High Auxin Concentrations Research Articles

An integrated targeted metabolome of phytohormones and transcriptomics analysis provides insight into the new generation of crops: Polygonatum kingianum var. grandifolium and Polygonatum kingianum.

Huangjing is becoming a new generation of crop. Polygonatum kingianum var. grandifolium (XHJ) is a variant of P. kingianum (DHJ), and they are treated as Huangjing. Unlike other Polygonatum species, the rhizome bud of XHJ can germinate both in spring and autumn, which contributes to its high rhizome yield. However, the molecular mechanism of the autumn shooting of XHJ was still unknown. In the present study, cellular observation, comparative targeted metabolome of phytohormones, and transcriptome analysis between XHJ and DHJ in autumn were conducted. Interestingly, 'Diterpenoid biosynthesis' (ko00904) and 'Plant hormone signal transduction' (ko04075) were commonly enriched by differentially accumulated phytohormones (DAPs) and differentially expressed genes (DEGs) in all tissues, which indicated the high auxin content, low cytokinin (CTK) content, and low abscisic acid/gibberellin (ABA/GA) ratio might contribute to the XHJ rhizome buds' differentiation and germination in autumn. Moreover, according to the weighted gene co-expression network analysis (WCGNA), transcript factors (TFs) related to auxin, CTK, GA, and jasmonic acid (JA) metabolism were screened, such as AP2/ERFs, WRKY, and NAC, which deserve further research. In conclusion, we comprehensively illustrated the mechanism of XHJ natural autumn shooting through cytological, metabolic, and transcriptomic analysis, which improves our understanding of the high yield of XHJ rhizomes and the diversity of shooting mechanisms in Polygonatum to lay the foundation for the further development of the Huangjing industry.

WUSCHEL RELATED HOMEOBOX5 and 7 maintain callus development by promoting cell division in Arabidopsis

In tissue culture, a high concentration of auxin in the callus induction medium (CIM) stimulates cell division and subsequent callus formation, which acquires root primordium-like characteristics necessary for cell pluripotency. In Arabidopsis, WUSCHEL-RELATED HOMEOBOX5 (WOX5) and its closest homolog WOX7, which are abundant in the middle cell layer of mature callus, play a crucial role in maintaining pluripotency by promoting auxin accumulation and enhancing cytokinin sensitivity. However, the mechanism by which WOX5/7 regulate callus formation remains unclear. In this study, we found that mutations in WOX5/7 resulted in a significant down-regulation of genes involved in the G2M and S phases during callus induction. Loss-of-function mutants of WOX5/7 exhibited reduced callus formation, which was correlated with decreased expression of CYCB1;1 compared to the wild-type. Furthermore, we provided evidence that WOX5 physically interacts with PHYTOCHROME A SIGNAL TRANSDUCTION1 (PAT1), which spatio-temporally co-expresses with WOX5 in early-induced callus, and up-regulates a subset of cycle-regulating genes targeted by PAT1. Collectively, our findings suggest a critical role for the WOX5-PAT1 protein complex in regulating cell cycle progression, thereby promoting the continuous growth capacity of pluripotent callus.

Comparison of plant biostimulating properties of Chlorella sorokiniana biomass produced in batch and semi-continuous systems supplemented with pig manure or acetate

Microalgae-derived biostimulants provide an eco-friendly biotechnology for improving crop productivity. The strategy of circular economy includes reducing biomass production costs of new and robust microalgae strains grown in nutrient-rich wastewater and mixotrophic culture where media is enriched with organic carbon. In this study, Chlorella sorokiniana was grown in 100 l bioreactors under sub-optimal conditions in a greenhouse. A combination of batch and semi-continuous cultivation was used to investigate the growth, plant hormone and biostimulating effect of biomass grown in diluted pig manure and in nutrient medium supplemented with Na-acetate. C. sorokiniana tolerated the low light (sum of PAR 0.99 ± 0.18 mol/photons/(m2/day)) and temperature (3.7–23.7° C) conditions to maintain a positive growth rate and daily biomass productivity (up to 149 mg/l/day and 69 mg/l/day dry matter production in pig manure and Na-acetate supplemented cultures respectively). The protein and lipid content was significantly higher in the biomass generated in batch culture and dilute pig manure (1.4x higher protein and 2x higher lipid) compared to the Na-acetate enriched culture. Auxins indole-3-acetic acid (IAA) and 2-oxindole-3-acetic acid (oxIAA) and salicylic acid (SA) were present in the biomass with significantly higher auxin content in the biomass generated using pig manure (> 350 pmol/g DW IAA and > 84 pmol/g DW oxIAA) compared to cultures enriched with Na-acetate and batch cultures (< 200 pmol/g DW IAA and < 27 pmol/g DW oxIAA). No abscisic acid and jasmonates were detected. All samples had plant biostimulating activity measured in the mungbean rooting bioassay with the Na-acetate supplemented biomass eliciting higher rooting activity (equivalent to 1–2 mg/l IBA) compared to the pig manure (equivalent to 0.5–1 mg/l IBA) and batch culture (equivalent to water control) generated biomass. Thus C. sorokiniana MACC-728 is a robust new strain for biotechnology, tolerating low light and temperature conditions. The strain can adapt to alternative nutrient (pig manure) and carbon (acetate) sources with the generated biomass having a high auxin concentration and plant biostimulating activity detected with the mungbean rooting bioassay.

