Molecular mechanisms of Evening Complex activity in Arabidopsis.

The Evening Complex (EC), composed of the DNA binding protein LUX ARRHYTHMO (LUX) and two additional proteins EARLY FLOWERING 3 (ELF3) and ELF4, is a transcriptional repressor complex and a core component of the plant circadian clock. In addition to maintaining oscillations in clock gene expression, the EC also participates in temperature and light entrainment, acting as an important environmental sensor and conveying this information to growth and developmental pathways. However, the molecular basis for EC DNA binding specificity and temperature-dependent activity were not known. Here, we solved the structure of the DNA binding domain of LUX in complex with DNA. Residues critical for high-affinity binding and direct base readout were determined and tested via site-directed mutagenesis in vitro and in vivo. Using extensive in vitro DNA binding assays of LUX alone and in complex with ELF3 and ELF4, we demonstrate that, while LUX alone binds DNA with high affinity, the LUX-ELF3 complex is a relatively poor binder of DNA. ELF4 restores binding to the complex. In vitro, the full EC is able to act as a direct thermosensor, with stronger DNA binding at 4 °C and weaker binding at 27 °C. In addition, an excess of ELF4 is able to restore EC binding even at 27 °C. Taken together, these data suggest that ELF4 is a key modulator of thermosensitive EC activity.

Variations in Circadian Clock Organization & Function: A Journey from Ancient to Recent.

MAIN CONCLUSION: Circadian clock components exhibit structural variations in different plant systems, and functional variations during various abiotic stresses. These variations bear relevance for plant fitness and could be important evolutionarily. All organisms on earth have the innate ability to measure time as diurnal rhythms that occur due to the earth's rotations in a 24-h cycle. Circadian oscillations arising from the circadian clock abide by its fundamental properties of periodicity, entrainment, temperature compensation, and oscillator mechanism, which is central to its function. Despite the fact that a myriad of research in Arabidopsis thaliana illuminated many detailed aspects of the circadian clock, many more variations in clock components' organizations and functions remain to get deciphered. These variations are crucial for sustainability and adaptation in different plant systems in the varied environmental conditions in which they grow. Together with these variations, circadian clock functions differ drastically even during various abiotic and biotic stress conditions. The present review discusses variations in the organization of clock components and their role in different plant systems and abiotic stresses. We briefly introduce the clock components, entrainment, and rhythmicity, followed by the variants of the circadian clock in different plant types, starting from lower non-flowering plants, marine plants, dicots to the monocot crop plants. Furthermore, we discuss the interaction of the circadian clock with components of various abiotic stress pathways, such as temperature, light, water stress, salinity, and nutrient deficiency with implications for the reprogramming during these stresses. We also update on recent advances in clock regulations due to post-transcriptional, post-translation, non-coding, and micro-RNAs. Finally, we end this review by summarizing the points of applicability, a remark on the future perspectives, and the experiments that could clear major enigmas in this area of research.

Light- and hormone-mediated development in non-flowering plants: An overview.

MAIN CONCLUSION: Light, hormones and their interaction regulate different aspects of development in non-flowering plants. They might have played a role in the evolution of different plant groups by conferring specific adaptive evolutionary changes. Plants are sessile organisms. Unlike animals, they lack the opportunity to abandon their habitat in unfavorable conditions. They respond to different environmental cues and adapt accordingly to control their growth and developmental pattern. While phytohormones are known to be internal regulators of plant development, light is a major environmental signal that shapes plant processes. It is plausible that light-hormone crosstalk might have played an important role in plant evolution. But how the crosstalk between light and phytohormone signaling pathways might have shaped the plant evolution is unclear. One of the possible reasons is that flowering plants have been studied extensively in context of plant development, which cannot serve the purpose of evolutionary comparisons. In order to elucidate the role of light, hormone and their crosstalk in the evolutionary adaptation in plant kingdom, one needs to understand various light- and hormone-mediated processes in diverse non-flowering plants. This review is an attempt to outline major light- and phytohormone-mediated responses in non-flowering plant groups such as algae, bryophytes, pteridophytes and gymnosperms.

