Proteomic insights into adventitious root formation in Larix kaempferi.

The regeneration of adventitious roots (ARF) in excised plant parts is essential for the survival of isolated plant fragments. In this study, we explored the complex mechanisms of ARF in Larix kaempferi by conducting a comprehensive proteomic analysis across three distinct stages: the induction of adventitious root primordia (C1, 0-25 days), the formation of adventitious root primordia (C2, 25-35 days), and the elongation of adventitious roots (C3, 35-45 days). We identified 1976 proteins, with 263 and 156 proteins exhibiting increased abundance in the C2/C1 and C3/C2 transitions, respectively. In contrast, a decrease in the abundance of 106 and 132 proteins suggests a significant demand for metabolic processes during the C2/C1 phase. The abundance of IAA-amino acid hydrolase and S-adenosylmethionine synthase: in the C2/C1 phase, underscoring the role of auxin in adventitious root induction. The decrease in abundance of photosynthesis-related proteins during the C2/C1 phase highlights the significance of initial light conditions in adventitious root induction. Moreover, variation in cell wall synthesis and metabolic proteins between the C2/C1 and C3/C2 stages suggests that cell wall metabolism is integral to adventitious root regeneration. Gene Ontology enrichment analysis revealed pathways related to protein modification enzymes, including deubiquitinases and kinases, which are crucial for modulating protein modifications to promote ARF. Furthermore, the increased abundance of antioxidant enzymes, such as peroxidases and glutathione peroxidases, indicates a potential approach for enhancing ARF by supplementing the culture medium with antioxidants. Our study provides insights into metabolic changes during ARF in L. kaempferi, offering strategies to enhance adventitious root regeneration. These findings have the potential to refine plant propagation techniques and expedite breeding processes. SIGNFICANCE: The main challenge in the asexual reproduction technology of Larix kaempferi lies in adventitious root regeneration (ARF). While numerous studies have concentrated on the efficiency of ARF, proteomic data are currently scarce. In this study, we collected samples from three stages of ARF in L. kaempferi and subsequently performed proteomic analysis. The data generated not only reveal changes in protein abundance but also elucidate key metabolic processes involved in ARF. These insights offer a novel perspective on addressing the challenge of adventurous root regeneration.

Regulation of ginseng adventitious root growth in Panax ginseng by the miR156-targeted PgSPL24-09 transcription factors.

MicroRNA (miRNA) is a class of non-coding endogenous small-molecule, single-stranded RNAs, and it is involved in post-transcriptional gene expression regulation in plants and plays an important role in plant growth and development. Among them, miRNA156 regulates members of target SPL gene family and thus participates in plant growth and development, hormonal response and adversity stress. However, it has not been reported in ginseng. In this study, based on the previous analysis of the SPL gene family, the age-related and stably expressed SPL gene PgSPL24-09 was obtained in roots. The binding site of miRNA156 to this gene was analyzed using target gene prediction tools, and the interactions between miRNA156 and PgSPL24-09 gene were verified by dual luciferase reporter gene assay and RT-qPCR. At the same time, miRNA156 silencing vector and overexpression vector were constructed and transformed into ginseng adventitious roots and Arabidopsis thaliana to analyze the molecular mechanism of miRNA156-SPL module in regulating the growth of ginseng adventitious roots. This study provides a theoretical basis for the in-depth study of the molecular role of miRNAs in ginseng growth, and also lays the foundation for the study of the role of miRNA156-SPL module in regulating the growth and development of ginseng.

Transcriptome Reveals the Regulation of Exogenous Auxin Inducing Rooting of Non-Rooting Callus of Tea Cuttings.

