Maintainer Lines Research Articles

Expression profiling of immature florets of IR58025A, a wild-abortive cytoplasmic male sterile line of rice and its cognate, isonuclear maintainer line, IR58025B.

Interaction between gene products encoded by the cytoplasm and nucleus form the core of wild abortive cytoplasmic male sterile (WA-CMS) system of hybrid breeding in rice. Gaining insights into such interactions can be helpful in the development of better three-line rice hybrids and also identify novel male sterility systems. In the present study, the whole transcriptome profiles of immature florets of IR58025A, a WA-CMS line and its isonuclear maintainer line, IR58025B, collected at pre-anthesis stage were compared to delineate the pathways involved in pollen abortion and male sterility. Among the 774 differentially expressed transcripts (DETs), 496 were down regulated and 278 were up regulated in IR58025A compared to IR58025B. The genes associated with oxidative stress response, defense response, etc. were significantly up-regulated, while those associated with respiration, cell wall modifications, pectinesterase activity, etc. were significantly down-regulated in the WA-CMS line. Gene ontology and pathway enrichment analyses revealed the down-regulation of both nuclear and organellar genes involved in key metabolic processes of cell respiration, photosynthesis and other energy yielding metabolites in IR58025A, relative to IR58025B, indicating a general shift toward conservation of energy and other key resources in the florets of WA-CMS line. The data derived from RNA-Seq analysis were validated through qRT-PCR analysis. Based on the results obtained, it can be hypothesized that pollen abortion principally occurs due to up-regulation of pathways leading to oxidative stress leading to energy starvation conditions in consonance with reduced expression of genes associated with the cell wall formation, respiration, and other key metabolic processes.

Evaluation and selection of sources of cytoplasmic male sterility in broccoli

Broccoli is an important Brassica vegetable that shows obvious heterosis. The main method for hybrid broccoli production is to use cytoplasmic male sterility (CMS) and pollination by bees. Therefore, the evaluation and selection of high quality sources of CMS is important for broccoli breeding. We aimed to evaluate the effects of different CMS sources on the morphology and size of floral organs, the attractiveness to pollinators and yield of hybrid seeds. Using broccoli CMS lines generated from different CMS sources with the same maintainer lines, we studied morphophysiological characteristics of flowers, such as flower shape and size, nectar production and sugar content, as well as the number of bee visits and seed yield. The degree of bud abortion, floral organs shape, degree of flower opening, nectar production, bee visits, and hybrid yield differed in CMS lines with same recurrent parent. When the CMS source was same and the recurrent parents were different, the degrees of bud abortion were different among the CMS lines, while the flowering characteristics were similar. Generally, larger floral organs and higher volumes of nectar were associated with higher frequency of bee visits and higher seed yield. Based on the morphological characteristics and size of floral organs, nectar secretion, bee-attracting ability and hybrid yield, we selected four CMS sources suitable for future use in broccoli breeding. Our results will provide an important reference for breeding high-quality CMS lines in broccoli and provide valuable CMS sources for breeding other cruciferous crops.

Breeding of Indica glutinous cytoplasmic male sterile line WX209A via CRISPR/Cas9 mediated genomic editing

Glutinous cytoplasmic male sterile (CMS) line is necessary to select hybrid glutinous rice combination with high yield and quality. To develop glutinous CMS with low amylose content, in this study, we firstly knocked out the granule-bound starch synthase OsWaxy in 209B using CRISPR/Cas9 mediated genome editing technology and successfully obtained a glutinous maintainer line WX209B. Comparing with maintainer line 209B, WX209B showed decreased amylose contents and similar agronomic characters. And then, through one generation of hybridization and two generations of backcrossing with WX209B as the male parent and 209A as the female parent, the glutinous CMS line WX209A was successfully achieved. Our study provides a strategy to efficiently breed for the glutinous cytoplasmic male sterile line by combining CRISPR/Cas9-mediated gene editing technology with conventional backcross breeding method in a short period, which prepares the ground for further breeding of hybrid glutinous rice variety.