Uncovering the molecular signature underlying the light intensity-dependent root development in Arabidopsis thaliana.

BACKGROUND: Root morphology is known to be affected by light quality, quantity and direction. Light signal is perceived at the shoot, translocated to roots through vasculature and further modulates the root development. Photoreceptors are differentially expressed in both shoot and root cells. The light irradiation to the root affects shoot morphology as well as whole plant development. The current work aims to understand the white light intensity dependent changes in root patterning and correlate that with the global gene expression profile. RESULTS: Different fluence of white light (WL) regulate overall root development via modulating the expression of a specific set of genes. Phytochrome A deficient Arabidopsis thaliana (phyA-211) showed shorter primary root compared to phytochrome B deficient (phyB-9) and wild type (WT) seedlings at a lower light intensity. However, at higher intensity, both mutants showed shorter primary root in comparison to WT. The lateral root number was observed to be lowest in phyA-211 at intensities of 38 and 75 µmol m - 2 s - 1. The number of adventitious roots was significantly lower in phyA-211 as compared to WT and phyB-9 under all light intensities tested. With the root phenotypic data, microarray was performed for four different intensities of WL light in WT. Here, we identified ~ 5243 differentially expressed genes (DEGs) under all light intensities. Gene ontology-based analysis indicated that different intensities of WL predominantly affect a subset of genes having catalytic activity and localized to the cytoplasm and membrane. Furthermore, when root is irradiated with different intensities of WL, several key genes involved in hormone, light signaling and clock-regulated pathways are differentially expressed. CONCLUSION: Using genome wide microarray-based approach, we have identified candidate genes in Arabidopsis root that responded to the changes in light intensities. Alteration in expression of genes such as PIF4, COL9, EPR1, CIP1, ARF18, ARR6, SAUR9, TOC1 etc. which are involved in light, hormone and clock pathway was validated by qRT-PCR. This indicates their potential role in light intensity mediated root development.

Carbon nanoparticles influence photomorphogenesis and flowering time in Arabidopsis thaliana.

KEY MESSAGE: Inclusion of carbon nanoparticles in growth medium accelerates timing to flower by down-regulating phytochrome B in a CONSTANS-independent but photoperiod-dependent manner in Arabidopsis thaliana. Despite the recognized importance of nanoparticles in plant development over the last decade, the effect of carbon nanoparticles (CNPs) on plant processes such as photomorphogenesis and flowering time control is poorly understood. We explored the uptake, accumulation and effect of CNPs on seedling development and flowering time control in Arabidopsis thaliana (At). CNPs uptake was demonstrated using Raman spectroscopy and light microscopy that affected At seedling growth and flowering time in a dose-dependent manner. The highest accumulation of CNPs was observed in leaves followed by stem and root tissues. CNPs treatment enhanced seed germination, showed elongated hypocotyl, larger cotyledon area and increased chlorophyll content in At seedlings. CNPs treatment induced early flowering in both long-day and short-day growth conditions indicating a photoperiod-dependent effect. CNPs-treated seedlings showed a drastic reduction in the relative abundance of phytochrome B (PHYB) transcript. Further, we analyzed the transcript abundance of at least one major component involved in various pathways that regulate flowering such as (1) photoperiod, (2) gibberellic acid (GA), (3) vernalization and (4) autonomous. An up-regulation of transcript levels of PHYTOCHROME INTERACTING FACTOR 4 (PIF4), GIGANTEA (GI), REPRESSOR OF GIBBERELLIC ACID 1 (RGA1) and LEAFY (LFY) were observed, however, there were no changes in the transcript levels of CONSTANS (CO), VERNALIZATION 1 (VRN1) and FLOWERING CONTROL LOCUS A (FCA). Despite the up-regulation of RGA1, we conclude that the earlier flowering is most likely GA-independent. Here, we demonstrated that the early flowering in CNPs-treated seedlings was PHYB and photoperiod-dependent.

