Knockout of OsHMA3 in an indica rice increases cadmium sensitivity and inhibits plant growth

Abstract

Cadmium (Cd) is a heavy metal that poses harm to both plants and humans. OsHMA3, a member of the heavy metal ATPase (HMA) family, plays a crucial role in sequestering Cd into the vacuoles of roots, thereby limiting its accumulation in rice grains. However, the response of rice plants to Cd under complete loss-of-function of OsHMA3 remains unclear. In this study, we successfully generated OsHMA3 null mutants in an indica variety 93 − 11 using CRISPR/Cas9 technology. A Cd resistance experiment revealed that the Oshma3 mutants exhibited increased sensitivity to Cd compared to the wild-type at a tested concentration of 10 µM CdCl₂. Furthermore, the seedlings of Oshma3 mutant lines displayed inhibited plant growth in the presence of 1 µM Cd, specifically suppressing aboveground growth. As expected, knockout lines of OsHMA3 showed lower Cd accumulation in roots but higher concentrations in shoots compared to wild-type plants, highlighting the role of OsHMA3 in root-to-shoot Cd translocation. We further performed RNA sequencing analysis on wild-type and Oshma3 plants under control and Cd treatment conditions and found that differentially expressed genes were mainly enriched in metal ion binding, integral component of the membranes, and biosynthesis pathways for secondary metabolites triggered by exposure to Cd. When grown in a paddy field, the Oshma3 mutants exhibited shorter plant height, lower seed setting rate, and higher Cd accumulation in grains compared to wild-type plants. Our results indicate that knockout of OsHMA3 in the 93 − 11 variety increases sensitivity to Cd and inhibits plant growth.