Exogenous Auxin Research Articles

Propagation of Sweetgale, Rhodora, and Catberry by Stem Cuttings

Sweetgale (Myrica gale), rhodora (Rhododendron canadense), and catberry (Ilex mucronata) are shrubs of eastern North America that may have potential for broader use in horticultural landscapes. Because information on their vegetative propagation is scarce, we conducted experiments over 2 years to evaluate the effects of cutting collection date, wounding, substrate composition, and the concentration of applied potassium salt of indole-3-butyric acid (K-IBA) on rooting of each species. In 2015, we collected cuttings of each species on three dates to obtain both softwood and semihardwood cuttings. Cuttings were unwounded or wounded with a razor blade, and treated by dipping into water containing K-IBA at concentrations ranging from 0 to 15,000 mg·L−1, after which they were inserted into a substrate of 3:1 perlite:peat (by volume) and placed under intermittent mist. In 2016, semihardwood cuttings of each species were all wounded, treated with K-IBA from 0 to 15,000 mg·L−1, and inserted into substrates of 100%, 75%, or 50% perlite, with the remaining volume occupied by peat. In both years, the greatest percentage of sweetgale cuttings rooted when no K-IBA was applied. K-IBA application also reduced root ratings, root dry weights, and root lengths of sweetgale. For rhodora and catberry, maximal responses for all measures of rooting occurred when 5000 to 15,000 mg·L−1 K-IBA was applied. We recommend that growers use no exogenous auxin to propagate sweetgale, and 5000 to 10,000 mg·L−1 K-IBA to propagate rhodora and catberry. Cuttings of all three species can be collected from softwood or semihardwood shoots. Finally, sweetgale can be rooted in perlite alone, whereas rhodora and catberry required the addition of peatmoss for satisfactory root development.

Stimulatory effect of copper and zinc sulphate on plant regeneration, glutathione-S-transferase analysis and assessment of antioxidant activities in Mucuna pruriens L. (DC)

The effect of heavy metals, CuSO4 and ZnSO4 on morphogenic response of cotyledonary node explants of Mucuna pruriens (L.), a fast growing tropical medicinal legume was evaluated. The climber holds economic importance in traditional as well as modern pharmaceutical areas. Murashige and Skoog (Physiol Plant 15:473–497, 1962) medium supplemented with various strength (0.5, 2.5, 4.5, 6.5 or 8.5 µM) of BA (6-benzyladenine), Kn (Kinetin) and 2-iP (2-isopentenyl adenine) were screened to establish optimum culture conditions for in vitro regeneration using cotyledonary node explant. Optimized medium (MS + BA 2.5 µM) was augmented with different concentration of CuSO4 (0.5–25.0 µM) and ZnSO4 (5–150 µM) to evaluate the effect of heavy metals on regeneration potential of the explants. Among various concentrations tested, MS medium with optimized BA (2.5 µM) along with 5.0 µM CuSO4 or 80.0 µM ZnSO4 proved beneficial, inducing 11.20 and 13.40 shoots per explant, respectively. The results demonstrated that glutathione-S-transferase (GSTs) was involved in fighting heavy metal stress, and might also have a role in in vitro regeneration. Elongated healthy microshoots on transfer to half strength MS medium produced 3.40 roots per shoot after 28 days of incubation without the necessity of exogenous auxin. The in vitro grown regenerants were hardened in Soilrite, and then established in garden and sandy soil (1:1) under natural light where they showed normal growth and development. The work highlights the enhanced multiplication and better growth of the regenerants using elevated concentration of CuSO4 and ZnSO4. GSTs overexpression activity not only confers to overcome the stress but enhanced the in vitro regeneration of M. pruriens also.

WEG1, which encodes a cell wall hydroxyproline-rich glycoprotein, is essential for parental root elongation controlling lateral root formation in rice.

