Genome-wide identification of Cd-responsive NRAMP transporter genes and analyzing expression of NRAMP 1 mediated by miR167 in Brassica napus

Abstract

In plants, metal transporters are responsible for metal uptake, translocation and homeostasis. These metals include essential nutrients such as zinc (Zn) and manganese (Mn) or non-essential metals like cadmium (Cd) and lead (Pb). Although a few metal transporters have been well characterized in model plants, little is known about their functionality in rapeseed (Brassica napus). In the study, 22 NRAMP transporter genes from B. napus genome were identified and annotated using bioinformatics and high-throughput RNA-sequencing (RNA-seq). Based on the sequence identity, these NRAMP transporters can be classified into 6 subfamilies. RNA-seq analysis revealed that 19 NRAMP transporters were detected and some of the genes were well confirmed by qRT-PCR. Ten NRAMP transporters (45.5%, 10/22) were found to be differentially expressed (> 2 fold change, p < 0.05) under Cd exposure. As an example, we specified expression of BnNRAMP1b under Cd exposure. BnNRAMP1b is a constitutive gene expressing throughout all development stages including seedlings, vegetative tissue, flowers and siliques. Expression of BnNRAMP1b can be strongly induced in seedlings exposed to 80, 160 and 240 μM Cd. To define whether BnNRAMP1b was specific for Cd transport, a yeast (wild-type, BY4741) system with its mutants (ycf1, zrc1, and smf1) defective in transport activity of Cd, Zn and Mn, respectively were tested. Compared to empty vectors (pYES2), cells carrying BnNRAMP1b can rescue the transport functions. As a consequence, excess Cd, Zn and Mn were taken in the cells, which led to metal toxicity, suggesting that BnNRAMP1b is responsible for transport of these metals in B. napus. Using our previously created degradome datasets, we found that BnNRAMP1b could be cleaved by miR167, suggesting that BnNRAMP1b is a target of miR167 in B. napus. The contrasting expression pattern of BnNRAMP1b and miR167 under Cd stress supported the post-transcriptional regulation of BnNRAMP1b by miR167.

Isolation and identification of rapeseed (Brassica napus) cultivars for potential higher and lower Cd accumulation

“…As no negative responses were observed in the study, we conclude that the cultivars were tolerant to Cd stress. Our data are in a line with a previous report of B. napus , which showed no significant growth reduction with a leaf Cd concentration up to ≈ 60 mg kg −1 DW when exposed to 3–50 mg Cd kg −1 soil ( Selvam and Wong , ), supporting the view that B. napus is one of the highly Cd‐tolerant species ( Zhou et al, ; Yadav and Srivastava , ; Feng et al, ; Meng et al, ).…”

High-Throughput Sequencing and Expression Analysis Suggest the Involvement of Pseudomonas putida RA-Responsive microRNAs in Growth and Development of Arabidopsis

“…The NRAMP gene family encodes a metal transporter, and is reported to be involved in the transport of bivalent metal ion throughout the plasma membranes. NRAMP1 has been shown to maintain iron (Fe) homoeostasis, and also act as a high-affinity transporter for manganese (Mn) and zinc (Zn) uptake in various plant species [ 62 , 63 , 64 , 65 ]. In a previous study, the NRAMP1b gene of Brassica napus was reported to be the target of miR167 [ 62 ].…”

“…NRAMP1 has been shown to maintain iron (Fe) homoeostasis, and also act as a high-affinity transporter for manganese (Mn) and zinc (Zn) uptake in various plant species [ 62 , 63 , 64 , 65 ]. In a previous study, the NRAMP1b gene of Brassica napus was reported to be the target of miR167 [ 62 ]. In our study, the up-regulated expression of miR167a mirrored the down-regulation of the NRAMP1 mRNA upon RA-inoculation.…”

Manganese in Plants: From Acquisition to Subcellular Allocation

“…Under Mn-deficient conditions, the expression of AtNRAMP1 is moderately up-regulated, and nramp1 knockout mutants accumulate less Mn in shoots under Mn deficiency, which points to a function of this protein as a high-affinity Mn 2+ uptake transporter (Cailliatte et al, 2010). NRAMP1 orthologs in cacao, rapeseed, and peanut are also expressed in roots and complement a Mn uptake-deficient yeast strain, smf1, lacking a Mn transporter located in the plasma membrane (Meng et al, 2017;Ullah et al, 2018;Wang et al, 2019). In addition, active Mn 2+ uptake may be accomplished by the ZIP transporter AtIRT1 (Castaings et al, 2016), that is considered as the major Fe uptake transporter of dicots.…”