Defense Responses in Aspen with Altered Pectin Methylesterase Activity Reveal the Hormonal Inducers of Tyloses

Abstract

(E.J.M.). Tyloses are ingrowths of parenchyma cells into the lumen of embolized xylem vessels, thereby protecting the remaining xylem from pathogens. They are found in heartwood, sapwood, and in abscission zones and can be induced by various stresses, but their molecular triggers are unknown. Here, we report that down-regulation of PECTIN METHYLESTERASE1 (PtxtPME1) in aspen (Populus tremula 3 tremuloides) triggers the formation of tyloses and activation of oxidative stress. We tested whether any of the oxidative stress-related hormones could induce tyloses in intact plantlets grown in sterile culture. Jasmonates, including jasmonic acid (JA) and methyl jasmonate, induced the formation of tyloses, whereas treatments with salicylic acid (SA) and 1-aminocyclopropane-1-carboxylic acid (ACC) were ineffective. SA abolished the induction of tyloses by JA, whereas ACC was synergistic with JA. The ability of ACC to stimulate tyloses formation when combined with JA depended on ethylene (ET) signaling, as shown by a decrease in the response in ET-insensitive plants. Measurements of internal ACC and JA concentrations in wild-type and ET-insensitive plants treated simultaneously with these two compounds indicated that ACC and JA regulate each other's concentration in an ET-dependent manner. The findings indicate that jasmonates acting synergistically with ethylene are the key molecular triggers of tyloses.

Immunoprofiling of Cell Wall Carbohydrate Modifications During Flooding-Induced Aerenchyma Formation in Fabaceae Roots

“…Our study also described the formation of previously reported space-filling parenchyma cells (Lu et al, 1991;Niki et al, 1998;Pegg et al, 2018) during periods of prolonged flooding stress that cosmetically resemble tyloses found in hardwood plants (Esau, 1965;Carlquist, 2013;Leśniewska et al, 2017). The biological significance of these "tylose-like cells" (TLCs) forming in Pisum and Cicer samples is unclear with respect to formation and eventual filling of aerenchyma cavities during periods of flooding stress.…”

“…Consistent with previous reports (Lu et al, 1991;Niki et al, 1998) aerenchyma became partly occluded with new tissue expanding from the margin of the vascular cavity within 24-48 h of flooding (Figures 1B, C, J and 2C, D). We described these tissues as being composed of large, nucleated "bubble-like" cells that we name "tylose-like cells" (TLCs) due to their cosmetic resemblance to tyloses found in xylem vessels of various hardwoods (Esau, 1965;Carlquist, 2013;Leśniewska et al, 2017). Interestingly, toluidine blue stained tissue near the margins of the aerenchyma and the TLCs a bright magenta color that was not found elsewhere in the root cross section ( Figures 1B, C).…”

Using the CODIT model to explain secondary metabolites of xylem in defence systems of temperate trees against decay fungi

“…Trauma induced gels have a high abundance of antimicrobial SMs from different chemical pathways including catechol, flavonoids and coumarins (Rioux et al, 1998;Del Rio et al, 2001;Baum and Schwarze, 2002), indicating that a different secondary metabolic pathway is possibly triggered in vessel-associated cells in response to pathogenesis (Wallis and Truter, 1978). A recent study by Lesniewska et al (2017) revealed that down regulation of Pectin Methlesterase1 (PtxtPME1) via jasmonates (i.e. jasmonic acid and metyl jasmonate) A c c e p t e d M a n u s c r i p t mediated ethylene signaling, when working in synergy with 1-aminocyclopropane-1carboxylic acid (ACC), trigger gel and tylosis development in aspen plantlets.…”

Ethylene-Related Gene Expression Networks in Wood Formation

“…Jasmonates have previously been connected to secondary growth in A. thaliana (Sehr et al, 2010 ). Also, treatment with jasmonates to aspen plantlets induced the formation of tyloses, which are occlusions of xylem vessels that serve as a barrier against pathogens (Leśniewska et al, 2017 ). This study also showed that combined exogenous application of ACC and jasmonic acid triggered tyloses formation in an ethylene signaling-dependent manner.…”