Overexpression of OsLCT2, a Low-Affinity Cation Transporter Gene, Reduces Cadmium Accumulation in Shoots and Grains of Rice

Li Tang,Yaokui Li,Zhongying Ji,Bingran Zhao,Longtao Tan,Caiyan Chen,Jiayu Dong,Yuanyi Hu,Qiming Lv,Bigang Mao,Yuantao Sun

doi:10.1186/s12284-021-00530-8

Abstract

Cadmium (Cd)-contaminated rice is a serious issue affecting food safety. Understanding the molecular regulatory mechanisms of Cd accumulation in rice grains is crucial to minimizing Cd concentrations in grains. We identified a member of the low-affinity cation transporter family, OsLCT2 in rice. It was a membrane protein. OsLCT2 was expressed in all tissues of the elongation and maturation zones in roots, with the strongest expression in pericycle and stele cells adjacent to the xylem. When grown in Cd-contaminated paddy soils, rice plants overexpressing OsLCT2 significantly reduced Cd concentrations in the straw and grains. Hydroponic experiment demonstrated its overexpression decreased the rate of Cd translocation from roots to shoots, and reduced Cd concentrations in xylem sap and in shoots of rice. Moreover, its overexpression increased Zn concentrations in roots by up-regulating the expression of OsZIP9, a gene responsible for Zn uptake. Overexpression of OsLCT2 reduces Cd accumulation in rice shoots and grains by limiting the amounts of Cd loaded into the xylem and restricting Cd translocation from roots to shoots of rice. Thus, OsLCT2 is a promising genetic resource to be engineered to reduce Cd accumulation in rice grains.

Highlights

In recent years, the widespread contamination of farmland by toxic heavy metals has become an environmental problem, raising concerns about health risks to people all over the world
OsLCT2 and its orthologs in Oryza rufipogon were in the same clade with 98.5% sequence identity, whereas the OsHMA2 and low-affinity cation transporter 1 (OsLCT1) showed high similarity to the low-affinity cation transporter (LCT)-like proteins in Oryza barthii, Oryza glaberrima, and Oryza nivara, with 98.6%, 98.6%, and 95.7% sequence identity, respectively (Additional file 1: Fig. S1a). These results revealed that orthologs of both OsLCT2 and OsLCT1 existed in wild rice species, and the considerable sequence divergence between
Effect of OsLCT2 Overexpression on Expression of OsZIP Genes Because the zincregulated/iron-regulated transporter-like protein (ZIP) family displays transport activity of various cations, including Zn, Fe, Mn and Cd (Lee and An 2009; Ajeesh Krishna et al 2020), we examined expression of ten genes belonging to the OsZIP family in roots of OsLCT2 overexpression lines and the WT in the presence or absence of 0.5 μM Cd for 24 h

Summary

Introduction

The widespread contamination of farmland by toxic heavy metals has become an environmental problem, raising concerns about health risks to people all over the world. Cadmium (Cd) is one of the most toxic heavy metals to organisms. It has a long biological halflife (10–30 years) in the human body and is associated with various diseases, including renal damage, osteoporosis, and cancers (Godt et al 2006; Uraguchi and Fujiwara 2013; Clemens and Ma 2016). Understanding the physiological and molecular mechanisms of Cd uptake, translocation, and distribution in rice is critical for developing rice cultivars with low Cd levels. Following Cd uptake from the soil by roots, Cd may be sequestered into the vacuoles of root cells or translocated from roots to shoots via xylem and distributed/ redistributed to different organs via nodes (Clemens and Ma 2016).

Methods

Results

Discussion

Conclusion