Lateral roots (LRs) determine the overall root system architecture, thus enabling plants to efficiently explore their underground environment for water and nutrients. However, the mechanisms regulating LR development are poorly understood in monocotyledonous plants. We characterized a rice mutant, wavy root elongation growth 1 (weg1), that produced higher number of long and thick LRs (L-type LRs) formed from the curvatures of its wavy parental roots caused by asymmetric cell growth in the elongation zone. Consistent with this phenotype, was the expression of the WEG1 gene, which encodes a putative member of the hydroxyproline-rich glycoprotein family that regulates cell wall extensibility, in the root elongation zone. The asymmetric elongation growth in roots is well known to be regulated by auxin, but we found that the distribution of auxin at the apical region of the mutant and the wild-type roots was symmetric suggesting that the wavy root phenotype in rice is independent of auxin. However, the accumulation of auxin at the convex side of the curvatures, the site of L-type LR formation, suggested that auxin likely induced the formation of L-type LRs. This was supported by the need of a high amount of exogenous auxin to induce the formation of L-type LRs. These results suggest that the MNU-induced weg1 mutated gene regulates the auxin-independent parental root elongation that controls the number of likely auxin-induced L-type LRs, thus reflecting its importance in improving rice root architecture.

Применение гидратцеллюлозной пленки для исследования роста и развития корневой системы модельного растения Arabidopsis thaliana L.

A new technique for Arabidopsis thaliana cultivation has been proposed that combines the use of a phytogel-based nutrient medium and a hydrophilic membrane of hydrate cellulose film, separating the root system of the plant from the medium thickness. Growth rates of both main and lateral roots were faster in the plants cultivated on the surface of hydrate cellulose film than in the plants grown in the phytogel volume. The location of the root system on the surface of the transparent hydrate film simplifies its observation and analysis and facilitates plant transplantation with preservation of the root system configuration. The proposed technique allowed us to first assess the effect of exogenous auxin on the growth of lateral roots at the 5-6 developmental stage. methods to study plant root systems, hydrate cellulose film, A. thaliana, lateral roots, differential root growth rate, auxin The work was financially supported by the Russian Foundation for Basic Research (Project Bel_mol_a 19-54-04015) and the basic topic of the Russian Academy of Sciences - IBMP RAS «Regularities of the Influence of Extreme Environmental Factors on the Processes of Cultivation of Higher Plants and the Development of Japanese Quail Tissues at Different Stages of its Ontogenesis under the Conditions of Regenerative Life Support Systems».

Genome-wide association study reveals new genes involved in leaf trichome formation in polyploid oilseed rape (Brassica napus L.).

Leaf trichomes protect against various biotic and abiotic stresses in plants. However, there is little knowledge about this trait in oilseed rape (Brassica napus). Here, we demonstrated that hairy leaves were less attractive to Plutella xylostella larvae than glabrous leaves. We established a core germplasm collection with 290 accessions for a genome-wide association study (GWAS) of the leaf trichome trait in oilseed rape. We compared the transcriptomes of the shoot apical meristem (SAM) between hairy- and glabrous-leaf genotypes to narrow down the candidate genes identified by GWAS. The single nucleotide polymorphisms and the different transcript levels of BnaA.GL1.a, BnaC.SWEET4.a, BnaC.WAT1.a and BnaC.WAT1.b corresponded to the divergence of the hairy- and glabrous-leaf phenotypes, indicating the role of sugar and/or auxin signalling in leaf trichome initiation. The hairy-leaf SAMs had lower glucose and sucrose contents but higher expression of putative auxin responsive factors than the glabrous-leaf SAMs. Spraying of exogenous auxin (8 μm) increased leaf trichome number in certain genotypes, whereas spraying of sucrose (1%) plus glucose (6%) slightly repressed leaf trichome initiation. These data contribute to the existing knowledge about the genetic control of leaf trichomes and would assist breeding towards the desired leaf surface type in oilseed rape.