Cuttage is the main propagation method of tea plant cultivars in China. However, some tea softwood cuttings just form an expanded and loose callus at the base, without adventitious root (AR) formation during the propagation period. Meanwhile, exogenous auxin could promote the AR formation of tea plant cuttings, but the regulation mechanism has not yet explained clearly. We conducted this study to elucidate the regulatory mechanism of exogenous auxin-induced adventitious root (AR) formation of such cuttings. The transcriptional expression profile of non-rooting tea calluses in response to exogenous IBA and NAA was analyzed using ONT RNA Seq technology. In total, 56,178 differentially expressed genes (DEGs) were detected, and most of genes were significantly differentially expressed after 12 h of exogenous auxin treatment. Among these DEGs, we further identified 80 DEGs involved in the auxin induction pathway and AR formation. Specifically, 14 auxin respective genes (ARFs, GH3s, and AUX/IAAs), 3 auxin transporters (AUX22), 19 auxin synthesis- and homeostasis-related genes (cytochrome P450 (CYP450) and calmodulin-like protein (CML) genes), and 44 transcription factors (LOB domain-containing protein (LBDs), SCARECROW-LIKE (SCL), zinc finger protein, WRKY, MYB, and NAC) were identified from these DEGs. Moreover, we found most of these DEGs were highly up-regulated at some stage before AR formation, suggesting that they may play a potential role in the AR formation of tea plant cuttings. In summary, this study will provide a theoretical foundation to deepen our understanding of the molecular mechanism of AR formation in tea cuttings induced by auxin during propagation time.

The auxin-responsive CsSPL9-CsGH3.4 module finely regulates auxin levels to suppress the development of adventitious roots in tea (Camellia sinensis).

The cutting technique is extensively used in tea breeding, with key emphasis on promoting the growth of adventitious roots (ARs). Despite its importance in tea cultivation, the mechanisms underlying AR development in tea remain unclear. In this study, we demonstrated the essential role of auxins in the initiation and progression of AR and established that the application of exogenous 1-naphthaleneacetic acid-enhanced AR formation in tissue-cultured seedlings and cuttings. Then, we found that the auxin-responsive transcription factor CsSPL9 acted as a negative regulator of AR development by reducing the levels of free indole-3-acetic acid (IAA) in tea plants. Furthermore, we identified CsGH3.4 as a downstream target of CsSPL9, which was activated by direct binding to its promoter. CsGH3.4 also inhibited AR development and maintained low levels of free IAA. Thus, these results revealed the inhibitory effect of the auxin-responsive CsSPL9-CsGH3.4 module on AR development by reducing free IAA levels in tea. These findings have significant theoretical and practical value for enhancing tea breeding practices.

PoARRO-1 regulates adventitious rooting through interaction with PoIAA27b in Paeonia ostii.

Adventitious root (AR) formation is a limiting factor in the vegetative propagation of tree peony (Paeonia suffruticosa Andr.). PoARRO-1, which encodes an auxin oxidase involved in AR formation, plays a role in the root development of P. ostii, but its associated molecular regulatory mechanisms are not yet understood. In this study, we examined the role of PoARRO-1 in AR formation in P. ostii. The overexpression of PoARRO-1 in P. ostii test-tube plantlets led to a notable enhancement in both the rooting rate and the average number of ARs in vitro, as well as increased activities of peroxidase (POD), superoxide dismutase (SOD), and indoleacetic acid oxidase (IAAO). PoARRO-1 was involved in the conversion of IAA-Asp and IAA-Glu to OxIAA and promoted IAA oxidation. RNA sequencing analysis revealed that PoARRO-1 overexpression led to upregulation of enzyme activity, auxin metabolism related genes. Further analyses showed that PoARRO-1 interacted with the 1-175 aa position of PoIAA27b to regulate the formation of ARs. We therefore propose that PoARRO-1 interacts with PoIAA27b to promote AR formation, and it may be useful targets for enhancing the in vitro propagation of P. ostii.

Cucumber JASMONATE ZIM-DOMAIN 6 interaction with transcription factor MYB6 impairs waterlogging-triggered adventitious rooting.

Waterlogging is a serious abiotic stress that drastically decreases crop productivity by damaging the root system. Jasmonic acid (JA) inhibits waterlogging-induced adventitious root (AR) formation in cucumber (Cucumis sativus L.). However, we still lack a profound mechanistic understanding of how JA governs AR formation under waterlogging stress. JAZ (JASMONATE ZIM-DOMAIN) proteins are responsible for repressing JA signaling in a transcriptional manner. In this study, we showed that overexpressing CsJAZ8 inhibited the formation of ARs triggered by waterlogging. Molecular analyses revealed that CsJAZ8 inhibited the activation of the R2R3-MYB transcription factor CsMYB6 via direct interaction. Additionally, silencing of CsMYB6 negatively impacted AR formation under waterlogging stress, as CsMYB6 could directly bind to the promoters of 1-aminocyclopropane-1-carboxylate oxidase2 gene CsACO2 and gibberellin 20-oxidases gene CsGA20ox2, facilitating the transcription of these genes. The overexpression of CsACO2 and CsGA20ox2 led to increased levels of ethylene and gibberellin, which facilitated AR formation under waterlogging conditions. On the contrary, silencing these genes resulted in contrasting phenotypes of AR formation. These results highlight that the transcriptional cascade of CsJAZ8 and CsMYB6 plays a critical role in regulating hormonal-mediated cucumber waterlogging-triggered AR formation by inhibiting ethylene and gibberellin accumulation. We anticipate that our findings will provide insights into the molecular mechanisms that drive the emergence of AR in cucumber plants under waterlogging stress.

