Phytohormone Abscisic Acid Research Articles

Salt stress affects the fruit quality of Lycium ruthenicum Murr.

Halophytic plant Lycium ruthenicum is rich with anthocyanin in fruit, and has thus attracted considerable attention due to its health-promoting effects. However, the effect of salt stress on fruit quality remains unknown. In this study, RNA-seq, LC-MS/MS coupling with TMT labeling, and GC-MS approaches were respectively used to examine the transcriptomic, proteomic, and metabolomic profiles in ripening fruit of 3-year-old trees treated with 0 or 300 mM NaCl, which resulting in 5608 differentially expressed genes (DEGs), 201 differentially expressed proteins (DEPs), and 23 differentially accumulated metabolites (DAMs). KEGG enrichment analysis showed that DEGs related to amino acid metabolism, the TCA cycle, flavonoid biosynthesis, inositol phosphate metabolism, and alpha-linolenic acid metabolism were significantly enriched. DEPs related to protein homeostasis and redox homeostasis were enriched. The contents of anthocyanins, proline, glucose, and glutamine are up-regulated in the salt-treated fruit. Our results indicate that the increased fruit anthocyanin might attribute to the up-regulated MYB component of the MYB-bHLH-WD40 complex and the post-transcriptionally up-regulated proteins encoded by anthocyanin structural genes under salt stress condition. Additionally, weighted gene correlation network analysis (WGCNA) results show that anthocyanin content is highly associated with three modules including multiple transcription factors, genes related to reactive oxygen species homeostasis and phytohormones (abscisic acid and ethylene), and that three FADs genes are involved in the biosynthesis of oleic acid and linoleic acid. Taken together, these findings provide a comprehensive understanding of salt stress-mediated regulation of fruit quality, thereby facilitating the breeding of high anthocyanin cultivars of L. ruthenicum in future.

ВЛИЯНИЕ ФИТОГОРМОНОВ НА РОСТ КОЛОНИЙ И СТЕПЕНЬ СПОРУЛЯЦИИ РАЗЛИЧНЫХ ИЗОЛЯТОВ ПАТОГЕНА STAGONOSPORA NODORUM

Currently, the phytohormones cytokinins (CK) and abscisic acid (ABA) are considered as important regulators of the interaction between pathogens and plants. However, data on the role of these phytohormones in pathogenesis are contradictory, and information on the role of CK and ABA in the regulation of fungal growth and development is very limited. In this work, we studied the effects of CK and ABA on the growth of colonies and the degree of sporulation of various isolates of the pathogen Stagonospora nodorum SnB, Sn9MH-3A, and Sn4VD. The choice of phytohormone concentrations was carried out using the S. nodorum SnB isolate, and it was shown that the concentration of both CK and ABA, 0.1 µM, had the greatest effect on the sporulation of the fungus and inhibited the radial growth of the mycelium least of all. The addition of CK or ABA to the cultivation medium inhibited the growth of mycelium, but increased the sporulation of aggressive isolates of S. nodorum SnB and Sn9MH-3A. Moreover, the degree of influence of ABA on the sporulation of these isolates differed. The avirulent Sn4VD isolate increased its radial growth in the presence of the phytohormones CK and ABA, but did not begin to sporulate. Thus, the effect of CK and ABA on the growth of colonies and the degree of sporulation of the pathogen S. nodorum may be opposite and depend both on the concentration of phytohormones and on the genotype of the pathogen strain.

CKL2 mediates the crosstalk between abscisic acid and brassinosteroid signaling to promote swift growth recovery after stress in Arabidopsis.

Plants must adapt to the constantly changing environment. Adverse environmental conditions trigger various defensive responses, including growth inhibition mediated by phytohormone abscisic acid (ABA). When the stress recedes, plants must transit rapidly from stress defense to growth recovery, but the underlying mechanisms by which plants switch promptly and accurately between stress resistance and growth are poorly understood. Here, using quantitative phosphoproteomics strategy, we discovered that early ABA signaling activates upstream components of brassinosteroid (BR) signaling through CASEIN KINASE 1-LIKE PROTEIN 2 (CKL2). Further investigations showed that CKL2 interacts with and phosphorylates BRASSINOSTEROID INSENSITIVE1 (BRI1), the main BR receptor, to maintain the basal activity of the upstream of BR pathway in plants exposed to continuous stress conditions. When stress recedes, the elevated phosphorylation of BRI1 by CKL2 contributes to the swift reactivation of BR signaling, which results in quick growth recovery. These results suggest that CKL2 plays a critical regulatory role in the rapid switch between growth and stress resistance. Our evidence expands the understanding of how plants modulate stress defense and growth by integrating ABA and BR signaling cascades.

Pepper stress-associated protein 14 is a substrate of CaSnRK2.6 that positively modulates abscisic acid-dependent osmotic stress responses.

