Salicylic Acid, a Plant Hormone, Suppresses Phytophagous Insect Immune Response by Interrupting HMG-Like DSP1.

Hyong Woo Choi,Inhwa Yeam,Md Mahi Imam Mollah,Yonggyun Kim,Je Min Lee

doi:10.3389/fphys.2021.744272

Abstract

Salicylic acid is a plant hormone that can mediate various plant physiological processes. Salicylic acid can bind to human high mobility group box 1 (HMGB1) and interrupt its role in mediating immune responses. Dorsal switch protein 1 (DSP1) is an insect homolog of HMGB1. In this study, a DSP1 (Se-DSP1) encoded in Spodoptera exigua, a phytophagous insect, was characterized, and its potential role in immune response was explored. Upon bacterial challenge, Se-DSP1 was localized in the nucleus and released into the hemolymph. The released Se-DSP1 could mediate both cellular and humoral immune responses by activating eicosanoid biosynthesis. Salicylic acid could bind to Se-DSP1 with a high affinity. The immune responses of S. exigua were significantly interrupted by SA feeding. Larvae reared on tomatoes with high endogenous SA levels became more susceptible to entomopathogens. Taken together, these results suggest a tritrophic defensive role of plant SA against phytophagous insects.

Highlights

High-mobility group proteins are non-histone DNA-binding proteins in eukaryotes
Se-Dorsal switch protein 1 (DSP1) shared 95.1, 77.1, 73, and 52.1% amino acid sequence similarities with the DSP genes of Helicoverpa armigera, Leptinotarsa decemlineata, D. melanogaster, and the high mobility group box 1 (HMGB1) of Homo sapiens, respectively
This study characterized the immunological role of Se-DSP1 by acting as a damage-associated molecular pattern (DAMP) and its significance in the co-evolutionary context of host plants

Summary

Introduction

High-mobility group proteins are non-histone DNA-binding proteins in eukaryotes. These highmobility group (HMG) proteins include at least three unrelated protein groups: HMGA, HMGB, and HMGN (Reeves, 2003). High-mobility group A proteins bind to A/T-rich DNA sequences and promote the binding of other transcription factors, while HMGN proteins bind to nucleosomes and promote chromatin decondensation (Bustin, 2001). Four HMGB proteins (HMGB1– 4) are known. They are ubiquitously expressed during embryogenesis, they show different spatial expression patterns in the adult stage (Stros, 2010)

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