our results. Our findings provide useful insights into decoding the potential regulatory network that retrieves pollen fertility in cotton and will help to further reveal the differences in the genetic basis of fertility restoration for two CMS systems.

Identification of fertility restoration candidate genes from a restorer line R186 for Gossypium harknessii cytoplasmic male sterile cotton

BACKGROUND

The utilization of heterosis based on three-line system is an effective strategy in crop breeding. However, cloning and mechanism elucidation of restorer genes for cytoplasmic male sterility (CMS) in upland cotton have yet been realized.

RESULTS

This research is based on CMS line 2074A with the cytoplasm from Gossypium harknessii (D_2-2) and restorer line R186. The offspring of 2074A × R186 were used to conduct genetic analysis. The fertility mechanism of 2074A can be speculated to be governed by multiple genes, since neither the single gene model nor the double genes model could be used. The bulked segregant analysis (BSA) for (2074A × R186) F₂ determined the genetic interval of restorer genes on a region of 4.30 Mb on chromosome D05 that contains 77 annotated genes. Four genes were identified as candidates for fertility restoration using the RNA-seq data of 2074A, 2074B, and R186. There are a number of large effect variants in the four genes between 2074A and R186 that could cause amino acid changes. Evolutionary analysis and identity analysis revealed that GH_D05G3183, GH_D05G3384, and GH_D05G3490 have high identity with their homologs in D_2-2, respectively. Tissue differential expression analysis revealed that the genes GH_D05G3183, GH_D05G3384, and GH_D05G3490 were highly expressed in the buds of the line R186. The predicted results demonstrated that GH_D05G3183, GH_D05G3384 and GH_D05G3490 might interact with GH_A02G1295 to regulate orf610a in mitochondria.

CONCLUSION

Our study uncovered candidate genes for fertility restoration in the restorer line R186 and predicted the possible mechanism for restoring the male fertility in 2074A. This research provided valuable insight into the nucleoplasmic interactions.

Development of mitochondrial simple sequence repeat markers to simultaneously distinguish cytoplasmic male sterile sources in cotton

Deleterious effects on anther development and main economy traits caused by sterile genes or cytoplasms are one of the important genetic characteristics of cytoplasmic male sterility (CMS) systems in cotton, which severely hinder the large-scale application of "three-line" hybrids in production. Therefore, distinct characterization of each cytoplasmic type is mandatory to improve the breeding efficiency of cotton hybrids. In this study, four isonuclear-alloplasmic cotton male sterile lines with G. hirsutum (CMS-(AD)1), G. barbadense (CMS-(AD)2), G. harknessii (CMS-D2), and G. trilobum (CMS-D8) cytoplasms were first created by multiple backcrosses with common genotype Shikang126. Then, 64 pairs of mitochondrial simple sequence repeat (mtSSR) markers were designed to explore the mitochondrial DNA diversities among four isonuclear-alloplasmic cotton male sterile lines, and a total of nine pairs of polymorphic mtSSR molecular markers were successfully developed. Polymorphism analysis indicated that mtSSR59 marker correlated to the atp1 gene could effectively divide the CMS-D2, CMS-(AD)1, and CMS-(AD)2 in one category while the CMS-D8 in another category. Further cytological observation and determination of ATP contents also confirmed the accurate classification of CMS-D2 and CMS-D8 lines. Moreover, the mtSSR59 marker was successfully applied in the marker-assisted selection (MAS) for breeding new male sterile lines and precise differentiation or purity identification of different CMS-based "three-line" and conventional cotton hybrids. This study provides new technical measures for classifying various cytoplasmic sterile lines, and our results will significantly improve the efficiency of there-line hybrid breeding in cotton.

A super PPR cluster for restoring fertility revealed by genetic mapping, homocap-seq and de novo assembly in cotton

Rf candidate genes were related to the super D05_PPR-cluster and verified to be individually nonfunctional. Restorer of fertility (Rf) genes of cytoplasmic male sterility (CMS) is commonly found to be PPR (pentatricopeptide repeat) genes, which are mostly located in a cluster of PPR genes with high similarity. Here, Homocap-seq was applied to analyze PPR clusters in 'three lines,' and we found broad variations within the D05_PPR-cluster in a restorer line and deduced that the D05_PPR-cluster was associated with fertility restoration. Genetic mapping of Rf and Homocap-seq analysis of three genotypes in the F₂ population validated that the D05_PPR-cluster was the origin of Rf. Three Rf candidates were cloned that were the most actively expressed genes in the D05_PPR-cluster in the restorer line as revealed by their high-depth amplicons. However, further transgenic experiments showed that none of the candidates could restore fertility of the CMS line independently. Then, the members of the brand-new super D05_PPR-cluster in the restorer line, containing 14 full-length PPRs and at least 13 PPR homologous sequences, were identified by long-read resequencing, which validated the effectiveness of variation and expression prediction of Homocap-seq. Additionally, we found that several PPR duplications, including 2 of the 3 Rf candidates, had undergone site-specific selection as potentially important anther development-associated genes. Finally, we proposed that multiple PPRs were coordinately responsible for the fertility restoration of the CMS line.

Exploration of Genetic Variants within the Goat A-Kinase Anchoring Protein 12 (AKAP12) Gene and Their Effects on Growth Traits

Simple Summary

AKAP12, the family of A-kinase anchoring proteins (AKAPs), plays an important role in the regulation of growth and development. There have been no corresponding studies of the effect of the AKAP12 gene on growth traits in goats. In our previous study, 7 bp (intron 3) and 13 bp (3′UTR) indels within the AKAP12 gene significantly influenced AKAP12 gene expression. This study expected to identify the association between these two genetic variations and growth-related traits in 1405 Shaanbei white cashmere (SBWC) goats. The P1–7 bp indel locus was significantly correlated with height at hip cross (HHC; p < 0.05) and the P2–13 bp indel locus was associated with body weight, body length, chest depth, chest width, hip width, chest circumference and cannon (bone) circumference in SBWC goats (p < 0.05). These results prove that the AKAP12 gene plays an important role in the growth and development of goats.

Abstract

The A-kinase anchoring protein 12 gene (AKAP12) is a scaffold protein, which can target multiple signal transduction effectors, can promote mitosis and cytokinesis and plays an important role in the regulation of growth and development. In our previous study, P1–7 bp (intron 3) and P2–13 bp (3′UTR) indels within the AKAP12 gene significantly influenced AKAP12 gene expression. Therefore, this study aimed to identify the association between these two genetic variations and growth-related traits in Shaanbei white cashmere goats (SBWC) (n = 1405). Herein, we identified two non-linkage insertions/deletions (indels). Notably, we found that the P1–7 bp indel mutation was related to the height at hip cross (HHC; p < 0.05) and the P2–13 bp indel was associated with body weight, body length, chest depth, chest width, hip width, chest circumference and cannon (bone) circumference in SBWC goats (p < 0.05). Overall, the two indels’ mutations of AKAP12 affected growth traits in goats. Compared to the P1–7 bp indel, the P2–13 bp indel is more suitable for the breeding of goat growth traits.