A user-friendly KASP molecular marker developed for the DGMS-based breeding system in Brassica oleracea species

Cabbage 79-399-3 is a spontaneous male-sterile mutant controlled by the dominant genic gene (DGMS) Ms-cd1. Dozens of DGMS lines in cabbage, broccoli, kohlrabi, and Chinese kale have been created using 79-399-3 as a donor. To realize fast and accurate marker-assisted selection (MAS) and build a high-efficiency breeding system based on DMGS, a high-throughput, user-friendly marker is needed. In this study, we resequenced the DGMS line DGMS01-20 (backcross lines with over 20 generations) and its maintainer line 01-20 and developed four markers linked to Ms-cd1 using a segregating population of DGMS01-20. Kompetitive allele specific PCR (KASP) markers K13 and K23 were the flanking markers with genetic distances of 0.76 cM and 1.09 cM, respectively. K6 cosegregated with Ms-cd1 in all 919 individuals of the population. K13 and K6 were tested for their accuracy and applicability using 18 different DGMS lines. K13 was not applicable in five broccoli, kohlrabi, and Chinese kale DGMS lines, resulting in 72.2% accuracy, whereas K6 showed 100% accuracy in these DGMS lines and in an additional assessment using 35 inbred lines. Moreover, K6 can be used to genotype the self-pollination progenies of heterozygous plants (heterozygous means one Ms-cd1 allele and one wild-type allele; such plants produce pollen grains in very rare cases). The results showed that K6 is a reliable marker for accurately and rapidly identifying Ms-cd1 loci in Brassica oleracea; thus, it is beneficial for the DGMS-based breeding program in B. oleracea.

Comparative profile analysis reveals differentially expressed microRNAs regulate anther and pollen development in kenaf cytoplasmic male sterility line.

Cytoplasmic male sterility (CMS) is advantageous in extensive crop breeding and represents a perfect model for understanding anther and pollen development research. MicroRNAs (miRNAs) play key roles in regulating various biological processes. However, the miRNA-mediated regulatory network in kenaf CMS occurrence remains largely unknown. In the present study, a comparative deep sequencing approach was used to investigate the miRNAs and their roles in regulating anther and pollen development during CMS occurrence. We identified 283 known and 46 new candidate miRNAs in kenaf anther. A total of 67 differentially expressed miRNAs (DEMs) were discovered between CMS and its maintainer line. Among them, 40 and 27 miRNAs were up- and downregulated, respectively. These 67 DEMs were predicted to target 189 genes. Validation of DEMs and putative target genes were confirmed by using real-time quantitative PCR. In addition, a potential miRNA-mediated regulatory network, which mainly involves the auxin signaling pathway, signal transduction, glycolysis and energy metabolism, gene expression, transmembrane transport, protein modification and metabolism, and floral development, that mediates anther development during CMS occurrence was proposed. Taken together, our findings provide a better understanding of the molecular mechanism of miRNA regulation in pollen development and CMS occurrence in kenaf.

Characterization and utilization of a cytoplasmic male sterility line of Wucai (Brassica campestris L.)

The novel male sterility line 12-14A of Wucai (Brassica campestris) was generated by backcrossing. In this study, morphological, molecular, and cytological analyses were performed to characterize this line. The phenotypes of flower organs of 12-14A were different from those of its maintainer line 12-14B, as the flowers of 12-14A were completely infertile. Molecular analysis confirmed that the male sterility line 12-14A was classified as the ogu CMS type. An analysis of anther development in the CMS line demonstrated that two types of abortion occur simultaneously: pollen mother cell abortion and tetrad-to-mononuclear microspore abortion. In addition, the mature anthers of 12-14A showed typical abortive features, such as appearing dry, shrunken, and scaly. A heterosis test of hybrids from CMS 12-14A and four inbred lines was carried out, and the F1 hybrids exhibited clear heterosis in plant weight, as well as in the protein, soluble sugar, and vitamin C content, suggesting high yields and high quality potential. These results indicate that this novel CMS line may have powerful potential in Wucai hybrid breeding.