The Developmental Mechanism of the Root System of Cultivated Terrestrial Watercress.

A well-developed root system is crucial for the rapid growth, asexual reproduction, and adaptation to the drought environments of the watercress. After analyzing the transcriptome of the watercress root system, we found that a high concentration of auxin is key to its adaptation to dry conditions. For the first time, we obtained DR5::EGFP watercress, which revealed the dynamic distribution of auxin in watercress root development under drought conditions. Via the application of naphthylphthalamic acid (NPA), 4-biphenylboronic acid (BBO), ethylene (ETH), abscisic acid (ABA), and other factors, we confirmed that auxin has a significant impact on the root development of watercress. Finally, we verified the role of auxin in root development using 35S::NoYUC8 watercress and showed that the synthesis of auxin in the root system mainly depends on the tryptophan, phenylalanine, and tyrosine amino acids (TAA) synthesis pathway. After the level of auxin increases, the root system of the watercress develops toward adaptation to dry environments. The formation of root aerenchyma disrupts the concentration gradient of auxin and is a key factor in the differentiation of lateral root primordia and H cells in watercress.

Effect of propagation dates, media and auxins treatments on rooting of Monterey cypress (Cupressus macrocarpa) semi-hard wood cuttings

This experiment was carried out from 15th October, 2021 to 15th May, 2022 in the plastic house in Duhok city, Iraq. A study included the effect of three factors, the first one is two different propagation dates 15th October and 15th December, second one is three propagation media includes peat moss + perlite (1:1), sand + perlite (1:1) and peat moss + sand + perlite (1:1:1), and third one included three auxin concentrations includes (control, 3000 IBA+1500 NAA and 6000 IBA + 3000 mg. L-1 NAA) on the rooting of Cupressus macrocarpa semi-hard wood cuttings. The results analyzed by (RCBD) design and indicated that the planting of cuttings at 15th October significantly gave the best results of all studied characters (rooting percentage (51.11%) and shoots characters) as compared with those date in 15th December which gave the lowest values. As for propagation media had significant effect only on rooting characters, the best results of rooting obtained when cuttings planted in both of (sand + perlite) and (sand + peat moss + perlite) media but the media hadn’t any significant effects on shoot characters. Auxin treatment meaningfully affected on rooting ability of cuttings, high concentrations of auxins (6000 IBA+3000 NAA mg.L-1) gave the best results of rooting characters comparison with low concentration (3000 IBA+1500 NAA mg.L-1) and control (0 mg.L-1) but hadn’t any significant effects on shoots characters. Generally, the interaction among three factors showed that the planting of cutting treated with both concentrations of auxins in both of (sand + perlite) and (sand + peat moss + perlite) media at 15th October provided the best results of rooting percentage and improve most roots and shoots characters.