Phosphorylation of CONSTANS and its COP1-dependent degradation during photoperiodic flowering of Arabidopsis.

Seasonal flowering involves responses to changes in day length. In Arabidopsis thaliana, the CONSTANS (CO) transcription factor promotes flowering in the long days of spring and summer. Late flowering in short days is due to instability of CO, which is efficiently ubiquitinated in the dark by the CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) E3 ligase complex. Here we show that CO is also phosphorylated. Phosphorylated and unphosphorylated forms are detected throughout the diurnal cycle but their ratio varies, with the relative abundance of the phosphorylated form being higher in the light and lower in the dark. These changes in relative abundance require COP1, because in the cop1 mutant the phosphorylated form is always more abundant. Inactivation of the PHYTOCHROME A (PHYA), CRYPTOCHROME 1 (CRY1) and CRYPTOCHROME 2 (CRY2) photoreceptors in the phyA cry1 cry2 triple mutant most strongly reduces the amount of the phosphorylated form so that unphosphorylated CO is more abundant. This effect is caused by increased COP1 activity, as it is overcome by introduction of the cop1 mutation in the cop1 phyA cry1 cry2 quadruple mutant. Degradation of CO is also triggered in red light, and as in darkness this increases the relative abundance of unphosphorylated CO. Finally, a fusion protein containing truncated CO protein including only the carboxy-terminal region was phosphorylated in transgenic plants, locating at least one site of phosphorylation in this region. We propose that CO phosphorylation contributes to the photoperiodic flowering response by enhancing the rate of CO turnover via activity of the COP1 ubiquitin ligase.

Balanced activity of microRNA166/165 and its target transcripts from the class III homeodomain-leucine zipper family regulates root growth in Arabidopsis thaliana.

Overexpression of miR166/165 down-regulates target HD - ZIP IIIs and promotes root growth by enhancing cell division and meristematic activity, whereas overexpression of HD - ZIP IIIs inhibits root growth in Arabidopsis thaliana. Post-embryonic growth of higher plants is maintained by active meristems harbouring undifferentiated cells. Shoot and root apical meristems (SAM and RAM) utilize both similar and distinct signalling mechanisms for their maintenance in Arabidopsis thaliana. An important regulatory role in this context has the interaction of microRNAs with their target mRNAs, mostly encoding transcription factors. One class of microRNA166/165 (miR166/165) has been implicated in the maintenance of SAM and vascular patterning. Here, we show that miR166/165 plays an important role in root growth also by negatively regulating its target transcripts, HD-ZIP IIIs, in the RAM. While overexpression of miR166 promotes RAM activity, overexpression of its targets reduces RAM activity. These results reveal a conserved role of miR166/165 in the maintenance of SAM and RAM activity in A. thaliana.

GIGANTEA supresses wilt disease resistance by down-regulating the jasmonate signaling in Arabidopsis thaliana.

GIGANTEA (GI) is a plant-specific nuclear protein that plays a pleiotropic role in the growth and development of plants. GI's involvement in circadian clock function, flowering time regulation, and various types of abiotic stress tolerance has been well documented in recent years. Here, the role of GI in response to Fusarium oxysporum (F. oxysporum) infection is investigated at the molecular level comparing Col-0 WT with the gi-100 mutant in Arabidopsis thaliana. Disease progression, photosynthetic parameters, and comparative anatomy confirmed that the spread and damage caused by pathogen infection were less severe in gi-100 than in Col-0 WT plants. F. oxysporum infection induces a remarkable accumulation of GI protein. Our report showed that it is not involved in flowering time regulation during F. oxysporum infection. Estimation of defense hormone after infection showed that jasmonic acid (JA) level is higher and salicylic acid (SA) level is lower in gi-100 compared to Col-0 WT. Here, we show that the relative transcript expression of CORONATINE INSENSITIVE1 (COI1) and PLANT DEFENSIN1.2 (PDF1.2) as a marker of the JA pathway is significantly higher while ISOCHORISMATE SYNTHASE1 (ICS1) and NON-EXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1), the markers of the SA pathway, are downregulated in the gi-100 mutants compared to Col-0 plants. The present study convincingly suggests that the GI module promotes susceptibility to F. oxysporum infection by inducing the SA pathway and inhibiting JA signaling in A. thaliana.

