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Plants are constantly exposed to a variety of environmental stresses, including herbivory. How plants perceive herbivores on a molecular level is poorly understood. Leucine‐rich repeat receptor‐like kinases (LRR‐RLKs), the largest subfamily of RLKs, are essential for plants to detect external stress signals, and may therefore also be involved in herbivore perception. Here, we employed RNA interference silencing, phytohormone profiling and complementation, as well as herbivore resistance assays, to investigate the requirement of an LRR‐RLK for the initiation of rice (Oryza sativa) defenses against the chewing herbivore striped stem borer (SSB) Chilo suppressalis. We discovered a plasma membrane‐localized LRR‐RLK, OsLRR‐RLK1, whose transcription is strongly up‐regulated by SSB attack and treatment with oral secretions of Spodoptera frugiperda. OsLRR‐RLK1 acts upstream of mitogen‐activated protein kinase (MPK) cascades, and positively regulates defense‐related MPKs and WRKY transcription factors. Moreover, OsLRR‐RLK1 is a positive regulator of SSB‐elicited, but not wound‐elicited, levels of jasmonic acid and ethylene, trypsin protease inhibitor activity and plant resistance towards SSB. OsLRR‐RLK1 therefore plays an important role in herbivory‐induced defenses of rice. Given the well‐documented role of LRR‐RLKs in the perception of stress‐related molecules, we speculate that OsLRR‐RLK1 may be involved in the perception of herbivory‐associated molecular patterns.

A salivary endo-β-1,4-glucanase in the rice brown planthopper Nilaparvata lugens facilitates access to the phloem by degrading celluloses in plant cell walls.

β-Glucosidase has been reported to induce the production of herbivore-induced plant volatiles. However, how it works remains unclear. Here, we investigated the levels of salicylic acid (SA), jasmonic acid (JA), ethylene, and H2O2, all of which are known signaling molecules that play important roles in induced plant defense in rice plants treated with β-glucosidase, and compared these to levels in plants infested by the rice brown planthopper Nilaparvata lugens (Stal). Results showed that wounding and treatment by β-glucosidase increased the levels of SA, ethylene, and H2O2, but not JA, in all plants compared to control plants. The signaling pathways activated by β-glucosidase treatment are similar to those activated by an infestation by N. lugens, although the magnitude and timing of the signals elicited by the two treatments are different. This may explain why both treatments have similar volatile profiles and are equally attractive to the parasitoid Anagrus nilaparvatae Pang et Wang.

Experiments were conducted in laboratory to study the impacts of rice genotypes and nitrogen levels on the preference of the egg predator, CyTtorhinuc liuidipennk , for eggs of brown planthopper(BPH) , Nilaparvata lugem ( SGl) , and their relation to the rice volatiles. In two-choice tests, the female predators showed daerent preference for BPH eggs on different rice genotypes, but not for BPH eggs on rice plants treated with different levels of nitrogen. The olfactory response test revealed that more predator oriented to the odour from healthy rice plants compared with the plain air (control) ;the predator preferred BPH nymph-damaged plants to healthy plants, and BPH female adult-dam- aged plants to BPH nymph-damaged plants. The comparative studies between rice genotypes and nitrogen levels indi- cated that there were obvious differences in attractiveness to the predator between rice genotypes, while there was no significant difference between rice plants treated with different levels of nitrogen . The results showed that rice volatiles played an important role in mediating the foraging behaviour of C. liwidipennis . Implications for augmenting the effec- tiveness of natural enemies by adjusting rice attributes and cultural practices are discussed.

The oxylipin pathway is of central importance for plant defensive responses. Yet, the first step of the pathway, the liberation of linolenic acid following induction, is poorly understood. Phospholipases D (PLDs) have been hypothesized to mediate this process, but data from Arabidopsis (Arabidopsis thaliana) regarding the role of PLDs in plant resistance have remained controversial. Here, we cloned two chloroplast-localized PLD genes from rice (Oryza sativa), OsPLDα4 and OsPLDα5, both of which were up-regulated in response to feeding by the rice striped stem borer (SSB) Chilo suppressalis, mechanical wounding, and treatment with jasmonic acid (JA). Antisense expression of OsPLDα4 and -α5 (as-pld), which resulted in a 50% reduction of the expression of the two genes, reduced elicited levels of linolenic acid, JA, green leaf volatiles, and ethylene and attenuated the SSB-induced expression of a mitogen-activated protein kinase (OsMPK3), a lipoxygenase (OsHI-LOX), a hydroperoxide lyase (OsHPL3), as well as a 1-aminocyclopropane-1-carboxylic acid synthase (OsACS2). The impaired oxylipin and ethylene signaling in as-pld plants decreased the levels of herbivore-induced trypsin protease inhibitors and volatiles, improved the performance of SSB and the rice brown planthopper Nilaparvata lugens, and reduced the attractiveness of plants to a larval parasitoid of SSB, Apanteles chilonis. The production of trypsin protease inhibitors in as-pld plants could be partially restored by JA, while the resistance to rice brown planthopper and SSB was restored by green leaf volatile application. Our results show that phospholipases function as important components of herbivore-induced direct and indirect defenses in rice.

