Yue Cao

Arsenic (As) contamination in paddy soils poses a threat to human health through rice consumption. Arsenate (AsV) uptake contributes to grain As accumulation, yet its upstream regulatory mechanisms remain largely unknown. Here, we identified a WRKY transcription factor, OsWRKY1, as a key regulator of AsV uptake in rice plant, whose expression is strongly induced by AsV at both transcript and protein levels. Loss of OsWRKY1 function increased rice root As concentration by 2.8-fold under hydroponic conditions and raised grain As concentration by 19–22% in soil-grown plants compared with wild type, indicating that OsWRKY1 is a negative regulator of As accumulation. Chromatin immunoprecipitation sequencing revealed that OsWRKY1 directly binds to the promoter of P-transporter OsPht1;4, an also major AsV transporter gene in rice, but not to other Pht1 family members. Dual-luciferase assays further showed that OsWRKY1 represses OsPht1;4 promoter activity. Under AsV exposure, OsPht1;4 transcript levels were upregulated by 2.5-fold in oswrky1 mutants and were downregulated by 90% compared with wild type in OsWRKY1-overexpressing lines. These results define the OsWRKY1–OsPht1;4 module as a critical transcriptional repression mechanism that limits AsV uptake and accumulation in rice grain, providing a mechanistic basis for restricting As accumulation through specific transcriptional regulation of AsV uptake.

Selenium (Se) deficiency is widespread, yet excess inorganic Se is toxic. Enhancing plant Se through genetic biofortification is a safe strategy. Rice phosphate transporters (OsPht1) mediate selenite (SeIV) uptake, but underlying mechanisms remain unclear. In hydroponic assays, the osphf1 mutant showed significantly reduced Se accumulation, confirming OsPht1s' involvement. The ospht1;8 and ospht1;10 mutants decreased root and shoot Se by 38.9-39.7% or 57.2-69.0%, whereas ospht1;1 reduced shoot Se by 37.2%, suggesting OsPht1;8 and OsPht1;10 mediate root Se uptake, and OsPht1;1 facilitates Se translocation. Overexpression of OsPht1;1 and OsPht1;10 enhanced shoot Se by 33.0-55.4%, whereas OsPht1;8 overexpression increased root Se by 32.3-36.2% and reduced Cd by 26.6-35.1% in shoots and 27.6-41.5% in grains through elevated cysteine and enhanced OsHMA3 and OsPCS2 expression. These findings demonstrate distinct roles of OsPht1 members in Se accumulation, providing candidate genes for breeding Se-enriched rice, with OsPht1;8 additionally lowering Cd risk.

Globally, 94–220 million people in regions with arsenic (As)-contaminated soil or groundwater face significant health risks. Rice, the primary staple food in these areas, is the main source of As exposure for a large portion of this population. Developing low-As rice cultivars provides a sustainable strategy to reduce dietary As exposure. However, As uptake in rice shares pathways with nutrient uptake, such as phosphate (P) transporters. The lack of As-specific transporters makes it challenging to reduce As accumulation in plants by regulating As uptake genes, as such approaches risk disrupting P uptake and plant growth. Here, we functionally characterized two phosphate transporter genes, OsPht1;9/OsPht1;10, which play a key role in arsenate (AsV) uptake and translocation in rice but minimally contribute to P utilization. Under hydroponic conditions, the double mutants of OsPht1;9/1;10 exhibited a 46.2–65.7% reduction in shoot As accumulation, with the As concentrations in xylem sap being 16.5–34.8% lower than the wild type controls. In multi-year field trials at two locations, simultaneous knockout of OsPht1;9/1;10 significantly decreased grain As concentration by 19.2–47.3%, without compromising yield. This study identifies novel gene-editing targets for low-As rice development and provides a breakthrough in mitigating As contamination exposure while enhancing food safety.

Pteris vittata is a well-known arsenic (As) hyperaccumulator, yet the genetic basis of its exceptional ability remains unclear. In this study, we constructed a comparative transcriptome database from seven Pteris species, including four As hyperaccumulators and three nonhyperaccumulators, to identify key genes driving As hyperaccumulation. We found that P. vittata uniquely possesses both plasma membrane-localized (Type-I) and tonoplast-localized (Type-II) ACR3s, facilitating AsIII translocation and sequestration. Additionally, P. vittata shows an expansion of HAC and ACR3 gene families, supporting enhanced AsV reduction and AsIII transport. Evolutionary analyses revealed strong positive selection on Type-II PvACR3s, with specific adaptive amino acid sites identified. Functional assays showed that coexpression of Type-I (PvACR3) and Type-II (PvACR3;1) ACR3s in an Arabidopsis thaliana hac1 mutant increased shoot As contents by 5.5-6.3-fold compared to wild-type plants, further supporting the important role of synergistic interaction between two ACR3 types in As hyperaccumulation. This study reveals unique genetic components that constitute the As hyperaccumulation pathway, providing valuable insights for enhancing phytoremediation of As-contaminated soils.

