Abstract
In Arabidopsis basal hypocotyls of dark-grown seedlings, xylary cells may form from the pericycle as an alternative to adventitious roots. Several hormones may induce xylogenesis, as Jasmonic acid (JA), as well as indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) auxins, which also affect xylary identity. Studies with the ethylene (ET)-perception mutant ein3eil1 and the ET-precursor 1-aminocyclopropane-1-carboxylic acid (ACC), also demonstrate ET involvement in IBA-induced ectopic metaxylem. Moreover, nitric oxide (NO), produced after IBA/IAA-treatments, may affect JA signalling and interact positively/negatively with ET. To date, NO-involvement in ET/JA-mediated xylogenesis has never been investigated. To study this, and unravel JA-effects on xylary identity, xylogenesis was investigated in hypocotyls of seedlings treated with JA methyl-ester (JAMe) with/without ACC, IBA, IAA. Wild-type (wt) and ein3eil1 responses to hormonal treatments were compared, and the NO signal was quantified and its role evaluated by using NO-donors/scavengers. Ectopic-protoxylem increased in the wt only after treatment with JAMe(10 μM), whereas in ein3eil1 with any JAMe concentration. NO was detected in cells leading to either xylogenesis or adventitious rooting, and increased after treatment with JAMe(10 μM) combined or not with IBA(10 μM). Xylary identity changed when JAMe was applied with each auxin. Altogether, the results show that xylogenesis is induced by JA and NO positively regulates this process. In addition, NO also negatively interacts with ET-signalling and modulates auxin-induced xylary identity.
Highlights
In vascular plants, the process leading to the differentiation of the xylem conducting elements is still not fully understood
The latter process causes the formation of cells that only subsequently differentiate into supernumerary xylary cells (XEs) and has been observed in the hypocotyls of Arabidopsis dark-grown seedlings treated with naphthaleneacetic acid (NAA) [5]
The aim of the present research is to determine the involvement of Jasmonic acid (JA), ET and nitric oxide (NO) in the control of endogenous/exogenous-auxin-induced xylogenesis through a possible crosstalk mediated by ETHYLENE INSENSITIVE 3 (EIN3)/EIN3-LIKE 1 (EIL1)
Summary
The process leading to the differentiation of the xylem conducting elements (xylary elements, XEs) is still not fully understood. In Arabidopsis dark-grown seedlings, it has been recently demonstrated that ET is involved in ectopic xylem formation through the activation of the ETHYLENE INSENSITIVE 3 (EIN3) and EIN3-LIKE 1 (EIL1) transcription factors (TFs) [11] Both these TFs activate numerous ET-responsive genes [18] and when mutated cause complete ET-insensitivity ([19] and references therein) and persistent auxin-sensitivity [20]. The aim of the present research is to determine the involvement of JA, ET and NO in the control of endogenous/exogenous-auxin-induced xylogenesis through a possible crosstalk mediated by EIN3/EIL1 To this aim, ectopic xylem formation was investigated in the hypocotyl of dark-grown Arabidopsis seedlings exposed to various concentrations of JAMe with/without ACC, and exogenous IBA or IAA. The role of JA in inducing xylogenesis and in modifying xylary cell identity is further discussed
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