Salt stress is one of the most serious limiting factors in worldwide agricultural production, resulting in huge annual yield loss. Since 1995, melatonin (N-acetyl-5-methoxytryptamine)—an ancient multi-functional molecule in eukaryotes and prokaryotes—has been extensively validated as a regulator of plant growth and development, as well as various stress responses, especially its crucial role in plant salt tolerance. Salt stress and exogenous melatonin lead to an increase in endogenous melatonin levels, partly via the phyto-melatonin receptor CAND2/PMTR1. Melatonin plays important roles, as a free radical scavenger and antioxidant, in the improvement of antioxidant systems under salt stress. These functions improve photosynthesis, ion homeostasis, and activate a series of downstream signals, such as hormones, nitric oxide (NO) and polyamine metabolism. Melatonin also regulates gene expression responses to salt stress. In this study, we review recent literature and summarize the regulatory roles and signaling networks involving melatonin in response to salt stress in plants. We also discuss genes and gene families involved in the melatonin-mediated salt stress tolerance.

The homeodomain-leucine zipper (HD-Zip) gene family, as plant-specific transcription factors, plays an important role in plant development and growth as well as in the response to diverse stresses. Although HD-Zip genes have been extensively studied in many plants, they had not yet been studied in wheat, especially those involved in response to abiotic stresses. In this study, 46 wheat HD-Zip genes were identified using a genome-wide search method. Phylogenetic analysis classified these genes into four groups, numbered 4, 5, 17 and 20 respectively. In total, only three genes with A, B and D homoeologous copies were identified. Furthermore, the gene interaction networks found that the TaHDZ genes played a critical role in the regulatory pathway of organ development and osmotic stress. Finally, the expression profiles of the wheat HD-Zips in different tissues and under various abiotic stresses were investigated using the available RNA sequencing (RNA-Seq) data and then validated by quantitative real-time polymerase chain reaction (qRT-PCR) to obtain the tissue-specific and stress-responsive candidates. This study systematically identifies the HD-Zip gene family in wheat at the genome-wide level, providing important candidates for further functional analysis and contributing to the better understanding of the molecular basis of development and stress tolerance in wheat.

The mitogen-activated protein kinase (MAPK) cascade is a universal signal transduction module that plays a vital role in regulating growth and development, as well as environmental stress responses in plants. Wheat is one of the most important crops worldwide. Although the MAPK kinase kinase (MAP3K) family in wheat has been investigated, the MAPK and MAPK kinase (MAP2K) gene families remain unknown at present. Here, 54 MAPK and 18 MAPKK genes were identified in wheat using recent genomic information. Phylogenetic analysis of Triticum aestivum L. MAPKs and MAPKKs (TaMAPKs and TaMAPKKs) together with homologous genes from other species classified them into four groups, and the clustering was consistent with the genomic exon/intron structures. Conserved motif analysis found that MAPK proteins contained a typical TXY phosphorylation site and MAPKK proteins contained an S/T-X5-S/T motif. RNA-seq data mapping analysis showed that MAPK and MAPKK genes in group IV had tissue-specific expression profiles, whereas each group I member showed relatively high expression in all organs. Expression patterns of TaMAPK and TaMAPKK genes under stress conditions were also investigated and stress-responsive candidates were identified. Co-expression network analysis identified 11 TaMAPK genes and 6 TaMAPKK genes involved in the interaction network pathway. Overall, this study provided useful information for evolutionary and functional surveys of MAPK and MAPKK gene families in wheat and beyond.

Grain development, as a vital process in the crop’s life cycle, is crucial for determining crop quality and yield. However, the molecular basis and regulatory network of barley grain development is not well understood at present. Here, we investigated the transcriptional dynamics of barley grain development through RNA sequencing at four developmental phases, including early prestorage phase (3 days post anthesis (DPA)), late prestorage or transition phase (8 DPA), early storage phase (13 DPA), and levels off stages (18 DPA). Transcriptome profiling found that pronounced shifts occurred in the abundance of transcripts involved in both primary and secondary metabolism during grain development. The transcripts’ activity was decreased during maturation while the largest divergence was observed between the transitions from prestorage phase to storage phase, which coincided with the physiological changes. Furthermore, the transcription factors, hormone signal transduction-related as well as sugar-metabolism-related genes, were found to play a crucial role in barley grain development. Finally, 4771 RNA editing events were identified in these four development stages, and most of the RNA editing genes were preferentially expressed at the prestore stage rather than in the store stage, which was significantly enriched in “essential” genes and plant hormone signal transduction pathway. These results suggested that RNA editing might act as a ‘regulator’ to control grain development. This study systematically dissected the gene expression atlas of barley grain development through transcriptome analysis, which not only provided the potential targets for further functional studies, but also provided insights into the dynamics of gene regulation underlying grain development in barley and beyond.

Abstract:Heat shock transcription factor (Hsf) is one of the conserved gene families in plants, playing a crucial role in growth and development, as well as in response to diverse stresses. Although it has been systematically studied in many species, little is known about the Hsf gene family in Chenopodium quinoa, especially those involved in the regulatory network of stress processes. In this study, we identified 23 Hsf genes in quinoa (CqHsfs) through a genome-wide search method based on the latest available genome information. Phylogenetic analysis classified them into three groups, and group A was further divided into nine subgroups, which was supported by conserved domain organizations. Gene structure and multiple sequence alignment analysis revealed that all of the CqHsfs possessed a similar structure organization and were highly conserved in BDB domain. Interaction network analysis identified 13 CqHsfs involved in the network pathway to regulate diverse biological processes. Expression profiles of these CqHsfs were further investigated using the RNA-seq data, and tissue-specific and stress-responsive candidates were identified. Finally, four heat-responsive CqHsfs were selected to validate their expression level through semi-quantitative RT-PCR analysis. This study reported the organization, structure, and expression profiles of the Hsf gene family in quinoa, which will contributes to further functional analysis, and helps to better understand the roles and regulatory mechanism of heat shock factors playing in quinoa 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.

Tibetan, one of the largest indigenous populations living in the high-altitude region of the Tibetan Plateau (TP), has developed a suite of physiological adaptation strategies to cope with the extreme highland environment in TP. Here, we reported genome-wide SNP data from 48 Kham-speaking Nagqu Tibetans and analyzed it with published data from 1,067 individuals in 167 modern and ancient populations to characterize the detailed Tibetan subgroup history and population substructure. Overall, the patterns of allele sharing and haplotype sharing suggested (1) the relatively genetic homogeny between the studied Nagqu Tibetans and ancient Nepalese as well as present-day core Tibetans from Lhasa, Nagqu, and Shigatse; and (2) the close relationship between our studied Kham-speaking Nagqu Tibetans and Kham-speaking Chamdo Tibetans. The fitted qpAdm models showed that the studied Nagqu Tibetans could be fitted as having the main ancestry from late Neolithic upper Yellow River millet farmers and deeply diverged lineages from Southern East Asians (represented by Upper Paleolithic Guangxi_Longlin and Laos_Hoabinhian), and a non-neglectable western Steppe herder-related ancestry (∼3%). We further scanned the candidate genomic regions of natural selection for our newly generated Nagqu Tibetans and the published core Tibetans via FST, iHS, and XP-EHH tests. The genes overlapping with these regions were associated with essential human biological functions such as immune response, enzyme activity, signal transduction, skin development, and energy metabolism. Together, our results shed light on the admixture and evolutionary history of Nagqu Tibetan populations.