Arinole, a novel auxin-stimulating benzoxazole, affects root growth and promotes adventitious root formation.

The triple response phenotype is characteristic for seedlings treated with the phytohormone ethylene or its direct precursor 1-aminocyclopropane-carboxylic acid and is often employed to find novel chemical tools to probe ethylene responses. We identified a benzoxazole-urea derivative (B2) partially mimicking ethylene effects in a triple response bioassay. A thorough phenotypic analysis demonstrated that B2 and its closest analogue arinole (ARI) induced phenotypic responses reminiscent of seedlings with elevated levels of auxin, including impaired hook development and inhibition of seedling growth. Specifically, ARI reduced longitudinal cell elongation in roots, while promoting cell division. In contrast to other natural or synthetic auxins, ARI mostly acts as an inducer of adventitious root development, with only limited effects on lateral root development. Quantification of free auxins and auxin biosynthetic precursors as well as auxin-related gene expression demonstrated that ARI boosts global auxin levels. In addition, analyses of auxin reporter lines and mutants, besides pharmacological assays with auxin-related inhibitors, confirmed that ARI effects are facilitated by TRYPTOPHAN AMINOTRANSFERASE1 (TAA1)-mediated auxin synthesis. ARI treatment resulted in AR formation in an array of species, including Arabidopsis, pea, tomato, poplar, and lavender, a desirable trait in both agriculture and horticulture.

Raffinose catabolism enhances maize waterlogging tolerance by stimulating adventitious root growth and development.

Raffinose mitigates plant heat-, drought- and cold- stresses; however, whether raffinose contributes to plant waterlogging tolerance is unknown. The maize zmrafs-1 mutant seedlings lacking raffinose, generate fewer and shorter adventitious root (AR) and are more sensitive to waterlogging stress, while overexpression of ZmRAFS increases raffinose content, stimulates AR formation, and enhances the waterlogging tolerance of maize seedlings. Transcriptome analysis of NS (Null segregant) seedlings compared with that of zmrafs-1, particularly when waterlogged, revealed that the expression of genes related to galactose metabolism and the auxin biosynthetic pathway were upregulated by raffinose. Additionally, Indole-3-acetic acid (IAA) amounts significantly decreased or increased in zmrafs-1 or ZmRAFS-overexpressing seedlings, respectively. Inhibition of the hydrolysis of raffinose by DGJ (1-deoxygalactonojirimycin) decreased the waterlogging tolerance of maize seedlings, decreased the expression of genes encoding proteins related to auxin transport-related genes as well as the IAA level in the seedlings, suggesting that the hydrolysis of raffinose is necessary for maize waterlogging tolerance. These data demonstrate that raffinose catabolism stimulates adventitious root formation via auxin signaling pathway to enhance maize waterlogging tolerance.

3,5-DCQA as a Major Molecule in MeJA-Treated Dendropanax morbifera Adventitious Root to Promote Anti-Lung Cancer and Anti-Inflammatory Activities.

(1) Background: Phytochemicals are crucial antioxidants that play a significant role in preventing cancer. (2) Methods: We explored the use of methyl jasmonate (MeJA) in the in vitro cultivation of D. morbifera adventitious roots (DMAR) and evaluated its impact on secondary metabolite production in DMAR, optimizing concentration and exposure time for cost-effectiveness. We also assessed its anti-inflammatory and anti-lung cancer activities and related gene expression levels. (3) Results: MeJA treatment significantly increased the production of the phenolic compound 3,5-Di-caffeoylquinic acid (3,5-DCQA). The maximum 3,5-DCQA production was achieved with a MeJA treatment at 40 µM for 36 h. MeJA-DMARE displayed exceptional anti-inflammatory activity by inhibiting the production of nitric oxide (NO) and reactive oxygen species (ROS) in LPS-induced RAW 264.7 cells. Moreover, it downregulated the mRNA expression of key inflammation-related cytokines. Additionally, MeJA-DMARE exhibited anti-lung cancer activity by promoting ROS production in A549 lung cancer cells and inhibiting its migration. It also modulated apoptosis in lung cancer cells via the Bcl-2 and p38 MAPK pathways. (4) Conclusions: MeJA-treated DMARE with increased 3,5-DCQA production holds significant promise as a sustainable and novel material for pharmaceutical applications thanks to its potent antioxidant, anti-inflammatory, and anti-lung cancer properties.