The phytohormone abscisic acid (ABA) plays a prominent role in various abiotic stress responses of plants. In the ABA-dependent osmotic stress response, SnRK2.6, one of the subclass III SnRK2 kinases, has been identified as playing a key role by phosphorylating and activating downstream genes. Although several modulatory proteins have been reported to be phosphorylated by SnRK2.6, the identities of the full spectrum of downstream targets have yet to be sufficiently established. In this study, we identified CaSAP14, a stress-associated protein in pepper (Capsicum annuum), as a downstream target of CaSnRK2.6. We elucidated the physical interaction between SnRK2.6 and CaSAP14, both invitro and invivo, and accordingly identified a C-terminal C2H2-type zinc finger domain of CaSAP14 as being important for their interaction. CaSAP14-silenced pepper plants showed dehydration- and high salt-sensitive phenotypes, whereas overexpression of CaSAP14 in Arabidopsis conferred tolerance to dehydration, high salinity, and mannitol treatment, with plants showing ABA-hypersensitive phenotypes. Furthermore, an in-gel kinase assay revealed that CaSnRK2.6 phosphorylates CaSAP14 in response to exogenous ABA, dehydration, and high-salinity stress. Collectively, these findings suggest that CaSAP14 is a direct substrate of CaSnRK2.6 and positively modulates dehydration- and high salinity-induced osmotic stress responses.

Mitochondrial alternative oxidase enhanced ABA-mediated drought tolerance in Solanum lycopersicum

The phytohormone abscisic acid (ABA) plays essential roles in modulating drought stress responses. Mitochondrial alternative oxidase (AOX) is critical for reactive oxygen species (ROS) scavenging in drought stress responses. However, whether ABA signal in concert with AOX to moderate drought stress response remains largely unclear. In our study, we uncover the positive role of AOX in ABA-mediated drought tolerance in tomato (Solanum lycopersicum). Here, we report that ABA participates in the regulation of alternative respiration, and the increased AOX was found to improve drought tolerance by reducing total ROS accumulation. We also found that transcription factor ABA response element-binding factor 1 (SlAREB1) can directly bind to the promoter of AOX1a to activate its transcription. Virus-induced gene silencing (VIGS) of SlAREB1 compromised the ABA-induced alternative respiratory pathway, disrupted redox homeostasis and decreased plant resistance to drought stress, while overexpression of AOX1a in TRV2-SlAREB1 plants partially rescued the severe drought phenotype. Taken together, our results indicated that AOX1a plays an essential role in ABA-mediated drought tolerance partially in a SlAREB1-dependent manner, providing new insights into how ABA modulates ROS levels to cope with drought stress by AOX.

Genome-wide characterization and expression profiling of GASA gene family in Triticum turgidum ssp. durum (desf.) husn. (Durum wheat) unveils its involvement in environmental stress responses

Family members within the plant-specific gibberellic acid-stimulated Arabidopsis (GASA) gene serve a crucial role in plant growth and development, particularly in flower induction and seed development. Through a genome-wide analysis of Triticum turgidum ssp. Durum (durum wheat), we identified 19 GASA genes, designated as TdGASA1‒19. Moreover, the chromosomal locations, exon–intron distribution and the physiochemical properties of these genes were determined and the subcellular localization of their encoded proteins was estimated. Analyses of their domain structure, motif arrangements, and phylogeny revealed four distinct groups that share a conserved GASA domain. Additionally, a real-time q-PCR analysis revealed differential expression patterns of TdGASA genes in various tissues (including leaves, roots, stems, and seeds) and in response to salinity, osmotic stress, and treatment with exogenous phytohormones (abscisic and gibberellic acid), implying that these genes may play a role in the growth, development, and stress responses of Triticum turgidum. Heterologous expression of TdGASA1, TdGASA4, TdGASA14, and TdGASA19 in Saccharomyces cerevisiae improved its tolerance to salt, osmotic, oxidative, and heat stresses, which suggests the involvement of these genes in abiotic stress tolerance mechanisms. The present study is the first to identify and analyze the expression profile of T. turgidum GASA genes, therefore offering novel insights for their further functional characterization, which may serve as a novel resource for molecular breeding of durum wheat.

AabHLH113 integrates jasmonic acid and abscisic acid signaling to positively regulate artemisinin biosynthesis in Artemisia annua.