Effect of male sterile and fertile cytoplasm on nuclear DNA methylation in hybrid rice

Nucleus-controlled fertility restoration and cytoplasmic male sterility are important mechanisms to exploit heterosis. However, the effect of DNA methylation on cytoplasmic-nuclear interaction is not well understood yet. The current study used a methylation-sensitive amplified polymorphism to characterize polymorphism in nuclear DNA methylation among cytoplasmic male sterile line (D62A), corresponding maintainer line (D62B), and two F1 hybrids (D62A × R527 and D62B × R527). In results, 495 fragments were amplified between the parental D62A and D62B lines. The total methylation (double + single-stranded) and full methylation (double-stranded) rates of D62A (33.13%, 24.24%) both were found to be lower than that of corresponding maintainer D62B (33.94%, 24.85%). Analysis of methylation revealed that male sterile line D62A was less methylated than that of corresponding maintainer line D62B in all methylation types I, II and III. A total of 516 fragments were amplified between two F1 hybrids (D62A × R527 and D62B × R527). The total methylation in both hybrids (D62A × R527 and D62B × R527) was identical (34.69%). While full methylation rates for D62A × R527 and D62B × R527 were 25.78% and 25.58%, respectively, that is non-significant. Moreover, polymorphism in DNA methylation was found higher in F1 hybrids (5.43%) than parents (4.24%). These results implied that different cytoplasm leads to changes in nuclear DNA methylation and sterile cytoplasm has reduced the effect on nuclear methylation than non-sterile cytoplasm. Current study explains the interaction between cytoplasmic male sterility and DNA methylation which may contribute to further research.

A new male sterile line of “Duanye-13” radish (Raphanus sativus L.) produced by ethyl methanesulfonate mutagenesis

Mutations in radish can be induced by exposure to ethyl methanesulfonate (EMS), and this method is suitable for obtaining target traits in new radish materials. We investigated the optimal concentration of EMS for mutagenesis on the radish variety Duan-Ye No. 13 (DY13). Treating DY13 radish seeds with 0.5% EMS led to the development of sterile mutants. During 3 years of continuous hybridization and tracing, male fertility remained stable at 100% sterility. Morphological observations showed that the anthers of these male sterile were wrinkled, curled, and browned; disintegration of the wall structure at the pollen tetrad stage caused eventual pollen abortion. Detection of the molecular marker ORF138-F/R confirmed that the target band could be amplified in this radish line; however, the band was not amplified in the corresponding maintainer line. Together, these results show that male sterile lines were successfully selected from DY13 radishes, demonstrating a new and effective method for breeding male sterile radish lines.

Map-Based Cloning, Phylogenetic, and Microsynteny Analyses of ZmMs20 Gene Regulating Male Fertility in Maize.

Genic male sterility (GMS) mutant is a useful germplasm resource for both theory research and production practice. The identification and characterization of GMS genes, and assessment of male-sterility stability of GMS mutant under different genetic backgrounds in Zea may (maize) have (1) deepened our understanding of the molecular mechanisms controlling anther and pollen development, and (2) enabled the development and efficient use of many biotechnology-based male-sterility (BMS) systems for hybrid breeding. Here, we reported a complete GMS mutant (ms20), which displays abnormal anther cuticle and pollen development. Its fertility restorer gene ZmMs20 was found to be a new allele of IPE1 encoding a glucose methanol choline (GMC) oxidoreductase involved in lipid metabolism in anther. Phylogenetic and microsynteny analyses showed that ZmMs20 was conserved among gramineous species, which provide clues for creating GMS materials in other crops. Additionally, among the 17 maize cloned GMS genes, ZmMs20 was found to be similar to the expression patterns of Ms7, Ms26, Ms6021, APV1, and IG1 genes, which will give some clues for deciphering their functional relationships in regulating male fertility. Finally, two functional markers of ZmMs20/ms20 were developed and tested for creating maize ms20 male-sterility lines in 353 genetic backgrounds, and then an artificial maintainer line of ms20 GMS mutation was created by using ZmMs20 gene, ms20 mutant, and BMS system. This work will promote our understanding of functional mechanisms of male fertility and facilitate molecular breeding of ms20 male-sterility lines for hybrid seed production in maize.