A Small Auxin-Up RNA Gene, IbSAUR36, Regulates Adventitious Root Development in Transgenic Sweet Potato.

Small auxin-upregulated RNAs (SAURs), as the largest family of early auxin-responsive genes, play important roles in plant growth and development processes, such as auxin signaling and transport, hypocotyl development, and tolerance to environmental stresses. However, the functions of few SAUR genes are known in the root development of sweet potatoes. In this study, an IbSAUR36 gene was cloned and functionally analyzed. The IbSAUR36 protein was localized to the nucleus and plasma membrane. The transcriptional level of this gene was significantly higher in the pencil root and leaf.This gene was strongly induced by indole-3-acetic acid (IAA), but it was downregulated under methyl-jasmonate(MeJA) treatment. The promoter of IbSAUR36 contained the core cis-elements for phytohormone responsiveness. Promoter ß-glucuronidase (GUS) analysis in Arabidopsis showed that IbSAUR36 is highly expressed in the young tissues of plants, such as young leaves, roots, and buds. IbSAUR36-overexpressing sweet potato roots were obtained by an efficient Agrobacterium rhizogenes-mediated root transgenic system. We demonstrated that overexpression of IbSAUR36 promoted the accumulation of IAA, upregulated the genes encoding IAA synthesis and its signaling pathways, and downregulated the genes encoding lignin synthesis and JA signaling pathways. Taken together, these results show that IbSAUR36 plays an important role in adventitious root (AR) development by regulating IAA signaling, lignin synthesis, and JA signaling pathways in transgenic sweet potatoes.

Integrating histology and phytohormone/metabolite profiling to understand rooting in yellow camellia cuttings.

Vegetative propagation through cutting is a widely used clonal approach for maintaining desired genotypes. However, some woody species have difficulty forming adventitious roots (ARs) with this approach, including yellow camellia (YC) C. nitidissima. Yellow camellias, prized for their ornamental value and potential health benefits in tea, remain difficult to propagate clonally due to this rooting recalcitrance. As part of the efforts to understand YC cuttings' recalcitrance, we conducted a detailed investigation into AR formation in yellow camellia cuttings via histology and endogenous phytohormone dynamics during this process. We also compared YC endogenous phytohormone and metabolite phytohormone profiles with those of easy-to-root poplar and willow cuttings. Our results indicate that the induction of ARs in YC cuttings is achievable through auxin treatment, and YC ARs are initiated from cambial derivatives and develop a vascular system connected with that of the stem. During AR induction, endogenous hormones showed a dynamic profile, with IAA continuing to increase starting 9 days after auxin induction. JA, JA-Ile, and OPDA showed a similar trend as IAA but decreased by the 45th day. Cytokinin first decreased to its lowest level by the 18th day and then increased. SA largely exhibited an increasing trend with a drop on the 36th day, while ABA first increased to its peak level by the 18th day and then decreased. Compared to poplar, YC cuttings had a low level of IAA, IAA-Asp, and OPDA, and a high level of cytokinin and SA. Metabolite profiling highlighted significant down-accumulation of compounds associated with AR formation in yellow camellias, such as citric and ascorbic acid, fructose, sucrose, flavonoids, and phenolic acid derivatives. Our study reveals the unfavorable endogenous hormone and metabolite profiles underlying the rooting recalcitrance of YC cuttings, providing valuable knowledge for addressing this challenge in clonal propagation.

The Slow Growth of Adventitious Roots in Tetraploid Hybrid Poplar (Populus simonii × P. nigra var. italica) May Be Caused by Endogenous Hormone-Mediated Meristem Shortening.