Artemisinin, a sesquiterpene lactone isolated from Artemisia annua, is in huge market demand due to its efficient antimalarial action, especially after the COVID-19 pandemic. Many researchers have elucidated that phytohormones jasmonic acid (JA) and abscisic acid (ABA) positively regulate artemisinin biosynthesis via types of transcription factors (TFs). However, the crosstalk between JA and ABA in regulating artemisinin biosynthesis remains unclear. Here, we identified a novel ABA- and JA-induced bHLH TF, AabHLH113, which positively regulated artemisinin biosynthesis by directly binding to the promoters of artemisinin biosynthetic genes, DBR2 and ALDH1. The contents of artemisinin and dihydroartemisinic acid increased by 1.71- to 2.06-fold and 1.47- to 2.23-fold, respectively, in AabHLH1113 overexpressed A.annua, whereas they decreased by 14-36% and 26-53%, respectively, in RNAi-AabHLH113 plants. Furthermore, we demonstrated that AabZIP1 and AabHLH112, which, respectively, participate in ABA and JA signaling pathway to regulate artemisinin biosynthesis, directly bind to and activate the promoter of AabHLH113. Collectively, we revealed a complex network in which AabHLH113 plays a key interrelational role to integrate ABA- and JA-mediated regulation of artemisinin biosynthesis.

The RNA N6 -methyladenosine demethylase ALKBH9B modulates ABA responses in Arabidopsis.

The mRNA modification N6 -methyladenosine (m6 A) plays vital roles in plant development and biotic and abiotic stress responses. The RNA m6 A demethylase ALKBH9B can remove m6 A in alfalfa mosaic virus RNA and plays roles in alfalfa mosaic virus infection in Arabidopsis. However, it is unknown whether ALKBH9B also exhibits demethylation activity and has a biological role in endogenous plant mRNA. We demonstrated here that mRNA m6 A modification is induced by the phytohormone abscisic acid (ABA) and that ALKBH9B has m6 A demethylation activity on endogenous mRNA. Knocking out ALKBH9B led to hypersensitivity to ABA treatment during seed germination and early seedling development. We further showed that ALKBH9B removes the m6 A modification in the ABA INSENSITIVE 1 (ABI1) and BRI1-EMS-SUPPRESSOR 1 (BES1) transcripts following ABA treatment, affecting the stability of these mRNAs. Furthermore, we determined that ALKBH9B acts genetically upstream of the transcription factors ABI3 and ABI5, and its regulatory function in ABA responses depended on ABI3 and ABI5. Our findings reveal the important roles of the m6 A modification in ABA responses and highlight the role of ALKBH9B-mediated m6 A demethylation in regulating ABA responses post-transcriptionally.

MdPP2C24/37, Protein Phosphatase Type 2Cs from Apple, Interact with MdPYL2/12 to Negatively Regulate ABA Signaling in Transgenic Arabidopsis.

The phytohormone abscisic acid (ABA) plays an important role in the ability of plants to cope with drought stress. As core members of the ABA signaling pathway, protein phosphatase type 2Cs (PP2Cs) have been reported in many species. However, the functions of MdPP2Cs in apple (Malus domestica) are unclear. In this study, we identified two PP2C-encoding genes, MdPP2C24/37, with conserved PP2C catalytic domains, using sequence alignment. The nucleus-located MdPP2C24/37 genes were induced by ABA or mannitol in apple. Genetic analysis revealed that overexpression of MdPP2C24/37 in Arabidopsis thaliana led to plant insensitivity to ABA or mannitol treatment, in terms of inhibiting seed germination and overall seedling establishment. The expression of stress marker genes was upregulated in MdPP2C24/37 transgenic lines. At the same time, MdPP2C24/37 transgenic lines displayed inhibited ABA-mediated stomatal closure, which led to higher water loss rates. Moreover, when exposed to drought stress, chlorophyll levels decreased and MDA and H2O2 levels accumulated in the MdPP2C24/37 transgenic lines. Further, MdPP2C24/37 interacted with MdPYL2/12 in vitro and vivo. The results indicate that MdPP2C24/37 act as negative regulators in response to ABA-mediated drought resistance.

Targeted in vivo mutagenesis of a sensor histidine kinase playing an essential role in ABA signaling of the moss Physcomitrium patens

Land plants exhibit various adaptation responses to unfavorable water environments, such as drought and flooding. The phytohormone abscisic acid (ABA) and ethylene play essential roles in plant adaptation to drought and flooding, respectively. It remains largely unknown how plants integrate environmental information for water availability. In the moss Physcomitrium patens, we recently reported that not only ethylene/flooding signaling but also ABA/osmostress signaling are mediated by ethylene receptor-related sensor histidine kinases (ETR-HKs). Subfamily I ETR-HKs of this moss were found to interact with a RAF kinase (ARK) and were required for ABA-dependent activation of SNF1-related protein kinase 2 (SnRK2) via ARK activation. To elucidate the mechanisms of ARK regulation by ETR-HKs, here we employed targeted in vivo mutagenesis of PpHK5, a member of subfamily I ETR-HKs. Analyses of ABA-insensitive Pphk5 mutants indicated that PpHK5 mutations affecting the interaction with ARK resulted in loss of PpHK5 function to activate ABA signaling. We also identified a PpHK5 mutation that does not affect ARK interaction but resulted in loss of PpHK5 function. These results suggest that physical interaction between ETR-HK and ARK is essential but not sufficient for the regulation of ARK activity, and the C-terminal response regulator domain is involved in regulating ARK activation.

