Comparative transcriptomic analysis reveals the coordinated mechanisms of Populus × canadensis ‘Neva’ leaves in response to cadmium stress

Xiang Li,Xiuhong Mao,Yujin Xu,Yan Li,Nan Zhao,Junxiu Yao,Yufeng Dong,Mulualem Tigabu,Xiyang Zhao,Shanwen Li

doi:10.1016/j.ecoenv.2021.112179

Abstract

Cadmium (Cd), a heavy metal element has strong toxicity to living organisms. Excessive Cd accumulation directly affects the absorption of mineral elements, inhibits plant tissue development, and even induces mortality. Populus × canadensis ‘Neva’, the main afforestation variety planted widely in northern China, was a candidate variety for phytoremediation. However, the genes relieving Cd toxicity and increasing Cd tolerance of this species were still unclear. In this study, we employed transcriptome sequencing on two Cd–treated cuttings to identify the key genes involved in Cd stress responses of P. × canadensis ‘Neva’ induced by 0 (CK), 10 (C10), and 20 (C20) mg/L Cd(NO3)2 4H2O. We discovered a total of 2,656 (1,488 up-regulated and 1,168 down-regulated) and 2,816 DEGs (1,470 up-regulated and 1,346 down-regulated) differentially expressed genes (DEGs) between the CK vs C10 and CK vs C20, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses in response to the Cd stress indicated that many DEGs identified were involved in the catalytic activity, the oxidoreductase activity, the transferase activity, and the biosynthesis of secondary metabolites. Based on the enrichment results, potential candidate genes were identified related to the calcium ion signal transduction, transcription factors, the antioxidant defense system, and transporters and showed divergent expression patterns under the Cd stress. We also validated the reliability of transcriptome data with the real-time PCR. Our findings deeper the understanding of the molecular responsive mechanisms of P. × canadensis ‘Neva’ on Cd tolerance and further provide critical resources for phytoremediation applications.

Highlights

Cadmium (Cd) is one of the most universal and harmful heavy metals and has stronger physicochemical activities in soil compared with other metals (Jian et al, 2020; Wang et al, 2015)
The CAT, proline, and superoxide dismutase (SOD) antioxidase content of treatment samples were significantly increased compared with the control, indi cating a key response for eliminating oxygen free radical produced by organism metabolism (Fig. 2A, C and D)
The results showed that differentially expressed genes (DEGs) in the comparison between CK vs C10 and CK vs C20 mainly were enriched for catalytic activity, response to stimuli, plasma membrane, response to toxic substance, response to metal ions, and response to oxidative stress, which indicated that Cd stress has an important effect on growth, metabolism and gene regulation in P. × canadensis ‘Neva’, and a series of resistance mechanisms were activated in response to Cd stress (Table S3)

Summary

Introduction

Cadmium (Cd) is one of the most universal and harmful heavy metals and has stronger physicochemical activities in soil compared with other metals (Jian et al, 2020; Wang et al, 2015). Under the Cd stress, plants are vulnerable to the toxic effects in terms of the physiology and biochemistry characters, including chlorophyll synthe sis, photosynthetic efficiency, membrane permeability, respiratory action and other key biosynthetic pathway (Hu et al, 2020b; Wang et al, 2019e; Wu et al, 2019b; Monteiro et al, 2009; Burzynski and Buckzek, 1989). Such metabolic disorders of basic physiological pro cesses cause significant mortality of the vast majority of plants. Phytor emediation technology is an ideal heavy metal remediation methods due to the safety, inexpensiveness, and none secondary pollution, and is widely applied in the soil-plant ecological system in the past ten years (Atia et al, 2019; Yang et al, 2020a; Yuan et al, 2019a; Deng et al, 2004)

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Discussion

Conclusion