Defense responses in aspen with altered pectin methylesterase activity reveal the hormonal inducers of tyloses
Plant Physiol. 2017, 173(2):1409-1419

Leśniewska J, Öhman D, Krzesłowska M, Kushwah S, Barciszewska-Pacak M, Kleczkowski L, Sundberg B, Moritz T, Mellerowicz EJ

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 METHYLESTERASE 1 (PtxtPME1) in aspen 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 (MeJA), induced the formation of tyloses whereas treatments with salicylic acid (SA) and 1-aminocyclopropane-1-carboxylic acid (ACC) were ineffective. SA abolished the 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 mann

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