(28b) Real-Time Detection of Salicylic Acid in Living Plants Using Nanosensors

Salicylic acid (SA) is an important plant hormone that regulates numerous plant growth and developmental processes, and activates defences against biotic and abiotic stresses. It is a key signalling molecule that triggers systemic acquired resistance (SAR) in plants, which initiates enhanced resistance in uninfected distal parts of the plant, priming them against further pathogen attacks. Traditional chromatography-based analytical methods of SA quantification are costly and labor-intensive. They are also destructive techniques that could not provide real-time information of SA levels in living plants¹. More recently, genetically engineered Acinetobacter sp. ADP1 that produces bioluminescence upon detection of SA have been developed as an in situ SA assay². However, application of the biosensor is limited to model plants such as tobacco. Aptamer-based nanosensor have also been studied for rapid salicylic acid detection but applicability of this nanosensor remain limited to SA detection in plant extracts³. In this work, we have developed a selective SA plant nanobionic sensor which enables non-destructive, real-time monitoring of SA in living plants. Crucially, the nanosensor will provide new insights into the biological function of SA and its derivatives in SAR and other plant developmental processes. The nanosensor is discovered by screening a library of cationic polymers wrapped around single-walled carbon nanotubes (SWNTs) in vitro against a list of common plant hormones analytes. Addition of 100 μM of SA or methyl salicylate (MeSA), the volatile derivative of SA, to the nanosensor resulted in a 35% and 42% near-infrared SWNT fluorescence quenching. In comparison, addition of other plant hormones resulted in <±20% fluorescence change. Arabidopsis thaliana mutants in which SA levels are controllable precisely upon inducer treatment have been used to validate and calibrate the SA nanosensor response in planta. Further, versatility of the SA nanosensor is demonstrated in non-model Brassica rapa subsp. chinensis (Pak Choy) plants, which were infected with Xanthomonas campestris pv. campestris (Xcc) causing black rot in brassica varieties. In response to Xcc infection, SA accumulation is detected by the nanosensor, and confirmed via liquid chromatography–mass spectrometry (LC-MS), in the infected Pak Choy leaves. The SA nanosensor is also interfaced with a portable nanosensor imaging platform, which extends the potential of plant nanobionic approach beyond plant biology studies and towards real-time plant health monitoring in the field.

REFERENCES

1. Matsuura, H.; Aoi, A.; Satou, C.; Nakaya, M.; Masuta, C.; Nabeta, K., Simultaneous UPLC MS/MS analysis of endogenous jasmonic acid, salicylic acid, and their related compounds. Plant Growth Regulation 2008, 57 (3), 293.
2. Huang, W. E.; Huang, L.; Preston, G. M.; Naylor, M.; Carr, J. P.; Li, Y.; Singer, A. C.; Whiteley, A. S.; Wang, H., Quantitative in situ assay of salicylic acid in tobacco leaves using a genetically modified biosensor strain of Acinetobacter sp. ADP1. The Plant Journal 2006, 46 (6), 1073-1083.
3. Chen, C.; Feng, S.; Zhou, M.; Ji, C.; Que, L.; Wang, W., Development of a structure-switching aptamer-based nanosensor for salicylic acid detection. Biosensors and Bioelectronics 2019, 140, 111342.