Abstract
Auxins induce adventitious roots (ARs) in numerous culture-systems, and indole-3-butyric acid (IBA) is frequently the best AR-inducer. Vitamin requirements vary according to species, explant, and culture-conditions. Arabidopsis thaliana thin cell layers (AtTCLs) are uncapable of AR-formation on hormone-free medium containing thiamine and myo-inositol, whereas ARs are induced when IBA (10 μM), with/without kinetin (Kin, 0.1 μM), is added. The research first aim was to determine whether a synergism between IBA and myo-inositol and thiamine was necessary for AR-formation. Results showed that IBA induced AR-formation without myo-inositol and thiamine, but better when both vitamins were also present. Deciphering hormonal action on AR formation under optimal vitamin content would be essential for improving the AR process. Ethylene (ET)/jasmonic acid (JA) signaling cross-talk has been demonstrated as being involved in AR-formation in IBA + Kin-cultured AtTCLs, by using ein3eil1 and coi1-16 mutants. ETHYLENE INSENSITIVE3 (EIN3)/EIN3-LIKE1 (EIL1) are positive regulators of ethylene (ET)-signaling, whereas CORONATINE INSENSITIVE1 (COI1) is involved in JA-signaling. The ETHYLENE INSENSITIVE2 (EIN2) protein activates EIN3/EIL1 in ET-presence. To understand whether EIN2 was also involved, the AR-response of ein2-1 and coi1-16 TCLs was evaluated adding the ET-precursor 1-aminocyclopropane-1-carboxylic acid (ACC, 0.1 μM) and/or the JA-donor methyl jasmonate (JAMe, 0.01 μM) to IBA + vitamins-containing medium. AR-formation was enhanced by JAMe, reduced by ACC, but unchanged by JAMe + ACC in the wild type TCLs, whereas remained similarly low in ein2-1 and coi1-16 under all treatments. Collectively, these results demonstrate that the antagonism between JA and ET in AR-formation from AtTCLs involves a cross-talk by EIN2 and COI1.
Highlights
The plant root system is formed by a primary root of embryonic origin, and by lateral roots (LRs) formed post-embryonically by the pericycle of the primary root (Fahn 1990)
The two vitamins were needed for optimizing the indole-3-butyric acid (IBA)-promoting action on adventitious roots (ARs)-formation and branching
The comparison between TCLs of Col-0 genotype cultured for 15 days on MS medium including the two vitamins myo-inositol and thiamine, either in the presence of IBA alone or IBA and Kin, showed that there was no significant difference caused by the presence of Kin for each type of the morphogenic responses obtained
Summary
The plant root system is formed by a primary root of embryonic origin, and by lateral roots (LRs) formed post-embryonically by the pericycle of the primary root (Fahn 1990). There are several plants with a fibrous root system formed in large part by adventitious roots (ARs), and by LRs developed from the ARs. Various tissues of the aerial organs are able to form ARs (Fahn 1990). In plants with a fibrous root system, AR-formation is essential for survival, contributing to water and inorganic salts uptake from the soil and to. Cereals are examples of plants of economic value with a root system largely formed by ARs. The formation of ARs is essential for successful micropropagation programs (Ricci et al 2016, and references therein), and for various biotechnological applications, as, for example, the production of antifungals from ARs-derived extracts (Simonetti et al 2016)
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