Tobacco Hornworm (Manduca sexta) Oral Secretion Elicits Reactive Oxygen Species in Isolated Tomato Protoplasts.

Akanksha Gandhi,Cruz Chappa,Rupesh R Kariyat,Nirakar Sahoo,Mandeep Tayal

doi:10.3390/ijms21218297

Akanksha Gandhi, Cruz Chappa + Show 3 more

Open Access

https://doi.org/10.3390/ijms21218297

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Abstract

Plants are under constant attack by a suite of insect herbivores. Over millions of years of coexistence, plants have evolved the ability to sense insect feeding via herbivore-associated elicitors in oral secretions, which can mobilize defense responses. However, herbivore-associated elicitors and the intrinsic downstream modulator of such interactions remain less understood. In this study, we show that tobacco hornworm caterpillar (Manduca sexta) oral secretion (OS) induces reactive oxygen species (ROS) in tomato (Solanum lycopersicum) protoplasts. By using a dye-based ROS imaging approach, our study shows that application of plant-fed (PF) M. sexta OS generates significantly higher ROS while artificial diet-fed (DF) caterpillar OS failed to induce ROS in isolated tomato protoplasts. Elevation in ROS generation was saturated after ~140 s of PF OS application. ROS production was also suppressed in the presence of an antioxidant NAC (N-acetyl-L-cysteine). Interestingly, PF OS-induced ROS increase was abolished in the presence of a Ca2+ chelator, BAPTA-AM (1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid). These results indicate a potential signaling cascade involving herbivore-associated elicitors, Ca2+, and ROS in plants during insect feeding. In summary, our results demonstrate that plants incorporate a variety of independent signals connected with their herbivores to regulate and mount their defense responses.

Highlights

Herbivory is an unavoidable part of a plant’s life
While herbivores prey on the plant, protoplasts come into contact with oral secretions that induce plant defense signaling, and reactive oxygen species (ROS) has been known to play a critical role in these defense responses
We found that the application of M. sexta OS induced a drastic increase of ROS generation in isolated tomato protoplasts

Summary

Introduction

Herbivory is an unavoidable part of a plant’s life. Over millions of years, plants and herbivorous insects have been involved in a relentless war where plants are actively attacked by herbivores, reducing plant growth, development, and, their fitness [1]. It has been proposed that following insect attack the foremost event is plasma membrane potential change (Vm) [18,19], followed by generation of second messengers such as cytosolic calcium (Ca2+) [16,20] and reactive oxygen species (ROS) [21,22,23,24] that facilitate plant defense signal transduction This leads to a suite of defense-related traits, including induction of trichomes, spines, and secondary metabolites (e.g., alkaloids, phenolics, and volatile organic compounds) that negatively impact herbivore fitness and mediate multi-trophic interactions [7,25,26]. While ecological aspects of plant-herbivore interactions and their molecular mechanisms are well understood, early initiation mechanisms associated with alterations in Vm, Ca2+, and ROS production immediately after herbivore assault warrants more empirical testing in various systems [27]

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