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Adventitious root (AR) formation in excised plant parts is a bottleneck for survival of isolated plant fragments. AR formation plays an important ecological role and is a critical process in cuttings for the clonal propagation of horticultural and forestry crops. Therefore, understanding the regulation of excision-induced AR formation is essential for sustainable and efficient utilization of plant genetic resources. Recent studies of plant transcriptomes, proteomes and metabolomes, and the use of mutants and transgenic lines have significantly expanded our knowledge concerning excision-induced AR formation. Here, we integrate new findings regarding AR formation in the cuttings of diverse plant species. These findings support a new system-oriented concept that the phytohormone-controlled reprogramming and differentiation of particular responsive cells in the cutting base interacts with a co-ordinated reallocation of plant resources within the whole cutting to initiate and drive excision-induced AR formation. Master control by auxin involves diverse transcription factors and mechanically sensitive microtubules, and is further linked to ethylene, jasmonates, cytokinins and strigolactones. Hormone functions seem to involve epigenetic factors and cross-talk with metabolic signals, reflecting the nutrient status of the cutting. By affecting distinct physiological units in the cutting, environmental factors such as light, nitrogen and iron modify the implementation of the genetically controlled root developmental programme. Despite advanced research in the last decade, important questions remain open for future investigations on excision-induced AR formation. These concern the distinct roles and interactions of certain molecular, hormonal and metabolic factors, as well as the functional equilibrium of the whole cutting in a complex environment. Starting from model plants, cell type- and phase-specific monitoring of controlling processes and modification of gene expression are promising methodologies that, however, need to be integrated into a coherent model of the whole system, before research findings can be translated to other crops.

Populus spp. are among the most economically important species worldwide. These trees are used not only for wood and fiber production, but also in the rehabilitation of degraded lands. Since they are clonally propagated, the ability of stem cuttings to form adventitious roots is a critical point for plant establishment and survival in the field, and consequently for the forest industry. Adventitious rooting in different Populus clones has been an agronomic trait targeted in breeding programs for many years, and many factors have been identified that affect this quantitative trait. A huge variation in the rooting capacity has been observed among the species in the Populus genus, and the responses to some of the factors affecting this trait have been shown to be genotype-dependent. This review analyses similarities and differences between results obtained from studies examining the role of internal and external factors affecting rooting of Populus species cuttings. Since rooting is the most important requirement for stand establishment in clonally propagated species, understanding the physiological and genetic mechanisms that promote this trait is essential for successful commercial deployment.

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.

Developmental and environmental signaling networks often converge during plant growth in response to changing conditions. Stress-induced hormones, such as jasmonates (JAs), can influence growth by crosstalk with other signals like brassinosteroids (BRs) and ethylene (ET). Nevertheless, it is unclear how avoidance of an abiotic stress triggers local changes in development as a response. It is known that stress hormones like JAs/ET and BRs can regulate the division rate of cells from the first asymmetric cell divisions (ACDs) in meristems, suggesting that stem cell activation may take part in developmental changes as a stress-avoidance-induced response. The root system is a prime responder to stress conditions in soil. Together with the primary root and lateral roots (LRs), adventitious roots (ARs) are necessary for survival in numerous plant species. AR and LR formation is affected by soil pollution, causing substantial root architecture changes by either depressing or enhancing rooting as a stress avoidance/survival response. Here, a detailed overview of the crosstalk between JAs, ET, BRs, and the stress mediator nitric oxide (NO) in auxin-induced AR and LR formation, with/without cadmium and arsenic, is presented. Interactions essential in achieving a balance between growth and adaptation to Cd and As soil pollution to ensure survival are reviewed here in the model species Arabidopsis and rice.

