Abstract
Plants growing in constantly changeable environmental conditions are compelled to evolve regulatory mechanisms to cope with biotic and abiotic stresses. Effective defence to invaders is largely connected with phytohormone regulation, resulting in the production of numerous defensive proteins and specialized metabolites. In our work, we elucidated the role of the Abscisic Acid Insensitive 4 (ABI4) transcription factor in the plant response to the two-spotted spider mite (TSSM). This polyphagous mite is one of the most destructive herbivores, which sucks mesophyll cells of numerous crop and wild plants. Compared to the wild-type (Col-0) Arabidopsis thaliana plants, the abi4 mutant demonstrated increased susceptibility to TSSM, reflected as enhanced female fecundity and greater frequency of mite leaf damage after trypan blue staining. Because ABI4 is regarded as an important player in the plastid-to-nucleus retrograde signalling process, we investigated the plastid envelope membrane dynamics using stroma-associated fluorescent marker. Our results indicated a clear increase in the number of stroma-filled tubular structures deriving from the plastid membrane (stromules) in the close proximity of the site of mite leaf damage, highlighting the importance of chloroplast-derived signals in the response to TSSM feeding activity.
Highlights
The two-spotted spider mite (TSSM), Tetranychus urticae Koch, represents one of the most destructive generalist mite herbivores
Our results indicated a clear increase in the number of stroma-filled tubular structures deriving from the plastid membrane in the close proximity of the site of mite leaf damage, highlighting the importance of chloroplast-derived signals in the response to TSSM feeding activity
The rate of female oviposition was significantly greater on the abi4 mutants than on Arabidopsis Col-0 plants (Fig. 1), suggesting that the abi4 mutants were more susceptible to mite attack
Summary
The two-spotted spider mite (TSSM), Tetranychus urticae Koch, represents one of the most destructive generalist mite herbivores. There is limited information about the molecular mechanism of ABA engagement in plant defence to mite infestation, based on the research on Pieris rapae caterpillars, Vos et al (2013) postulated that ABA is a regulator of herbivore-induced resistance by activating primed JA-regulated defence responses upon secondary herbivore attack in Arabidopsis This regulation especially targets the MYC2 dependent branch of JA signalling. The same effect was observed after the exogenous application of pro-defence signals such as hydrogen peroxide (H2O2) and SA (Caplan et al 2015) This in turn emphasizes the role of chloroplast redox signalling pathways and ROS metabolism in local and systemic responses to light stress and pathogen infection which was shown by Kangasjarvi et al (2014). Our results for the first time indicate the engagement of retrograde signalling in plant response to TSSM attack
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