Chromosome-level genome assembly and resequencing of camphor tree (Cinnamomum camphora) provides insight into phylogeny and diversification of terpenoid and triglyceride biosynthesis of Cinnamomum.

Cinnamomum species attract attentions owing to their scents, medicinal properties, and ambiguous relationship in the phylogenetic tree. Here, we report a high-quality genome assembly of Cinnamomum camphora, based on which two whole-genome duplication (WGD) events were detected in the C. camphora genome: one was shared with Magnoliales, and the other was unique to Lauraceae. Phylogenetic analyses illustrated that Lauraceae species formed a compact sister clade to the eudicots. We then performed whole-genome resequencing on 24 Cinnamomum species native to China, and the results showed that the topology of Cinnamomum species was not entirely consistent with morphological classification. The rise and molecular basis of chemodiversity in Cinnamomum were also fascinating issues. In this study, six chemotypes were classified and six main terpenoids were identified as major contributors of chemodiversity in C. camphora by the principal component analysis. Through in vitro assays and subcellular localization analyses, we identified two key terpene synthase (TPS) genes (CcTPS16 and CcTPS54), the products of which were characterized to catalyze the biosynthesis of two uppermost volatiles (i.e. 1,8-cineole and (iso)nerolidol), respectively, and meditate the generation of two chemotypes by transcriptional regulation and compartmentalization. Additionally, the pathway of medium-chain triglyceride (MCT) biosynthesis in Lauraceae was investigated for the first time. Synteny analysis suggested that the divergent synthesis of MCT and long-chain triglyceride (LCT) in Lauraceae kernels was probably controlled by specific medium-chain fatty acyl-ACP thioesterase (FatB), type-B lysophosphatidic acid acyltransferase (type-B LPAAT), and diacylglycerol acyltransferase 2b (DGAT 2b) isoforms during co-evolution with retentions or deletions in the genome.

Pseudomonas sp. TCd-1 significantly alters the rhizosphere bacterial community of rice in Cd contaminated paddy field.

Cadmium (Cd) pollution of paddy soils is one of the main concerns causing food security and environmental problems. Microbial bioremediation is an effective and eco-friendly measure that uses microbes to reduce Cd accumulation in crops. Additionally, rhizosphere bacterial communities also act essential roles in crop tolerance of heavy metals. However, the effects of inoculations with Cd resistant bacteria on crop rhizosphere bacterial communities under Cd exposure are largely unknown. In this study, we used high-throughput 16S rRNA gene sequencing technologies to explore the community structure and co-occurrence network of the rhizosphere bacterial communities associated with the rice crop under different Cd treatments and the application of Cd-tolerant strain Pseudomonas sp. TCd-1. We found that the strain TCd-1 both significantly reduced the rhizobacterial alpha diversity and changed the beta diversity. PERMANOVA and NMDS analysis showed that Cd stress and TCd-1 strain could act as strong environmental filters resulting in observable differentiation of rhizobacterial community composition among different groups. In addition, RDA results indicated that the rhizosphere pH, root Cd content, catalase (CAT), urease (URE), gibberellic acid (GA3) exert significant association with rhizosphere bacterial assembly. PICRUSt analysis revealed that the TCd-1 strain improved the metabolic capacity of rhizosphere bacteria under Cd stress. Furthermore, co-occurrence network topological features and keystone taxa also varied among different groups. This study could provide necessary insights into developing an efficient bioremediation and safe production of rice crops in Cd contaminated paddy fields with the application of Pseudomonas sp. TCd-1 strain, as well as advance our understanding of the principles of rhizosphere bacterial community assembly under Cd stress.

Effects of Pseudomonas TCd-1 on rice (Oryza sativa) cadmium uptake, rhizosphere soils enzyme activities and cadmium bioavailability under cadmium contamination.

