Rice Master Regulator 'HYR' Enhances Growth and Defense Mechanisms with Consequences for Fall Armyworm Growth and Host Selection.

Abstract

Rice (Oryza sativa L.), the staple food for half of the world's population, suffers heavy damage by insect herbivores, especially the emerging Fall Armyworm (FAW), Spodoptera frugiperda. HYR (HIGHER YIELD RICE), a master regulator of multiple biological pathways with an established gene regulatory network, has been found to improve rice yield to ~29% and tolerance to environmental stress. However, its impact on defense has not been explored. We hypothesized that, FAW would target HYR plants because of its vigorous growth, and lead to trade offs for defense. Through a series of experiments with HYR and its wild type, we show that HYR plants have enhanced below-ground growth, physiological traits, direct and indirect defense traits including leaf trichomes, wax and volatile organic compounds. To test possible phytohormone mediated defense signalling, we focussed on jasmonic acid and salicylic acid gene expression panel and found most of these genes are highly expressed in HYR when compared to its wildtype counterpart. Bioassays examining developmental milestones also revealed that HYR plants effectively deter FAW, and when force fed, caused negative effects. Collectively, our findings suggest that the master regulator HYR (Higher Yield Rice expressing) plants enhance growth and physiological traits, as well as physical and chemical defense mechanisms through co-ordinated defense gene expression, that deter herbivore feeding, growth, development and host selection.