ROOTING OF Inga edulis Mart. (LEGUMINOSAE-MIMOSOIDEAE) MINI-CUTTINGS

Seeds of the species Inga edulis are recalcitrant and lose viability quickly, which restricts seedling production at only a certain time of the year. Thus, this study aimed to analyze the potential of mini-cutting and the influence of different indole-3-butyric acid (IBA) concentrations on the vegetative propagation of Inga edulis. The vegetative material was collected from juvenile plants from a clonal mini-garden. The experiment was carried out in a completely randomized design, with five replications and each experimental unit with eight cuttings. Treatments consisted of different IBA concentrations (0, 1000, 2000, 4000, and 8000 mg kg−1). The percentage of live and rooted mini-cuttings, number of roots emitted from the base, longest root length, total number of roots, fine root length, total root length, root surface area, weighted average root diameter, root volume, shoot dry matter, root dry matter, total dry matter, specific root length, specific root surface area, and root density were analyzed after 45 days in a greenhouse. All Inga edulis mini-cuttings survived, and rooting was over 85%. IBA concentrations had no significant effect on most of the analyzed variables. However, exogenous auxin concentration between 2000 and 4636.96 mg kg−1 provided mini-cuttings with a higher number of roots, surface area, and root volume. Rooting of juvenile Inga edulis mini-cuttings may occur without the use of IBA.

A gain-of-function mutation in Brassinosteroid-insensitive 2 alters Arabidopsis floral organ development by altering auxin levels.

Auxin can alter the fertility of bin2-1 plants and depends on the expression of SHY2. Brassinosteroids (BRs) play important roles in plant growth and developmental processes. By systematically evaluating the phenotypes of BR biosynthesis and BR signaling mutants, researchers have reported that BRs positively regulate floral development. In this study, we found that brassinosteroid-insensitive 2 (bin2-1) and short-hypocotyl 2 (shy2-2) mutants exhibited significantly reduced fertility. These mutants had short inflorescences, decreased floral organ length (short petals, stamens, carpels, and stigmas), and short siliques. Exogenous auxin applications could partially rescue the shortened length of the floral organs and siliques of the bin2-1 mutants. Additional experiments revealed that a lack of SHY2 activity increased the fertility of the bin2-1 mutants. A search for downstream affected genes revealed that auxin influences the expression of ARFs and PINs in the bin2-1 mutants, suggesting that auxin plays a major role in the regulation of bin2-1 plant fertility. Thus, BIN2 plays a role in fertility by affecting auxin levels, mainly by altering the expression of SHY2.

Exogenous Auxin Induces Transverse Microtubule Arrays Through TRANSPORT INHIBITOR RESPONSE1/AUXIN SIGNALING F-BOX Receptors.

Auxin plays a central role in controlling plant cell growth and morphogenesis. Application of auxin to light-grown seedlings elicits both axial growth and transverse patterning of the cortical microtubule cytoskeleton in hypocotyl cells. Microtubules respond to exogenous auxin within 5 min, although repatterning of the array does not initiate until 30 min after application and is complete by 2 h. To examine the requirements for auxin-induced microtubule array patterning, we used an Arabidopsis (Arabidopsis thaliana) double auxin f-box (afb) receptor mutant, afb4-8 afb5-5, that responds to conventional auxin (indole-3-acetic acid) but has a strongly diminished response to the auxin analog, picloram. We show that 5 µm picloram induces immediate changes to microtubule density and later transverse microtubule patterning in wild-type plants, but does not cause microtubule array reorganization in the afb4-8 afb5-5 mutant. Additionally, a dominant mutant (axr2-1) for the auxin coreceptor AUXIN RESPONSIVE2 (AXR2) was strongly suppressed for auxin-induced microtubule array reorganization, providing additional evidence that auxin functions through a transcriptional pathway for transverse patterning. We observed that brassinosteroid application mimicked the auxin response, showing both early and late microtubule array effects, and induced transverse patterning in the axr2-1 mutant. Application of auxin to the brassinosteroid synthesis mutant, diminuto1, induced transverse array patterning but did not produce significant axial growth. Thus, exogenous auxin induces transverse microtubule patterning through the TRANSPORT INHIBITOR 1/AUXIN F-BOX (TIR1/AFB) transcriptional pathway and can act independently of brassinosteroids.