Arabidopsis COP1 shapes the temporal pattern of CO accumulation conferring a photoperiodic flowering response.

The transcriptional regulator CONSTANS (CO) promotes flowering of Arabidopsis under long summer days (LDs) but not under short winter days (SDs). Post-translational regulation of CO is crucial for this response by stabilizing the protein at the end of a LD, whereas promoting its degradation throughout the night under LD and SD. We show that mutations in CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), a component of a ubiquitin ligase, cause extreme early flowering under SDs, and that this is largely dependent on CO activity. Furthermore, transcription of the CO target gene FT is increased in cop1 mutants and decreased in plants overexpressing COP1 in phloem companion cells. COP1 and CO interact in vivo and in vitro through the C-terminal region of CO. COP1 promotes CO degradation mainly in the dark, so that in cop1 mutants CO protein but not CO mRNA abundance is dramatically increased during the night. However, in the morning CO degradation occurs independently of COP1 by a phytochrome B-dependent mechanism. Thus, COP1 contributes to day length perception by reducing the abundance of CO during the night and thereby delaying flowering under SDs.

Red Light and Glucose Enhance Cytokinin-Mediated Bud Initial Formation in Physcomitrium patens.

Growth and development of Physcomitrium patens is endogenously regulated by phytohormones such as auxin and cytokinin. Auxin induces the transition of chloronema to caulonema. This transition is also regulated by additional factors such as quantity and quality of light, carbon supply, and other phytohormones such as strigolactones and precursors of gibberrelic acid. On the other hand, cytokinins induce the formation of bud initials following caulonema differentiation. However, the influence of external factors such as light or nutrient supply on cytokinin-mediated bud initial formation has not been demonstrated in Physcomitrium patens. This study deals with the effect of light quality and nutrient supply on cytokinin-mediated bud initial formation. Bud initial formation has been observed in wild type plants in different light conditions such as white, red, and blue light in response to exogenously supplied cytokinin as well as glucose. In addition, budding assay has been demonstrated in the cry1a mutant of Physcomitrium in different light conditions. The results indicate that carbon supply and red light enhance the cytokinin response, while blue light inhibits this process in Physcomitrium.

Integrated Expression Analysis of Small RNA, Degradome and Microarray Reveals Complex Regulatory Action of miRNA during Prolonged Shade in Swarnaprabha Rice.

Prolonged shade during the reproductive stage can result in significant yield losses in rice. For this study, we elucidated the role of microRNAs in prolonged-shade tolerance (~20 days of shade) in a shade-tolerant rice variety, Swarnaprabha (SP), in its reproductive stage using small RNA and degradome sequencing with expression analysis using microarray and qRT-PCR. This study demonstrates that miRNA (miR) regulation for shade-tolerance predominately comprises the deactivation of the miR itself, leading to the upregulation of their targets. Up- and downregulated differentially expressed miRs (DEms) presented drastic differences in the category of targets based on the function and pathway in which they are involved. Moreover, neutrally regulated and uniquely expressed miRs also contributed to the shade-tolerance response by altering the differential expression of their targets, probably due to their differential binding affinities. The upregulated DEms mostly targeted the cell wall, membrane, cytoskeleton, and cellulose synthesis-related transcripts, and the downregulated DEms targeted the transcripts of photosynthesis, carbon and sugar metabolism, energy metabolism, and amino acid and protein metabolism. We identified 16 miRNAs with 21 target pairs, whose actions may significantly contribute to the shade-tolerance phenotype and sustainable yield of SP. The most notable among these were found to be miR5493-OsSLAC and miR5144-OsLOG1 for enhanced panicle size, miR5493-OsBRITTLE1-1 for grain formation, miR6245-OsCsIF9 for decreased stem mechanical strength, miR5487-OsGns9 and miR168b-OsCP1 for better pollen development, and miR172b-OsbHLH153 for hyponasty under shade.