Abstract Magnolia biondii Pamp is an important ornamental tree species widely grown and used as a rootstock in the propagation of different Magnolia varieties. In the current studies, anatomical, physiological and endogenous hormones were studied to check the effect of IBA 750 mg/L on the adventitious rooting and to provide theoretical and technical support for the propagation of Magnolia biondii Pamp through stem cuttings. Two thousand stem cuttings were prepared and divided into two groups i.e., IBA treated cuttings and water control. For the evaluation of antioxidant enzyme activities, and endogenous hormones levels, samples were collected on the day of planting and each 5th day and further steps were carried out in the laboratory according to the protocols and proper precautions. For the anatomical observations, samples were collected on the 13th, 15th, and 17th day for IBA treated cuttings while 21st, 23rd, and 25th day for control. Collected samples were preserved in the FAA solution and further observations were carried out in the laboratory. Anatomical observations showed that it took 13 days for the differentiation of root primordia to the appearance of young adventitious roots in IBA treated cuttings, while it took 21 days to develop primordia in the control. Antioxidant enzyme activities involved in ROS were significantly higher in the IBA treated cuttings compared to control. POD showed a peak on the 13th day before the emergence of roots in IBA treated cuttings while it showed a peak on the 21st day in the control. PPO showed a peak on the 21st day in the IBA treated cuttings while it showed a peak on the 29th day in the control. SOD showed a peak on the 17th day in IBA treated cuttings, while it showed a peak on the 25th day in the control. Exogenous application of IBA enhanced the endogenous IAA and GA3 levels compared to CK, while it reduced the levels of ABA continuously at the time of rooting and then increased gradually. Inclusively, our study suggests that IBA 750 mg/L is efficient for the rooting of Magnolia biondii Pamp cuttings, as it enhanced the process of antioxidant enzyme activities, endogenous hormones levels and reduced the time of root formation which is evident from the anatomical observations. Resumo Magnolia biondii Pamp é uma importante espécie de árvore ornamental muito cultivada e utilizada como porta-enxerto na propagação de diferentes variedades de Magnolia. Nos estudos atuais, hormônios anatômicos, fisiológicos e endógenos foram estudados para verificar o efeito do AIB na dose de 750 mg / L no enraizamento adventício e fornecer suporte teórico e técnico para a propagação de M. biondii Pamp por meio de estacas. Duas mil estacas foram preparadas e divididas em dois grupos, ou seja, tratadas com AIB e controle de água. Para a avaliação das atividades das enzimas antioxidantes e dos níveis de hormônios endógenos, as amostras foram coletadas no dia do plantio e a cada 5 dias, enquanto as demais etapas foram realizadas em laboratório de acordo com os protocolos e os devidos cuidados. Para as observações anatômicas, as amostras foram coletadas no 13º, 15º e 17º dias para estacas tratadas com AIB e no 21º, 23º e 25º dias para o controle. As amostras coletadas foram preservadas em solução FAA, e outras observações foram realizadas em laboratório. Observações anatômicas mostraram a necessidade de 13 dias para a diferenciação dos primórdios radiculares até o aparecimento de raízes adventícias jovens em estacas tratadas com AIB e de 21 dias para o desenvolvimento dos primórdios no controle. As atividades das enzimas antioxidantes envolvidas nas ROS foram significativamente maiores nas estacas tratadas com AIB em comparação com o controle. A POD apresentou pico no 13º dia antes da emergência das raízes nas estacas tratadas com AIB, enquanto no 21º dia apresentou pico no controle. A PPO teve pico no 21º dia nas estacas tratadas com AIB e no 29º dia no controle. A SOD apresentou pico no 17º dia nas estacas tratadas com AIB e no 25º dia no controle. A aplicação exógena de AIB aumentou os níveis endógenos de IAA e GA3 em relação ao controle, enquanto reduziu os níveis de ABA continuamente no momento do enraizamento e, em seguida, aumentou gradativamente. Inclusive, nosso estudo sugere que o AIB na dose de 750 mg / L é eficiente para o enraizamento de estacas de M. biondii Pamp, visto que potencializou o processo de atividades de enzimas antioxidantes e os níveis de hormônios endógenos, além de reduzir o tempo de formação de raízes, o que fica evidente nas observações anatômicas.