Dual regulation of xylem formation by an auxin-mediated PaC3H17-PaMYB199 module in Populus.

Wood (secondary xylem) formation in tree species is dependent on auxin-mediated vascular cambium activity in stems. However, the complex regulatory networks underlying xylem formation remain elusive. Xylem development in Populus was characterized based on microscopic observations of stem sections in transgenic plants. Transcriptomic, quantitative real-time PCR, chromatin immunoprecipitation PCR, and electrophoretic mobility shift assay analyses were conducted to identify target genes involved in xylem development. Yeast two-hybrid, pull-down, bimolecular fluorescence complementation, and co-immunoprecipitation assays were used to validate protein-protein interactions. PaC3H17 and its target PaMYB199 were found to be predominantly expressed in the vascular cambium and developing secondary xylem in Populus stems and play opposite roles in controlling cambial cell proliferation and secondary cell wall thickening through an overlapping pathway. Further, PaC3H17 interacts with PaMYB199 to form a complex, attenuating PaMYB199-driven suppression of its xylem targets. Exogenous auxin application enhances the dual control of the PaC3H17-PaMYB199 module during cambium division, thereby promoting secondary cell wall deposition. Dual regulation of xylem formation by an auxin-mediated PaC3H17-PaMYB199 module represents a novel regulatory mechanism in Populus, increasing our understanding of the regulatory networks involved in wood formation.

A Strigolactone Signal Inhibits Secondary Lateral Root Development in Rice.

Strigolactones (SLs) and their derivatives are plant hormones that have recently been identified as regulators of primary lateral root (LR) development. However, whether SLs mediate secondary LR production in rice (Oryza sativa L.), and how SLs and auxin interact in this process, remain unclear. In this study, the SL-deficient (dwarf10) and SL-insensitive (dwarf3) rice mutants and lines overexpressing OsPIN2 (OE) were used to investigate secondary LR development. The effects of exogenous GR24 (a synthetic SL analogue), 1-naphthylacetic acid (NAA; an exogenous auxin), 1-naphthylphthalamic acid (NPA; a polar auxin transport inhibitor), and abamine (a synthetic SL inhibitor) on rice secondary LR development were investigated. Rice d mutants with impaired SL biosynthesis and signaling exhibited increased secondary LR production compared with wild-type (WT) plants. Application of GR24 decreased the numbers of secondary LRs in dwarf10 (d10) plants but not in dwarf3 (d3), plants. These results indicate that SLs negatively regulate rice secondary LR production. Higher expression of DR5::GUS and more secondary LR primordia were found in the d mutants than in the WT plants. Exogenous NAA application increased expression of DR5::GUS in the WT, but had no effect on secondary LR formation. No secondary LRs were recorded in the OE lines, although DR5::GUS levels were higher than in the WT plants. However, on application of NPA, the numbers of secondary LRs were reduced in d10 and d3 mutants. Application of NAA increased the number of secondary LRs in the d mutants. GR24 eliminated the effect of NAA on secondary LR development in the d10, but not in the d3, mutants. These results demonstrate the importance of auxin in secondary LR formation, and that this process is inhibited by SLs via the D3 response pathway, but the interaction between auxin and SLs is complex.

