VAPYRIN attenuates defence by repressing PR gene induction and localized lignin accumulation during arbuscular mycorrhizal symbiosis ofPetunia hybrida

Abstract

SummaryThe intimate association of host and fungus in arbuscular mycorrhizal (AM) symbiosis can potentially trigger induction of host defence mechanisms against the fungus, implying that successful symbiosis requires suppression of defence.We addressed this phenomenon by using AM-defective vapyrin (vpy) mutants in Petunia hybrida, including a new allele (vpy-3) with a transposon insertion close to the ATG start codon. We explore whether abortion of fungal infection in vpy mutants is associated with the induction of defence markers such as cell wall alterations, accumulation of reactive oxygen species (ROS), defence hormones, and induction of pathogenesis-related (PR) genes.We show that vpy mutants exhibit a strong resistance against intracellular colonization, which is associated with the generation of thick cell wall appositions (papillae) with lignin impregnation at fungal entry sites, while no accumulation of defence hormones, ROS, or callose was observed. Systematic analysis of PR gene expression revealed that several PR genes are induced in mycorrhizal roots of the wild type, and even more in vpy plants. Some PR genes are induced exclusively in vpy mutants.Taken together, these results suggest that VPY is involved in avoiding or suppressing the induction of a cellular defence syndrome that involves localized lignin deposition and PR gene induction.

Symbiotic responses of Lotus japonicus to two isogenic lines of a mycorrhizal fungus differing in the presence/absence of an endobacterium

“…To understand whether the lignin deposition involved colonized cells, roots from the same plants were stained with fluoroglucinol. Lignin was detected exclusively in the xylem elements, while no lignin deposition was observed in the epidermal layer or in the arbusculated cells (Figure S9), differently from the lignin impregnation detected in cell wall appositions (papillae) at fungal entry sites in Petunia roots (Chen et al, 2021). Thicker older roots from clover revealed, however, random lignified epidermal cells, which were not associated with fungal entry points.…”

Common and lifestyle-specific traits of mycorrhiza-associated metabolite alterations in plant roots reflects strategies of root-mycorrhizal interactions

“…If these genetic/transcriptional traits could be translated to chemistry/metabolite alterations, one would expect no accumulation or lower-level of defense/stress related specialized compounds in established mycorrhizal roots. This is supported by observations that the establishment of mycorrhizas were associated with decreased or unaffected levels of protective compounds in roots (e.g., cell-wall bound ferulic acids, tannins, Münzenberger et al, 1995;Solaiman et al, 2018;Sebastiana et al, 2021) and lack of additional lignin deposition (Chen et al, 2021). On the other hand, mycorrhizas have been shown to induce substantial accumulation of phenolic compounds in the endodermis or exodermis of root cortex (Ling-Lee et al, 1977;Weiss et al, 1997Weiss et al, , 1999, with these specific root compartments proposed crucial in the evolution of mycorrhizas by forming a barrier to detrimental fungal penetration (Brundrett, 2002;Strullu-Derrien et al, 2009).…”

Optical Clearing of Plant Tissues for Fluorescence Imaging

“…CS is applicable to a wide range of plant species, such as Arabidopsis thaliana, Physcomitrium patens 7 , Chrysanthemum morifolium, Cucumis sativus, Nicotiana benthamiana, Nicotiana tabacum, Torenia fournieri 8 , Allium ochotense 19 , Astragalus sinicus 20 , avocado 21 , barley 22 , Brassica rapa 23 , Callitriche 24 , Eucalyptus 25 , maize 26 , Marchantia polymorpha 27 , Monophyllaea glabra 28 , Orobanche minor 29 , petunia 30 , rice 31 , Solanum lycopersicum 32 , soybean 33 , strawberry 34 , wheat 35 , and Wolffiella hyalina 36 . For thicker tissues, CS can also make the vibratome sections transparent 37 , 38 .…”