Biomass-derived carbon dots (CDs) are promising nanotools for agricultural applications and function as a reactive oxygen species (ROS) scavenger to alleviate plant oxidative stress under adverse environments. Nevertheless, plants need ROS burst to fully activate Ca 2+ -regulated defensive signaling pathway. The underlying mechanism of CDs to improve plant environmental adaptability without ROS is largely unknown. Here, Salvia miltiorrhiza-derived CDs triggered ROS-independent Ca 2+ mobilization in plant roots. Mechanistic investigation attributed this function mainly to the hydroxyl and carboxyl groups on CDs. CDs-triggered Ca 2+ mobilization was found to be dependent on the production of cyclic nucleotides and cyclic nucleotide-gated ion channels. Lectin receptor kinases were verified as essential for this Ca 2+ mobilization. CDs hydroponic application promoted Ca 2+ signaling and plant environmental adaptability under salinity and nutrient-deficient conditions. All these findings uncover that CDs have a Ca 2+ -mobilizing property and thus can be used as a simultaneous Ca 2+ signaling amplifier and ROS scavenger for crop improvement.
Phosphatidylserine synthase (PSS)-mediated phosphatidylserine (PS) synthesis is crucial for plant development. However, little is known about the contribution of PSS to Na + homeostasis regulation and salt tolerance in plants. Here, we cloned the IbPSS1 gene, which encodes an ortholog of Arabidopsis AtPSS1, from sweet potato (Ipomoea batatas (L.) Lam.). The transient expression of IbPSS1 in Nicotiana benthamiana leaves increased PS abundance. We then established an efficient Agrobacterium rhizogenes-mediated in vivo root transgenic system for sweet potato. Overexpression of IbPSS1 through this system markedly decreased cellular Na + accumulation in salinized transgenic roots (TRs) compared with adventitious roots. The overexpression of IbPSS1 enhanced salt-induced Na + /H + antiport activity and increased plasma membrane (PM) Ca 2+-permeable channel sensitivity to NaCl and H 2 O 2 in the TRs. We confirmed the important role of IbPSS1 in improving salt tolerance in transgenic sweet potato lines obtained from an Agrobacterium tumefaciens-mediated transformation system. Similarly, compared with the wild-type (WT) plants, the transgenic lines presented decreased Na + accumulation, enhanced Na + exclusion, and increased PM Ca 2+-permeable channel sensitivity to NaCl and H 2 O 2 in the roots. Exogenous application of lysophosphatidylserine triggered similar shifts in Na + accumulation and Na + and Ca 2+ fluxes in the salinized roots of WT. Overall, this study provides an efficient and reliable transgenic method for functional genomic studies of sweet potato. Our results revealed that IbPSS1 contributes to the salt tolerance of sweet potato by enabling Na + homeostasis and Na + exclusion in the roots, and the latter process is possibly controlled by PS reinforcing Ca 2+ signaling in the roots.
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In China, iron (Fe) availability is low in most soils but cadmium (Cd) generally exceeds regulatory soil pollution limits. Thus, biofortification of Fe along with mitigation of Cd in edible plant parts is important for human nutrition and health. Carbon dots (CDs) are considered as potential nanomaterials for agricultural applications. Here, Salvia miltiorrhiza‐derived CDs are an efficient modulator of Fe, manganese (Mn), zinc (Zn), and Cd accumulation in plants. CDs irrigation (1 mg mL−1, performed every week starting at the jointing stage for 12 weeks) increased Fe content by 18% but mitigated Cd accumulation by 20% in wheat grains. This finding was associated with the Fe3+‐mobilizing properties of CDs from the soil and root cell wall, as well as endocytosis‐dependent internalization in roots. The resulting excess Fe signaling mitigated Cd uptake via inhibiting TaNRAMP5 expression. Foliar spraying of CDs enhanced Fe (44%), Mn (30%), and Zn (19%) content with an unchanged Cd accumulation in wheat grains. This result is attributed to CDs‐enhanced light signaling, which triggered shoot‐to‐root Fe deficiency response. This study not only reveals the molecular mechanism underlying CDs modulation of Fe signaling in plants but also provides useful strategies for concurrent Fe biofortification and Cd mitigation in plant‐based foods.
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