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Summary Several varieties of small RNAs including microRNAs (miRNAs) and small interfering RNAs (siRNAs) are generated in plants to regulate development, genome stability and response to adverse environments. Phased siRNA (phasiRNA) is a type of secondary siRNA that is processed from a miRNA‐mediated cleavage of RNA transcripts, increasing silencing efficiency or simultaneously suppressing multiple target genes. Trans‐acting siRNAs (ta‐siRNAs) are a particular class of phasiRNA produced from noncoding transcripts that silence targets in trans. It was originally thought that ‘one‐hit’ and ‘two‐hit’ models were essential for processing distinct TAS precursors; however, a single hit event was recently shown to be sufficient at triggering all types of ta‐siRNAs. This review discusses the findings about biogenesis, targeting modes and regulatory networks of plant ta‐siRNAs. We also summarize recent advances in the generation of other phasiRNAs and their possible biological benefits to plants.

Timing of reproductive transition is precisely modulated by environmental cues in flowering plants. Facultative long-day plants, including Arabidopsis and temperate grasses, trigger rapid flowering in long-day conditions (LDs) and delay flowering under short-day conditions (SDs). Here, we characterize a SD-induced FLOWERING LOCUS T ortholog, FT-like 9 (FTL9), that promotes flowering in SDs but inhibits flowering in LDs in Brachypodium distachyon . Mechanistically, like photoperiod-inductive FT1, FTL9 can interact with FD1 to form a flowering activation complex (FAC), but the floral initiation efficiency of FTL9-FAC is much lower than that of FT1-FAC, thereby resulting in a positive role for FTL9 in promoting floral transition when FT1 is not expressed, but a dominant-negative role when FT1 accumulates significantly. We also find that CONSTANS 1 (CO1) can suppress FTL9 in addition to stimulate FT1 to enhance accelerated flowering under LDs. Our findings on the antagonistic functions of FTL9 under different day-length environments will contribute to understanding the multifaceted roles of FT in fine-tune modulation of photoperiodic flowering in plants. Plant flowering time is modified by day length. Here the authors show that the model grass Brachypodium distachyon expresses different homologs of FT in short and long days to produce floral activator complexes with altered activities contributing to photoperiod-dependence of flowering time.

Background Mitogen-activated protein kinase kinase kinases (MAPKKKs) are the important components of MAPK cascades, which play the crucial role in plant growth and development as well as in response to diverse stresses. Although this family has been systematically studied in many plant species, little is known about MAPKKK genes in wheat ( Triticum aestivum L.), especially those involved in the regulatory network of stress processes. Results In this study, we identified 155 wheat MAPKKK genes through a genome-wide search method based on the latest available wheat genome information, of which 29 belonged to MEKK, 11 to ZIK and 115 to Raf subfamily, respectively. Then, chromosome localization, gene structure and conserved protein motifs and phylogenetic relationship as well as regulatory network of these TaMAPKKKs were systematically investigated and results supported the prediction. Furthermore, a total of 11 homologous groups between A, B and D sub-genome and 24 duplication pairs among them were detected, which contributed to the expansion of wheat MAPKKK gene family. Finally, the expression profiles of these MAPKKKs during development and under different abiotic stresses were investigated using the RNA-seq data. Additionally, 10 tissue-specific and 4 salt-responsive TaMAPKKK genes were selected to validate their expression level through qRT-PCR analysis. Conclusions This study for the first time reported the genome organization, evolutionary features and expression profiles of the wheat MAPKKK gene family, which laid the foundation for further functional analysis of wheat MAPKKK genes, and contributed to better understanding the roles and regulatory mechanism of MAPKKKs in wheat.

Long non-coding RNAs（lncRNAs） are gene regulators that have vital roles in development and adaptation to the environment in eukaryotes. However, the structural and evolutionary analyses of plant lncRNAs are limited. In this study, we performed an analysis of lncRNAs in five monocot and five dicot species. Our results showed that plant lncRNA genes were generally shorter and had fewer exons than protein-coding genes. The numbers of lncRNAs were positively correlated with the numbers of protein-coding genes in different plant species, despite a high range of variation. Sequence conservation analysis showed that the majority of lncRNAs had high sequence conservation at the intra-species and sub-species levels, reminiscent of protein-coding genes. At the inter-species level, a subset of lncRNAs were highly diverged at the nucleotide level, but conserved by position.Interestingly, we found that plant lncRNAs have identical splicing signals, and those which can form precursors or targets of miRNAs have a conservative identity in different species. We also revealed that most of the lowly expressed lncRNAs were tissue-specific, while those highly conserved were constitutively transcribed. Meanwhile, we characterized a subset of rice lncRNAs that were co-expressed with their adjacent protein-coding genes, suggesting they may play cis-regulatory roles. These results will contribute to understanding the biological significance and evolution of lncRNAs in plants.