MicroRNAs modulate ethylene induced retrograde signal for rice endosperm starch biosynthesis by default expression of transcriptome.

Control of stage specific spike in ethylene production at anthesis has been a vauable route to potentially enhance genetic ceiling for grain filling of rice spikelet. A number of genes controlling ethylene homeostasis and starch synthesis have been identified so long, but lack of credible information on master modulation of gene expression by miRNAs and their target genes associated with hormonal dynamics obfuscate mechanisms controlling genotype difference in quantum of grain filling. The confusion accounts for consequent shrinkage of options for yield manipulation. In a two by two factorial design, miRNA regulation of spikelet specific grain development in low against high sterile recombinant inbred lines of rice Oryza sativa L. namely CR 3856-62-11-3-1-1-1-1-1-1 (SR 157) and CR 3856-63-1-1-1-1-1-1-1 (SR 159) respectively, and inferior verses superior spikelets were compared during first 10 days after anthesis. Grain filling was poorer in SR159 than SR157 and inferior spikelets in the former were most vulnerable. Between the cultivars, overall expression of unique miRNAs with targets on ethylene pathway genes was higher in SR159 than SR157 and the situation was opposite for auxin pathway genes. Precision analysis in psTarget server database identified up-regulation of MIR2877 and MIR530-5p having Os11t0141000-02 and Os07t0239400-01 (PP2A regulatory subunit-like protein and ethylene-responsive small GTP-binding proteins) and MIR396h having Os01t0643300-02 (an auxin efflux carrier protein) and Os01t0643300-01 (a PIN1-like auxin transport protein), as targets with highest probability at anthesis and 5 days after anthesis respectively, in the inferior spikelet and the fold change values of DGE matched with pattern of gene expression (relative transcript level) in the qRT-PCR studies conducted for relevant miRNAs and protein factors for ethylene and auxin signalling. In conclusion, epigenetic regulation of both auxin and ethylene homeostasis control grain filling of rice spikelet was established, but evidences were more robust for the latter.

Low-light and its effects on crop yield: Genetic and genomic implications.

Shade indicates decreased sunlight. The agricultural importance of shade imparts to its deteriorative effect of crop yield. Rice is not only the most widely used food crop by a third of the population of the world, but it has also been established as the modelmonocot plant for study. This article describes several important aspects of shade on rice yield with appropriate examples in other plants such as Arabidopsis. To start with, how different environmental or growth conditions create shade is explained. Themorphological, physiological and biochemical characteristics due to different kinds of shade are selectively explained. The molecular characteristics of rice under shade from genetic, genomic and epigenetic studied are discussed. Signalling components for the manifestation of shade tolerance responses and their interconnection with other signalling networks and hormone pathway components are from recent reports. A list of genes, micro-RNAs and metabolites that are involved in shade responses is presented. Lastly, implications for sustainable yield under shade is discussed. This review will be useful not only for cutting-edge information on shade tolerance but will also build framework for upcoming new rice varieties with sustainable yield under shade.

Auxin-binding proteins without KDEL sequence in the moss Funaria hygrometrica.