Polyploidization produces abundant phenotypic variation. Little is currently known about adventitious root (AR) development variation due to polyploidization. In this study, we analyzed the morphological, cytological, and physiological variations in AR development between tetraploid and diploid Populus plants during in vitro rooting culture. Compared to the diploids, the AR formation times and rooting rates of the tetraploids' stem explants had non-significant changes. However, the tetraploid ARs exhibited significantly slower elongation growth than the diploid ARs. Cytological observation showed that the tetraploid ARs were characterized by shorter root meristems and reduced meristem cell numbers, suggesting the reasons for the slow AR elongation. Analysis of hormones and related metabolites during AR development demonstrated that the total auxin, cytokinin, and jasmonic acid contents were significantly lower in the tetraploid ARs than in those of the diploids, and that the ratio of total auxins to total CKs at 0 h of AR development was also lower in the tetraploids than in the diploids, whereas the total salicylic acid content of the tetraploids was consistently higher than that of the diploids. qPCR analysis showed that the expression levels of several hormone signaling and cell division-related genes in the tetraploid ARs significantly differed from those in the diploids. In conclusion, the slow elongation of the tetraploid ARs may be caused by the endogenous hormone-mediated meristem shortening. Our findings enhance the understanding of polyploidization-induced variation in AR development of forest trees.

Systematic identification and functional analysis of root meristem growth factors (RGFs) reveals role of PgRGF1 in modulation of root development and ginsenoside production in Panax ginseng.

Panax ginseng C.A. Mey., known for its medicinal and dietary supplement properties, primarily contains pharmacologically active ginsenosides. However, the regulatory mechanisms linking ginseng root development with ginsenoside biosynthesis are still unclear. Root meristem growth factors (RGFs) are crucial for regulating plant root growth. In our study, we identified five ginseng RGF peptide sequences from the ginseng genome and transcriptome libraries. We treated Arabidopsis and ginseng adventitious roots with exogenous Panax ginseng RGFs (PgRGFs) to assess their activities. Our results demonstrate that PgRGF1 influences gravitropic responses and reduces lateral root formation in Arabidopsis. PgRGF1 has been found to restrict the number and length of ginseng adventitious root branches in ginseng. Given the medicinal properties of ginseng, We determined the ginsenoside content and performed transcriptomic analysis of PgRGF1-treated ginseng adventitious roots. Specifically, the total ginsenoside content in ginseng adventitious roots decreased by 19.98 % and 63.71 % following treatments with 1 µM and 10 µM PgRGF1, respectively, compared to the control. The results revealed that PgRGF1 affects the accumulation of ginsenosides by regulating the expression of genes associated with auxin transportation and ginsenoside biosynthesis. These findings suggest that PgRGF1, as a peptide hormone regulator in ginseng, can modulate adventitious root growth and ginsenoside accumulation.

Adventitious rooting in response to long-term cold: a possible mechanism of clonal growth in alpine perennials.

Arctic alpine species experience extended periods of cold and unpredictable conditions during flowering. Thus, often, alpine plants use both sexual and asexual means of reproduction to maximize fitness and ensure reproductive success. We used the arctic alpine perennial Arabis alpina to explore the role of prolonged cold exposure on adventitious rooting. We exposed plants to 4°C for different durations and scored the presence of adventitious roots on the main stem and axillary branches. Our physiological studies demonstrated the presence of adventitious roots after 21 weeks at 4°C saturating the effect of cold on this process. Notably, adventitious roots on the main stem developing in specific internodes allowed us to identify the gene regulatory network involved in the formation of adventitious roots in cold using transcriptomics. These data and histological studies indicated that adventitious roots in A. alpina stems initiate during cold exposure and emerge after plants experience growth promoting conditions. While the initiation of adventitious root was not associated with changes of DR5 auxin response and free endogenous auxin level in the stems, the emergence of the adventitious root primordia was. Using the transcriptomic data, we discerned the sequential hormone responses occurring in various stages of adventitious root formation and identified supplementary pathways putatively involved in adventitious root emergence, such as glucosinolate metabolism. Together, our results highlight the role of low temperature during clonal growth in alpine plants and provide insights on the molecular mechanisms involved at distinct stages of adventitious rooting.

PagMYB180 regulates adventitious rooting via a ROS/PCD-dependent pathway in poplar.