MicroRNAs (miRNAs) play fundamental roles in many developmental and physiological processes in eukaryotes. MiRNAs in plants generally regulate their targets via either mRNA cleavage or translation repression; however, which approach plays a major role and whether these two function modes can shift remains elusive. Here, we identify a miRNA, miR408-5p that regulates AUXIN/INDOLE ACETIC ACID 30 ( IAA30 ), a critical repressor in the auxin pathway via switching action modes in rice. We find that miR408-5p usually inhibits IAA30 protein translation, but in a high auxin environment, it promotes the decay of IAA30 mRNA when it is overproduced. We further demonstrate that IDEAL PLANT ARCHITECTURE1 (IPA1), an SPL transcription factor regulated by miR156, mediates leaf inclination through association with miR408-5p precursor promoter. We finally show that the miR156-IPA1-miR408-5p-IAA30 module could be controlled by miR393, which silences auxin receptors. Together, our results define an alternative auxin transduction signaling pathway in rice that involves the switching of function modes by miR408-5p, which contributes to a better understanding of the action machinery as well as the cooperative network of miRNAs in plants. miR408-5p typically regulates target IAA30 via translation repression, but switches to cleaving IAA30 mRNA under high auxin conditions. miR393, miR156, miR408-5p and their targets could hierarchically act in auxin pathway and regulate leaf inclination.

Lesion mimic phenotypes, characterized by leaf spots formed in the absence of pathogens or pests, are often associated with reactive oxygen species (ROS) accumulation and cell necrosis. This study identified a novel and stable homozygous spotted phenotype (HSP) from the F8 population of common wheat (XN509 × N07216). The yellow spots that appeared at the booting stage were light-sensitive, and accompanied by cell necrosis and H2O2 accumulation. Compared with homozygous normal plants (HNPs), HSPs exhibited enhanced resistance to stripe rust and powdery mildew without compromising yield. RNA-Seq analysis at three stages revealed that differentially expressed genes (DEGs) between HSPs and HNPs were significantly enriched in KEGG pathways related to photosynthesis and photosynthesis-antenna proteins. GO analysis highlighted chloroplast and light stimulus-related down-regulated DEGs. Fine mapping identified TaSpl1 within a 0.91 Mb interval on chromosome 3DS, flanked by the markers KASP188 and KASP229, using two segregating populations comprising 1117 individuals. The candidate region contained 42 annotated genes, including 14 DEGs based on previous BSR-Seq data. PCR amplification and qRT-PCR verification identified the expression of TraesCS3D02G022100 was consistent with RNA-Seq data. Gene homology analysis and silencing experiments confirmed that TraesCS3D02G022100 was associated with stay-green traits. These findings provide new insights into the genetic regulation of lesion mimics, photosynthesis, and disease resistance in wheat.

Background Agricultural insects are one of the major threats to crop yield. It is a known fact that pesticide application is an extensive approach to eliminate insect pests, and has severe adverse effects on environment and ecosystem; however, there is lack of knowledge whether it could influence the physiology and metabolic processes in plants. Results Here, we systemically analyzed the transcriptomic changes in rice after a spray of two commercial pesticides, Abamectin (ABM) and Thiamethoxam (TXM). We found only a limited number of genes (0.91%) and (1.24%) were altered by ABM and TXM respectively, indicating that these pesticides cannot dramatically affect the performance of rice. Nevertheless, we characterized 1140 Differentially Expressed Genes (DEGs) interacting with 105 long non-coding RNAs (lncRNAs) that can be impacted by the two pesticides, suggesting their certain involvement in response to farm chemicals. Moreover, we detected 274 alternative splicing (AS) alterations accompanied by host genes expressions, elucidating a potential role of AS in control of gene transcription during insecticide spraying. Finally, we identified 488 transposons that were significantly changed with pesticides treatment, leading to a variation in adjacent coding or non-coding transcripts. Conclusion Altogether, our results provide valuable insights into pest management through appropriate timing and balanced mixture, these pesticides have no harmful effects on crop physiology over sustainable application of field drugs.