Whereas the important plant growth regulator auxin has multiple effects in flowering plants, it induces a specific cell differentiation step in the filamentous moss protonema. Here, we analyse the presence of classical auxin-binding protein (ABP1) homologues in the moss Funaria hygrometrica. Microsomal membranes isolated from protonemata of F. hygrometrica have specific indole acetic acid-binding sites, estimated to be about 3-5 pmol/mg protein with an apparent dissociation constant (K (d)) between 3 and 5 microM. Western analyses with anti-ABP1 antiserum detected the canonical endoplasmic reticulum (ER)-localised 22-24 kDa ABP1 in Zea mays, but not in F. hygrometrica. Instead, polypeptides of 31-33 and 46 kDa were labelled in the moss as well as in maize. In F. hygrometrica these proteins were found exclusively in microsomal membrane fractions and were confirmed as ABPs by photo-affinity labelling with 5-azido-[7-(3)H]-indole-3-acetic acid. Unlike the classical corn ABP1, these moss ABPs did not contain the KDEL ER retention sequence. Consistently, the fully sequenced genome of the moss Physcomitrella patens, a close relative of F. hygrometrica, encodes an ABP1-homologue without KDEL sequence. Our study suggests the presence of putative ABPs in F. hygrometrica that share immunological epitopes with ABP1 and bind auxin but are different from the classical corn ABP1.

Light and auxin signaling cross-talk programme root development in plants.

Root development in plants is affected by light and phytohormones. Different ranges of light wavelength influence root patterning in a particular manner. Red and white light promote overall root development, whereas blue light has both positive as well as negative role in these processes. Light-mediated root development primarily occurs through modulation of synthesis, signaling and transport of the phytohormone auxin. Auxin has been shown to play a critical role in root development. It is being well-understood that components of light and auxin signaling cross-talk with each other. However, the signaling network that can modulate the root development is an intense area of research. Currently, limited information is available about the interaction of these two signaling pathways. This review not only summarizes the current findings on how different quality and quantity of light affect various aspects of root development but also present the role of auxin in these developmental aspects starting from lower to higher plants.

Shade tolerance in Swarnaprabha rice is associated with higher rate of panicle emergence and positively regulated by genes of ethylene and cytokinin pathway.

This study identifies characteristics of seedling, mature plant phenotypes, changes at genetic and genomic level associated with Swarnaprabha (SP) rice grown under prolonged shade and compared with Nagina 22 (N22). Coleoptile length under low red/far-red was intermediate between that in dark and red light in a 7-days growth frame. Whereas, highest rootlet number was discriminating in seedlings grown for 28 days in hydroponics. In shade, SP and N22 both showed several tolerant mature plant phenotypes, except the panicle length, yield per plant and % grain filling, which were higher in SP. Percentage decrease in yield / plant in shade showed significant positive correlation with increase in NDVI, decrease in panicle length and % grain filling (p ≤ 0.01). Rate of panicle emergence in shade was higher in SP than N22. Expression patterns of PHYTOCHROME INTERACTING FACTOR LIKE-13 and PHYTOCHROME B were contrasting in SP and N22 seedlings under continuous red or red/far-red. Microarray analysis revealed the up-regulation of most of the ethylene and cytokinin pathway genes in shade grown panicles of SP. Significant up-regulation of ETHYLENE RESPONSE ELEMENT BINDING PROTEIN-2, MOTHER OF FLOWERING TIME 1, and SHORT PANICLE1 genes in shade grown panicles of SP could explain its sustainable higher yield in shade.

Perspective of mitigating atmospheric heavy metal pollution: using mosses as biomonitoring and indicator organism.

Mosses were proved as an ideal and reliable biomonitor as well as an indicator of atmospheric trace metal pollution. They are used as model indicator species of air pollution since long back due to their simple structure, genetic diversity, totipotency, rapid colony-forming ability, and high metal resistance behavior. Bryomonitoring technique is gradually being popularized as an economically viable procedure for estimating the degrees of environmental health and evaluating the toxic pollutants in biosphere. Thus, in the present scenario, many parts of the world use these organisms for monitoring the air pollution. This article describes an overview of the relationship of terrestrial mosses with trace metals with respect to their uptake, accumulation, and toxification as well as detoxification and tolerance mechanisms. The review article explicitly expresses the caliber of the cryptogamic mosses in establishing the pristine environment around the world. It also highlights the underpinning mechanisms and potential for future research directions. We have referred more than 250 articles, which deals with the assessment and impact of different heavy metals on 52 numbers of different moss species belongs to different climatic zones. The present review covers the research work in this area carried out worldwide since 1965.

