Heavy metal pollution possesses potential hazards to plant, animal and human health, which has become the focus of recent attention. Hence, phytoremediation has been regarded as one of the most important remediation technologies for heavy-metal-contaminated soils. In this research, a dominant mine tailing plant, Macleaya cordata, was used as the experimental material to compare the metal transport and oxidative stress response in its roots under lead (Pb) and zinc (Zn) treatments. The result showed that Pb was mainly accumulated in the roots of M. cordata under the Pb treatment; less than 1% Pb was transported to the parts above. An analysis of the Zn content demonstrated a 39% accumulation in the shoots. The production of reactive oxygen species was detected using the in situ histological staining of roots, which showed that hydrogen peroxide in the root tips was observed to increase with the increase in both Pb and Zn concentrations. No significant superoxide anion changes were noted in the root tips under the Pb treatment. An analysis of the root enzyme activity showed that increase in NADPH oxidase activity can be responsible for the production of superoxide anions, subsequent the inhibition of root growth and decrease in antioxidant enzyme activities in the roots of M. cordata exposed to excess Zn. In total, this research provides evidence that the root of M. cordata has a high antioxidant capacity for Pb stress, so it can accumulate more Pb without oxidative damage. On the other hand, the Zn accumulated in the roots of M. cordata causes oxidative damage to the root tips, which can stimulate more Zn transport to the shoots to reduce the damage to the roots. This result will provide a basis for the application of M. cordata in the phytoremediation of soil polluted by Pb-Zn compounds.

Corynebacterium glutamicum is an important industrial production strain that is widely used in amino acid fermentation, biopharmaceuticals, and other fields. It is particularly important to develop efficient genome editing methods for the targeted modification of C. glutamicum production strains. Currently, the gene editing system of C. glutamicum is inefficient and time-consuming. In this paper, we reported on a Francisella novicida (Fn) CRISPR-Cpf1-based system for genome editing. The system used linear DNA detached from the plasmid, and, with the assistance of the recombinase RecET, gene deletion was achieved by simultaneous electrotransformation of linear DNA with a plasmid carrying the FnCpf1 and crRNA expression cassette for double-strand breaks of the genome. Compared with previous all-in-one plasmids, this system reduced the time for one round of constructing recombinant plasmids and shortened the editing cycle by about 24 h. Finally, we successfully constructed an engineered strain (X−2) with high L-valine production by using the linear DNA-mediated gene deletion system. This method is of great importance for accelerating the process of metabolic engineering modification of C. glutamicum and its further application in high value-added products.