Plant Defensin-Dissimilar Thionin <i>OsThi9</i> Alleviates Cadmium Toxicity in Rice Plants and Reduces Cadmium Accumulation in Rice Grains

Abstract

Thionins are important antibacterial peptides in plants. However, the roles of plant thionins, especially the defensin-dissimilar thionins, in alleviating heavy-metal toxicity and accumulation remain unclear. Here, cadmium (Cd)-related functions and mechanisms of the defensin-dissimilar rice thionin <i>OsThi9</i> were investigated. <i>OsThi9</i> was significantly upregulated in response to Cd exposure. <i>OsThi9</i> was localized to the cell wall and was shown to bind Cd; these characters help to increase Cd tolerance. In Cd-exposed rice plants, <i>OsThi9</i> overexpression significantly increased cell wall Cd binding, decreasing upward Cd translocation and subsequent Cd accumulation in shoots and straw, while <i>OsThi9</i> knockout had inverse effects. Importantly, in rice plants grown in Cd-contaminated soils, <i>OsThi9</i> overexpression significantly reduced Cd accumulation in brown rice (decrease of ≥ 51.8%) without negatively impairing the crop yield and essential elements. Thus, <i>OsThi9</i> plays an important role in the alleviation of Cd toxicity and accumulation and has significant potential for developing low-Cd rice.