A R2R3-MYB, BpMYB1, from paper mulberry interacts with DELLA protein BpGAI1 in soil cadmium phytoremediation

Mechanisms of BpTT2 overexpression in enhancing cadmium tolerence of Broussonetia papyrifera

The development of cadmium-resistant plants has become a promising green biotechnology in the field of soil heavy metal remediation due to its advantages of low cost, wide adaptability and no secondary pollutants, it is the key to realize the application of this technology. In this study, we clarified the role of BpTT2 in Broussonetia papyrifera in response to Cd stress. Under the induction of 500 μmol/L CdCl2, the anti-Cd ability of BpTT2-overexpressed B. papyrifera was enhanced, and the accumulation of Cd was significantly reduced (P < 0.05). The plant height, biomass and total chlorophyll content of BpTT2-overexpressed B. papyrifera were significantly higher than those of non-transgenic lines (P < 0.001). Moreover, more substances related to ROS accumulation, such as MDA and H2O2, were detected in non-transgenic lines. Transcriptome sequencing showed that the AUX/IAA signal transduction gene (ARF5), ABA signal transduction genes (PP2C and SNRK2), protein kinase-related genes (PHOT1, WAKL4, PK1 and MPK3), ROS accumulation-related genes (RbohD and CAT1), and TFs family genes highly sensitive to Cd stress were significantly up-regulated in BpTT2-overexpressed B. papyrifera (P < 0.01). Notably, these genes regulate multiple signaling cascades simultaneously in the same protein family, which not only regulate plant signal transduction pathways, but also participate in the scavenging ROS and the feedback regulation of H2O2 signal. This study confirmed that the overexpression of BpTT2 can enhance the remediation effect of B. papyrifera on soil Cd pollution, which has important significance for better utilization of phytoremediation technology to treat heavy metal pollution.

Unraveling cadmium tolerance mechanisms in Betula platyphylla through a hierarchical gene regulatory network in hormone signaling

Cadmium (Cd), a toxic heavy metal, is a significant pollutant that impacts plant productivity. While some studies have been conducted, the underlying mechanisms by which plants respond to Cd stress remain largely unclear. Here, we performed RNA-seq analysis of Betula platyphylla (birch) under CdCl2 treatment. The findings revealed a substantial enrichment of differentially expressed genes (DEGs) in pathways associated with plant hormones. A gene regulatory network (GRN) was constructed, and the regulatory relationships between genes were determined using a partial correlation coefficient algorithm. The GRN comprises 2151 regulatory interactions, including 7 transcription factors (TFs) from the first layer, 25 TFs from the second layer, and 168 structural genes from the third layer, all of which are linked to ten enriched biological processes. ChIP-PCR and qRT-PCR assays validated approximately 85.2 % of the predicted interactions between the first and second layers, along with 88.3 % of the interactions between the second and third layers, supporting the validity of the GRN. Eighteen genes were selected from the third layer of multiple biological pathways to analyze their functions, and the results indicated that these genes can enhance Cd tolerance in birch plants. Additionally, two TFs in the first layer, BpHD-zip7 and BpRAV1, were successfully introduced into birch plants, confirming their role in improving Cd tolerance. Our findings elucidate the regulatory mechanisms and key determinants that function in the adaptation of B. platyphylla to Cd stress.

Transcriptomic Analysis of Broussonetia papyrifera Fruit Under Manganese Stress and Mining of Flavonoid Synthesis Genes

Broussonetia papyrifera is a deciduous tree with significant economic and medicinal value. It demonstrates notable physiological adaptability to mining areas with severe manganese contamination and is a pioneering species in the field of ecological restoration. Flavonoids are vital secondary metabolites that improve plant resilience to environmental stresses. In the study presented herein, immature and mature fruits of B. papyrifera grown in normal and high manganese environments were used as the test materials. B. papyrifera fruit was subjected to transcriptome sequencing via high-throughput sequencing technology to analyze its flavonoid metabolic pathways and related genes. Transcriptome sequencing identified a total of 46,072 unigenes, with an average length of 1248 bp and a percentage of Q30 bases ranging from 92.45 to 93.17%. Furthermore, 31,792 unigenes (69% of the total) were annotated using eight databases, including the GO and KEGG. Analysis of KEGG metabolic pathways and flavonoid content trends in B. papyrifera fruits revealed four unigenes with strong links to the flavonoid biosynthesis pathway under manganese stress: flavone 3-hydroxylase, flavonoids 3',5'-O-methyltransferase, chalcone synthase, and flavonol synthase. These unigenes may play important roles in regulating flavonoid synthesis in B. papyrifera fruits under manganese stress. This study lays the groundwork for functional gene research in B. papyrifera.