Development and Validation of Markers for the Fertility Restorer Gene Rf1 in Sunflower.

Hybrid breeding in sunflowers based on CMS PET1 requires development of restorer lines carrying, in most cases, the restorer gene Rf1. Markers for marker-assisted selection have been developed, but there is still need for closer, more versatile, and co-dominant markers linked to Rf1. Homology searches against the reference sunflower genome using sequences of cloned markers, as well as Bacterial Artificial Chromosome (BAC)-end sequences of clones hybridizing to them, allowed the identification of two genomic regions of 30 and 3.9 Mb, respectively, as possible physical locations of the restorer gene Rf1 on linkage group 13. Nine potential candidate genes, encoding six pentatricopeptide repeat proteins, one tetratricopeptide-like helical domain, a probable aldehyde dehydrogenase 22A1, and a probable poly(A) polymerase 3 (PAPS3), were identified in these two genomic regions. Amplicon targeted next generation sequencing of these nine candidate genes for Rf1 was performed in an association panel consisting of 27 maintainer and 32 restorer lines and revealed the presence of 210 Single Nucleotide Polymorphisms (SNPs) and 67 Insertions/Deletions (INDELs). Association studies showed significant associations of 10 SNPs with fertility restoration (p-value < 10−4), narrowing Rf1 down to three candidate genes. Three new markers, one co-dominant marker 67N04_P and two dominant markers, PPR621.5R for restorer, and PPR621.5M for maintainer lines were developed and verified in the association panel of 59 sunflower lines. The versatility of the three newly developed markers, as well as of three existing markers for the restorer gene Rf1 (HRG01 and HRG02, Cleaved Amplified Polymorphic Sequence (CAPS)-marker H13), was analyzed in a large association panel consisting of 557 accessions.

Transcriptomic and Proteomic Analysis of Shaan2A Cytoplasmic Male Sterility and Its Maintainer Line in Brassica napus.

Cytoplasmic male sterility (CMS) lines are widely used for hybrid production in Brassica napus. The Shaan2A CMS system is one of the most important in China and has been used for decades; however, the male sterility mechanism underlying Shaan2A CMS remains unknown. Here, we performed transcriptomic and proteomic analysis, combined with additional morphological observation, in the Shaan2A CMS. Sporogenous cells, endothecium, middle layer, and tapetum could not be clearly distinguished in Shaan2A anthers. Furthermore, Shaan2A anther chloroplasts contained fewer starch grains than those in Shaan2B (a near-isogenic line of Shaan2A), and the lamella structure of chloroplasts in Shaan2A anther wall cells was obviously aberrant. Transcriptomic analysis revealed differentially expressed genes (DEGs) mainly related to carbon metabolism, lipid and flavonoid metabolism, and the mitochondrial electron transport/ATP synthesis pathway. Proteomic results showed that differentially expressed proteins were mainly associated with carbohydrate metabolism, energy metabolism, and genetic information processing pathways. Importantly, nine gene ontology categories associated with anther and pollen development were enriched among down-regulated DEGs at the young bud (YB) stage, including microsporogenesis, sporopollenin biosynthetic process, and tapetal layer development. Additionally, 464 down-regulated transcription factor (TF) genes were identified at the YB stage, including some related to early anther differentiation such as SPOROCYTELESS (SPL, also named NOZZLE, NZZ), DYSFUNCTIONAL TAPETUM 1 (DYT1), MYB80 (formerly named MYB103), and ABORTED MICROSPORES (AMS). These results suggested that the sterility gene in the Shaan2A mitochondrion might suppress expression of these TF genes in the nucleus, affecting early anther development. Finally, we constructed an interaction network of candidate proteins based on integrative analysis. The present study provides new insights into the molecular mechanism of Shaan2A CMS in B. napus.