Pan-transcriptomic Profiling Demarcates Serendipita Indica-Phosphorus Mediated Tolerance Mechanisms in Rice Exposed to Arsenic Toxicity

Inadvertent accumulation of arsenic (As) in rice (Oryza sativa L.) is a concern for people depending on it for their subsistence, as it verily causes epigenetic alterations across the genome as well as in specific cells. To ensure food safety, certain attempts have been made to nullify this highest health hazard encompassing physiological, chemical and biological methods. Albeit, the use of mycorrhizal association along with nutrient reinforcement strategy has not been explored yet. Mechanisms of response and resistance of two rice genotypes to As with or without phosphorus (P) nutrition and Serendipita indica (S. indica; S.i) colonization were explored by root transcriptome profiling in the present study. Results revealed that the resistant genotype had higher auxin content and root plasticity, which helped in keeping the As accumulation and P starvation response to a minimum under alone As stress. However, sufficient P supply and symbiotic relationship switched the energy resources towards plant’s developmental aspects rather than excessive root proliferation. Higher As accumulating genotype (GD-6) displayed upregulation of ethylene signaling/biosynthesis, root stunting and senescence related genes under As toxicity. Antioxidant defense system and cytokinin biosynthesis/signaling of both genotypes were strengthened under As + S.i + P, while the upregulation of potassium (K) and zinc (Zn) transporters depicted underlying cross-talk with iron (Fe) and P. Differential expression of phosphate transporters, peroxidases and GSTs, metal detoxification/transport proteins, as well as phytohormonal metabolism were responsible for As detoxification. Taken together, S. indica symbiosis fortified with adequate P-fertilizer can prove to be effective in minimizing As acquisition and accumulation in rice plants.

Metabolomic and transcriptomic analyses reveal novel mechanisms underlying the long-storage trait of apricot (Prunus armeniaca L.)

Apricot is a climacteric fruit, whose respiration increases rapidly after harvest, and thus, it can generally not be stored for a long period. However, the 'Pearl' variety was identified as a long-storage variety, but the mechanisms underlying long-storage remain unclear. Herein, we analyzed the physiological phenotype, transcriptome, and plant hormones of the 'Pearl' and 'Sungold' (short-storage) varieties. The results showed that 'Sungold' respiratory intensity increased from 37.33 to 58.07 mg/kg*h during postharvest storage (D1 ∼ D6), while 'Pearl' respiratory intensity fluctuated from 28.50 to 36.03 mg/kg*h during the same period and did not show a significant increase. Furthermore, glycolytic pathway genes in 'Pearl' were found to be generally down-regulated. The hub-gene with the highest K-score in the 'MEblack' module was determined to be an auxin response gene, and the expression pattern of this module was contrary to the trend for respiratory intensity. The auxin content of 'Pearl' was consistently higher than that of 'Sungold' during storage. The genetic transformation experiment of tomato showed that the SNP variation of PaYUC10 gene resulted in high auxin content, thus inhibiting respiratory intensity and prolonging fruit storage time. Our findings could help ensure longer storage of apricot, thereby reducing waste and improving economic returns.

Pruning and additional fertilizer applications affect morphophysiological characters and flavonoid content of winged bean

Excessive leaf production in winged bean may delay the flowering time and reduces the yield, therefore, shoot pruning and additional fertilizer were applied in order to improve yield. The research was carried out at Leuwikopo Experimental Station, IPB University, Bogor from January to July 2022. The study used a randomized complete block design with 2 factors and three replications. The first factor was three types of shoot pruning, namely without shoot pruning, shoot pruning at 15, and 30 cm height. Pruning was conducted at 7 weeks after transplanting (WAT). The second factor was four doses of fertilizers (0, 6.25, 12.5, and 18.75 g of NPK (16-16-16) per plant). The additional fertilizer was given every two weeks from 7 until 15 WAT. The variables observed were the morphophysiological characters, shoot auxin levels, plant nutrient levels, pod yield, pod number, and pod flavonoid content. The results showed that plant’s biomass increased with additional fertilizer, lower relative growth rate and higher auxin content was from 15 cm pruning. The interaction of two factors affected flowering time and flavonoid content. Shoot pruning and 6.25 g NPK delayed flowering by 0.7-1 day. The highest flavonoid content was found in the plant without pruning and additional fertilizer. Plant yields were not significantly affected by treatments.&#x0D; Keywords: auxin; flavonoid content; flowering time; leaf nutrient; young pods

Developmental trajectory of pluripotent stem cell establishment in Arabidopsis callus guided by a quiescent center-related gene network.

