A multiomics approach reveals the pivotal role of subcellular reallocation in determining rapeseed resistance to cadmium toxicity.

Oilseed rape (Brassica napus) has great potential for phytoremediation of cadmium (Cd)-polluted soils due to its large plant biomass production and strong metal accumulation. Enhanced plant Cd resistance (PCR) is a crucial prerequisite for phytoremediation through hyper-accumulation of excess Cd. However, the complexity of the allotetraploid genome of rapeseed hinders our understanding of PCR. To explore rapeseed Cd-resistance mechanisms, we examined two genotypes, 'ZS11' (Cd-resistant) and 'W10' (Cd-sensitive), that exhibit contrasting PCR while having similar tissue Cd concentrations, and characterized their different fingerprints in terms of plant morphophysiology (electron microscopy), ion abundance (inductively coupled plasma mass spectrometry), DNA variation (whole-genome resequencing), transcriptomics (high-throughput mRNA sequencing), and metabolomics (ultra-high performance liquid chromatography-mass spectrometry). Fine isolation of cell components combined with ionomics revealed that more Cd accumulated in the shoot vacuoles and root pectins of the resistant genotype than in the sensitive one. Genome and transcriptome sequencing identified numerous DNA variants and differentially expressed genes involved in pectin modification, ion binding, and compartmentalization. Transcriptomics-assisted gene co-expression networks characterized BnaCn.ABCC3 and BnaA8.PME3 as the central members involved in the determination of rapeseed PCR. High-resolution metabolic profiles revealed greater accumulation of shoot Cd chelates, and stronger biosynthesis and higher demethylation of root pectins in the resistant genotype than in the sensitive one. Our comprehensive examination using a multiomics approach has greatly improved our understanding of the role of subcellular reallocation of Cd in the determination of PCR.

Balance between nitrogen use efficiency and cadmium tolerance in Brassica napus and Arabidopsis thaliana.

The transmembrane transport of NO3- and Cd2+ into plant cell vacuoles relies on the energy from their tonoplast proton pumps, V-ATPase and V-PPase. If the activity of these pumps is reduced, it results in less NO3- and Cd2+ being transported into the vacuoles, which contributes to better nitrogen use efficiency (NUE) and lower Cd2+ tolerance in plants. The physiological mechanisms that regulate the balance between NUE and Cd2+ tolerance remain unknown. In our study, two Brassica napus genotypes with differential NUEs, xiangyou 15 and 814, and Atclca-2 mutant and AtCAX4 over-expression line (AtCAX4-OE) of Arabidopsis thaliana, were used to investigate Cd2+ stress responses. We found that the Brassica napus genotype, with higher NUE, was more sensitive to Cd2+ stress. The AtCAX4-OE mutant, with higher Cd2+ vacuolar sequestration capacity (VSC), limited NO3- sequestration into root vacuoles and promoted NUE. Atclca-2 mutants, with decreased NO3- VSC, enhanced Cd2+ sequestration into root vacuoles and conferred greater Cd2+ tolerance than the WT. This may be due to the competition between Cd2+ andNO3- in the vacuoles for the energy provided by V-ATPase and V-PPase. Regulating the balance between Cd2+ and NO3- vacuolar accumulation by inhibiting the activity of CLCa transporter and increasing the activity of CAX4 transporter will simultaneously enhance both the NUE and Cd2+ tolerance of Brassica napus, essential for improving its Cd2+ phytoremediation potential.

[Key enzymes in starch synthesis in plants].

Starch, the most common form of stored carbon in plants, is both the major food source for mankind and important raw material for many industries. It is composed of two types of alpha-1,4-linked glucan polymer: essentially unbranched amylose and regularly branched amylopectin, and synthesized in photosynthetic and non-photosynthetic organs. Starch is synthesized via four committed enzyme steps: ADP-Glc pyrophosphorylase, which synthesizes sugar nucleotide precursors; starch synthase, which extends the alpha-1,4-linked glucan chains using ADP-Glc; starch-branching enzymes, which introduce alpha-1,6 branch points to form amylopectin; and starch debranching enzymes, which hydrolyze alpha-1,6 branches in glucans. In this paper, recent advances in biochemical characterizations and gene engineering concerning these enzymes were reviewed, and the achievements in gene engineering involved in manipulation of starch amount and quality were also cited.