Microbial remediation is a promising technique to reduce Cd accumulation in rice (Oryza sativa). In present study, a set of pot experiments were conducted to evaluate the effects of Cd-tolerate Pseudomonas TCd-1 inoculation on rice Cd uptake, soil enzyme activities and Cd bioavailability in the rhizosphere soils under Cd contaminated conditions. The results showed that at the ripening stage, with the inoculation of TCd-1, Cd contents in root, culm, leaf, hull and brown rice significantly reduced by 60.7%, 47.7%, 50.6%, 58.1% and 47.9%, respectively, and the cadmium bioconcentration factor (BCF) of rice lowered by 66.2% under 5 mg kg-1 Cd treatment. At the meantime, in the rhizosphere soils, pH increased by 0.05, the contents of exchangeable Cd (EX-Cd) and Fe-Mn oxides (OX-Cd) increased by 107.8% and 33.5%, whereas organic matter (OM-Cd) and residual (Res-Cd) decreased by 31.9% and 60.0%, respectively. The activity of acid phosphatase (ACP) increased by 28.3%, catalase (CAT), saccharase (SUC) activity decreased by 28.5% and 26.0%. Similarly, the Cd contents in root, culm, leaf, hull and brown rice reduced by 42.1%, 42.5%, 58.0%, 50.3%, and 68.8%, respectively, and the BCF lowered by 57.1%, under 10 mg kg-1 Cd treatment. Simultaneously, the soil pH increased by 0.06, the activities of CAT, SUC, urease (URE), ACP decreased by 26.4%, 34.6%, 63.8% and 15.3%, respectively. Furthermore, the correlation analysis showed that the inoculation of TCd-1 changed the correlation between rice Cd content and the biomass of roots, leaves, soil pH, CAT, PPO, URE activities, OM-Cd in rhizosphere soils. It suggested that Pseudomonas TCd-1 effectively reduced Cd uptake and Cd accumulation in rice was closely linked to the changes of soil pH, enzyme activities and Cd availability.

Drought resistance of Camellia oleifera under drought stress: Changes in physiology and growth characteristics.

To investigate the growth, physiological changes and mechanism of drought resistance of Camellia oleifera GWu-2 under drought stress conditions, changes in the main growth and physiological indices of GWu-2 under different water gradients were studied. Factor analysis was used to study the differences between indicators under different water gradients, and correlation analysis was implemented to analyze the relationship between different factors. We observed that the growth state, enzyme secretion, stomatal morphology and leaf osmotic adjustment substances were significantly affected by drought stress. In particular, increases in leaf abscisic acid (ABA), indole acetic acid (IAA) and methyl jasmonate (MeJA) contents under drought stress were negatively correlated with the stomatal opening degree, and the ratio of ZR/GA3 was significantly correlated with the growth and physiological indicators of GWu-2, indicating that different hormones respond differently to drought stress and have different functions in the growth regulation and drought resistance of GWu-2. We concluded that the drought resistance mechanism of GWu-2 was controlled by maintaining root growth to obtain the necessary water, increasing the contents of osmotic substances of leaves to maintain water holding capacity, reducing the transpiration of water by increasing leaf ABA, IAA and MeJA content to close stomata and reducing the damage caused by drought by increasing the activity of superoxide dismutase (SOD).

Development of the HPLC-ELSD method for the determination of phytochelatins and glutathione in Perilla frutescens under cadmium stress conditions.

A rapid, accurate and simple method was developed for the simultaneous determination of glutathione (GSH) and phytochelatins (PCs) by high-performance liquid chromatography (HPLC) with an evaporative light-scattering detector. GSH, phytochelatin 2 (PC2), PC3, PC4, PC5 and PC6 can be separated with baseline separation within 9 min using a Venusil AA column (250 mm × 4.6 mm i.d., 5 µm particle sizes). Acetonitrile and water containing 0.1% trifluoroacetic acid (0.1%) were employed as the mobile phase for the gradient elution. The drift tube temperature and flow rate of the carrier gas (N2) were 50°C and 1.5 l min-1, respectively. Under optimum conditions, good linear regression equations of six analytes were obtained with the detection limits ranging from 0.2 to 0.5 µg ml-1. The proposed method has been applied successfully for the quantification of GSH and PCs in Perilla frutescens (a cadmium hyperaccumulator) under cadmium stress. The recoveries were between 82.9% and 115.3%.