Ethylene functions as a suppressor of volatile production in rice

Abstract

We examined the role of ethylene in the production of rice (Oryza sativa) volatile organic compounds (VOCs), which act as indirect defense signals against herbivores in tritrophic interactions. Rice plants were exposed to exogenous ethylene (1 ppm) after simulated herbivory which consisted of mechanical wounds supplemented with the oral secretions (WOS) from the generalist herbivore larvae, Mythimna loreyi. Ethylene treatment highly suppressed VOCs in WOS-treated rice leaves, which was further corroborated by the reduced transcript levels of major VOC biosynthesis genes in ethylene-treated rice. In contrast, the accumulation of jasmonates (JA), known to control the VOCs in higher plants, and transcript levels of primary JA response genes, including OsMYC2, were not largely affected by ethylene application. At the functional level, flooding that is known to promote internode elongation in the young rice via ethylene signaling, consistent with the negative role of ethylene, suppressed the accumulation of VOCs in water-submerged rice leaves. Furthermore, in the maturing stage rice that naturally produced less volatiles, VOCs could be rescued by the application of ethylene perception inhibitor, 1-methylcyclopropene (1-MCP). Our data suggest that ethylene acts as an endogenous suppressor of VOCs in rice that applies to both plant stress responses and development.