Identification and gene cloning of a male‐sterile mutant Oswbc11 in rice

AbstractCommercial application of nuclear genetic male sterility has been improved recently by a novel technique, Seed Production Technology (SPT), which incorporates transgenic maintainer lines capable of propagating non‐transgenic nuclear male‐sterile lines for use as female parents in hybrid production. Here, we identified a rice nuclear male‐sterile mutant, Oswbc11, with abnormal pollen development and lipid transport. We finely mapped the Oswbc11 gene into a 12.5‐kb region on chromosome 10 and found one candidate gene, which had a base substitution (C to T) resulting in a premature stop codon and was functionally confirmed by CRISPR/Cas9 technology. Gene OsWBC11 encodes a sub‐family member of adenosine triphosphate‐binding cassette transporter, which participates in the active transport of a wide range of molecules across membranes. Moreover, the agronomic traits of Oswbc11 mutants showed no significant differences compared to the wild‐type control except for the seed setting rate. These results indicated that Oswbc11 gene could be used in rice hybrid breeding as a recessive nuclear male‐sterile gene combined with CRISPR/Cas9 and the SPT technology and applied in different rice varieties.

Enhanced Expression of QTL qLL9/DEP1 Facilitates the Improvement of Leaf Morphology and Grain Yield in Rice.

In molecular breeding of super rice, it is essential to isolate the best quantitative trait loci (QTLs) and genes of leaf shape and explore yield potential using large germplasm collections and genetic populations. In this study, a recombinant inbred line (RIL) population was used, which was derived from a cross between the following parental lines: hybrid rice Chunyou84, that is, japonica maintainer line Chunjiang16B (CJ16); and indica restorer line Chunhui 84 (C84) with remarkable leaf morphological differences. QTLs mapping of leaf shape traits was analyzed at the heading stage under different environmental conditions in Hainan (HN) and Hangzhou (HZ). A major QTL qLL9 for leaf length was detected and its function was studied using a population derived from a single residual heterozygote (RH), which was identified in the original population. qLL9 was delimitated to a 16.17 kb region flanked by molecular markers C-1640 and C-1642, which contained three open reading frames (ORFs). We found that the candidate gene for qLL9 is allelic to DEP1 using quantitative real-time polymerase chain reaction (qRT-PCR), sequence comparison, and the clustered regularly interspaced short palindromic repeat-associated Cas9 nuclease (CRISPR/Cas9) genome editing techniques. To identify the effect of qLL9 on yield, leaf shape and grain traits were measured in near isogenic lines (NILs) NIL-qLL9CJ16 and NIL-qLL9C84, as well as a chromosome segment substitution line (CSSL) CSSL-qLL9KASA with a Kasalath introgressed segment covering qLL9 in the Wuyunjing (WYJ) 7 backgrounds. Our results showed that the flag leaf lengths of NIL-qLL9C84 and CSSL-qLL9KASA were significantly different from those of NIL-qLL9CJ16 and WYJ 7, respectively. Compared with NIL-qLL9CJ16, the spike length, grain size, and thousand-grain weight of NIL-qLL9C84 were significantly higher, resulting in a significant increase in yield of 15.08%. Exploring and pyramiding beneficial genes resembling qLL9C84 for super rice breeding could increase both the source (e.g., leaf length and leaf area) and the sink (e.g., yield traits). This study provides a foundation for future investigation of the molecular mechanisms underlying the source–sink balance and high-yield potential of rice, benefiting high-yield molecular design breeding for global food security.

Abnormal tapetum development and energy metabolism associated with sterility in SaNa-1A CMS of Brassica napus L.