Phytate enhances arsenic metabolism in As-hyperaccumulator Pteris vittata, but the underlying mechanisms remain unclear. Using P. multifida and P. ensiformis as comparisons, we investigated the plant growth, As/P uptake, and phytate synthesis, sequestration, and exudation in P. vittata under 10-100 μM As exposure. The expressions of P transporters Pht1;2-1;4, phytate synthesis genes including myo-inositol 3-phosphate synthase (MIPS), myo-inositol monophosphatase (IMP), and 2-phosphoglyceric acid kinase (2-PGK), and phytate transporter multidrug resistance-associated protein 5 (MRP5) were analyzed. After 3 weeks of growth, P. vittata accumulated the greatest As in the fronds at 155-3098 mg kg^-1, with biomass being increased by 9.8-63%. While greater expression of PvPht1;2/1;4 helped P. vittata maintain stable plant P contents at 3005-3552 mg kg^-1, PmPht1;2/1;4 and PePht1;2/1;4 expressions were reduced by 10-55%. Arsenic exposure enhanced phytate accumulation in P. vittata by upregulating phytate synthesis genes MIPS, IMP, and 2-PGK and phytate transporter gene MRP5 by 1.3-1.7-fold, increasing phytate contents by 1.1-2.1-fold to 69.2-371 mg kg^-1. Further, P. vittata increased phytate root exudation by 1.5-3.6-fold under As exposure, whereas P. multifida and P. ensiformis mainly exuded tartrate. In short, As-enhanced phytate metabolism in P. vittata is unique and contributes to its superior As-accumulation ability, showing implication for phytoremediation of As-contaminated soils.

Soil is the largest organic matter repository on land and the virosphere is an essential component of soil carbon cycling. While a few carbon-related auxiliary metabolic genes (AMGs) in viruses are reported to potentially influence the hosts, the effects of virus-host interactions on soil carbon fixation, particularly in carbon-deficient contaminated soils, need further validation. Here, we explore the impact of viruses on carbon fixation in contaminated soils from 58 metal mining areas across eastern China. Eleven different functional categories of carbon fixation AMGs are identified via metagenomic analysis in 323 contaminated soil samples. Enzymatic activities of three key AMGs (i.e., rbcL , ppdK and TKT ) are experimentally characterized, indicating the positive role of these genes in carbon fixation. Furthermore, transcriptomic sequencing reveals that after active virus inoculation the carbon fixation genes significantly up-regulate (~73%, p < 0.05). In mesocosms with stable isotope labeling, the accumulation of ¹³ C-labeled organic carbon significantly increases (~10%, p < 0.01). Our results provide theoretical and experimental evidence for incorporating viral contributions into the assessments of carbon fixation, and improve the understanding of viral roles within the processes of carbon cycling.

Plant and rhizosphere soil samples of the rare earth element (REE) hyperaccumulator plant Dicranopteris linearis were collected across tropical and subtropical China to elucidate how rhizosphere microbiota drive soil REE solubilization and accumulation in this species. The results show that this facultative REE hyperaccumulator species grows under severe phosphorus deficiency conditions, with soil available phosphorus concentrations ∼2 mg kg^-1 and a leaf nitrogen-to-phosphorus ratio >20. The core rhizosphere microbiota comprise 111 OTUs (occupancy >95%, relative abundance >0.1%), with community structure primarily correlated with soil phosphorus availability, rather than with geographical location or climatic variables. Foliar phosphorus and REE concentrations are positively associated with soil total phosphorus concentrations and glucose dehydrogenase (GCD) gene abundance─a key biomarker of microbial phosphate solubilization activity─but exhibit no significant association with soil available phosphorus or soil extractable REE concentrations. Combined 16S rRNA sequencing and metagenomic analyses further reveal abundant phosphate-solubilizing microbes within the core microbiome. These results show that REE mineral weathering in the rhizosphere soil and subsequent accumulation in D. linearis are side effects of phosphate solubilization promoted by the rhizosphere microbiome under phosphorus deficiency conditions.