The spermatophyte root system is composed of a primary root that develops from an embryonically formed root meristem, and of different post-embryonic root types: lateral and adventitious roots. Adventitious roots, arising from the stem of the plants, are the main component of the mature root system of many plants. Their development can also be induced in response to adverse environmental conditions or stresses. Here, in this review, we report on the morphological and functional diversity of adventitious roots and their origin. The hormonal and molecular regulation of the constitutive and inducible adventitious root initiation and development is discussed. Recent data confirmed the crucial role of the auxin/cytokinin balance in adventitious rooting. Nevertheless, other hormones must be considered. At the genetic level, adventitious root formation integrates the transduction of external signals, as well as a core auxin-regulated developmental pathway that is shared with lateral root formation. The knowledge acquired from adventitious root development opens new perspectives to improve micropropagation by cutting in recalcitrant species, root system architecture of crops such as cereals, and to understand how plants adapted during evolution to the terrestrial environment by producing different post-embryonic root types.

• Keywords
• adventitious root, genetic control, phytohormones, plant development, response to the environment,
• Publication type
• Journal Article MeSH
• Review MeSH

Stevia rebaudiana (Bertoni) is widely studied because of its foliar steviol glycosides. Fructan-type polysaccharides were recently isolated from its roots. Fructans are reserve carbohydrates that have important positive health effects and technological applications in the food industry. The objective of the present study was to isolate and characterize fructo-oligosaccharides (FOSs) from S. rebaudiana roots and in vitro adventitious root cultures and evaluate the potential prebiotic effect of these molecules. The in vitro adventitious root cultures were obtained using a roller bottle system. Chemical analyses (gas chromatography-mass spectrometry, (1)H nuclear magnetic resonance, and off-line electrospray ionization-mass spectrometry) revealed similar chemical properties of FOSs that were obtained from the different sources. The potential prebiotic effects of FOSs that were isolated from S. rebaudiana roots enhanced the growth of both bifidobacteria and lactobacilli, with strains specificity in their fermentation ability.

• Keywords
• Adventitious root cultures, Agar (PubChem CID: 76645041), Ethanol (PubChem CID: 702), Fructo-oligosaccharides, Fructose (PubChem CID: 5984), Glucose (PubChem CID: 5793), Inulin from chicory (PubChem CID: 16219508), Prebiotic potential, Stevia rebaudiana, Sucrose (PubChem CID: 5988), Trifluoroacetic Acid (PubChem CID: 6422), Tween 80 (PubChem CID: 86289060), l-Cysteine Hydrochloride (PubChem CID: 60960), α-Naphthaleneacetic Acid (PubChem CID: 6862),
• MeSH
• Plant Roots cytology   metabolism   MeSH
• Oligosaccharides biosynthesis   MeSH
• Prebiotics * MeSH
• Plant Cells metabolism   MeSH
• Stevia cytology   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Oligosaccharides MeSH
• Prebiotics * MeSH

Adventitious rooting is a post-embryonic developmental program governed by a multitude of endogenous and environmental cues. Auxin, along with other phytohormones, integrates and translates these cues into precise molecular signatures to provide a coherent developmental output. Auxin signaling guides every step of adventitious root (AR) development from the early event of cell reprogramming and identity transitions until emergence. We have previously shown that auxin signaling controls the early events of AR initiation (ARI) by modulating the homeostasis of the negative regulator jasmonate (JA). Although considerable knowledge has been acquired about the role of auxin and JA in ARI, the genetic components acting downstream of JA signaling and the mechanistic basis controlling the interaction between these two hormones are not well understood. Here we provide evidence that COI1-dependent JA signaling controls the expression of DAO1 and its closely related paralog DAO2. In addition, we show that the dao1-1 loss of function mutant produces more ARs than the wild type, probably due to its deficiency in accumulating JA and its bioactive metabolite JA-Ile. Together, our data indicate that DAO1 controls a sensitive feedback circuit that stabilizes the auxin and JA crosstalk during ARI.

