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The biological functions of the circadian clock on growth and development have been well elucidated in model plants, while its regulatory roles in crop species, especially the roles on yield-related traits, are poorly understood. In this study, we characterized the core clock gene CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) homoeologs in wheat and studied their biological functions in seedling growth and spike development. TaCCA1 homoeologs exhibit typical diurnal expression patterns, which are positively regulated by rhythmic histone modifications including histone H3 lysine 4 trimethylation (H3K4me3), histone H3 lysine 9 acetylation (H3K9Ac), and histone H3 lysine 36 trimethylation (H3K36me3). TaCCA1s are preferentially located in the nucleus and tend to form both homo- and heterodimers. TaCCA1 overexpression (TaCCA1-OE) transgenic wheat plants show disrupted circadian rhythmicity coupling with reduced chlorophyll and starch content, as well as biomass at seedling stage, also decreased spike length, grain number per spike, and grain size at the ripening stage. Further studies using DNA affinity purification followed by deep sequencing [DNA affinity purification and sequencing (DAP-seq)] indicated that TaCCA1 preferentially binds to sequences similarly to “evening elements” (EE) motif in the wheat genome, particularly genes associated with photosynthesis, carbon utilization, and auxin homeostasis, and decreased transcriptional levels of these target genes are observed in TaCCA1-OE transgenic wheat plants. Collectively, our study provides novel insights into a circadian-mediated mechanism of gene regulation to coordinate photosynthetic and metabolic activities in wheat, which is important for optimal plant growth and crop yield formation.

Additional file 1: Figure S1. (A) and (B): Distribution of two sub-gene families on wheat chromosome. Distribution of two gene families on wheat chromosome. All wheat chromosomes have HKMT gene distribution, which are relatively uniform. However, chromosome 2 and chromosome 3 also tend to cluster. Compared with the HKMT genes, the number of PRMT genes is relatively small, and the distribution of PRMT genes in the whole wheat genome is uneven. In addition, compared with previous research results, most HMT genes have been located in a clear range, and there is only one HKMT gene on the U chromosome, may also indicate that the genome quality of wheat has been greatly improved. Figure S2. Analysis of cis-elements of promoters of TaHMT genes. The 2kb sequence before the CDS of each HMT gene was extracted as the promoter region and submitted to PlantCARE database for cis-regulatory response elements prediction, and the results were visualized by TBtools. Figure S3. Expression analysis all selected TaHMT genes. (A) Expression analysis of 19 genes in spike. (B) Expression analysis of 12 genes in tiller. The relative expression of the female parent of each combination was relative 1, and the expression values for each parent are placed in front of each combination. The horizontal column is the gene name and the vertical column is the name of the samples. Figure S4. The phenotype as well as sampling times at different periods of wheat development. (A) Different periods of wheat spike development and sampling were conducted on this basis at anther separation stage. The length of the red ruler represents 1mm. (B) Tillers from root base to stem about 0.5 cm in length were sampled which contains the apical meristem at about four-leaf stage; P: male parent, M: maternal parent. (C) Phenotypic trait combinations for different tillers at harvest time, from left to right, they were: high parent (HP), middle parent (MP) and low parent (LP). In the picture, the three plants were photographed as a whole. Figure S5. The phylogenetic trees of HKMT (A) and PRMT (B) proteins from wheat, rice, Arabidopsis, Sorghum bicolor, Hordeum vulgare, and Brachypodium distachyon were constructed by MEGA-X using Maximum likelihood method. The HKMT proteins were divided into seven subfamilies and PRMT were divided into four subfamilies based on the previous methods. The members of wheat were marked with red circles in Fig. S5B. Figure S6. Interaction networks of miRNAs and HMT targets. miRNAs were marked as a blue node and HMT targets were marked as a yellow node. The size of the node represents the number of action sites. The black solid line represents that the mismatch expectation is 3.0, the red thick solid line represents that the mismatch expectation is 1.5, and the green thick solid line represents that the mismatch expectation is 2.5.