The formation of adventitious roots (AR) is an essential step in the vegetative propagation of economically woody species. Reactive oxygen species (ROS) function as signaling molecules in regulating root growth and development. Here, we identified an R2R3-MYB transcription factor PagMYB180 as a regulator of AR formation in hybrid poplar (Populus alba × Populus glandulosa). PagMYB180 was specifically expressed in the vascular tissues of poplar roots, stems and leaves, and its protein was localized in the nucleus and acted as a transcriptional repressor. Both dominant repression and overexpression of PagMYB180 resulted in a significant reduction of AR quantity, a substantial increase of AR length, and an elevation of both the quantity and length of lateral roots (LR) compared to the wild type (WT) plants. Furthermore, PagMYB180 regulates programmed cell death (PCD) in root cortex cells, which is associated with elevated levels of ROS. Transcriptome and reverse transcription-quantitative PCR (RT-qPCR) analyses revealed that a series of differentially expressed genes are related to ROS, PCD and ethylene synthesis. Taken together, these results suggest that PagMYB180 may regulate AR development via a ROS/PCD-dependent pathway in poplar.

Ocimum kilimandscharicum 4CL11 negatively regulates adventitious root development via accumulation of flavonoid glycosides.

4-Coumarate-CoA Ligase (4CL) is an important enzyme in the phenylpropanoid biosynthesis pathway. Multiple 4CLs are identified in Ocimum species; however, their in planta functions remain enigmatic. In this study, we independently overexpressed three Ok4CL isoforms from Ocimum kilimandscharicum (Ok4CL7, -11, and -15) in Nicotiana benthamiana. Interestingly, Ok4CL11 overexpression (OE) caused a rootless or reduced root growth phenotype, whereas overexpression of Ok4CL15 produced normal adventitious root (AR) growth. Ok4CL11 overexpression in N. benthamiana resulted in upregulation of genes involved in flavonoid biosynthesis and associated glycosyltransferases accompanied by accumulation of specific flavonoid-glycosides (kaempferol-3-rhamnoside, kaempferol-3,7-O-bis-alpha-l-rhamnoside [K3,7R], and quercetin-3-O-rutinoside) that possibly reduced auxin levels in plants, and such effects were not seen for Ok4CL7 and -15. Docking analysis suggested that auxin transporters (PINs/LAXs) have higher binding affinity to these specific flavonoid-glycosides, and thus could disrupt auxin transport/signaling, which cumulatively resulted in a rootless phenotype. Reduced auxin levels, increased K3,7R in the middle and basal stem sections, and grafting experiments (intra and inter-species) indicated a disruption of auxin transport by K3,7R and its negative effect on AR development. Supplementation of flavonoids and the specific glycosides accumulated by Ok4CL11-OE to the wild-type N. benthamiana explants delayed the AR emergence and also inhibited AR growth. While overexpression of all three Ok4CLs increased lignin accumulation, flavonoids, and their specific glycosides were accumulated only in Ok4CL11-OE lines. In summary, our study reveals unique indirect function of Ok4CL11 to increase specific flavonoids and their glycosides, which are negative regulators of root growth, likely involved in inhibition of auxin transport and signaling.

NnARF17 and NnARF18 from lotus promote root formation and modulate stress tolerance in transgenic Arabidopsis thaliana.

Auxin response factors (ARFs) play a crucial role in regulating gene expression within the auxin signal transduction pathway, particularly during adventitious root (AR) formation. In this investigation, we identified full-length sequences for ARF17 and ARF18, encompassing 1,800 and 2,055 bp, encoding 599 and 684 amino acid residues, respectively. Despite exhibiting low sequence homology, the ARF17- and ARF18-encoded proteins displayed significant structural similarity and shared identical motifs. Phylogenetic analysis revealed close relationships between NnARF17 and VvARF17, as well as NnARF18 and BvARF18. Both ARF17 and ARF18 demonstrated responsiveness to exogenous indole-3-acetic acid (IAA), ethephon, and sucrose, exhibiting organ-specific expression patterns. Beyond their role in promoting root development, these ARFs enhanced stem growth and conferred drought tolerance while mitigating waterlogging stress in transgenic Arabidopsis plants. RNA sequencing data indicated upregulation of 51 and 75 genes in ARF17 and ARF18 transgenic plants, respectively, including five and three genes associated with hormone metabolism and responses. Further analysis of transgenic plants revealed a significant decrease in IAA content, accompanied by a marked increase in abscisic acid content under normal growth conditions. Additionally, lotus seedlings treated with IAA exhibited elevated levels of polyphenol oxidase, IAA oxidase, and peroxidase. The consistent modulation of IAA content in both lotus and transgenic plants highlights the pivotal role of IAA in AR formation in lotus seedlings.

