Editing of a Novel Cd Uptake-Related Gene CUP1 Contributes to Reducing Cd Accumulations in Arabidopsis thaliana and Brassica napus.

Brassica napus is a Cd hyperaccumulator, which is a serious threat to food and fodder safety. However, no related studies on developing Cd-safe B. napus have been reported yet. Here, we screened out a novel Cd uptake-related gene, AtCUP1, from the major facilitator superfamily in Arabidopsis thaliana. The mutation of AtCUP1 decreased Cd accumulation, both in roots and shoots of A. thaliana. Furthermore, the disruption of the AtCUP1 gene by the CRISPR/Cas9 system significantly reduced Cd accumulation in A. thaliana. Interestingly, the disruption of the BnCUP1 gene, an orthologous gene of AtCUP1, by the CRISPR/Cas9 system also diminished Cd accumulation in both roots and shoots of B. napus based on the hydroponics assay. Furthermore, for the field experiment, the Cd accumulations of BnCUP1-edited lines were reduced by 52% in roots and 77% in shoots compared to that of wild-type (WT) lines, and the biomass and yield of BnCUP1-edited lines increased by 42% and 47% of that of WT, respectively. Noteworthily, agronomic characteristics of B. napus were not apparently affected by BnCUP1-editing. Thus, BnCUP1-edited lines are excellent non-transgenic germplasm resources for reducing Cd accumulation without a distinct compromise in yield, which could be applied to agricultural production in Cd-contaminated soils.

A Gain-of-Function Mutant of IAA7 Inhibits Stem Elongation by Transcriptional Repression of EXPA5 Genes in Brassica napus.

Plant height is one of the most important agronomic traits of rapeseeds. In this study, we characterized a dwarf Brassica napus mutant, named ndf-2, obtained from fast neutrons and DES mutagenesis. Based on BSA-Seq and genetic properties, we identified causal mutations with a time-saving approach. The ndf-2 mutation was identified on chromosome A03 and can result in an amino acid substitution in the conserved degron motif (GWPPV to EWPPV) of the Auxin/indole-3-acetic acid protein 7 (BnaA03.IAA7) encoded by the causative gene. Aux/IAA protein is one of the core components of the auxin signaling pathway, which regulates many growth and development processes. However, the molecular mechanism of auxin signal regulating plant height is still not well understood. In the following work, we identified that BnaARF6 and BnaARF8 as interactors of BnaA03.IAA7 and BnaEXPA5 as a target of BnaARF6 and BnaARF8. The three genes BnaA03.IAA7, BnaARF6/8 and BnaEXPA5 were highly expressed in stem, suggesting that these genes were involved in stem development. The overexpression of BnaEXPA5 results in larger rosettes leaves and longer inflorescence stems in Arabidopsis thaliana. Our results indicate that BnaA03.IAA7- and BnaARF6/8-dependent auxin signal control stem elongation and plant height by regulating the transcription of BnaEXPA5 gene, which is one of the targets of this signal.