Hydrogen peroxide regulated salicylic acid– and jasmonic acid–dependent systemic defenses in tomato seedlings

Abstract

To investigate the regulation of hydrogen peroxide (H 2 O 2) in SA-and JA-dependent systemic defense pathways in tomato seedlings damaged by cotton bollworm. The lower two leaves of four-leaf tomato plant seedlings were treated with cotton bollworms. The upper leaves were then removed at various time points and assessed for systemic changes in H 2 O 2 levels, enzyme activity and defense-related genes expression. Wild-type seedlings, def-5 mutant seedlings (deficient in JA accumulation) and transgenic nahG seedlings(deficient in SA content) were constructed at four-leaf stage. Wild-type plants were further treated with dimethylthiourea (DMTU) and 2,5-dihydroxycinnamic acid methyl ester (DHC). Bollworm feeding in the lower leaves induced rapid systemic accumulation of H 2 O 2 in the upper leaves. H 2 O 2 accumulation further increased activities for SA-and JA-dependent enzymes including proteinase inhibitors (PIs), pathogenesis-related gene 1 (PR-1), cathepsin D inhibitor (CDI), β-1,3-glucanse (BGL) and polyphenol oxidase (PPO). Furthermore, H 2 O 2 accumulation enhanced mRNA expression of BGL-2, PR-1, PI, CDI and PPO genes. Suppression of H 2 O 2 accumulation using H 2 O 2 scavengers substantially diminished these effects. mRNA expression of PR-1 was not induced in transgenic nahG plants. SA-and JA-dependent signaling pathways are involved in the tomato systemic defense responses to herbivores, and that H 2 O 2 generation is required for both systemic pathways.

Phytohormone Priming of Tomato Plants Evoke Differential Behavior in Rhizoctonia solani During Infection, With Salicylate Priming Imparting Greater Tolerance Than Jasmonate

“…The appropriate balance between accumulation of ROS and removal of ROS is an important target for the pathogen and the host for the sake of their own survival ( Kou et al, 2019 ). Although there are numerous studies in this area of research, the molecular mechanism involved in H 2 O 2 mediated regulation of plant systemic defense responses against infection is not clear ( Zhang et al, 2021 ). In our experiments, H 2 O 2 accumulation was maximum in the control plants followed by MeJA-primed and least in the SA-primed plants.…”

“…The extremely high expression of PINII in the first 8 hpi was therefore due to the direct effect of MeJA priming. SA can suppress the octadecanoid pathway and accumulation of PIN-II in JA-treated tomato seedlings ( Zhang et al, 2021 ). This can explain our observation that there was a decline of PINII in SA-primed plants up to 8 hpi (i.e., 32 hours post-priming) and then gradually rising due to infection.…”

“…Earlier studies show that exogenous application of SA increases expression of PR ( Chen et al, 2017 ) and that H 2 O 2 does not function downstream of SA in the induction of PR protein expression ( Bi et al, 1995 ; Zhang et al, 2021 ). Consistent with earlier studies, our results show that even though there was less H 2 O 2 in the SA-primed plants compared to control plants (due to less infection), the PR1 gene expression was higher than that of control at all time points in the SA-primed plants.…”