Will different land uses affect heavy metal pollution in soils of roadside trees? An empirical study from Shanghai.

Heavy metal pollution in roadside soil may harm humans, animals, plants, and local ecosystems. This study aimed to explore the sources and potential ecological risks of heavy metals in soils of roadside trees under different land uses, using soil samples collected from 136 roads across 16 administrative districts in Shanghai. The contents, pollution characteristics, potential ecological risks, and sources of seven heavy metals were analyzed, including Cr, Ni, Cd, Pb, As, Cu, and Zn. Results showed that (1) land use patterns affected the heavy metal contents, with industrial and construction areas showing higher contents while agricultural and forestry areas lower; (2) the ranking of heavy metal pollution levels was Cd > As > Pb > Cu > Ni > Cr > Zn. Cd exhibited the highest potential ecological risk, falling within the moderate to considerable potential ecological risk interval; (3) the sources of Cu, Zn, Cr, Ni, Cd, and Pb were associated with traffic emissions, whereas As had independent other sources and Pb in industrial and construction areas was also influenced by industrial emissions. These results provide valuable references on the control of heavy metal pollutants and the management of land uses in megacities.

Identification and genetic diversity analysis of hybrid offspring of azalea based on EST-SSR markers.

Azalea is a world famous flower with high economic and ornamental value. The breeding of new azalea varieties is mainly done by cross breeding. However, there is a risk that cross breeding may cause errors in the hybrid offspring due to contamination by exogenous pollen. Therefore, the identification of hybrid offspring is an important part of azalea breeding. In this study, the parents of three hybrid combinations and their 88 F1 hybrid offspring were selected to screen 15 pairs of EST-SSR primers to identify the authenticity of azalea hybrid offspring. The results showed that the authenticity of 88 azalea F1 hybrid progenies could be determined by at least four primer pairs. Genetic diversity analysis of azalea hybrid progeny revealed that the number of alleles and polymorphic information content of the progeny increased to different degrees, and the more distant the genetic distance between parents, the richer the polymorphic information. It is suggested that EST-SSR molecular marker can be applied for the early identification and genetic diversity analysis of the progeny of azalea hybrids. This method is of positive significance for improving the breeding efficiency of new varieties and exploring the genetic background of azalea.

Insights into heat response mechanisms in Clematis species: physiological analysis, expression profiles and function verification.

KEY MESSAGE: Our results provide insights into heat response mechanisms among Clematis species. Overexpressing CvHSFA2 enhanced the heat resistance of yeast and silencing NbHSFA2 reduced the heat resistance of tobacco. Clematis species are commonly grown in western and Japanese gardens. Heat stress can inhibit many physiological processes mediating plant growth and development. The mechanism regulating responses to heat has been well characterized in Arabidopsis thaliana and some crops, but not in horticultural plants, including Clematis species. In this study, we found that Clematis alpina 'Stolwijk Gold' was heat-sensitive whereas Clematis vitalba and Clematis viticella 'Polish Spirit' were heat-tolerant based on the physiological analyses in heat stress. Transcriptomic profiling identified a set of heat tolerance-related genes (HTGs). Consistent with the observed phenotype in heat stress, 41.43% of the differentially expressed HTGs between heat treatment and control were down-regulated in heat-sensitive cultivar Stolwijk Gold, but only 9.80% and 20.79% of the differentially expressed HTGs in heat resistant C. vitalba and Polish Spirit, respectively. Co-expression network, protein-protein interaction network and phylogenetic analysis revealed that the genes encoding heat shock transcription factors (HSFs) and heat shock proteins (HSPs) may played an essential role in Clematis resistance to heat stress. Two clades of heat-induced CvHSFs were further identified by phylogenetic tree, motif analysis and qRT-PCR. Ultimately, we proposed that overexpressing CvHSFA2-2 could endow yeast with high temperature resistance and silencing its homologous gene NbHSFA2 reduced the heat resistance of tobacco. This study provides first insights into the diversity of the heat response mechanisms among Clematis species.

One Heat Shock Transcription Factor Confers High Thermal Tolerance in Clematis Plants.

Clematis plants play an important role in botanical gardens. Heat stress can destroy the activity, state and conformation of plant proteins, and its regulatory pathway has been well characterized in Arabidopsis and some crop plants. However, the heat resistance response mechanism in horticultural plants including Clematis has rarely been reported. Here, we identified a heat-tolerant clematis species, Clematis vitalba. The relative water loss and electrolytic leakage were significantly lower under heat treatment in Clematis vitalba compared to Stolwijk Gold. Differential expression heat-tolerant genes (HTGs) were identified based on nonparametric transcriptome analysis. For validation, one heat shock transcription factor, CvHSF30-2, extremely induced by heat stimuli in Clematis vitalba, was identified to confer tolerance to heat stress in Escherichia coli and Saccharomyces cerevisiae. Furthermore, silencing of HSF30-2 by virus-induced gene silencing (VIGS) led to heat sensitivity in tobacco and Clematis, suggesting that the candidate heat-resistant genes identified in this RNA-seq analysis are credible and offer significant utility. We also found that CvHSF30-2 improved heat tolerance of Clematis vitalba by elevating heat shock protein (HSP) expression, which was negatively regulated by CvHSFB2a. Taken together, this study provides insights into the mechanism of Clematis heat tolerance and the findings can be potentially applied in horticultural plants to improve economic efficiency through genetic approaches.

