Zinc biofortification of rice using carbon nanodots

Increasing Zn content of cereals, particularly rice, is an approach for combating global Zn malnutrition. This project aimed to investigate the use of CNPs as a Zn carrier to increase rice Zn content. CDs bound with Zn were used as a foliar spray in the study to determine their effectiveness in delivering Zn to rice plants. The CNPs utilized in the study neither had detrimental effect on the growth nor showed deleterious effect on physiology of the rice plants tested. The possible physiological and molecular mechanism of a Zn efficient rice variety (IR36) and a Zn inefficient variety (IR26) were also studied under CNP. ZnCD application significantly increased shoot and seed Zn content of the IR36 variety, and this response was not seen in the IR26 variety. In contrast, the Fe content of IR 36 seeds increased significantly compared to the bulk Zn application. This validates prior research that found a positive relationship between Zn and Fe uptake in rice. Nonetheless, the responses of the two rice varieties revealed differences in Zn uptake and grain loading demonstrating varying Zn utilization efficiency. Comparative transcriptome and proteome analysis were used to determine the molecular mechanism by which rice responds to CNP-under contrast Zn utilization genetics. RNA-Seq-based transcriptomic analysis found 251 upregulated genes in IR36 in response to ZnCDs that were not upregulated in IR26. These set of activated IR36-specific genes implicated in Zn uptake, grain filling, auxin signalling, and abiotic stress signalling pathways. Our finding clearly demonstrates that the genetics of Zn use efficiency is further amplified by ZnCDs. The comparative proteomics analysis showed ZnCD application to IR36 upregulated 38 proteins, while IR26 upregulated 210 proteins, with just 2 similarities between the two groups. These IR36-specific proteins were heavily implicated in pathways like glucose metabolism, and photosynthesis. Findings of this study could be successfully used in formulation of a CNP based nano-fertilizer which could be used to address the global Zn malnutrition. In addition, greater understanding of the genetic mechanism of Zn utilization efficiency will open up new avenues for breeding and engineering cereals to increase their grain Zn content.