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Cinnamaldehyde (Cin) and citral (Cit) have been studied as antimicrobial agents and natural preservatives, but their action modes are controversial, and the knowledge of their antifungal mechanism against P. expansum is still incomplete. The present study was conducted to evaluate the antifungal mechanism of the combination of Cin and Cit (Cin/Cit) against P. expansum by observing the cellular ultrastructure, fourier transform infrared spectroscopy (FT-IR) fingerprints, plasma membrane, oxidative stress and volatile profile. Cin/Cit caused membrane invaginations, organelles and cytoplasm destruction, as shown by transmission electron microscopy (TEM) observations. The FT-IR spectra and followed principle component analysis (PCA) presented the significant differences in chemical compounds, particularly phospholipid, protein and fatty acids of cells exposed to Cin/Cit. Compared to controls, Cin/Cit induced a decrease of ergosterol by 39.40%, an increase of unsaturated fatty acid, and protein release level (3.5 times). Besides, membrane damage was further verified through the reduction of the membrane integrity by using a flow cytometer. Moreover, the increase of malondialdehyde (MDA) (40.09%) and reactive oxygen species (ROS) accumulation indicated an induction of oxidative stress in cells by Cin/Cit. To resist the unfavorable stress caused by Cin/Cit, P. expansum metabolized Cin or Cit to the predominant detoxification compounds, cinnamic alcohol, nerol, and geraniol. The alterations in volatile profile demonstrated the influences on specific metabolisms in P. expansum caused by Cin/Cit.

BACKGROUND Fungal development in agricultural products may cause mycotoxin contamination that are a significant threat to food safety. Patulin (PAT) and PAT-producers contamination has been established as a worldwide problem. The present study was conducted to investigate the mycoflora and PAT-producers present in kiwifruits and environmental samples collected from orchards and processing plants in Shaanxi Province, China. RESULTS Variations in mycoflora were observed in different samples, with penicillia and aspergilli as the predominant genera. Approximately 42.86% of dropped fruits were contaminated with PAT-producers, which harbored the 6-methylsalicylic acid synthase and the isoepoxydon dehydrogenase genes that are involved in PAT biosynthesis. The growth of P. expansum, P. griseofulvum and P. paneum in kiwi puree agar (KPA) medium and kiwi juice (KJ) well fitted the modified Gompertz and Baranyi and Roberts models (R2 ≥ 0.95). A significant positive correlation between colony diameter and PAT content in KPA medium of P. expansum and P. griseofulvum was observed (p < 0.05). CONCLUSIONS This research analyzed the mycofloral composition and the potential risk for PAT and PAT-producer contamination in kiwifruit, which may be utilized in the establishment of proper management practices in the kiwifruit industry.

MicroRNAs (miRNA) are a class of small, endogenous RNAs that play a negative regulatory role in various developmental and metabolic processes of plants. Wild barley (Hordeum vulgare subsp. spontaneum), as the progenitor of cultivated barley (Hordeum vulgare subsp. vulgare), has served as a valuable germplasm resource for barley genetic improvement. To survey miRNAs in wild barley, we sequenced the small RNA library prepared from wild barley using the Illumina deep sequencing technology. A total of 70 known miRNAs and 18 putative novel miRNAs were identified. Sequence analysis revealed that all of the miRNAs identified in wild barley contained the highly conserved hairpin sequences found in barley cultivars. MiRNA target predictions showed that 12 out of 52 miRNA families were predicted to target transcription factors, including 8 highly conserved miRNA families in plants and 4 wheat–barley conserved miRNA families. In addition to transcription factors, other predicted target genes were involved in diverse physiological and metabolic processes and stress defense. Our study for the first time reported the large-scale investigation of small RNAs in wild barley, which will provide essential information for understanding the regulatory role of miRNAs in wild barley and also shed light on future practical utilization of miRNAs for barley improvement.