In plant tissue culture, callus formation is induced by a high auxin concentration. Among the three cell layers (the outer, middle and inner cell layers) of the callus, pluripotency acquisition in the middle cell layer is required for the potential ability of the callus to regenerate organs. Here, we reveal the developmental trajectory of middle cell layer initiation and maintenance in callus tissue originating from Arabidopsis thaliana hypocotyls. The S phase of the cell cycle is essential for the expression of quiescent center-related SCARECROW (SCR), PLETHORA1 (PLT1) and WUSCHEL-RELATED HOMEOBOX5 (WOX5) genes during the division of callus founder cells to initiate the callus primordium. After callus initiation, SHOOT-ROOT (SHR) proteins move from the inner to the middle cell layer and act together with SCR to promote the expression of PLT1 and WOX5. WOX5 represses the expression of VASCULAR-RELATED NAC-DOMAIN (VND) genes, thereby preventing callus tissue from differentiating into xylem cells. PLT1 and PLT2 directly activate JACKDAW (JKD), which is necessary for pluripotency acquisition in the middle cell layer. We hypothesize that the middle cell layer could have pluripotent stem cell activity and its establishment requires the quiescent center-related SCR-SHR-WOX5-PLT1/2-JKD gene network.

ПУТИ МОРФОГЕНЕЗА В КУЛЬТУРЕ IN VITRO ИЗОЛИРОВАННЫХ ПЫЛЬНИКОВ ПШЕНИЦЫ: РОЛЬ БАЛАНСА ФИТОГОРМОНОВ

The study is aimed to the study of the peculiarities of the induction of morphogenesis pathways in vitro of morphogenetically competent anther cells - microspores in the isolated anther culture of a number of spring soft wheat genotypes, recommended for cultivation in the climatic conditions of the Republic of Bashkortostan. The content of IAA in seedlings of the studied genotypes of spring sof wheat was analyzed to determine the class of the genotype – characterized by high or low auxin content. Such morphogenesis pathways in vitro as embryoidogenesis, polyembryoidogenesis and callusogenesis have been identified and studied. Morpho-histological assessment of androclinic structures is given. It was established that the induction of a certain morphogenesis pathway in vitro is determined mainly by the balance between the content of endogenous auxin IAA in anthers before inoculation on a nutrient medium and the concentration of exogenous synthetic auxin 2,4-D in the composition of the nutrient medium. The fundamental possibility of regulation of morphogenesis pathways in vitro in isolated anther culture of wheat by selecting for each genotype an adequate balance of endogenous and exogenous auxins for the induction of a specific pathway has been shown.

High auxin stimulates callus through SDG8-mediated histone H3K36 methylation in Arabidopsis.

Callus induction, which results in fate transition in plant cells, is considered as the first and key step for plant regeneration. This process can be stimulated in different tissues by a callus-inducing medium (CIM), which contains a high concentration of phytohormone auxin. Although a few key regulators for callus induction have been identified, the multiple aspects of the regulatory mechanism driven by high levels of auxin still need further investigation. Here, we find that high auxin induces callus through a H3K36 histone methylation-dependent mechanism, which requires the methyltransferase SET DOMAIN GROUP 8 (SDG8). During callus induction, the increased auxin accumulates SDG8 expression through a TIR1/AFBs-based transcriptional regulation. SDG8 then deposits H3K36me3 modifications on the loci of callus-related genes, including a master regulator WOX5 and the cell proliferation-related genes, such as CYCB1.1. This epigenetic regulation in turn is required for the transcriptional activation of these genes during callus formation. These findings suggest that the massive transcriptional reprogramming for cell fate transition by auxin during callus formation requires epigenetic modifications including SDG8-mediated histone H3K36 methylation. Our results provide insight into the coordination between auxin signaling and epigenetic regulation during fundamental processes in plant development.

Transcriptomic and Metabolomic Analysis of Korean Pine Cell Lines with Different Somatic Embryogenic Potential.

The embryogenesis capacity of conifer callus is not only highly genotype-dependent, but also gradually lost after long-term proliferation. These problems have seriously limited the commercialization of conifer somatic embryogenesis (SE) technology. In this study, the responsive SE cell line (R-EC), the blocked SE cell line (B-EC), and the loss of SE cell line (L-EC) were studied. The morphological, physiological, transcriptomic, and metabolomic profiles of these three types of cells were analyzed. We found that R-EC had higher water content, total sugar content, and putrescine (Put) content, as well as lower superoxide dismutase (SOD) activity and H2O2 content compared to B-EC and L-EC. A total of 2566, 13,768, and 13,900 differentially expressed genes (DEGs) and 219, 253, and 341 differentially expressed metabolites (DEMs) were found in the comparisons of R-EC versus B-EC, R-EC versus B-EC, and B-EC versus L-EC, respectively. These DEGs and DEMs were mainly found to be involved in plant signal transduction, starch and sugar metabolism, phenylpropane metabolism, and flavonoid metabolism. We found that the AUX1 and AUX/IAA families of genes were significantly up-regulated after the long-term proliferation of callus, resulting in higher auxin content. Most phenylpropane and flavonoid metabolites, which act as antioxidants to protect cells from damage, were found to be significantly up-regulated in R-EC.