Proteome and transcriptome reveal the involvement of heat shock proteins and antioxidant system in thermotolerance of Clematis florida.

Clematis florida Thun (CfT) is an ornamental and medicinal plant. It is a cold resistant but heat sensitive species and deserves to be further investigated to improve its adaptability to heat stress. Exploring the molecular mechanism potential via an omic-analysis constitutes a promising approach towards improving heat tolerance of CfT. Two CfT lines, heat resistance (HR) and heat sensitive (HS), with differential thermotolerance capacities were used for the integrative analyses of proteomics and transcriptomes. Transcriptomes analysis showed that various pathways were significantly enriched including plant hormone signal transduction and carbon fixation pathways in prokaryotes. Proteomics study revealed the enrichment of some other pathways comprising antioxidant activity and carbohydrates metabolism. Based on combined transcriptomes and proteomics analyses and following heat stress treatment, a total of 1724 annotated genes were overlapped between both CfT lines. Particularly, 84 differential expressed genes (DEGs) were overlapped in both CfT lines. Fifteen out of these 84 genes were up-regulated solely for HR line (PS) but not for HS one (SG). This strongly suggests a potential prominent role for these genes in the thermotolerance process in PS line. We corroborate that two Hsps (Hsp18 and Hsp70) out of 20 detected proteins with higher expression levels in PS than in SG based on either global transcripts or proteins levels. According to the transcriptomes and proteomics analyses, 6 proteins and their corresponding genes were found to be significantly abundant in HR line (PS). Data are available via ProteomeXchange with identifier PXD018192. The expressions levels of these 6 genes were checked also for both CfT lines to evaluate their potential contributions in the heat tolerance process. Thus, their expression levels were approximately 2~4 times higher in HR than in HS line. We provided as well a representative schematic model to highlight the key genes involved in ROS scavenging and photorespiratory pathway in CfT. This model could be helpful also in understanding the mechanism of heat tolerance in CfT.

Expression of RcHSP70, heat shock protein 70 gene from Chinese rose, enhances host resistance to abiotic stresses.

There exist differences in the heat tolerance of Chinese rose varieties, and high temperature in summer can lead to failure of blooming in non-heat-tolerant Chinese rose varieties. We cloned a heat shock protein 70 gene (designated RcHSP70) from heat-tolerant varieties of Chinese rose (Rosa hybrida L.) to elucidate the molecular mechanism of heat tolerance and improve the quality of Chinese rose. Degenerate primers were designed for RcHSP70 according to the 5'- and 3'-end sequences of HSP70 genes in apple and tea. RcHSP70 was cloned from heat-tolerant Chinese rose varieties after heat shock. The heat shock-induced expression patterns of RcHSP70 in different Chinese rose varieties were analyzed by RT-PCR. Following heat shock (38 °C/3 h), RcHSP70 was highly expressed in the heat-tolerant varieties but not in the non-heat-tolerant varieties, indicating a close relationship between RcHSP70 and heat resistance in Chinese rose. To verify the function of RcHSP70, we constructed a prokaryotic expression recombinant vector for this gene and transformed it into Escherichia coli BL21. The tolerance of recombinant strains to abiotic stresses, including high temperature, low temperature, high salt, heavy metals, high pH, and oxidation, was evaluated. Additionally, RcHSP70 was transformed into tobacco plants. Because of the overexpression of this gene, transgenic tobacco plants improved their tolerance to high temperature and cold. In addition, transgenic tobacco showed better photosynthetic performance, relative electrical conductivity and proline content than wild tobacco after heat stress and cold stress. Our findings indicate that RcHSP70 is involved in the resistance of Chinese rose to abiotic stresses.

[Comparison of light response models of photosynthesis in Nelumbo nucifera leaves under different light conditions].

The light responses of Nelumbo nucifera 'Boli Furen', a local N. nucifera species was investigated under full light and 50% shading conditions in Shanghai. The net photosynthetic rate-light response curves of N. nucifera leaves were fitted and analyzed through four light response models to identify the best-fit models of different light conditions and explore the adaptability of N. nucifera to shading environment. The results showed that the sequence of fitting effect of the four light response models was in descending order of modified rectangular hyperbola model > exponential model > non-rectangular hyperbola model > rectangular hyperbola model. The latter three models had no extreme values, and could not directly and accurately provide values of light saturation point (LSP) and maximum net photosynthetic rate (Pn max). In contrast, the modified rectangular hyperbola model showed the best fit for LSP, Pn max, dark respiration rate (Rd) and LCP resulting in the minimum relative errors between the measured and fitted values. Light response parameters of N. nucifera declined with the decreasing light. There were no significant differences between full light and shade treatments except for Rd. It was indicated that N. nucifera had good photosynthetic adaptive response and adjustment to weak light to maintain normal growth.