Modulation of plant defense responses to herbivores by simultaneous recognition of different herbivore-associated elicitors in rice.

Tomonori Shinya,Kazunori Okada,Naoto Shibuya,John T Christeller,Yuko Hojo,Ivan Galis,Yoshitake Desaki

doi:10.1038/srep32537

Abstract

Induced plant defense responses against insect herbivores are triggered by wounding and/or perception of herbivore elicitors from their oral secretions (OS) and/or saliva. In this study, we analyzed OS isolated from two rice chewing herbivores, Mythimna loreyi and Parnara guttata. Both types of crude OS had substantial elicitor activity in rice cell system that allowed rapid detection of early and late defense responses, i.e. accumulation of reactive oxygen species (ROS) and defense secondary metabolites, respectively. While the OS from M. loreyi contained large amounts of previously reported insect elicitors, fatty acid-amino acid conjugates (FACs), the elicitor-active P. guttata’s OS contained no detectable FACs. Subsequently, elicitor activity associated with the high molecular mass fraction in OS of both herbivores was identified, and shown to promote ROS and metabolite accumulations in rice cells. Notably, the application of N-linolenoyl-Gln (FAC) alone had only negligible elicitor activity in rice cells; however, the activity of isolated elicitor fraction was substantially promoted by this FAC. Our results reveal that plants integrate various independent signals associated with their insect attackers to modulate their defense responses and reach maximal fitness in nature.

Highlights

Role in the amino acid metabolism in some insects[11]
Larvae of M. loreyi are generalist pests feeding on grasses including rice plants[31,36,37,38], providing a suitable model for identification and purification of insect elicitors active in rice
Mythimna (Leucania) loreyi (MYL) feeding significantly promoted the accumulation of two previously reported phenolamides, p-coumaroylputrescine (CoP) and feruloylputrescine (FP) (Fig. 1a), and it elicited two diterpene phytoalexins, momilactone A (MoA) and momilactone B (MoB) in rice leaves. This was in contrast with the previous report on low and inconsistent elicitation of MoA and MoB in rice leaves by two other chewing herbivores, S. mauritia and P. guttata[23,24]

Summary

Introduction

Role in the amino acid metabolism in some insects[11]. Hydrogen peroxide (H2O2) and other reactive oxygen species (ROS) are well-known modulators and/or activators of plant defense[12,13]. In addition to PAs, rice plants accumulate momilactone diterpenes[25], proteinase inhibitors[26], and emit many VOCs in response to herbivore attack[27]. Direct feeding on plants is less convenient for high throughput experiments due to its low reproducibility and demand for insect/damage-free plant material to avoid systemic signaling and memory effects in plants[32,33]. At this point, cultivated rice cells may be of use, following the well-established examples of monitoring the activity of many microbial elicitors, based on the reproducible changes in secondary metabolism, defense gene expression, and ROS production in treated cells[34,35]. Elicitors and/or purified fractions can be applied to cells directly without excessive wounding, normally required for penetration of plant cuticle, a protective film covering the epidermis of leaves

Methods

Results

Conclusion