Heterologous Expression of a Potential 'Paulownia fortunei' MYB Factor Gene, PfMYB90, Improves Salt and Cold Tolerance in Arabidopsis

The paulownia tree belongs to the Paulowniaceae family. Paulownia has strong vitality; has strong adaptability to harsh environmental conditions; and can be used as building raw material, as well as processing drugs and having other purposes. In the research field of MYB transcription factors of the paulownia tree, it is rare to discuss the resistance to abiotic stress. The research in this area has not received sufficient attention and depth, which also indicates an important potential direction for future research. In this study, we performed bioinformatics analysis of the stress-related gene PfMYB90, a potential transcription factor, and investigated its mechanism of action under salt and cold stresses. PfMYB90 was strongly expressed in the fully unfolded leaf and root of plants in both stress treatments. Transgenic PfMYB90 Arabidopsis plants had a greater survival rate under salt and cold stresses, and the degree of leaf damage was comparatively smaller, according to phenotypic observation and survival rate calculations. By measuring the corresponding physiological indexes after stress and detecting the expression levels of corresponding stress genes (AtNHX1, AtSOS1, AtSOS2, AtSOS3, AtCBF1, AtCBF3, AtCOR15a, AtRD29a), it was found that after PfMYB90 gene transfer, Arabidopsis showed strong tolerance to salt and cold stresses. This is consistent with the results mentioned above. This transgenic technology enables Arabidopsis to survive under adverse environmental conditions, allowing it to maintain a relatively stable growth state despite salt accumulation and cold stress. Therefore, PfMYB90 may be a key gene in the regulatory network of salt damage and cold damage, as well as one of the key transcription factors for Paulownia fortunei environmental conditions.

Overexpression of tae-miR9670 enhances cadmium tolerance in wheat by targeting mTERFs without yield penalty

Cadmium (Cd) is a widely distributed heavy metal that poses significant hazards to both crop productivity and human health. MicroRNAs (miRNAs) play pivotal roles in plant growth, development and responses to environmental stresses, yet little is known about their roles in regulating Cd tolerance in wheat. In this study, we identified tae-miR9670, a Triticeae-specific miRNA, as responsive to Cd exposure in wheat through miRNAome analysis. Tae-miR9670 can target genes that encode mitochondrial transcription termination factors (mTERFs), mediating their mRNA cleavage and suppressing their expression. Overexpression of tae-miR9670 significantly enhanced Cd tolerance in wheat seedlings, as demonstrated by increased biomass and reduced levels of malondialdehyde (MDA), H2O2, and Cd content. Consequently, multiple downstream genes involved in ROS scavenging, detoxification and heavy metal transport were upregulated in tae-miR9670 overexpression plants. Moreover, the grain Cd content in mature plants overexpressing tae-miR9670 was reduced by over 60 % compared to wild-type controls. Our results also indicated that overexpressing tae-miR9670 in wheat preserved yield-related traits, thereby overcoming the trade-off between stress resistance and grain yield. Overall, our findings provide new insights into the role of tae-miR9670 in Cd tolerance in wheat and its potential application in breeding low-Cd cultivars.

The correlation between heavy metal chelation and transcriptional potential of GRAS genes in Broussonetia papyrifera