Background: Known as the prerequisite component for the heterosis breeding system, the male sterile line determined the hybrid yield and seed purity. Therefore, a deep understanding of the mechanism and gene network that leads to male sterility is crucial. BS366, a temperature-sensitive genic male sterile (TGMS) line, were male sterile under cold condition (12℃ with 12 h daylight) but fertile under normal temperature (20℃ with 12 h daylight). Results: During the meiosis, BS366 was defective in forming tetrad and dyad due to the abnormal cell plate. During the pollen development, unusual vacuolated pollen that cannot accumulate starch grains at the binucleate stage was also observed. Transcriptome analysis revealed that genes involved in the meiotic process like sister chromatid segregation and microtubule-based movement were repressed, while genes involved in DNA and histone methylation were induced in BS366 under cold condition. MethylRAD was used for a reduced DNA methylation sequencing for BS366 under both cold and control conditions. The differentially methylated sites (DMSs) located in the gene region were mainly involved in carbohydrate and fatty acid metabolism, lipid metabolism, and transport. Genes differentially and methylated were mainly involved in cell division. Conclusions: These results indicated that methylation of genes involved in carbon metabolism or fatty acid metabolism would contribute to the male sterility in BS366, which will provide a novel insight into the molecular mechanism of wheat male sterility.

Transcriptome analysis was carried out for wheat seedlings and spikes from hybrid Jingmai 8 and both inbred lines to unravel mechanisms underlying heterosis. Heterosis, known as one of the most successful strategies for increasing crop yield, has been widely exploited in plant breeding systems. Despite its great importance, the molecular mechanism underlying heterosis remains elusive. In the present study, RNA sequencing (RNA-seq) was performed on the seedling and spike tissues of the wheat (Triticum aestivum) hybrid Jingmai 8 (JM8) and its homozygous parents to unravel the underlying mechanisms of wheat heterosis. In total, 1686 and 2334 genes were identified as differentially expressed genes (DEGs) between the hybrid and the two inbred lines in seedling and spike tissues, respectively. Gene Ontology analysis revealed that DEGs from seedling tissues were significantly enriched in processes involved in photosynthesis and carbon fixation, and the majority of these DEGs expressed at a higher level in JM8 compared to both inbred lines. In addition, cell wall biogenesis and protein biosynthesis-related pathways were also significantly represented. These results confirmed that a combination of different pathways could contribute to heterosis. The DEGs between the hybrid and the two inbred progenitors from the spike tissues were significantly enriched in biological processes related to transcription, RNA biosynthesis and molecular function categories related to transcription factor activities. Furthermore, transcription factors such as NAC, ERF, and TIF-IIA were highly expressed in the hybrid JM8. These results may provide valuable insights into the molecular mechanisms underlying wheat heterosis.

Fast fracture evaluation strategy is receiving earnest concern in the structural integrity analysis of nuclear equipment which subjected to the effects of neutron irradiation during operation. The increment of ductile and brittle transition temperature is mainly due to the neutron irradiation which increases the risk of brittle fracture failure. In addition to the neutron irradiation, the high carbon macro-segregation of low-alloy steels also increases the risk of brittle fracture failure as the carbon positive macro-segregation will lead to the increasing ductile and brittle transition temperature of low-alloy steels. In the present study, a conservative relationship between the carbon content and the increment of ductile and brittle transition temperature is developed based on data and is used to the brittle fracture failure analysis of the highest carbon content region in SG channel head. A special defect size is assumed considering capability of non-destructive evaluation technology in the brittle fracture failure analysis. Results show that ratio between the calculated stress intensity factor according to safety coefficient suggested by ASME design code and the critical stress intensity factor is less than one, which indicates a safe design and no risk of brittle fracture failure for steam generator channel head considering high carbon macro-segregation.

Under stress conditions such as drought, high-salinity and low-temperature, the transcription factor of DREB (dehydration responsive element binding proteins) improved efficiently stress resistance by regulating the expression of its downstream genes with various environmental stress resistance in plants.GmDREB gene (GenBank Accession No. AF514908) encoding a stress-inducible transcription factor was cloned by screening a cDNA library ofGlycine max cv. Jinong 27 with yeast one-hybrid method.GmDREB gene was 910 bp in length and encoded 174 amino acids containing a conserved AP2/EREBP DNA-binding domain of 58 amino acids. Two conserved functional amino acids, valine and glutamic acid, were located on the 14th and the 19th amino acid residues in the conserved structural domain. An alkaline amino acid region (KKR) related to a nuclear localization signal was at the N-terminal, while an acidic amino acid region (DDD) related totrans-activation was at the C-terminal. Plant expression vectors were constructed and transformed into wheat by bombardment. In total, 13 transgenic plants withUbi::GmDREB and 11 transgenic plants withrd29A::GmDREB were identified from 103 regeneration plants by molecular analysis. The drought and salt tolerances of T1 transgenic lines withUbi::GmDREB orrd29A::GmDREB were demonstrated to be improved as compared to wild type. The result also suggested that bothUbiquitin andrd29A promoters could effectively drive the expression of theGmDREB gene and enhance drought and salt tolerance of T1 plants.