Adventitious root (AR) formation in cuttings is a multiphase developmental process, resulting from wounding at the cutting site and isolation from the resource and signal network of the whole plant. Though, promotive effects of auxins are widely used for clonal plant propagation, the regulation and function of plant hormones and their intricate signaling networks during AR formation in cuttings are poorly understood. In this focused review, we discuss our recent publications on the involvement of polar auxin transport (PAT) and transcriptional regulation of auxin and ethylene action during AR formation in petunia cuttings in a broad context. Integrating new findings on cuttings of other plant species and general models on plant hormone networks, a model on the regulation and function of auxin, ethylene, and jasmonate in AR formation of cuttings is presented. PAT and cutting off from the basipetal auxin drain are considered as initial principles generating early accumulation of IAA in the rooting zone. This is expected to trigger a self-regulatory process of auxin canalization and maximization to responding target cells, there inducing the program of AR formation. Regulation of auxin homeostasis via auxin influx and efflux carriers, GH3 proteins and peroxidases, of flavonoid metabolism, and of auxin signaling via AUX/IAA proteins, TOPLESS, ARFs, and SAUR-like proteins are postulated as key processes determining the different phases of AR formation. NO and H2O2 mediate auxin signaling via the cGMP and MAPK cascades. Transcription factors of the GRAS-, AP2/ERF-, and WOX-families link auxin signaling to cell fate specification. Cyclin-mediated governing of the cell cycle, modifications of sugar metabolism and microtubule and cell wall remodeling are considered as important implementation processes of auxin function. Induced by the initial wounding and other abiotic stress factors, up-regulation of ethylene biosynthesis, and signaling via ERFs and early accumulation of jasmonic acid stimulate AR formation, while both pathways are linked to auxin. Future research on the function of candidate genes should consider their tissue-specific role and regulation by environmental factors. Furthermore, the whole cutting should be regarded as a system of physiological units with diverse functions specifically responding to the environment and determining the rooting response.

The formation of adventitious roots (ARs) is an ecologically and economically important developmental process in plants. The evolution of AR systems is an important way for plants to cope with various environmental stresses. This review focuses on identified genes that have known to regulate the induction and initiation of ARs and offers an analysis of this process at the molecular level. The critical genes involved in adventitious rooting are the auxin signaling-responsive genes, including the AUXIN RESPONSE FACTOR ( ARF ) and the LATERAL ORGAN BOUNDARIES-DOMAIN ( LOB ) gene families, and genes associated with auxin transport and homeostasis, the quiescent center (QC) maintenance, and the root apical meristem (RAM) initiation. Several genes involved in cell wall modulation are also known to be involved in the regulation of adventitious rooting. Furthermore, the molecular processes that play roles in the ethylene, cytokinin, and jasmonic acid signaling pathways and their crosstalk modulate the generation of ARs. The crosstalk and interaction among many molecular processes generates complex networks that regulate AR generation.

This study investigated the relationship between internal nitrogen and carbohydrate distribution in chrysanthemum cuttings of two cultivars (‘Puma’, ‘Cassa’) when affected by nitrogen supply to stock plants (0.6, 1.5, or 4.0g N m−2week−1) and different periods (2, 3, or 4 weeks) of dark cold-storage (0.5 or 5°C), and adventitious rooting. Concentrations of total nitrogen (Nt) and nitrate in cuttings and the levels of sugars, starch and fructan in different cutting parts (leaves, upper stem, and basal stem) were studied in relation to subsequent adventitious rooting at natural radiation in a greenhouse. Increasing nitrogen supply resulted in substantially lower starch levels and higher sucrose concentrations in leaves when cuttings were excised. Fructan concentrations were low and decreased with increasing nitrogen levels. Starch completely disappeared from leaves and to a large extent from stems within the shortest storage period. A less pronounced decrease in sugar concentration was observed, particularly in low-nitrogen cuttings and the cuttings of ‘Puma’. The number and length of adventitious roots subsequently formed by unstored and stored cuttings was positively correlated with initial Nt, and to a lesser extent with initial nitrate concentrations in cuttings. Whereas rooting was not limited by pre-rooting concentrations of carbohydrates in the different cutting parts, the generally higher rooting capability of nitrogen-rich cuttings, a stronger nitrogen response of ‘Cassa’, and increased rooting at a particular harvest date, were associated with higher sucrose:starch ratios in leaves at harvest. This reflected an increased assimilate export. By using this characteristic in a linear regression model, total variability of root numbers, ranging from three–35 per cutting, could be predicted to 57% for the unstored and to 40% for all cuttings. Increased basipetal transport of carbohydrates, of nitrogen compounds, and of auxins may be causally involved in these associations.