In order to understand the adaptation mechanism of Broussonetia papyrifera to heavy metal stress and then promote its remediation and utilization, in this study, a total of 24 GRAS transcription factors were identified from B. papyrifera transcriptomes. Their complete ORFs were 597-2250 bp in length with encoding proteins 22.40-84.13 kDa. The 24 BpGRASs were distributed across nine chromosomes and two scaffolds. Their promoters contained numerous cis-acting elements involving in plant development, environmental stimuli, and hormonal regulation. These BpGRAS genes were predominantly transcribed in flowers and fruits. The most prominent genes were BpSCL21b and BpDELLA1, whose expression levels in flowers were 4.11- and 4.56-fold higher than the minimal one in leaves. All BpGRASs were apparently induced by ABA and at least one treatment of Cd, Cu, Mn, and Zn. The expression of some BpGRAS genes (including BpSCL1d, BpSCL7, BpSCL27, BpSCL34, etc.) was significantly correlated with HM chelation and the non-protein thiols (NPT) accumulation, which was regarded as barriers to resist HM stress, under Cd, Cu, Mn, and Zn stress. Moreover, BpSCL15 and BpSCL21b transgenic yeast displayed significantly enhanced growth and viability (1.23--2.71-fold, 1.30--1.96-fold of control OD600, accordingly) and metal accumulation (1.81--3.58-fold, 1.91--3.17-fold of control, accordingly). These results suggested that BpGRASs, especial BpSCL15, BpSCL21b, and BpSCL34, are essential for B. papyrifera response to HM stress depending on ABA signaling. It's the first time to investigate the correlation of BpGRASs' expression with HM and NPT accumulation, which may benefit for revealing the HM adaptation mechanism of B. papyrifera and provide candidate genes for HM resistance breeding in woody plants.

Populus euphratica R2R3-MYB transcription factor RAX2 binds ANN1 promoter to increase cadmium enrichment in Arabidopsis

The expression of R2R3-MYB transcription factor PeRAX2 increased transiently upon CdCl2 exposure (100 μM, 48 h) in leaves and roots of Populus euphratica. We observed that overexpression of PeRAX2 increased Cd2+ concentration in Arabidopsis root cells and Cd2+ amount in whole plant, which was due to the increased Cd2+ influx into root tips. However, the Cd2+ influx facilitated by PeRAX2 overexpression was substantially reduced by LaCl3 (an inhibitor of Ca2+-channels), suggesting that PeRAX2 could promote the Cd2+ entering through PM Ca2+-permeable channels (CaPCs) in the roots. It is noting that the expression of annexin1 (AtANN1), which mediates the influx of divalent cations through the PM calcium channels, was upregulated by Cd2+ in PeRAX2-transgenic Arabidopsis. Bioinformatic analysis revealed that the AtANN1 promoter (AtANN1-pro) contains four cis-elements for MYB binding. The PeRAX2 interaction with AtANN1-pro was validated by LUC reporter assay, EMSA, and Y1H assay. Our data showed that PeRAX2 binds to the AtANN1 promoter region to regulate gene transcription and that AtANN1 mediates the Cd2+ entry through CaPCs in the PM, leading to a Cd2+ enrichment in transgenic plants. The PeRAX2-stimulated Cd2+ enrichment consequently resulted in high H2O2 production in root cells of transgenic plants. The expression of AtSOD and AtPOD and activities of CAT, SOD, POD increased in the transgenic lines under Cd2+ stress. However, the Cd2+-upregulated expression and activity of antioxidative enzymes were less pronounced in the PeRAX2-overexpressed lines, compared to the wildtype and vector controls. As a result, root length and plant growth were more suppressed by Cd2+ in the transgenic lines. Our data suggest that transcriptional regulation of AtANN1 by PeRAX2 can be utilized to improve Cd2+ enrichment and phytoremediation, although the enriched Cd2+ affected antioxidant defense system and plant growth in the model species.

The Uptake, Transfer, and Detoxification of Cadmium in Plants and Its Exogenous Effects

Cadmium (Cd) exerts a toxic influence on numerous crucial growth and development processes in plants, notably affecting seed germination rate, transpiration rate, chlorophyll content, and biomass. While considerable advances in Cd uptake and detoxification of plants have been made, the mechanisms by which plants adapt to and tolerate Cd toxicity remain elusive. This review focuses on the relationship between Cd and plants and the prospects for phytoremediation of Cd pollution. We highlight the following issues: (1) the present state of Cd pollution and its associated hazards, encompassing the sources and distribution of Cd and the risks posed to human health; (2) the mechanisms underlying the uptake and transport of Cd, including the physiological processes associated with the uptake, translocation, and detoxification of Cd, as well as the pertinent gene families implicated in these processes; (3) the detrimental effects of Cd on plants and the mechanisms of detoxification, such as the activation of resistance genes, root chelation, vacuolar compartmentalization, the activation of antioxidant systems and the generation of non-enzymatic antioxidants; (4) the practical application of phytoremediation and the impact of incorporating exogenous substances on the Cd tolerance of plants.