Drought stress is one of the most adverse environmental limiting factors for wheat (Triticum aestivum L.) productivity worldwide. For better understanding of the molecular mechanism of wheat in response to drought, a comparative transcriptome approach was applied to investigate the gene expression change of two wheat cultivars, Jimai No. 47 (drought-tolerant) and Yanzhan No. 4110 (drought-sensitive) in the field under irrigated and drought-stressed conditions. A total of 3754 and 2325 differential expressed genes (DEGs) were found in Jimai No. 47 and Yanzhan No. 4110, respectively, of which 377 genes were overlapped, which could be considered to be the potential drought-responsive genes. GO (Gene Ontology) analysis showed that these DEGs of tolerant genotype were significantly enriched in signaling transduction and MAP (mitogen-activated protein) kinase activity, while that of sensitive genotype was involved in photosynthesis, membrane protein complex, and guard cell differentiation. Furthermore, 32 and 2 RNA editing sites were identified in drought-tolerant and sensitive genotypes under drought compared to irrigation, demonstrating that RNA editing also plays an important role in response to drought in wheat. This study investigated the gene expression pattern and RNA editing sites of two wheat cultivars with contrasting tolerance in field condition, which will contribute to a better understanding of the molecular mechanism of drought tolerance in wheat and beyond.

Summary Wheat is one of the most important staple crops worldwide and also an excellent model species for crop evolution and polyploidization studies. The breakthrough of sequencing the bread wheat genome and progenitor genomes lays the foundation to decipher the complexity of wheat origin and evolutionary process as well as the genetic consequences of polyploidization. In this study, we sequenced 3286 BACs from chromosome 7DL of bread wheat cv. Chinese Spring and integrated the unmapped contigs from IWGSC v1 and available PacBio sequences to close gaps present in the 7DL assembly. In total, 8043 out of 12 825 gaps, representing 3 491 264 bp, were closed. We then used the improved assembly of 7DL to perform comparative genomic analysis of bread wheat (Ta7DL) and its D donor, Aegilops tauschii (At7DL), to identify domestication signatures. Results showed a strong syntenic relationship between Ta7DL and At7DL, although some small rearrangements were detected at the distal regions. A total of 53 genes appear to be lost genes during wheat polyploidization, with 23% (12 genes) as RGA (disease resistance gene analogue). Furthermore, 86 positively selected genes (PSGs) were identified, considered to be domestication‐related candidates. Finally, overlapping of QTLs obtained from GWAS analysis and PSGs indicated that TraesCS7D02G321000 may be one of the domestication genes involved in grain morphology. This study provides comparative information on the sequence, structure and organization between bread wheat and Ae. tauschii from the perspective of the 7DL chromosome, which contribute to better understanding of the evolution of wheat, and supports wheat crop improvement.

Penicillium expansum, as a main postharvest pathogen of fruits, can secrete patulin (PAT), causing fruit decay and health problems. In this study, the antifungal test, SEM (scanning electron microscope) observation, transcriptional profile, PAT biosynthesis, and physiological characters of P. expansum exposed to cinnamaldehyde and citral combination (Cin/Cit) were evaluated. Cin/Cit could inhibit the mycelial growth and spore germination of P. expansum in a dose-dependent manner. Besides, Cin/Cit caused spores and mycelia wrinkled and depressed by SEM observation. Gene expression profiles of P. expansum were conducted by RNA sequencing (RNA-seq) in the presence or absence of Cin/Cit treatment. A total of 1713 differentially expressed genes (DEGs) were obtained, including 793 down-regulated and 920 up-regulated genes. Most of the DEGs participated in the biosynthesis of secondary metabolites, amino acid metabolism, and oxidation-reduction process, etc. Cin/Cit induced the dysfunction of the mitochondrial membrane, causing the potential influence on energy metabolism and reactive oxidative species production. The changes of superoxide dismutase (SOD) and catalase (CAT) activities combing with the increase of hydrogen peroxide content indicated the oxidative stress on P. expansum induced by Cin/Cit, which corresponded well with the transcriptional results. Moreover, both the RNA-seq data and the qRT-PCR showed the remarkable down-regulation of genes included in the PAT biosynthetic pathway under the Cin/Cit treatment. These findings provided more useful information about the antifungal mechanism of Cin/Cit against P. expansum at molecular and gene levels and suggested that Cin/Cit is a potential candidate to control P. expansum.