Differential responses of root growth to nutrition with different ammonium/nitrate ratios involve auxin distribution in two tobacco cultivars

Nitrogen (N), the major forms of which are nitrate (NO3–) and ammonium (NH4+), plays an important role in plant growth and mediation of root development. However, the role of auxin in root growth in response to different NH4+/NO3– ratios remains unclear. Two tobacco cultivars (Nicotiana tabacum L.) were adopted in this study, which displayed variant growth features under the situations with sole NO3– nutrition ratio (NH4+/NO3– ratio: 0/100), low NO3– nutrition ratio (NH4+/NO3– ratio: 97/3), and optimal NH4+/NO3– ratio (50/50). We investigated the effects of the different NH4+/NO3– ratios on the formation and elongation of lateral roots (LRs), auxin concentration, DR5::GUS expression, 3H-labeled indole acetic acid ([3H]IAA) transport, and the expression of six PIN genes in tobacco roots. We also examined the effects of exogenous auxin and a transport inhibitor on LRs growth. The results are shown as follows, compared to optimal N nutrition conditions, the biomass and nitrogen (N) accumulation were largely reduced by sole and low NO3– nutrition treatment in NC89, but no difference was observed in Zhongyan 100. In most cases, sole and low NO3– nutrition impaired the elongation and formation of first-order lateral roots (1° LRs), only in NC89, thus reducing the root growth. IAA concentration and DR5::GUS expression levels decreased in roots when NC89 was subjected to sole and low NO3– nutrition media, suggesting that different NH4+/NO3– ratios affect the transport of auxin from leaves to roots. Results were similar following exogenous NAA application to low NO3– nutrition treated seedlings. Based on direct [3H]IAA transport measurement, the transport of polar auxin from shoots to roots decreased due to low NO3– nutrition. PIN4 expression levels were markedly decreased in roots of NC89 by sole and low NO3– nutrition, while they were unaffected in Zhongyan 100 roots. Overall, our findings suggest that LRs formation in tobacco seedlings is regulated by NH4+/NO3– ratios via modifying polar transport of auxin.

A low-cost aeroponic phenotyping system for storage root development: unravelling the below-ground secrets of cassava (Manihot esculenta)

BackgroundRoot and tuber crops are becoming more important for their high source of carbohydrates, next to cereals. Despite their commercial impact, there are significant knowledge gaps about the environmental and inherent regulation of storage root (SR) differentiation, due in part to the innate problems of studying storage roots and the lack of a suitable model system for monitoring storage root growth. The research presented here aimed to develop a reliable, low-cost effective system that enables the study of the factors influencing cassava storage root initiation and development.ResultsWe explored simple, low-cost systems for the study of storage root biology. An aeroponics system described here is ideal for real-time monitoring of storage root development (SRD), and this was further validated using hormone studies. Our aeroponics-based auxin studies revealed that storage root initiation and development are adaptive responses, which are significantly enhanced by the exogenous auxin supply. Field and histological experiments were also conducted to confirm the auxin effect found in the aeroponics system. We also developed a simple digital imaging platform to quantify storage root growth and development traits. Correlation analysis confirmed that image-based estimation can be a surrogate for manual root phenotyping for several key traits.ConclusionsThe aeroponic system developed from this study is an effective tool for examining the root architecture of cassava during early SRD. The aeroponic system also provided novel insights into storage root formation by activating the auxin-dependent proliferation of secondary xylem parenchyma cells to induce the initial root thickening and bulking. The developed system can be of direct benefit to molecular biologists, breeders, and physiologists, allowing them to screen germplasm for root traits that correlate with improved economic traits.

The role of auxin transporters and receptors in adventitious rooting of Arabidopsis thaliana pre-etiolated flooded seedlings

Adventitious roots (ARs) form from above-ground organs, and auxins are major regulators of AR development. TIR1/AFB F-box proteins act as well-established auxin receptors. Auxin transport involves the PINFORMED (PIN) auxin efflux carriers and AUXIN RESISTANT 1/LIKE AUX1 (AUX1/LAX1) influx carriers. To further elucidate the basis of AR development, we investigated the participation of these proteins and phosphorylation of PINs during adventitious rooting in hypocotyls of pre-etiolated flooded Arabidopsis thaliana seedlings. Mutant and GUS localization studies indicated that AFB2 is important in AR development. AUX1 loss-of-function reduced AR numbers, which could not be reversed by exogenous auxin. Single mutations in LAX1, LAX2 and LAX3 had no negative impact on AR development and the first and last mutations even promoted it. Double and triple mutants of AUX1, LAX1, LAX2 and LAX3 significantly reduced rooting, which was reversed by exogenous auxin. AUX1 was essential in AR establishment, with LAX3 apparently acting in conjunction. Proper phosphorylation of PINs by PID, WAG1 and WAG2 and auxin transport direction were equally essential for AR establishment. PIN1, AUX1 and AFB2 (overexpression) and LAX1, LAX3, PIN4 and PIN7 (downregulation) emerged as potential targets for genetic manipulation aiming at improving AR development.

