Cadmium accumulation regulated by a rice heavy-metal importer is harmful for host plant and leaf bacteria

Introduction: Cadmium (Cd), one of the major toxic heavy metals, causes severe deleterious effects on all living organisms from prokaryotes to eukaryotes. Cadmium deposition affects bacterial diversity and bac-terial population in soil. Cadmium accumulation in plants is mainly controlled by transporters and the resulting Cd enrichment gives rise to phytotoxicity. Objective: This study aimed to mine transporters that control Cd import or accumulation in rice and uncover the underlying mechanisms that how accumulated Cd poses risks to host plant and leaf bacteria. Methods: RNA-seq analysis, histochemical assays, and elemental quantification were carried out to reveal the biological roles of OsABCG43 for Cd import. Pathogen inoculation, IC50 value, and bacterial virulence assays were conducted to disclose the effects of Cd on leaf bacteria. Results: OsABCG43 is characterized as a Cd importer controlling Cd accumulation in rice. OsABCG43 was induced under Cd stress and specifically expressed in the vasculature of leaves and roots. Overexpression of OsABCG43 caused Cd accumulation which inhibits photosynthesis and development and alters the antioxidant system, resulting in phytotoxicity. Moreover, overexpression of OsABCG43 resulted in retarded plant growth and enhanced rice sensitivity to Cd stress. Numerous differentially expressed genes were identified via RNA-seq analysis between the OsABCG43-overexpressing plants and wild type, which functioned in Cd or reactive oxygen species (ROS) homeostasis. In addition, OsABCG43 transcripts were induced by leaf bacteria Xanthomonas oryzae pv. oryzicola (Xoc) and X. oryzae pv. oryzae (Xoo). The enriched Cd directly impaired the formation of virulence factors for the leaf bacteria, preventing coloniza-tion or proliferation of Xoc or Xoo in rice leaves. Conclusion: This work reveals that OsABCG43 is expressed specifically in the vascular and plasma membrane-localized OsABCG43 functions as a Cd importer. OsABCG43-mediated import of Cd is harmful for both rice and the corresponding leaf bacteria.(c) 2023 The Authors. Published by Elsevier B.V. on behalf of Cairo University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study identified OsABCG43 as a transporter protein that controls Cd import or accumulation in rice, and investigated the underlying mechanisms of Cd-induced risks to host plant and leaf bacteria. The results showed that OsABCG43 is a Cd importer and its overexpression leads to Cd accumulation, inhibiting photosynthesis, development, and altering the antioxidant system, resulting in phytotoxicity. Additionally, overexpression of OsABCG43 slows plant growth and increases rice sensitivity to Cd stress. Cd enrichment also inhibits the formation of virulence factors in leaf bacteria, preventing colonization or proliferation in rice leaves.