The MdAux/IAA2 Transcription Repressor Regulates Cell and Fruit Size in Apple Fruit.

Auxin plays an important role in regulating plant development, and Auxin/indole acetic acid (Aux/IAA) is a type of auxin-responsive gene and plays an important role in auxin signaling; to date, although 29 Aux/IAA proteins have been reported in Abrabidopsis thaliana, only parts of the Aux/IAA family gene functions have been identified. We previously reported that a bud sport of ‘Longfeng’ (LF) apple (Malus domestica), named ‘Grand longfeng’ (GLF), which showed a larger fruit size than LF, has lower expression of MdAux/IAA2. In this study, we identified the function of the MdAux/IAA2 gene in apple fruit size difference using Agrobacterium-mediated genetic transformation. Overexpression of MdAux/IAA2 decreased the apple flesh callus increment and caused a smaller globular cell size. In addition, overexpression of MdAux/IAA2 in GLF fruit resulted in the reduction of apple fruit size, weight, and cell size, while silencing MdAux/IAA2 in LF apple fruit resulted in an increase in apple fruit weight and cell size. We suggest that the high auxin content depressed the expression of MdAux/IAA2, and that the downregulated expression of MdAux/IAA2 led to the formation of GLF. Our study suggests a mechanism for fruit size regulation in plants and we will explore the transcription factors functioning in this process in the future.

Overexpression of a SHORT-ROOT transcriptional factor enhances the auxin mediated formation of adventitious roots and lateral roots in poplar trees

SHORT-ROOT (SHR) defines root stem cells and maintains radial patterning, but its involvement in adventitious root (AR) formation has not been reported. In this study, we showed that PtSHR2 was transcriptionally upregulated by excision before the formation of AR and responded dynamically to auxin. PtSHR2 overexpression (SHR2BOE) in hybrid poplars resulted in an increased number of ARs with an initial delay. Despite a lower endogenous content in the stems than in wild-type plants, indole-3-acetic acid (IAA) content at the SHR2BOE basal stem increased rapidly after cutting and reached a higher maximum than in wild-type plants, which was accompanied by a more sustained and stronger induction of AR formation marker genes. In addition, the higher auxin content in SHR2BOE ARs resulted in more and longer lateral roots (LRs). Application of auxin abolished the early delay in the formation of AR and largely other AR phenotypes of SHR2BOE plants, whereas the polar auxin transport inhibitor N-1-naphthylphthalamic acid completely inhibited both AR and LR abnormalities. Since the enhanced rooting ability of SHR2BOE stem cuttings in hydroponics was clearly confirmed, our results suggest a novel role of poplar SHR2 as a positive regulator during the organogenesis of AR and LR by affecting local auxin homeostasis.

Studies on the Comparative Effects of Three Auxins and Seasons on the Rooting of Stem Cuttings of Moringa oleifera Lam (Moringaceae)

Rooting on mature stem cuttings of the Drumstick tree, Moringa oleifera, Lam. Moringaceae, was studied using three auxins (indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) and maphthalene acetic acid (NAA) at two seasons. The experiments were carried out at random using a 342 factorial design. The growth of stem cuttings prior to rooting was influenced by auxin concentrations and the seasons. Stem cuttings taken during the wet season and treated with 500 mg/L of IBA, NAA, and IAA sprouted 18-27 days sooner than dry season cuttings (24-30 days after planting or DAP). Wet-season bud development into leaves was found to be more affected by auxin application and seasons than dry-season bud development (2.0%-83.4% wet season and 10%-56.08% dry season). The results also demonstrated that the stem cuttings did not callus, but instead formed nodules at the base of the stem regardless of the treatment or time of year. Sizes ranging from small (S) to medium (M) to large (B) nodules were spotted. Larger concentrations of auxins (500 mg/L of IBA, NAA, and IAA) influenced the production of smaller nodules during the dry season, while in the wet season, 500 mg/L of the three auxins influenced the production of larger nodules (B), and 300 mg/L of the auxins influenced the production of smaller nodules (M). Auxin concentration and control affected the production of small (S) nodules. The results also showed that large nodules were associated with the tap, lateral, and feeding roots. High auxin concentration (500 mg/L) affected these. The wet season stem cuttings produced more tap roots than the dry season cuttings. The study showed that vegetative propagation of M. oleifera by rooting stem cuttings is best done in the wet season. Wet season cuttings produced proto-type seedlings of the parent stock.