Abnormal tapetum degradation and anther development in cytoplasmic male sterility SaNa-1A are the main reasons for the anther abortion. SaNa-1A is a novel cytoplasmic male sterility (CMS) line of Brassica napus derived from somatic hybrids of B. napus-Sinapis alba, and SaNa-1B is the corresponding maintainer line. Ultrastructural comparison between developing anthers of sterile and maintainer lines revealed abnormal subcellular structure of pollen mother cells (PMCs) in the CMS line. The PMC volume and size of nucleus and nucleolus in the CMS line were smaller than those in the maintainer line. The abnormal tapetum cell development and delayed tapetum degradation inhibited microspore development. Finally, anther abortion in the CMS line occurred. Physiological and biochemical analyses of developing anthers and mitochondria revealed that over-accumulation of reactive oxygen species (ROS) in the SaNa-1A and deficiency in antioxidant enzyme system aggravated the oxidization of membrane lipids, resulting in malondialdehyde (MDA) accumulation in anthers. High MDA content in the CMS line was toxic to the cells. ROS accumulation in SaNa-1A also affected anther development. Abnormal structure and function of terminal oxidase, which participates in the electron transport chain of mitochondrial membrane, were observed and affected the activity of cytochrome c oxidase and F1F0-ATPase, which inhibited ATP biosynthesis. Proline deficiency in SaNa-1A also affected anther development. Few hybridization signals of programmed cell death (PCD) in tetrads of SaNa-1A were identified using TdT-mediated dUTP Nick-End Labeling assay. PCD was not obvious in tapetum cells of SaNa-1A until the unicellular stage. These results validated the cytological differences mentioned above, and proved that abnormal tapetum degradation and anther development in SaNa-1A were the main reasons for the anther abortion.

Candidate Gene Selection for Cytoplasmic Male Sterility in Pepper (Capsicum annuum L.) through Whole Mitochondrial Genome Sequencing.

Cytoplasmic male sterility (CMS), which is controlled by mitochondrial genes, is an important trait for commercial hybrid seed production. So far, genes controlling this trait are still not clear in pepper. In this study, complete mitochondrial genomes were sequenced and assembled for the CMS line 138A and its maintainer line 138B. The genome size of 138A is 504,210 bp, which is 8618 bp shorter than that of 138B. Meanwhile, more than 214 and 215 open reading frames longer than 100 amino acids (aas) were identified in 138A and 138B, respectively. Mitochondrial genome structure of 138A was quite different from that of 138B, indicating the existence of recombination and rearrangement events. Based on the mitochondrial genome sequence and structure variations, mitochondrion of 138A and FS4401, a Korean origin CMS line, may have inherited from a common female ancestor, but their CMS traits did originate separately. Candidate gene selection was performed according to the published characteristics of the CMS genes, including the presence SNPs and InDels, located in unique regions, their chimeric structure, co-transcription, and transmembrane domain. A total of 35 ORFs were considered as potential candidate genes and 14 of these were selected, with orf300a and 0rf314a as strong candidates. A new marker, orf300a, was developed which did co-segregate with the CMS trait.

Marker assisted introgression of a major bacterial blight resistance gene, Xa38 into a rice maintainer line, APMS 6B

Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae is a major production constraint for rice in India. We introgressed a major dominant BB resistance gene, Xa38 in the genetic background of APMS 6B, a maintainer line of APMS 6A (female parent of DRRH 3) through marker-assisted backcross breeding (MABB). The BB resistance gene, Xa38 was transferred to APMS 6B from the donor, PR 114 (Xa38) through two backcrosses. A single selected true BC2F1 plant having maximum recovery of recurrent parent genome and also high degree of BB resistance was selfed to generate BC2F2s. At BC2F2, plants homozygous for Xa38 were identified and were further confirmed for the absence of two major fertility restorer genes, Rf3 and Rf4. Eight best BC2F2 plants, homozygous positive for Xa38 and homozygous negative for Rf3 and Rf4 were selected and advanced up to BC2F6. At BC2F6, these introgression lines exhibited high degree of BB resistance against multiple Xoo strains and were similar to APMS 6B in respect to different agro-morphological traits.