Comparative chloroplast genome analysis presents new opportunities for performing molecular phylogeny studies and revealing the significant evolutionary features in higher plants, which has been widely documented from conifers to grass family. However, a systematic analysis of chloroplast genomes in Asteraceae family has not been conducted up to now. In this study, we compared and analyzed the gene content, genomic organization, and RNA editing sites of eight representative Asteraceae chloroplast genomes. Results showed that Asteraceae chloroplast had relatively conservative gene content. No gain or loss events occurred in the protein-coding genes, while some differences were found to be present in the gene structure and transfer RNA (tRNA) abundance. Genome structure analysis found some Asteraceae-specific or species-specific structure variations, and sequence rearrangement events were present in these genomes, suggesting specific evolutionary processes have occurred in this family. Some DNA regions containing parsimony-informative characters higher than 5 % were also identified, which could be used as the new molecular markers for phylogenetic analysis and plant identification of Asteraceae species. Furthermore, RNA editing in these genomes was investigated through computational analysis, and some species-specific sites were identified. Finally, phylogenetic analysis of 81 genes from 70 species supported the monophyly of the Asteraceae. Our study for the first time compared the organization, structure, and sequence divergence of eight Asteraceae chloroplast genomes, which will provide the valuable resource for molecular phylogeny of Asteraceae species and also facilitate the genetic and evolutionary studies in this family.

Codon usage bias (CUB) is an important evolutionary feature in a genome and has been widely documented from prokaryotes to eukaryotes. However, the significance of CUB in the Asteraceae family has not been well understood, with no Asteraceae species having been analyzed for this characteristic. Here, we use bioinformatics approaches to comparatively analyze the general patterns and influencing factors of CUB in five Asteraceae chloroplast (cp) genomes. The results indicated that the five genomes had similar codon usage patterns, showing a strong bias towards a high representation of NNA and NNT codons. Neutrality analysis showed that these cp genomes had a narrow GC distribution and no significant correlation was observed between GC12 and GC3. Parity Rule 2 (PR2) plot analysis revealed that purines were used more frequently than pyrimidines. Effective number of codons (ENc)-plot analysis showed that most genes followed the parabolic line of trajectory, but several genes with low ENc values lying below the expected curve were also observed. Furthermore, correspondence analysis of relative synonymous codon usage (RSCU) yielded a first axis that explained only a partial amount of variation of codon usage. These findings suggested that both natural selection and mutational bias contributed to codon bias, while selection was the major force to shape the codon usage in these Asteraceae cp genomes. Our study, which is the first to investigate codon usage patterns in Asteraceae plastomes, will provide helpful information about codon distribution and variation in these species, and also shed light on the genetic and evolutionary mechanisms of codon biology within this family.

Microsatellites are an important constituent of plant genome and distributed across entire genome. In this study, genome-wide analysis of microsatellites in 8 Triticeae species and 9 model plants revealed that microsatellite characteristics were similar among the Triticeae species. Furthermore, genome-wide microsatellite markers were designed in wheat and then used to analyze the evolutionary relationship of wheat and other Triticeae species. Results displayed that Aegilops tauschii was found to be the closest species to Triticum aestivum, followed by Triticum urartu, Triticum turgidum and Aegilops speltoides, while Triticum monococcum, Aegilops sharonensis and Hordeum vulgare showed a relatively lower PCR amplification effectivity. Additionally, a significantly higher PCR amplification effectivity was found in chromosomes at the same subgenome than its homoeologous when these markers were subjected to search against different chromosomes in wheat. After a rigorous screening process, a total of 20,666 markers showed high amplification and polymorphic potential in wheat and its relatives, which were integrated with the public available wheat markers and then anchored to the genome of wheat (CS). This study not only provided the useful resource for SSR markers development in Triticeae species, but also shed light on the evolution of polyploid wheat from the perspective of microsatellites.