Background Long noncoding RNAs (lncRNAs) are emerging as the important regulators involving in growth and development as well as stress response in plants. However, current lncRNA studies were mainly performed at the individual level and the significance of it is not well understood in wheat. Results In this study, the lncRNA landscape of wheat spike was characterized through analysing a total of 186 spike RNA-seq datasets from 93 wheat genotypes. A total of 35,913 lncRNAs as well as 1,619 lncRNA-mRNA pairs comprised of 443 lncRNAs and 464 mRNAs were obtained. Compared to coding genes, these lncRNAs displayed rather low conservation among wheat and other gramineous species. Based on re-sequencing data, the genetic variations of these lncRNA were investigated and obvious genetic bottleneck were found on them during wheat domestication process. Furthermore, 122 lncRNAs were found to act as ceRNA to regulate endogenous competition. Finally, association and co-localization analysis of the candidate lncRNA-mRNA pairs identified 170 lncRNAs and 167 target mRNAs significantly associated with spike-related traits, including lncRNA.127690.1/TraesCS2A02G518500.1 ( PMEI ) and lncRNA.104854.1/TraesCS6A02G050300.1 ( ATG5 ) associated with heading date and spike length, respectively. Conclusions This study reported the lncRNA landscape of wheat spike through the population transcriptome analysis, which not only contribute to better understand the wheat evolution from the perspective of lncRNA, but also lay the foundation for revealing roles of lncRNA playing in spike development.

Salinity is a major limiting factor for agricultural production worldwide. A better understanding of the mechanisms of salinity stress response will aid efforts to improve plant salt tolerance. In this study, a combination of small RNA and mRNA degradome sequencing was used to identify salinity responsive-miRNAs and their targets in barley. A total of 152 miRNAs belonging to 126 families were identified, of which 44 were found to be salinity responsive with 30 up-regulated and 25 down-regulated respectively. The majority of the salinity-responsive miRNAs were up-regulated at the 8h time point, while down-regulated at the 3h and 27h time points. The targets of these miRNAs were further detected by degradome sequencing coupled with bioinformatics prediction. Finally, qRT-PCR was used to validate the identified miRNA and their targets. Our study systematically investigated the expression profile of miRNA and their targets in barley during salinity stress phase, which can contribute to understanding how miRNAs respond to salinity stress in barley and other cereal crops.

Fusarium head blight (FHB) has become a major challenge in global wheat production, causing severe yield losses and exacerbating food safety concerns. In recent years, FHB-related research has focused on understanding resistance mechanisms, identifying genetic markers, and breeding resistant varieties to mitigate the disease’s impact on yield and quality. This study comparatively analyzed transcriptome data from six wheat materials with differing levels of resistance following infection by Fusarium graminearum ( F. graminearum ). The results displayed that a total of 26,767 protein-coding genes and 2,463 long non-coding RNAs (lncRNAs) showed differential expression levels between normal and FHB treatment in at least one material. Among them, 14,130 FHB-responsive protein-coding genes and 913 lncRNAs were identified as material-specific, with functions related to the unique disease resistance mechanisms of the respective materials. Some of these genes have previously been reported to participate in physiological processes related to wheat FHB resistance, including Pm3-like resistance proteins, lactoylglutathione lyase, serine/threonine protein phosphatases, NBS-LRR resistance proteins, glutathione S-transferase (GST), and RPM1 resistance proteins. Additionally, we integrated FHB-responsive genes and lncRNAs with previously reported FHB QTLs, and constructed an interaction regulatory network between pathogen and host through a co-expression network. Based on this network, we identified five genes (one gene encoding glutathione synthetase and four genes encoding glutathione transferase) in the glutathione metabolism pathway, which overlapped with Fhb2 QTLs regions and exhibited material-specific expression patterns. These results will provide new insights into further dissecting of the functional genes and lncRNAs involved in wheat FHB resistance.