A role for auxin signaling in the acquisition of longevity during seed maturation.

Seed longevity, the maintenance of viability during dry storage, is a crucial factor to preserve plant genetic resources and seed vigor. Inference of a temporal gene-regulatory network of seed maturation identified auxin signaling as a putative mechanism to induce longevity-related genes. Using auxin-response sensors and tryptophan-dependent auxin biosynthesis mutants of Arabidopsis thaliana L., the role of auxin signaling in longevity was studied during seed maturation. DII and DR5 sensors demonstrated that, concomitant with the acquisition of longevity, auxin signaling input and output increased and underwent a spatiotemporal redistribution, spreading throughout the embryo. Longevity of seeds of single auxin biosynthesis mutants with altered auxin signaling activity was affected in a dose-response manner depending on the level of auxin activity. Longevity-associated genes with promoters enriched in auxin response elements and the master regulator ABSCISIC ACID INSENSITIVE3 were induced by auxin in developing embryos and deregulated in auxin biosynthesis mutants. The beneficial effect of exogenous auxin during seed maturation on seed longevity was abolished in abi3-1 mutants. These data suggest a role for auxin signaling activity in the acquisition of longevity during seed maturation.

Exogenous auxins and leaf area affect the rooting of Xylopia aethiopica (Dunal A. Rich.) stem cuttings

ABSTRACTThe amenability of Xylopia aethiopica to vegetative propagation was assessed. Twelve auxin treatments and three ranges of leaf area were investigated for their effects on the propagation of stem cuttings in non-mist propagator. Results showed that the highest mortality rate (58.3%) was recorded with leafless cuttings while the lowest (5%) was recorded with 25–35 cm2 leaf area cuttings. There was no linearity in the relationship between auxin concentration and the mortality rate. Cuttings with 10–15 cm2 and those with 25–35 cm2 leaf areas rooted at higher percentages (74.5% and 73.6%, respectively) than leafless cuttings which rooted at 32%. Considering all leaf areas together the highest rooting percentage (90%) was recorded with 1% IBA powder while the lowest (22.2%) was recorded with the control. Whilst leaf area did not affect roots count, the highest mean number of roots per cutting (7.6) was recorded with 1% IBA powder. IBA powder treatment at 1% and 25–35 cm2 leaf area resulted in the highest mean root biomass (520.6 and 480.5 mg/cutting, respectively). The use of cuttings with 25–35 cm2 leaf area and treatment with 1% (w/w) IBA powder is thus recommended for vegetative propagation of X. aethiopica through stem cutting.

Accumulation of and Response to Auxins in Roots and Nodules of the Actinorhizal Plant Datisca glomerata Compared to the Model Legume Medicago truncatula.