Herbivore-induced plant volatiles prime plant defenses and resistance. How volatiles are integrated into early defense signaling is not well understood. Furthermore, whether there is a causal relationship between volatile defense priming and herbivore resistance is unclear. Here, we investigated the impact of indole, a common herbivore-induced plant volatile and known modulator of a wide range of physiological processes in plants, bacteria and animals, on early defense signaling and herbivore resistance in rice. We show that rice plants infested by Spodoptera frugiperda caterpillars release indole up to 25 ng*h-1. Exposure to equal doses of exogenous indole enhances rice resistance to S. frugiperda. Screening of early signaling components reveals that indole pre-exposure directly enhances the expression of the receptor like kinase OsLRR-RLK1. Furthermore, indole-pre exposure followed by simulated herbivory increases (i.e. primes) the transcription, accumulation and activation of the mitogen-activated protein kinase OsMPK3 as well as the expression of the downstream WRKY transcription factor OsWRKY70 and several jasmonate biosynthesis genes, resulting in a higher accumulation of jasmonic acid (JA). Using transgenic plants defective in early signaling, we show that OsMPK3 is required, and that OsMPK6 and OsWRKY70 contribute to indole-mediated defense priming of JA-dependent herbivore resistance. We conclude that herbivore-induced plant volatiles can increase herbivore resistance of plants through positive regulation of early defense signaling components.

Plant‐mediated interactions between herbivores are important determinants of community structure and plant performance in natural and agricultural systems. Current research suggests that the outcome of the interactions is determined by herbivore and plant identity, which may result in stochastic patterns that impede adaptive evolution and agricultural exploitation. However, few studies have systemically investigated specificity versus general patterns in a given plant system by varying the identity of all involved players. We investigated the influence of herbivore identity and plant genotype on the interaction between leaf‐chewing and root‐feeding herbivores in maize using a partial factorial design. We assessed the influence of leaf induction by oral secretions of six different chewing herbivores on the response of nine different maize genotypes and three different root feeders. Contrary to our expectations, we found a highly conserved pattern across all three dimensions of specificity: The majority of leaf herbivores elicited a negative behavioral response from the different root feeders in the large majority of tested plant genotypes. No facilitation was observed in any of the treatment combinations. However, the oral secretions of one leaf feeder and the responses of two maize genotypes did not elicit a response from a root‐feeding herbivore. Together, these results suggest that plant‐mediated interactions in the investigated system follow a general pattern, but that a degree of specificity is nevertheless present. Our study shows that within a given plant species, plant‐mediated interactions between herbivores of the same feeding guild can be stable. This stability opens up the possibility of adaptations by associated organisms and suggests that plant‐mediated interactions may contribute more strongly to evolutionary dynamics in terrestrial (agro)ecosystems than previously assumed.

Plants generally respond to herbivore attack by increasing resistance and decreasing growth. This prioritization is achieved through the regulation of phytohormonal signaling networks. However, it remains unknown how this prioritization affects resistance against non-target herbivores. In this study, we identify WRKY70 as a specific herbivore-induced, mitogen-activated protein kinase-regulated rice transcription factor that physically interacts with W-box motifs and prioritizes defence over growth by positively regulating jasmonic acid (JA) and negatively regulating gibberellin (GA) biosynthesis upon attack by the chewing herbivore Chilo suppressalis. WRKY70-dependent JA biosynthesis is required for proteinase inhibitor activation and resistance against C. suppressalis. In contrast, WRKY70 induction increases plant susceptibility against the rice brown planthopper Nilaparvata lugens. Experiments with GA-deficient rice lines identify WRKY70-dependent GA signaling as the causal factor in N. lugens susceptibility. Our study shows that prioritizing defence over growth leads to a significant resistance trade-off with important implications for the evolution and agricultural exploitation of plant immunity.

The mechanisms by which plants activate and enhance defense responses have been well studied; however, the regulatory mechanisms that allow plants to avoid excessive defense responses are poorly understood. Here, we identified a group D mitogen-activated protein kinase (MAPK) gene from rice (Oryza sativa), OsMAPK20-5, whose expression was rapidly induced by infestation of gravid female adults of a destructive rice pest, brown planthopper (BPH, Nilaparvata lugens), but not by BPH nymphs. Expression silencing of OsMAPK20-5 (irMAPK) increased the accumulation of ethylene and nitric oxide (NO) after gravid female BPH infestation, and thereby increased rice plant resistance to BPH adults and oviposited eggs. However, when exposed to high densities of gravid BPH females, irMAPK plants wilted earlier than wild-type plants, which could be attributed to the hyperaccumulation of ethylene and NO in irMAPK plants. Interestingly, when released into the field, irMAPK plants displayed broad resistance to BPH and white-backed planthopper (Sogatella furcifera), the two most destructive pests of rice, and produced higher yield. Taken together, our study shows that although OsMAPK20-5 can reduce the resistance of rice plants to planthoppers, it also enables rice plants to control excessive defense responses and thereby prevents defense-response–related autotoxicity.