Background Adventitious roots (ARs) are often necessary for plant survival, and essential for successful micropropagation. In Arabidopsis thaliana dark-grown seedlings AR-formation occurs from the hypocotyl and is enhanced by application of indole-3-butyric acid (IBA) combined with kinetin (Kin). The same IBA + Kin-treatment induces AR-formation in thin cell layers (TCLs). Auxin is the main inducer of AR-formation and xylogenesis in numerous species and experimental systems. Xylogenesis is competitive to AR-formation in Arabidopsis hypocotyls and TCLs. Jasmonates (JAs) negatively affect AR-formation in de-etiolated Arabidopsis seedlings, but positively affect both AR-formation and xylogenesis in tobacco dark-grown IBA + Kin TCLs. In Arabidopsis the interplay between JAs and auxin in AR-formation vs xylogenesis needs investigation. In de-etiolated Arabidopsis seedlings, the Auxin Response Factors ARF6 and ARF8 positively regulate AR-formation and ARF17 negatively affects the process, but their role in xylogenesis is unknown. The cross-talk between auxin and ethylene (ET) is also important for AR-formation and xylogenesis, occurring through EIN3/EIL1 signalling pathway. EIN3/EIL1 is the direct link for JA and ET-signalling. The research investigated JA role on AR-formation and xylogenesis in Arabidopsis dark-grown seedlings and TCLs, and the relationship with ET and auxin. The JA-donor methyl-jasmonate (MeJA), and/or the ET precursor 1-aminocyclopropane-1-carboxylic acid were applied, and the response of mutants in JA-synthesis and -signalling, and ET-signalling investigated. Endogenous levels of auxin, JA and JA-related compounds, and ARF6 , ARF8 and ARF17 expression were monitored. Results MeJA, at 0.01 μM, enhances AR-formation, when combined with IBA + Kin, and the response of the early-JA-biosynthesis mutant dde2–2 and the JA-signalling mutant coi1–16 confirmed this result . JA levels early change during TCL-culture, and JA/JA-Ile is immunolocalized in AR-tips and xylogenic cells. The high AR-response of the late JA-biosynthesis mutant opr3 suggests a positive action also of 12-oxophytodienoic acid on AR-formation . The crosstalk between JA and ET-signalling by EIN3/EIL1 is critical for AR-formation, and involves a competitive modulation of xylogenesis. Xylogenesis is enhanced by a MeJA concentration repressing AR-formation, and is positively related to ARF17 expression. Conclusions The JA concentration-dependent role on AR-formation and xylogenesis, and the interaction with ET opens the way to applications in the micropropagation of recalcitrant species.

Main conclusion NO was involved in H 2 -induced adventitious rooting by regulating the protein and gene expressions of PM H + -ATPase and 14-3-3. Simultaneously, the interaction of PM H + -ATPase and 14-3-3 protein was also involved in this process. Hydrogen gas (H 2 ) and nitric oxide (NO) have been shown to be involved in plant growth and development. The results in this study revealed that NO was involved in H 2 -induced adventitious root formation. Western blot (WB) analysis showed that the protein abundances of plasma membrane H + -ATPase (PM H + -ATPase) and 14-3-3 protein were increased after H 2 , NO, H 2 plus NO treatments, whereas their protein abundances were down regulated when NO scavenger carboxy‐2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide (cPTI O) was added. Moreover, the mRNA abundances of the HA3 and 14-3-3(7) gene as well as the activities of PM H + -ATPase (EC 3.6.1.35) and H + pump were in full agreement with the changes of protein abundance. Phosphorylation of PM H + -ATPase and the interaction of PM H + -ATPase and 14-3-3 protein were detected by co-immunoprecipitation analysis. H 2 and NO significantly up regulated the phosphorylation of PM H + -ATPase and the interaction of PM H + -ATPase and 14-3-3 protein. Conversely, the stimulation of PM H + -ATPase phosphorylation and protein interaction were significantly diminished by cPTIO. Protein interaction activator fusicoccin (FC) and inhibitor adenosine monophosphate (AMP) of PM H + -ATPase and 14-3-3 were used in this study, and the results showed that FC significantly increased the abundances of PM H + -ATPase and 14-3-3, while AMP showed opposite trends. We further proved the critical roles of PM H + -ATPase and 14-3-3 protein interaction in NO–H 2 -induced adventitious root formation. Taken together, our results suggested that NO might be involved in H 2 -induced adventitious rooting by regulating the expression and the interaction of PM H + -ATPase and 14-3-3 protein.