Actinorhizal nodules are structurally different from legume nodules and show a greater similarity to lateral roots. Because of the important role of auxins in lateral root and nodule formation, auxin profiles were examined in roots and nodules of the actinorhizal species Datisca glomerata and the model legume Medicago truncatula. The auxin response in roots and nodules of both species was analyzed in transgenic root systems expressing a beta-glucuronidase gene under control of the synthetic auxin-responsive promoter DR5. The effects of two different auxin on root development were compared for both species. The auxin present in nodules at the highest levels was phenylacetic acid (PAA). No differences were found between the concentrations of active auxins of roots vs. nodules, while levels of the auxin conjugate indole-3-acetic acid-alanine were increased in nodules compared to roots of both species. Because auxins typically act in concert with cytokinins, cytokinins were also quantified. Concentrations of cis-zeatin and some glycosylated cytokinins were dramatically increased in nodules compared to roots of D. glomerata, but not of M. truncatula. The ratio of active auxins to cytokinins remained similar in nodules compared to roots in both species. The auxin response, as shown by the activation of the DR5 promoter, seemed significantly reduced in nodules compared to roots of both species, suggesting the accumulation of auxins in cell types that do not express the signal transduction pathway leading to DR5 activation. Effects on root development were analyzed for the synthetic auxin naphthaleneacetic acid (NAA) and PAA, the dominant auxin in nodules. Both auxins had similar effects, except that the sensitivity of roots to PAA was lower than to NAA. However, while the effects of both auxins on primary root growth were similar for both species, effects on root branching were different: both auxins had the classical positive effect on root branching in M. truncatula, but a negative effect in D. glomerata. Such a negative effect of exogenous auxin on root branching has previously been found for a cucurbit that forms lateral root primordia in the meristem of the parental root; however, root branching in D. glomerata does not follow that pattern.

Maize Inoculation with Microbial Consortia: Contrasting Effects on Rhizosphere Activities, Nutrient Acquisition and Early Growth in Different Soils.

The benefit of plant growth-promoting microorganisms (PGPMs) as plant inoculants is influenced by a wide range of environmental factors. Therefore, microbial consortia products (MCPs) based on multiple PGPM strains with complementary functions, have been proposed as superior, particularly under challenging environmental conditions and for restoration of beneficial microbial communities in disturbed soil environments. To test this hypothesis, the performance of a commercial MCP inoculant based on 22 PGPM strains was investigated in greenhouse experiments with maize on three soils with contrasting pH, organic matter content and microbial activity, under different P and N fertilization regimes. Interestingly, the MCP inoculant stimulated root and shoot growth and improved the acquisition of macronutrients only on a freshly collected field soil with high organic matter content, exclusively in combination with stabilized ammonium fertilization. This was associated with transiently increased expression of AuxIAA5 in the root tissue, a gene responsive to exogenous auxin supply, suggesting root growth promotion by microbial auxin production as a major mode of action of the MCP inoculant. High microbial activity was indicated by intense expression of soil enzyme activities involved in C, N and P cycling in the rhizosphere (cellulase, leucine peptidase, alkaline and acid phosphatases) but without MCP effects. By contrast, the MCP inoculation did not affect maize biomass production or nutrient acquisition on soils with very little Corg and low microbial activity, although moderate stimulation of rhizosphere enzymes involved in N and P cycling was recorded. There was also no indication for MCP-induced solubilization of Ca-phosphates on a calcareous sub-soil fertilized with rock-phosphate. The results demonstrate that the combination of multiple PGPM strains with complementary properties as MCP inoculants does not necessarily translate into plant benefits in challenging environments. Thus, a better understanding of the conditions determining successful MCP application is mandatory.

PtrARF2.1 Is Involved in Regulation of Leaf Development and Lignin Biosynthesis in Poplar Trees.

Auxin response factors (ARFs) are important regulators modulating the expression of auxin-responsive genes in various biological processes in plants. In the Populus genome, a total of 39 ARF members have been identified, but their detailed functions are still unclear. In this study, six poplar auxin response factor 2 (PtrARF2) members were isolated from P. trichocarpa. Expression pattern analysis showed that PtrARF2.1 is highly expressed in leaf tissues compared with other PtrARF2 genes and significantly repressed by exogenous auxin treatment. PtrARF2.1 is a nuclear-localized protein without transcriptional activation activity. Knockdown of PtrARF2.1 by RNA interference (RNAi) in poplars led to the dwarf plant, altered leaf shape, and reduced size of the leaf blade, while overexpression of PtrARF2.1 resulted in a slight reduction in plant height and the similar leaf phenotype in contrast to the wildtype. Furthermore, histological staining analysis revealed an ectopic deposition of lignin in leaf veins and petioles of PtrARF2.1-RNAi lines. RNA-Seq analysis showed that 74 differential expression genes (DEGs) belonging to 12 transcription factor families, such as NAM, ATAF and CUC (NAC), v-myb avian myeloblastosis viral oncogene homolog (MYB), ethylene response factors (ERF) and basic helix–loop–helix (bHLH), were identified in PtrARF2.1-RNAi leaves and other 24 DEGs were associated with the lignin biosynthetic pathway. Altogether, the data indicate that PtrARF2.1 plays an important role in regulating leaf development and influences the lignin biosynthesis in poplars.