• Keywords
• adventitious roots, auxin, auxin oxidation, jasmonates, organogenesis,
• MeSH
• Arabidopsis genetics   metabolism   MeSH
• Cyclopentanes metabolism   MeSH
• Plant Roots genetics   growth & development   MeSH
• Indoleacetic Acids metabolism   MeSH
• Oxidoreductases genetics   metabolism   MeSH
• Oxylipins metabolism   MeSH
• Arabidopsis Proteins genetics   metabolism   MeSH
• Signal Transduction MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cyclopentanes MeSH
• jasmonic acid MeSH Browser
• Indoleacetic Acids MeSH
• Oxidoreductases MeSH
• Oxylipins MeSH
• Arabidopsis Proteins MeSH

Adventitious rooting is a de novo organogenesis process that enables plants to propagate clonally and cope with environmental stresses. Adventitious root initiation (ARI) is controlled by interconnected transcriptional and hormonal networks, but there is little knowledge of the genetic and molecular programs orchestrating these networks. Thus, we have applied genome-wide transcriptome profiling to elucidate the transcriptional reprogramming events preceding ARI. These reprogramming events are associated with the down-regulation of cytokinin (CK) signaling and response genes, which could be triggers for ARI. Interestingly, we found that CK free base (iP, tZ, cZ, and DHZ) content declined during ARI, due to down-regulation of de novo CK biosynthesis and up-regulation of CK inactivation pathways. We also found that MYC2-dependent jasmonate (JA) signaling inhibits ARI by down-regulating the expression of the CYTOKININ OXIDASE/DEHYDROGENASE1 (CKX1) gene. We also demonstrated that JA and CK synergistically activate expression of the transcription factor RELATED to APETALA2.6 LIKE (RAP2.6L), and constitutive expression of this transcription factor strongly inhibits ARI. Collectively, our findings reveal that previously unknown genetic interactions between JA and CK play key roles in ARI.

• Keywords
• Adventitious roots, Arabidopsis, CKX1, MYC2, RAP2.6L, cytokinins, jasmonate, light, vegetative propagation,
• MeSH
• Arabidopsis * genetics   metabolism   MeSH
• Cyclopentanes MeSH
• Plant Roots genetics   metabolism   MeSH
• Oxylipins MeSH
• Arabidopsis Proteins * genetics   metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Transcription Factors genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cyclopentanes MeSH
• jasmonic acid MeSH Browser
• Oxylipins MeSH
• Arabidopsis Proteins * MeSH
• RAP2.6L protein, Arabidopsis MeSH Browser
• Transcription Factors MeSH

Vegetative propagation relies on the capacity of plants to regenerate de novo adventitious roots (ARs), a quantitative trait controlled by the interaction of endogenous factors, such as hormones and environmental cues among which light plays a central role. However, the physiological and molecular components mediating light cues during AR initiation (ARI) remain largely elusive. Here, we explored the role of red light (RL) on ARI in de-rooted Norway spruce seedlings. We combined investigation of hormone metabolism and gene expression analysis to identify potential signaling pathways. We also performed extensive anatomical characterization to investigate ARI at the cellular level. We showed that in contrast to white light, red light promoted ARI likely by reducing jasmonate (JA) and JA-isoleucine biosynthesis and repressing the accumulation of isopentyl-adenine-type cytokinins. We demonstrated that exogenously applied JA and/or CK inhibit ARI in a dose-dependent manner and found that they possibly act in the same pathway. The negative effect of JA on ARI was confirmed at the histological level. We showed that JA represses the early events of ARI. In conclusion, RL promotes ARI by repressing the accumulation of the wound-induced phytohormones JA and CK.

• Keywords
• Picea abies, adventitious roots, auxin, conifers, cytokinins, jasmonate, red light, root development,
• Publication type
• Journal Article MeSH

Flax (Linum usitatissimum L.) is an important crop for the production of oil and fiber. In vitro manipulations of flax are used for genetic improvement and breeding while improvements in adventitious root formation are important for biotechnological programs focused on regeneration and vegetative propagation of genetically valuable plant material. Additionally, flax hypocotyl segments possess outstanding morphogenetic capacity, thus providing a useful model for the investigation of flax developmental processes. Here, we investigated the crosstalk between hydrogen peroxide and auxin with respect to reprogramming flax hypocotyl cells for root morphogenetic development. Exogenous auxin induced the robust formation of adventitious roots from flax hypocotyl segments while the addition of hydrogen peroxide further enhanced this process. The levels of endogenous auxin (indole-3-acetic acid; IAA) were positively correlated with increased root formation in response to exogenous auxin (1-Naphthaleneacetic acid; NAA). Histochemical staining of the hypocotyl segments revealed that hydrogen peroxide and peroxidase, but not superoxide, were positively correlated with root formation. Measurements of antioxidant enzyme activities showed that endogenous levels of hydrogen peroxide were controlled by peroxidases during root formation from hypocotyl segments. In conclusion, hydrogen peroxide positively affected flax adventitious root formation by regulating the endogenous auxin levels. Consequently, this agent can be applied to increase flax regeneration capacity for biotechnological purposes such as improved plant rooting.

