ZmHMA3 enhances Zn stress tolerance and mediates Zn transport in Maize

Abstract Excessive levels of Zn have the potential to be detrimental to plant health. ZmHMA3, a member of the heavy metal ATPase (HMA) family, is responsible for the transport of Zn2+ and Cd2+ across cellular membranes. In order to investigate the role of the ZmHMA3 gene in response to Zn stress, ZmHMA3 knockout mutants were created using the CRISPR-Cas9 technique. Subsequently, gene specific expression, as well as agronomic traits, root morphology indicators, relative conductivity, antioxidant indicators, and Zn content in the leaf, root, and their subcellular components were assessed. The results demonstrated a significant accumulation of ZmHMA3 in both the leaf and root after 48 hours of Zn stress compared to the control group. The Zmhma3 knockout line exhibited decreased tolerance to toxic levels of Zn as compared to the wild type, resulting in a reduction in maize plant height, fresh weight, dry weight, water content, root morphology indicators (Length, SurfArea, AvgDiam, Rootvolume, Tips and Forks) and antioxidant enzyme activity (CAT, POD, SOD, and MDA), while also leading to an increase in membrane permeability and zinc accumulation. In conclusion, it can be inferred that ZmHMA3 likely functions as a crucial positive regulator in the response to Zn stress in maize.