Aquasorbent guargum grafted hyperbranched poly (acrylic acid): A potential culture medium for microbes and plant tissues.

This study reports the synthesis of an unprecedented bio-based aquasorbent guargum-g-hyperbranched poly (acrylic acid); bGG-g-HBPAA by employing graft-copolymerization and "Strathclyde methodology" simultaneously in emulsion and its possible use as a sustainable nutrient bed for the effective growth of Anabaena cylindrica and Vigna radiata seedlings. The formation of bGG-g-HBPAA and the presence of hyperbranched architectures was confirmed from XRD, FTIR, 13C NMR, solubility, intrinsic viscosity, BET surface area/ pore size, SEM and rheology analyses. The synthesized grade with a branching percent of 65.4% and a swelling percentage of 13,300% facilitated maximum growth of the cultured species as compared to guargum and its linear graft. Semi synthetic bGG-g-HBPAA culture medium was optically transparent, dried at a controlled rate, held a huge amount of water for growth, provided sufficient space for unhindered growth and featured dimensional stability.

Carbohydrates and polyphenolics of extracts from genetically altered plant acts as catalysts for in vitro synthesis of silver nanoparticle.

Eco-friendly biosynthetic approach for silver nanoparticles production using plant extracts is an exciting advancement in bio-nanotechnology and has been successfully attempted in nearly 41 plant species. However, an established model plant system for systematically unraveling the biochemical components required for silver nanoparticles production is lacking. Here we used Arabidopsis thaliana as the model plant for silver nanoparticles biosynthesis in vitro. Employing biochemical, spectroscopic methods, selected mutants and over-expressor plants of Arabidopsis involved in pleotropic functions and sugar homeostasis, we show that carbohydrates, polyphenolics and glyco-proteins are essential components which stimulated silver nanoparticles synthesis. Using molecular genetics as a tool, our data enforces the requirement of sugar conjugated proteins as essentials for AgNPs synthesis over protein alone. Additionally, a comparative analysis of AgNPs synthesis using the aqueous extracts of some of the plant species found in a brackish water ecosystem (Gracilaria, Potamogeton, Enteromorpha and Scendesmus) were explored. Plant extract of Potamogeton showed the highest potential of nanoparticles production comparable to that of Arabidopsis among the species tested. Silver nanoparticles production in the model plant Arabidopsis not only opens up a possibility of using molecular genetics tool to understand the biochemical pathways and components in detail for its synthesis.

Hydrolases of the ILR1-like family of Arabidopsis thaliana modulate auxin response by regulating auxin homeostasis in the endoplasmic reticulum.

Amide-linked conjugates of indole-3-acetic acid (IAA) have been identified in most plant species. They function in storage, inactivation or inhibition of the growth regulator auxin. We investigated how the major known endogenous amide-linked IAA conjugates with auxin-like activity act in auxin signaling and what role ILR1-like proteins play in this process in Arabidopsis. We used a genetically encoded auxin sensor to show that IAA-Leu, IAA-Ala and IAA-Phe act through the TIR1-dependent signaling pathway. Furthermore, by using the sensor as a free IAA reporter, we followed conjugate hydrolysis mediated by ILR1, ILL2 and IAR3 in plant cells and correlated the activity of the hydrolases with a modulation of auxin response. The conjugate preferences that we observed are in agreement with available in vitro data for ILR1. Moreover, we identified IAA-Leu as an additional substrate for IAR3 and showed that ILL2 has a more moderate kinetic performance than observed in vitro. Finally, we proved that IAR3, ILL2 and ILR1 reside in the endoplasmic reticulum, indicating that in this compartment the hydrolases regulate the rates of amido-IAA hydrolysis which results in activation of auxin signaling.