• MeSH
• Antioxidants metabolism   MeSH
• Biotechnology MeSH
• Hypocotyl drug effects   growth & development   metabolism   MeSH
• Plant Roots drug effects   growth & development   metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Naphthaleneacetic Acids pharmacology   MeSH
• Flax drug effects   growth & development   metabolism   MeSH
• Hydrogen Peroxide metabolism   pharmacology   MeSH
• Cellular Reprogramming drug effects   MeSH
• Plant Growth Regulators metabolism   pharmacology   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• 1-naphthaleneacetic acid MeSH Browser
• Antioxidants MeSH
• indoleacetic acid MeSH Browser
• Indoleacetic Acids MeSH
• Naphthaleneacetic Acids MeSH
• Hydrogen Peroxide MeSH
• Plant Growth Regulators MeSH

Adventitious root initiation (ARI) is a de novo organogenesis program and a key adaptive trait in plants. Several hormones regulate ARI but the underlying genetic architecture that integrates the hormonal crosstalk governing this process remains largely elusive. In this study, we use genetics, genome editing, transcriptomics, hormone profiling and cell biological approaches to demonstrate a crucial role played by the APETALA2/ETHYLENE RESPONSE FACTOR 115 transcription factor. We demonstrate that ERF115 functions as a repressor of ARI by activating the cytokinin (CK) signaling machinery. We also demonstrate that ERF115 is transcriptionally activated by jasmonate (JA), an oxylipin-derived phytohormone, which represses ARI in NINJA-dependent and independent manners. Our data indicate that NINJA-dependent JA signaling in pericycle cells blocks early events of ARI. Altogether, our results reveal a previously unreported molecular network involving cooperative crosstalk between JA and CK machineries that represses ARI.

• Keywords
• AP2/ERF transcription factors, adventitious rooting, cytokinins, de novo organogenesis, jasmonate,
• MeSH
• Arabidopsis * genetics   metabolism   MeSH
• Cyclopentanes pharmacology   MeSH
• Cytokinins MeSH
• Ethylenes MeSH
• Plant Roots metabolism   MeSH
• Oxylipins pharmacology   MeSH
• Arabidopsis Proteins * genetics   metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Transcription Factors MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cyclopentanes MeSH
• Cytokinins MeSH
• ERF115 protein, Arabidopsis MeSH Browser
• Ethylenes MeSH
• jasmonic acid MeSH Browser
• Oxylipins MeSH
• Arabidopsis Proteins * MeSH
• Transcription Factors MeSH

In Arabidopsis thaliana, canonical auxin-dependent gene regulation is mediated by 23 transcription factors from the AUXIN RESPONSE FACTOR (ARF) family that interact with auxin/indole acetic acid repressors (Aux/IAAs), which themselves form co-receptor complexes with one of six TRANSPORT INHIBITOR1/AUXIN-SIGNALLING F-BOX (TIR1/AFB) proteins. Different combinations of co-receptors drive specific sensing outputs, allowing auxin to control a myriad of processes. ARF6 and ARF8 are positive regulators of adventitious root initiation upstream of jasmonate, but the exact auxin co-receptor complexes controlling the transcriptional activity of these proteins has remained unknown. Here, using loss-of-function mutants we show that three Aux/IAA genes, IAA6, IAA9, and IAA17, act additively in the control of adventitious root (AR) initiation. These three IAA proteins interact with ARF6 and/or ARF8 and likely repress their activity in AR development. We show that TIR1 and AFB2 are positive regulators of AR formation and TIR1 plays a dual role in the control of jasmonic acid (JA) biosynthesis and conjugation, as several JA biosynthesis genes are up-regulated in the tir1-1 mutant. These results lead us to propose that in the presence of auxin, TIR1 and AFB2 form specific sensing complexes with IAA6, IAA9, and/or IAA17 to modulate JA homeostasis and control AR initiation.