MicroRNAs (miRNAs) are a class of endogenous small noncoding RNAs which regulate diverse molecular and biochemical processes at a post-transcriptional level in plants. As the ancestor of domesticated wheat, wild emmer wheat (Triticum turgidum ssp. dicoccoides) has great genetic potential for wheat improvement. However, little is known about miRNAs and their functions on salinity stress in wild emmer. To obtain more information on miRNAs in wild emmer, we systematically investigated and characterized the salinity-responsive miRNAs using deep sequencing technology. A total of 88 conserved and 124 novel miRNAs were identified, of which 50 were proven to be salinity-responsive miRNAs, with 32 significantly up-regulated and 18 down-regulated. miR172b and miR1120a, as well as mi393a, were the most significantly differently expressed. Targets of these miRNAs were computationally predicted, then Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis found that the targets of salinity-responsive miRNAs were enriched in transcription factors and stress-related proteins. Finally, we investigated the expression profiles of seven miRNAs ranging between salt-tolerant and sensitive genotypes, and found that they played critical roles in salinity tolerance in wild emmer. Our results systematically identified the salinity-responsive miRNAs in wild emmer, not only enriching the miRNA resource but also laying the foundation for further study on the biological functions and evolution of miRNAs in wild wheat and beyond.

Bacterial artificial chromosome (BAC) libraries are extremely valuable large-insert DNA libraries for physical mapping, positional cloning, comparative genomic analysis, complete genome sequencing, and evolutionary studies. Due to their stability and relative simplicity BAC libraries are most preferred over other approaches for cloning large genomic DNA fragments for large-insert libraries. Isolation of intact high molecular weight (HMW) DNA is a critical step underlying the success of large-insert genomic DNA library construction. It requires the isolation of purified nuclei, embedding them into LMP agarose plugs, restriction digestion of the plugs, and quite often size selection using PFGE and electro-elution of insert DNA. The construction of BAC libraries is complex and challenging for most molecular laboratories. To facilitate the construction of BAC libraries, we present a step-by-step protocol for isolation of HMW DNA and construction of plant BAC libraries.

Background The AP2/ERF transcription factor is one of the most important gene families in plants, which plays the vital role in regulating plant growth and development as well as in response to diverse stresses. Although AP2/ERFs have been thoroughly characterized in many plant species, little is known about this family in the model plant Brachypodium distachyon, especially those involved in the regulatory network of stress processes. Results In this study, a comprehensive genome-wide search was performed to identify AP2/ERF gene family in Brachypodium and a total of 141 BdAP2/ERFs were obtained. Phylogenetic analysis classified them into four subfamilies, of which 112 belonged to ERF, four to RAV and 24 to AP2 as well as one to soloist subfamily respectively, which was in accordance with the number of AP2 domains and gene structure analysis. Chromosomal localization, gene structure, conserved protein motif and cis-regulatory elements as well as gene duplication events analysis were further performed to systematically investigate the evolutionary features of these BdAP2/ERF genes. Furthermore, the regulatory network between BdAP2/ERF and other genes were constructed using the orthology-based method, and 39 BdAP2/ERFs were found to be involved in the regulatory network and 517 network branches were identified. The expression profiles of BdAP2/ERF during development and under diverse stresses were investigated using the available RNA-seq and microarray data and ten tissue-specific and several stress-responsive BdAP2/ERF genes were identified. Finally, 11 AP2/ERF genes were selected to validate their expressions in different tissues and under different stress treatments using RT-PCR method and results verified that these AP2/ERFs were involved in various developmental and physiological processes. Conclusions This study for the first time reported the characteristics of the BdAP2/ERF family, which will provide the invaluable information for further evolutionary and functional studies of AP2/ERF in Brachypodium, and also contribute to better understanding the molecular basis for development and stresses tolerance in this model species and beyond. Electronic supplementary material The online version of this article (doi:10.1186/s12864-016-2968-8) contains supplementary material, which is available to authorized users.