Abstract
The jasmonic acid (JA) pathway plays a key role in plant defense responses against herbivorous insects. CORONATINE INSENSITIVE1 (COI1) is an F-box protein essential for all jasmonate responses. However, the precise defense function of COI1 in monocotyledonous plants, especially in rice (Oryza sativa L.) is largely unknown. We silenced OsCOI1 in rice plants via RNA interference (RNAi) to determine the role of OsCOI1 in rice defense against rice leaf folder (LF) Cnaphalocrocis medinalis, a chewing insect, and brown planthopper (BPH) Nilaparvata lugens, a phloem-feeding insect. In wild-type rice plants (WT), the transcripts of OsCOI1 were strongly and continuously up-regulated by LF infestation and methyl jasmonate (MeJA) treatment, but not by BPH infestation. The abundance of trypsin protease inhibitor (TrypPI), and the enzymatic activities of polyphenol oxidase (PPO) and peroxidase (POD) were enhanced in response to both LF and BPH infestation, but the activity of lipoxygenase (LOX) was only induced by LF. The RNAi lines with repressed expression of OsCOI1 showed reduced resistance against LF, but no change against BPH. Silencing OsCOI1 did not alter LF-induced LOX activity and JA content, but it led to a reduction in the TrypPI content, POD and PPO activity by 62.3%, 48.5% and 27.2%, respectively. In addition, MeJA-induced TrypPI and POD activity were reduced by 57.2% and 48.2% in OsCOI1 RNAi plants. These results suggest that OsCOI1 is an indispensable signaling component, controlling JA-regulated defense against chewing insect (LF) in rice plants, and COI1 is also required for induction of TrypPI, POD and PPO in rice defense response to LF infestation.
Highlights
Plants are frequently exposed to herbivorous insect attack and microbial pathogen infection in the natural environment
brown planthopper (BPH) infestation did not significantly change the transcript abundance of OsCOI1 (F1, 29 = 0.951, P = 0.338) (Fig. 1B). These results suggest that OsCOI1 may only be involved in JA-related rice defense to chewing insects
We found that trypsin protease inhibitor (TrypPI) levels in wild-type rice plants (WT) plants were induced by 107% and 130% by BPH and leaf folder (LF) infestation, compared with un-infested control plants (Fig. 2D)
Summary
Plants are frequently exposed to herbivorous insect attack and microbial pathogen infection in the natural environment. The jasmonate pathway plays a key role in plant defense responses against herbivorous insects. Insect feeding activates a wide variety of genes that are responsive to JA and related octadecanoids, including methyl jasmonate (MeJA) and 12-oxo-phytodienoic acid (OPDA) [3]. It has been well studied that feeding damage by herbivorous insect elicits a rapid burst of octadecanoid signals in dicotyledonous plants, such as Arabidopsis thaliana, tobacco (Nicotiana attenuata), and tomato (Lycopersicon esculentum) [4,5,6], to trigger production of defense compounds and anti-nutritive substances that deter further insect damage [7,8,9,10,11]. The jasmonate pathway regulates production of volatiles in tomato plants, which can attract natural enemies of herbivorous insects [12]
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