Differential roles of melatonin in plant-host resistance and pathogen suppression in cucurbits

Authors: MANDAL, MIHIR - Oak Ridge Institute For Science And Education (ORISE); SUREN, HAKTAN - Virginia Tech; WARD, BRIAN - Clemson University; BOROUJERDI, AREZUE - Claflin University; Kousik, Chandrasekar - Shaker

Submitted to: Journal of Pineal Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2018
Publication Date: 6/6/2018
Citation: Mandal, M., Suren, H., Ward, B., Boroujerdi, A., Kousik, C.S. 2018. Differential roles of melatonin in plant-host resistance and pathogen suppression in cucurbits. Journal of Pineal Research. e12505. https://doi.org/10.1111/jpi.12505.
DOI: https://doi.org/10.1111/jpi.12505

Interpretive Summary: Melatonin is a naturally occurring hormone present in animals and humans and it plays important roles in patients suffering from sleep disorders, dementia, for treatment of delirium and Alzheimer’s disease. Recently, melatonin has been discovered in plants and is known to help plant growth and development. USDA ARS scientists discovered melatonin in watermelon plants. Further USDA ARS research points out that melatonin plays a role in disease resistance against two important diseases; powdery mildew and Phytophthora fruit rot. Both these diseases are prevalent in most parts of the USA and can limit productivity of watermelon. Application of melatonin reduced the severity of these two diseases. The genetic information developed by this study will help plant pathologists and physiologists further elucidate the role of melatonin in plants. The results of this study will also help scientists in the development of alternative approaches for managing watermelon diseases by manipulating melatonin levels in plants.

Technical Abstract: Since the 1950s, research on the animal neurohormone melatonin, has focused on its multi-regulatory effect on patients suffering from insomnia, cancer, and Alzheimer’s. Previous studies on melatonin in plants have focused primarily on plant growth and development. However, studies on the physiological function of melatonin in host-pathogen defense mechanism are lacking. This study provides insight on the predicted biosynthetic pathway of melatonin in watermelon (Citrullus lanatus) and how application of melatonin, an environmental-friendly immune inducer, can boost plant immunity and suppress pathogen growth in a field situation where fungicide resistance and lack of genetic resistance are major problems. We evaluated the effect of spray-applied melatonin and also transformed watermelon plants with the melatonin biosynthetic gene SNAT to determine the role of melatonin in plant defense. Increased melatonin levels in plants were found to boost resistance against the foliar pathogen Podosphaera xanthii (powdery mildew), and the soilborne oomycete Phythophthora capsici in watermelon and other cucurbits. Further, transcriptomic data on melatonin sprayed (1mM) watermelon leaves, suggests that melatonin alters the expression of genes involved in both PAMP and ETI mediated defenses. Twenty seven upregulated genes were associated with constitutive defense as well as initial priming of the melatonin induced plant resistance response. Our results indicate that developing strategies to increase melatonin levels in specialty crops such as watermelon can lead to resistance against diverse filamentous pathogens.