In nature, heavy metal (HM) stress is one of the most destructive abiotic stresses for plants. Heavy metals produce toxicity by targeting key molecules and important processes in plant cells. The mitogen-activated protein kinase (MAPK) cascade transfers the signals perceived by cell membrane surface receptors to cells through phosphorylation and dephosphorylation and targets various effector proteins or transcriptional factors so as to result in the stress response. Signal molecules such as plant hormones, reactive oxygen species (ROS), and nitric oxide (NO) can activate the MAPK cascade through differentially expressed genes, the activation of the antioxidant system and synergistic crosstalk between different signal molecules in order to regulate plant responses to HMs. Transcriptional factors, located downstream of MAPK, are key factors in regulating plant responses to heavy metals and improving plant heavy metal tolerance and accumulation. Thus, understanding how HMs activate the expression of the genes related to the MAPK cascade pathway and then phosphorylate those transcriptional factors may allow us to develop a regulation network to increase our knowledge of HMs tolerance and accumulation. This review highlighted MAPK pathway activation and responses under HMs and mainly focused on the specificity of MAPK activation mediated by ROS, NO and plant hormones. Here, we also described the signaling pathways and their interactions under heavy metal stresses. Moreover, the process of MAPK phosphorylation and the response of downstream transcriptional factors exhibited the importance of regulating targets. It was conducive to analyzing the molecular mechanisms underlying heavy metal accumulation and tolerance.

Sedum plumbizincicola, a cadmium (Cd) hyperaccumulating herbaceous plant, can accumulate large amounts of Cd in the above-ground tissues without being poisoned. However, the molecular mechanisms regulating the processes are not fully understood. In this study, Transcriptional and proteomic analyses were integrated to investigate the response of S. plumbizincicola plants to Cd stress and to identify key pathways that are potentially responsible for Cd tolerance and accumulation. A total of 630 DAPs (differentially abundant proteins, using fold change >1.5 and adjusted p-value <0.05) were identified from Tandem Mass Tag (TMT)- based quantitative proteomic profiling, which were enriched in processes including phenylpropanoid biosynthesis, protein processing in endoplasmic reticulum, and biosynthesis of secondary metabolites. Combined with the previous transcriptomic study, 209 genes and their corresponding proteins showed the identical expression pattern. The identified genes/proteins revealed the potential roles of several metabolism pathways, including phenylpropanoid biosynthesis, oxidative phosphorylation, phagosome, and glutathione metabolism, in mediating Cd tolerance and accumulation. Lignin staining and Cd accumulation assay of the transgenic lines over-expressing a selected Cd up-regulated gene SpFAOMT (Flavonoid 3',5'-methyltransferase) showed its functions in adapting to Cd stress, and provided insight into its role in lignin biosynthesis and Cd accumulation in S. plumbizincicola during Cd stress.

Evolutionarily, polyploidy represents a smart method for adjusting agronomically important in crops through impacts on genomic abundance and chromatin condensation. Autopolyploids have a relatively concise genetic background with great diversity and provide an ideal system to understand genetic and epigenetic mechanisms attributed to the genome-dosage effect. However, whether and how genome duplication events during autopolyploidization impact chromatin signatures are less understood in crops. To address it, we generated an autotetraploid rice line from a diploid progenitor, Oryza sativa ssp. indica 93-11. Using transposase-accessible chromatin sequencing, we found that autopolyploids lead to a higher number of accessible chromatin regions (ACRs) in euchromatin, most of which encode protein-coding genes. As expected, the profiling of ACR densities supported that the effect of ACRs on transcriptional gene activities relies on their positions in the rice genome, regardless of genome doubling. However, we noticed that genome duplication favors genic ACRs as the main drivers of transcriptional changes. In addition, we probed intricate crosstalk among various kinds of epigenetic marks and expression patterns of ACR-associated gene expression in both diploid and autotetraploid rice plants by integrating multiple-omics analyses, including chromatin immunoprecipitation sequencing and RNA-seq. Our data suggested that the combination of H3K36me2 and H3K36me3 may be associated with dynamic perturbation of ACRs introduced by autopolyploidization. As a consequence, we found that numerous metabolites were stimulated by genome doubling. Collectively, our findings suggest that autotetraploids reshape rice morphology and products by modulating chromatin signatures and transcriptional profiling, resulting in a pragmatic means of crop genetic improvement.

Salicylic acid (SA) is an important plant hormone involved in the activation of defense responses against environmental stresses. However, there are still large of unsolved mysteries about how SA pretreatment affects the establishment of plant...

The F-box genes, which form one of the largest gene families in plants, are vital for plant growth, development and stress response. However, F-box gene family in Sedum alfredii remains unknown. Comprehensive studies addressing their function responding to cadmium stress is still limited. In the present study, 193 members of the F-box gene (SaFbox) family were identified, which were classified into nine subfamilies. Most of the SaFboxs had highly conserved domain and motif. Various functionally related cis-elements involved in plant growth regulation, stress and hormone responses were located in the upstream regions of SaFbox genes. RNA-sequencing and co-expression network analysis revealed that the identified SaFbox genes would be involved in Cd stress. Expression analysis of 16 hub genes confirmed their transcription level in different tissues. Four hub genes (SaFbox40, SaFbox51, SaFbox136 and SaFbox170) were heterologously expressed in a Cd-sensitive yeast cell to assess their effects on Cd tolerance. The transgenic yeast cells carrying SaFbox40, SaFbox51, SaFbox136, or SaFbox170 were more sensitive and accumulated more cadmium under Cd stress than empty vector transformed control cells. Our results performed a comprehensive analysis of Fboxs in S. alfredii and identified their potential roles in Cd stress response.