Genome-wide analysis and expression profiling of the HMA gene family in Brassica napus under cd stress

Abstract

Brassica napus (B. napus), one of the most important oil crop species, is highly tolerant to and accumulates high amounts of cadmium (Cd). Many iron transporters in plants have been identified to be Cd transporters. For example, some members of the heavy metal P1B-ATPase transporter family are responsible for Cd translocation in various plant species and play a vital role in Cd detoxification. However, the Cd translocation mechanism in B. napus and the characterization of the heavy metal ATPase (HMA) in B. napus remain unknown. B. napus plants were treated with 50 μM or 200 μM Cd in soil for 30 days during the initial flowering stage. The dry weight of the plants and the Cd contents within their various tissues were then measured, after which the RNA in the leaves was extracted for transcriptomic analysis and subsequent quantitative real-time PCR (qRT-PCR) assays. After all the significantly regulated iron transporters were screened in response to Cd stress, the BnHMA gene family was identified and shown to link BnHMA genes with Cd translocation in the leaves of B. napus. The transcriptomic analysis of B. napus leaves in response to Cd treatment revealed that several HMA genes (BnHMA2;2, BnHMA2;3 and BnHMA2;5) respond to Cd stress. We further examined the whole HMA family in B. napus; 31 BnHMA genes were subsequently identified. Their expression levels in different tissues and stages as well as their phylogenetic tree, gene structure, chromosomal location, conserved motifs, 3D models and subcellular localization were analyzed. The results showed that these HMA genes exhibit typical characteristics of HMA genes. In addition, the qRT-PCR results showed that the BnHMA2;3 expression levels in the B. napus plants treated with 50 μM or 200 μM Cd were seven- and ninefold greater than those under Cd-free conditions, respectively. Additional yeast experiment assays verified that BnHMA2;3 can transport Cd. BnHMA2;3 may play an important role in Cd translocation in the leaves of B. napus. The results of this study may provide direction and useful information for increased understanding of the Cd stress-response mechanism.