Transcriptome analysis of waterlogging-induced adventitious root and control taproot of Mentha arvensis.

KEY MESSAGE: The present study reports differentially expressed transcripts in the waterlogging-induced adventitious root (AR) of Mentha arvensis; the identified transcripts will help to understand AR development and improve waterlogging stress response. Waterlogging notably hampers plant growth in areas facing waterlogged soil conditions. In our previous findings, Mentha arvensis was shown to adapt better in waterlogging conditions by initiating the early onset of adventitious root development. In the present study, we compared the transcriptome analysis of adventitious root induced after the waterlogging treatment with the control taproot. The biochemical parameters of total carbohydrate, total protein content, nitric oxide (NO) scavenging activity and antioxidant enzymes, such as catalase activity (CAT) and superoxide dismutase (SOD) activity, were enhanced in the adventitious root compared with control taproot. Analysis of differentially expressed genes (DEGs) in adventitious root compared with the control taproot were grouped into four functional categories, i.e., carbohydrate metabolism, antioxidant activity, hormonal regulation, and transcription factors that could be majorly involved in the development of adventitious roots. Differential expression of the upregulated and uniquely expressing thirty-five transcripts in adventitious roots was validated using qRT-PCR. This study has generated the resource of differentially and uniquely expressing transcripts in the waterlogging-induced adventitious roots. Further functional characterization of these transcripts will be helpful to understand the development of adventitious roots, leading to the resistance towards waterlogging stress in Mentha arvensis.

Suberin deficiency and its effect on the transport physiology of young poplar roots.

The precise functions of suberized apoplastic barriers in root water and nutrient transport physiology have not fully been elucidated. While lots of research has been performed with mutants of Arabidopsis, little to no data are available for mutants of agricultural crop or tree species. By employing a combined set of physiological, histochemical, analytical, and transport physiological methods as well as RNA-sequencing, this study investigated the implications of remarkable CRISPR/Cas9-induced suberization defects in young roots of the economically important gray poplar. While barely affecting overall plant development, contrary to literature-based expectations significant root suberin reductions of up to 80-95% in four independent mutants were shown to not evidently affect the root hydraulic conductivity during non-stress conditions. In addition, subliminal iron deficiency symptoms and increased translocation of a photosynthesis inhibitor as well as NaCl highlight the involvement of suberin in nutrient transport physiology. The multifaceted nature of the root hydraulic conductivity does not allow drawing simplified conclusions such as that the suberin amount must always be correlated with the water transport properties of roots. However, the decreased masking of plasma membrane surface area could facilitate the uptake but also leakage of beneficial and harmful solutes.

Molecular Mechanism of Different Rooting Capacity between Two Clones of Taxodium hybrid 'Zhongshanshan'.

The conifer Taxodium hybrid 'Zhongshanshan' (T. hybrid 'Zhongshanshan') is characterized by rapid growth, strong stress resistance, and high ornamental value and has significant potential for use in afforestation, landscaping, and wood production. The main method of propagating T. hybrid 'Zhongshanshan' is tender branch cutting, but the cutting rooting abilities of different T. hybrid 'Zhongshanshan' clones differ significantly. To explore the causes of rooting ability differences at a molecular level, we analyzed the transcriptome data of cutting base and root tissues of T. hybrid 'Zhongshanshan 149' with a rooting rate of less than 5% and T. hybrid 'Zhongshanshan 118' with rooting rate greater than 60%, at the developmental time points in this study. The results indicated that differentially expressed genes between the two clones were mainly associated with copper ion binding, peroxidase, and oxidoreductase activity, response to oxidative stress, phenylpropanoid and flavonoid biosynthesis, and plant hormone signal transduction, among others. The expression pattern of ThAP2 was different throughout the development of the adventitive roots of the two clone cuttings. Therefore, this gene was selected for further study. It was shown that ThAP2 was a nuclear-localized transcription factor and demonstrated a positive feedback effect on rooting in transgenic Nicotiana benthamiana cuttings. Thus, the results of this study explain the molecular mechanism of cutting rooting and provide candidate gene resources for developing genetic breeding strategies for optimizing superior clones of T. hybrid 'Zhongshanshan'.