The effect of auxin and auxin inhibitor application on induction and proliferation of protocorms in immature fruit Phalaenopsis amabilis in vitro culture

Abstract. Cahyaningsih AP, Pitoyo A, Solichatun. 2019. The effect of auxin and auxin inhibitor application on induction and proliferation of protocorms in immature fruit Phalaenopsis amabilis in vitro culture. Cell Biol Dev 3: 49-55. Auxin is a hormone that plays an important role in the ovulum development of moth orchid Phalaenopsis amabilis after pollination. Using immature fruit 60 days after pollination as explants are presumed to cause cessation of endogenous auxin distribution due to early fruit harvesting. The research was aimed to investigate the effect of exogenous auxin addition on induction and proliferation protocorm in moth orchid immature fruit explant through in vitro culture. This study used NAA (?-Naphthaleneacetic acid) as auxin in MS medium with 4 treatments: (i) control, (ii) NAA 1 ppm, (iii) NAA 5 ppm, and (iv) TIBA (2,3,5- triiodobenzoic acid) 5 ppm. Observed data include explants' color change, development, anatomy after planting, and protocorm development. Morphological and anatomical data were presented descriptively, and protocorm measurement data were analyzed using One Way ANOVA and followed by a DMRT test of 5% level. The results showed that the culture of immature fruit P. amabilis 60 DAP with the addition of NAA 1 and 5 ppm in immature fruit culture induced protocorm. Still, the protocorm was not able to develop further. Without adding exogenous hormone-induced protocorm formation, immature fruit culture developed some protocorm to form leaf primordia. Next, adding TIBA as auxin transport inhibitor, 5 ppm induced protocorm and developed all protocorms to form leaf primordia.

Putative Auxin and Light Responsive Promoter Elements From the Tomato spotted wilt tospovirus Genome, When Expressed as cDNA, Are Functional in Arabidopsis

Members of the virus order Bunyavirales cause serious diseases in animals, humans and plants. Family Tospoviridae in this order contains only one genus Orthotospovirus, and members in this genus exclusively infect plants. Tomato spotted wilt tospovirus (TSWV) is considered one of the most economically important plants viruses. Little is known about the regulatory elements in the TSWV genome. Here we show that, when in the cDNA form, the 5′-upstream region of the TSWV-coded GN/GC gene (pGN/GC) possesses putative cis-regulatory elements, including an auxin responsive element (AuxRE) for binding of auxin response factors (ARFs), as well as a circadian clock-associated 1 (CCA1) protein binding site (CBS). Due to the lack of a reverse genetics system, we verified the functionality of these elements in Arabidopsis. pGN/GC showed light-suppressive promoter activity in transgenic Arabidopsis, and mutation in the CBS was sufficient to switch the activity to light inducible. Additionally, exogenous auxin treatments repressed the promoter activity of both wild type and CBS-mutated pGN/GC. Mutation in AuxRE in both promoters abolished their sensitivity to auxin. As transcriptional repressors, both CCA1 and ARF2 were able to bind to pGN/GC directly. To our knowledge, this is the first report that a 5′-terminal sequence of an RNA virus has light-and hormone-responsive promoter activities when expressed as cDNA in host plant’s nuclear background. Our findings suggest new clues on the possible origin, evolution and function of the TSWV genomic sequence and its non-coding regions.