• Keywords
• Arabidopsis, AuxIAA, TIR1/AFB, adventitious roots, jasmonate,
• MeSH
• Arabidopsis cytology   genetics   growth & development   metabolism   MeSH
• F-Box Proteins metabolism   MeSH
• Hypocotyl metabolism   MeSH
• Plant Roots growth & development   MeSH
• Indoleacetic Acids metabolism   MeSH
• Arabidopsis Proteins metabolism   MeSH
• Receptors, Cell Surface metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Signal Transduction * MeSH
• Protein Stability MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• AFB2 protein, Arabidopsis MeSH Browser
• F-Box Proteins MeSH
• indoleacetic acid MeSH Browser
• Indoleacetic Acids MeSH
• Arabidopsis Proteins MeSH
• Receptors, Cell Surface MeSH
• TIR1 protein, Arabidopsis MeSH Browser

A supernodulating and Nts (nitrate-tolerant symbiosis) symbiotic mutation of pea (Pisum sativum L.) line RisfixC was found to retain its expression in the distant genetic background of pea lines Afghanistan L1268, Zhodino E900, and cv. Arvika. This finding allowed for reliable scoring for the trait in mapping crosses. The RisfixC mutation was localized 8.2cM apart from SYM2 and cosegregated with molecular markers for SYM2-NOD3 region Psc923 and OA-1. Grafting experiments showed that supernodulation is root-determined, consistently with mutants in the NOD3 locus. Therefore, the mutation of RisfixC can be localized in gene NOD3. Like in other published nod3 alleles, the RisfixC mutation determines supernodulation when it is expressed in the root but not in the shoot. Supernodulated adventitious roots that are spontaneously formed in the wild-type scions on mutant rootstocks indicate that the descending systemic signal, which is inhibitory to nodule formation, is absent in this type of chimeric plants. Since the descending signal production in the wild-type shoot reflects the presence of the ascending root signal, the nod3-associated lesion must be located in the beginning of the systemic circuit regulating nodule number.

• Publication type
• Journal Article MeSH

BACKGROUND AND AIMS: Root sprouting (RS), i.e. the ability to form adventitious buds on roots, is an important form of clonal growth in a number of species, and serves as both a survival strategy and a means of spatial expansion, particularly in plants growing in severely and recurrently disturbed habitats. Occurrence and/or success of plants in severely and recurrently disturbed habitats are determined by two components, namely the ability to produce adventitious buds on roots and the vigour of their production. As mechanisms behind different magnitudes of RS remain unclear, our study investigates: (1) whether the presence or absence of specific tissues in roots can promote or limit RS; and (2) whether there is some relationship between RS ability, RS vigour and species niche. METHODS: We studied RS ability together with RS vigour in 182 Central European herbaceous species under controlled experimental conditions. We used phylogenetic logistic regressions to model the presence of RS, RS vigour, the relationship between RS and anatomical traits and the relationship between RS and parameters of species niches. KEY RESULTS: A quarter of herbs examined were able to produce adventitious buds on roots. They were characterized by their preference for open dry habitats, the presence of secondary root thickening and the occurrence of sclerified cortical cells in roots. Root sprouting vigour was not associated with any specific anatomical pattern, but was correlated with the environmental niches of different species, indicating that preferred disturbed and dry habitats might represent a selection pressure for more vigorous root sprouters than undisturbed and wet habitats. CONCLUSIONS: Our study shows that sprouting from roots is quite common in temperate dicotyledonous herbs. Two components of RS - ability and vigour - should be considered separately in future studies. We would also like to focus more attention on RS in herbs from other regions as well as on external forces and internal mechanisms regulating evolution and the functions of RS in both disturbed and undisturbed habitats.

• Keywords
• Adventitious bud, Ellenberg indicator values, anatomical features, disturbance regime, eudicot herbs, niche preference, root sprouting vigour,
• MeSH
• Ecosystem MeSH
• Phylogeny MeSH
• Plant Roots * MeSH
• Magnoliopsida * MeSH
• Plants MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH