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To investigate the effect of lignin in the cultivar-dependent Cd detoxification of Brassica chinensis L., Cd and lignin contents, lignin composition and laccase genes expressions in low-Cd-accumulating (LAJK) and high-Cd-accumulating (HAJS) cultivars grown under control (CK) and 25 μM Cd-treatment were determined. The results showed that lignin combined about 14 % of total Cd in both LAJK and HAJS. LAC genes were more up-regulated in HAJS than in LAJK, indicating that the LAC genes were involved in the cultivar-dependent lignin functions. Higher β-aryl ether (A) proportion in the lignin side chain region in LAJK than in HAJS were observed, whereas resinol (B) and phenylcoumaran (C) constitute much higher proportions in HAJS than in LAJK. Chemical calculation to estimate Cd affinity associating with lignin side chain region displayed that i) β-aryl ether (A) exhibited major coupling with lignin aromatic region; ii) resinol (B) and phenylcoumaran (C) displayed major participation in complexation with Cd. We therefore conclude that Cd compartmentalization in the secondary cell wall (SCW) by coupling with lignin side chain region is responsible for Cd detoxification related to cultivar-dependent Cd accumulation of Brassica chinensis. This is the first study on lignin composition in relation to Cd retention mechanisms in SCW., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Cultivar-dependent cadmium (Cd) accumulation was principal in developing Cd-pollution safe cultivars (PSCs). Proteins related to different Cd accumulations of the low-Cd-accumulating (SJ19) and high-Cd-accumulating (CX4) cultivars were investigated by iTRAQ analysis. Higher Cd bioaccumulation factors and translocation factor in CX4 than in SJ19 were consistent with the cultivar-dependent Cd accumulations. The Cd uptake was promoted in CX4 due to its higher expression of Cd-binding proteins and the lower expression of Cd-efflux proteins in roots. What's more, significantly elevated thiol groups (PC 2 and PC 3 ) in CX4 under Cd stress might contribute to the high Cd accumulation in roots and the root-to-shoot translocation of Cd-PC complex. Up-regulated proteins involved in cellulose biosynthesis and pectin de-esterification in SJ19 enhanced the Cd sequestration of root cell walls, which was considered as the predominant strategy for reducing Cd accumulation in shoots. The present study provided novel insights in the cultivar-dependent Cd accumulation in shoots of B. parachinensis., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Two pot experiments were conducted to compare and verify Cd accumulation capacities of different cultivars under Cd exposures (0.215, 0.543, and 0.925 mg kg -1 in Exp-1 and 0.143, 0.619, and 1.407 mg kg -1 in Exp-2) and Cd subcellular distributions between low- and high-Cd cultivars. Shoot Cd concentrations between the selected low- and high-Cd cultivars were 1.4-fold different and the results were reproducible. The proportions of Cd-in-cell-wall of shoots and roots were all higher in a typical low-Cd cultivar (DX102) than in a typical high-Cd cultivar (HJK), while those of Cd-in-chloroplast or Cd-in-trophoplast and Cd-in-membrane-and-organelle were opposite. The proportions of Cd-in-vacuoles-and-cytoplasm of roots in DX102 were always higher than in HJK under Cd stresses, while there was no clear pattern in those of shoots. These findings may help to reduce health risk of Cd from Chinese kale consumption and explained biochemical mechanisms of cultivar-dependent Cd accumulation among the species.

To reduce cadmium (Cd) pollution of food chains, screening and breeding of low-Cd-accumulating cultivars are the focus of much study. Two previously identified genotypes, a low-Cd-accumulating genotype (LAJK) and a high-Cd-accumulating genotype (HAJS) of pakchoi (Brassica chinesis L.), were stressed by Cd (12.5 μM) for 0 h (T0), 3 h (T3) and 24 h (T24). By comparative transcriptome analysis for root tissue, 3005 and 4343 differentially expressed genes (DEGs) were identified in LAJK at T3 (vs T0) and T24 (vs T3), respectively, whereas 8677 and 5081 DEGs were detected in HAJS. Gene expression pattern analysis suggested a delay of Cd responded transcriptional changes in LAJK compared to HAJS. DEG functional enrichments proposed genotype-specific biological processes coped with Cd stress. Cell wall biosynthesis and glutathione (GSH) metabolism were found to involve in Cd resistance in HAJS, whereas DNA repair and abscisic acid (ABA) signal transduction pathways played important roles in LAJK. Furthermore, the genes participating in Cd efflux such as PDR8 were overexpressed in LAJK, whereas those responsible for Cd transport such as YSL1 were more enhanced in HAJS, exhibiting different Cd transport processes between two genotypes. These novel findings should be useful for molecular assisted screening and breeding of low-Cd-accumulating genotypes for pakchoi.

Aims: Cadmium (Cd) contamination in arable soils presents a serious threat to agricultural crops and public health. Cd pollution-safe cultivars (Cd-PSCs) can effectively restrict human intake of Cd through food chain. However, not much is known on the genetic basis of low-Cd-accumulating trait. Here, we aim to investigate the microRNA (miRNA)-mediated post-transcriptional regulation underlying different capacities of Cd accumulation in Brassica parachinensis L. Methods: Using small RNA sequencing, miRNAs were identified and characterized in two previously identified cultivars, a low- (SJ19) and a high-Cd-accumulating cultivar (CX4) of B. parachinensis. Results: 18 known and 148 novel miRNAs were identified to be differentially expressed in response to Cd (Cd-responsive miRNAs) in the two cultivars. Distinct Cd responsive pathways were employed by the two cultivars. In CX4, the overexpression of miR395 was indicated to engage in Cd tolerance by regulating sulfur assimilation and associated with its high Cd accumulation. In SJ19, miRNA-mediated oxidative resistance was enhanced in response to Cd exposure. Furthermore, miR397, miR393 and miR160 were involved in the Cd-induced growth improvement in both roots and shoots of the low-Cd-accumulating cultivar. Conclusions: Our findings provide new insights into miRNAs-mediated Cd response in B. parachinensis, and shed light on molecular-assisted Cd-PSC screening and breeding for agricultural crops and vegetables. [ABSTRACT FROM AUTHOR]