Heterologous expression of a Fraxinus velutina SnRK2 gene in Arabidopsis increases salt tolerance by modifying root development and ion homeostasis.

FvSnRK2182 is involved in regulating the growth and stress response. SnRK2 family members are positive regulators of downstream signals in the abscisic acid (ABA) signaling pathway, playing key roles in the plant responses to abiotic stresses. Fraxinus velutina Torr. is a candidate phytoremediator of saline-alkali areas, and is a valuable research subject because of its adaptability in saline soil. We identified a SnRK2 gene in F. velutina (named FvSnRK2182), which was significantly upregulated under salt stress. A bioinformatics analysis showed that FvSnRK2182 has a Ser/Thr kinase domain typical of the SnRK2 subfamily. Compared with wild-type (WT) Arabidopsis, its heterologous expression in Arabidopsis resulted in higher auxin content during seed germination and seedling growth, leading to longer primary roots and more lateral roots. The transgenic lines were better able to tolerate treatments with NaCl (100mM) and/or ABA (0.2 and 0.5µM), producing a greater biomass than the WT plants. Under NaCl treatment, the shoots of the transgenic lines had lower Na+ contents and higher K+ contents than the WT plants, and the genes encoding the ion transport-related proteins SOS1, HKT1, NHX1, and AKT1 were significantly upregulated. In addition, the expression of the genes functioning downstream of SnRK2 in the ABA signaling pathway (Rboh, AREB4, ABF2, and ABF3) were significantly upregulated in transgenic lines under NaCl stress. These results showed that expressing FvSnRK2182 in Arabidopsis significantly increased their resistance to ABA and salt stress by regulating root development and maintaining ion homeostasis, which suggests that FvSnRK2182 may be involved in regulating the growth and stress response of F. velutina.

Establishment of an Efficient Protoplast Regeneration and Transfection Protocol for Field Cress (Lepidium campestre).

Field cress (Lepidium campestre) is a potential oilseed crop that has been under domestication in recent decades. CRISPR/Cas9 is a powerful tool for rapid trait improvement and gene characterization and for generating transgene-free mutants using protoplast transfection system. However, protoplast regeneration remains challenging for many plant species. Here we report an efficient protoplast regeneration and transfection protocol for field cress. Important factors such as type of basal media, type/combination of plant growth regulators, and culture duration on different media were optimized. Among the basal media tested, Nitsch was the best for protoplast growth in MI and MII media. For cell wall formation during the early stage of protoplast growth, relatively high auxin concentrations (0.5 mg L−1 NAA and 2,4-D), without addition of cytokinin was preferred for maintaining protoplast viability. After cell wall formation, 1.1 mg L−1 TDZ combined with either 0.05 mg L−1 NAA or 2,4-D was found to efficiently promote protoplast growth. On solid shoot induction medium, 1.1 mg L−1 TDZ without any auxin resulted in over 80% shoot generation frequency. A longer culture duration in MI medium would inhibit protoplast growth, while a longer culture duration in MII medium significantly delayed shoot formation. Using this optimized protoplast regeneration protocol, we have established an efficient PEG-mediated transfection protocol using a vector harboring the GFP gene, with transfection efficiencies of 50–80%. This efficient protoplast protocol would facilitate further genetic improvement of field cress via genome editing, and be beneficial to development of protoplast regeneration protocols for related plant species.

Comparison of Auxin and Cytokinins Concentrations, and the Structure of Bacterial Community between Host Twigs and Lithosaphonecrus arcoverticus Galls.