Feature of blast resistant near-isogenic lines using an elite maintainer line II-32B by marker-assisted selection

Rice plays a crucial role in food production worldwide as one of the most important cereal crops. Breeding blast disease resistant varieties is a long-term aim for sustainable rice production. II-32B is an elite maintainer line of II-32A which has been widely used as a hybrid rice parent in China. However, it is significantly susceptible to rice blast. In this study, multiple alleles, Pi-2 and Pi-9, and the chromosomal segment of blast resistance genes, Pi-1 and Pi-kh, were introgressed to receptor parents II-32B by marker-assisted backcross breeding. Eleven near-isogenic lines (NILs) with single Pi-gene and 12 pyramid lines containing double or three homozygous resistance genes were obtained. These improved lines were identified by inoculating Magnaporthe oryzae isolates in the field/greenhouses; the result showed that the resistance of pyramid lines containing three resistance genes was stronger than the lines with double or single gene, whereas the lines with double genes were stronger than the one with single-gene. Additionally, pyramiding of different Pi-genes was effective in obtaining the durable blast resistance in rice. This implies that gene pyramiding in rice can increase spectrum and strength of resistance to blast. Furthermore, three-line retention of sixteen improved NILs was kept well and the agronomic traits were consistence with II-32B. We conclude that gene pyramiding is an effective breeding approach for the improvement of rice varieties with durable resistance to blast in the future.

Studies on genetic parameters, correlation and path analysis for yield attributes in the maintainer and restorer lines of pearl millet [Pennisetum glacum.(L.) R. Br

Studies on genetic parameters, correlation and path analysis for yield attributes in the maintainer and restorer lines of pearl millet [<i>Pennisetum glacum.(L.</i>) R. Br

Genetic analysis of variability, heritability and genetic advance in F3 populations of sunflower (Helianthus annuus L.)

The field experiment was carried out by using 46 sunflower progenies of two cross combinations (COSF6B x CMS 335B and COSF7B x 343 B) of F3 generation at Department of Oilseeds, CPBG, TNAU, Coimbatore during kharif 2018 to study the genotypic coefficient of variation, phenotypic coefficient of variation, heritability and genetic advance. The analysis of variance imparted significant differences for all the characters. In the B (maintainer ) line development programme, the characters like head diameter, percent disease index (PDI), seed yield per plant, 100 seed weight, volume weight and oil yield in both the populations recorded high heritability associated with high genetic advance, whereas the traits; days to flowering and days to maturity showed low values of GAM in both the populations. The results indicated that the characters with high heritability and high or moderate genetic advance can be further improved with individual plant selection, whereas characters with high heritability and low genetic advance indicated little scope for further improvement through individual plant selection.

Identification of genes related to the regulation of anther and pollen development in Mu-type cytoplasmic male sterile wheat (Triticum aestivum) by transcriptome analysis

Cytoplasmic male sterile (CMS) lines are important tools for hybrid production but they cannot produce viable pollen. Breeding new CMS lines and studying their sterility mechanism in wheat (Triticum aestivum L.) greatly facilitates the process of hybrid wheat breeding. We conducted transcriptome sequencing for a recently identified Mu-CMS line with Aegilops uniaristata Vis. cytoplasm, named U706A, and its isonuclear maintainer line (706B) at the binucleate stage, which was a critical period when abortion occurred. We found that most of the genes involved in phosphatidylinositol metabolism and pectin degradation were downregulated, as well as genes encoding the MYB21 and MYC2 transcription factors, in U706A compared with 706B. In addition, pectin contents indicated that the production of pectin has been enhanced from the binucleate stage to the trinucleate stage, owing to the downregulation of pectin-degradation-related genes in U706A at the binucleate stage, which confirmed the reliability of the sequencing results. We also discovered that the accumulation period of pectin content in U706A is abnormal compared with 706B, which may be an important reason for abortion. Some differentially expressed genes that might be related to the sterile phenotype were verified by quantitative RT-PCR. Therefore, we suggest that the downregulation of these genes possibly leads to the anther not to crack; the tapetum and microspore membrane system is less metabolised, and the abnormal pectin accumulation results in microspore nutrient deficiencies and abnormal development. These findings provide novel insights into the mechanism responsible for pollen abortion in CMS, which may facilitate hybrid wheat breeding.