Identification of rice (Oryza sativa L.) mutant with increased sensitivity to the phytotoxic metalloid germanium

Authors: Tai, Thomas; Magee, Sarah; SHIM, KYU-CHAN - Chungnam National University; KIM, HYUNJUNG - University Of California, Davis; Liebscher, Anna

Submitted to: SABRAO J. of Breeding and Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2026
Publication Date: 6/1/2026
Citation: Tai, T., Magee, S.C., Shim, K., Kim, H., Liebscher, A.V. 2026. Identification of rice (Oryza sativa L.) mutant with increased sensitivity to the phytotoxic metalloid germanium. SABRAO J. of Breeding and Genetics. 58(3):1095-1102. https://doi.org/10.54910/sabrao2026.58.3.14.
DOI: https://doi.org/10.54910/sabrao2026.58.3.14

Interpretive Summary: Metalloid elements (e.g., silicon, arsenic, germanium, boron) have properties of both metals and non-metals. Rice plants are hyperaccumulators of silicon, which is the second most abundant element on earth. Silicon is considered to be beneficial for rice growth. Unlike silicon, germanium is found in trace amounts and can be toxic to plants, causing the formation of lesions and yellowing of leaves. Rice plants are unable to distinguish between silicon and germanium and researchers have successfully used germanium to screen for rice mutants that are tolerant to germanium. These mutants are defective in their uptake of germanium and silicon and the first silicon transporters in plants were identified using this approach. In this study, we hypothesized that rice mutants exhibiting more sensitivity to germanium could be identified using the same screen. Several potentially more germanium sensitive rice mutants were identified and one of these mutants, named KDS-557B, was the most sensitive, showing toxicity symptoms more rapidly that the normal (i.e., non-mutant or wild type) rice plants and also at ten-fold lower concentrations than those used for screening. Genetic analysis of KDS-557B indicates that the germanium sensitivity it displays is the result of a single gene mutation, providing a foundation for identifying the gene involved and contributing to our understanding of plant interactions with germanium and potentially other metalloids.

Technical Abstract: Germanium (Ge) is a metalloid element with chemical properties similar to silicon (Si). In Si accumulators such as rice (Oryza sativa L.), low concentrations of Ge (µM) can result in the appearance of necrotic lesions and chlorosis. This attribute of Ge phytotoxicity has been employed to great effect in the identification of rice mutants defective in Si uptake and the subsequent cloning of the first Si transporters in plants. In this study, a population of M4 mutants derived from sodium azide seed mutagenesis of the temperate japonica rice variety Kitaake was subjected to Ge screening to identify rice mutants with more rapid development of Ge-induced lesions than wild type. Of thirty mutant lines identified in preliminary screening as more sensitive than Kitaake, the line designated KDS-557B was found to be hypersensitive to Ge, exhibiting a more rapid development of necrotic lesions even at 5 µM GeO2, a 10-fold lower concentration than used for screening. A single gene recessive mutation model was supported by genetic analysis of mapping populations derived from crosses of KDS-557B with Kitaake ('2 = 2.63, df = 1, P = 0.105, not significant at P = 0.01) and a tropical japonica variety Sabine ('2 = 0.04, df = 1, P = 0.841, not significant at P = 0.01). Further characterization of the KDS-557B mutant will be contribute to our understanding the interaction of metalloid elements and plants in the environment.