Simple SummaryInsect galls are characterized by high concentrations of auxins and cytokinins. We calculated the correlation between the concentrations of indoleacetic acid (IAA), trans-zeatin riboside (tZR) and isopentenyladenine (iP) and the bacterial community structure of Lithosaphonecrus arcoverticus galls. Our results indicated the concentrations of IAA, tZR and iP were positively correlated with the bacterial community structure of L. arcoverticus galls. We suggest the high concentrations of IAA, tZR and iP may affect the bacterial community structure of L. arcoverticus galls.Insect galls are the abnormal growth of plant tissues induced by a wide variety of galling insects and characterized by high concentrations of auxins and cytokinins. It remains unclear whether the auxins and cytokinins affect the bacterial community structure of insect galls. We determined the concentrations of indoleacetic acid (IAA) as an example of auxin, trans-zeatin riboside (tZR) and isopentenyladenine (iP) as cytokinins in Lithosaphonecrus arcoverticus (Hymenoptera: Cynipidae) galls and the galled twigs of Lithocarpus glaber (Fagaceae) using liquid chromatography–tandem mass spectrometry. Moreover, for the first time, we compared the bacterial community structure of L. arcoverticus galls and galled twigs by high-throughput sequencing, and calculated the Spearman correlation and associated degree of significance between the IAA, tZR and iP concentrations and the bacterial community structure. Our results indicated the concentrations of IAA, tZR and iP were higher in L. arcoverticus galls than in galled twigs, and positively correlated with the bacterial community structure of L. arcoverticus galls. We suggest the high concentrations of IAA, tZR and iP may affect the bacterial community structure of L. arcoverticus galls.

Purple nutsedge (Cyperus rotundus L.) extract as carrot growth and production inducer

There is evidence that the purple nutsedge (Cyperus rotundus L.) aqueous extract can induce the plants rooting due to the high auxin concentrations. This study aimed to evaluate the effect of application seasons and concentrations of purple nutsedge aqueous extract application on the growth and production of carrot, cultivar Brasília. The experimental design was in randomized blocks, in a 2 x 5 factorial scheme in two seasons of the extract application (25 and 50 days after sowing) and five concentrations of (0%, 10%, 20%, 30% and 40%) with four replicates. Harvesting was carried out at 90 days after sowing, being evaluated the following morphological parameters: root diameter (cm); root fresh mass (g plant-1); plant height (cm); aerial part fresh mass (g plant-1); root dry mass (g plant-1); aerial part dry mass (g plant-1); plant dry mass (g plant-1); ratio between root dry mass and aerial part dry mass; root length (cm); commercial productivity (t ha-1); defective root mass (t ha-1); total productivity (t ha-1); commercial yield (roots kg-1); and root classification by length. The extract application at 50th day was more efficient for the root diameter (3.37 cm); fresh root mass (120.7 g plant-1); root length (15.4 cm); commercial productivity (68.2 t ha-1); total productivity (73.6 t ha-1); and commercial roots (8.8 roots kg-1). Root classification by length showed a higher percentage in the 14 cm classification range. The parameters did not present significant differences in both seasons, at 25th and 50th days, respectively, for root dry mass (12.0 and 12.8 g plant-1), ratio between dry mass of roots and aerial part (1.66 and 1.57), and defective root mass (1.3 and 1.5 t ha-1).

TMK1-based auxin signaling regulates abscisic acid responses via phosphorylating ABI1/2 in Arabidopsis

Differential concentrations of phytohormone trigger distinct outputs, which provides a mechanism for the plasticity of plant development and an adaptation strategy among plants to changing environments. However, the underlying mechanisms of the differential responses remain unclear. Here we report that a high concentration of auxin, distinct from the effect of low auxin concentration, enhances abscisic acid (ABA) responses in Arabidopsis thaliana, which partially relies on TRANS-MEMBERANE KINASE 1 (TMK1), a key regulator in auxin signaling. We show that high auxin and TMK1 play essential and positive roles in ABA signaling through regulating ABA INSENSITIVE 1 and 2 (ABI1/2), two negative regulators of the ABA pathway. TMK1 inhibits the phosphatase activity of ABI2 by direct phosphorylation of threonine 321 (T321), a conserved phosphorylation site in ABI2 proteins, whose phosphorylation status is important for both auxin and ABA responses. This TMK1-dependent auxin signaling in the regulation of ABA responses provides a possible mechanism underlying the high auxin responses in plants and an alternative mechanism involved in the coordination between auxin and ABA signaling.