Phenotypically abnormal cotyledonary Vitis vinifera embryos differ in anatomy, endogenous hormone levels and transcriptome profiles.

In many perennial fruit species, including grapevine (Vitis vinifera L.), the highly complex process of somatic embryogenesis (SE) can result in the formation of a deformed embryo, although the underlying reasons are still poorly understood. Here, V. vinifera cv. 'Chardonnay' cotyledonary embryos with distinct morphologies were used to address this issue. Normal cotyledonary embryos (NCEs) and elongated cotyledonary embryos (ECEs) were observed to have better-developed vasculature and shoot meristems than the vitrified cotyledonary embryos (VCEs) and fused cotyledonary embryos (FCEs), but ECEs were less developed. We determined that the morphological differences in these phenotypically abnormal embryos were likely associated with endogenous hormone levels, since concentrations of the phytohormones indoleacetic acid (IAA) and abscisic acid (ABA) in NCEs were higher than in the other three types. Comparative transcriptome analysis revealed large differences in gene expression of the hormone signaling pathways in normal and abnormal cotyledonary embryos. Weighted gene co-expression network analysis of the different cotyledonary types allowed the identification of co-regulated gene modules associated with SE, suggesting a role for ERF family genes and other transcription factors (TFs) in regulating morphology. Moreover, an analysis of morphology-specific gene expression indicated that the activation of a specific protein kinase, small heat shock proteins (sHSPs) and certain TFs was closely associated with the formation of normal cotyledonary embryos. Our comparative analyses provide insights into the gene networks regulating somatic cotyledon development and open new avenues for research into plant regeneration and functional genomic studies of malformed embryos.

Cold stress combined with salt or abscisic acid supplementation enhances lipogenesis and carotenogenesis in Phaeodactylum tricornutum (Bacillariophyceae).

Compounds from microalgae such as ω3-fatty acids or carotenoid are commercially exploited within the pharmacology, nutraceutical, or cosmetic sectors. The co-stimulation of several compounds of interest may improve the cost-effectiveness of microalgal biorefinery pipelines. This study focussed on Phaeodactylum tricornutum to investigate the effects on lipogenesis and carotenogenesis of combined stressors, here cold temperature and addition of NaCl salt or the phytohormone abscisic acid, using a two-stage cultivation strategy. Cold stress with NaCl or phytohormone addition increased the neutral lipid content of the biomass (20 to 35%). These treatments also enhanced the proportions of EPA (22% greater than control) in the fatty acid profile. Also, these treatments had a stimulatory effect on carotenogenesis, especially the combination of cold stress with NaCl addition, which returned the highest production of fucoxanthin (33% increase). The gene expression of diacylglycerol acyltransferase (DGAT) and the ω-3 desaturase precursor (PTD15) were enhanced 4- and 16-fold relative to the control, respectively. In addition, zeaxanthin epoxidase 3 (ZEP3), was downregulated at low temperature when combined with abscisic acid. These results highlight the benefits of applying a combination of low temperature and salinity stress, to simultaneously enhance the yields of the valuable metabolites EPA and fucoxanthin in Phaeodactylum tricornutum.

Abscisic acid activates desiccation tolerance responses in intertidal seaweed Neoporphyra haitanensis

Intertidal macroalgae have adapted to deal with environmental stresses, in particular desiccation. The phytohormone abscisic acid (ABA) plays an important role in the regulation of a suite of critical responses in plants, including desiccation tolerance. The red alga Neoporphyra haitanensis contains a high level of ABA, but its mechanism of action in N. haitanensis is unknown. In this study, the effect of ABA treatment on the relative water content of thalli during the dehydration-rehydration cycle was evaluated and it was identified that ABA treatment resulted in decreased thalli water loss and an accelerated rehydration process. The effects of addition of ABA upon the activation of antioxidant responses, photosynthetic parameters and gene transcription profiles of N. haitanensis were also evaluated. The results revealed that exogenous ABA regulated the activation of the antioxidant system, including by increasing the activity of antioxidant enzymes, increasing the concentrations of ascorbic acid (AsA) and glutathione (GSH), as well as upregulating the expression of genes encoding antioxidant enzymes and enzymes that synthesize AsA and GSH. ABA treatment also inhibited photosynthesis by reducing light capture and down-regulating the Calvin cycle to save energy; ABA supplementation further simultaneously activated repair mechanisms to avoid excessive DNA and protein damage. The results presented herein demonstrate that ABA plays a crucial role in the regulation of stress tolerance in seaweeds, which may be of great importance when examining the adaptation of this organism to the intertidal environment.

Application of insecticides on peppermint (Mentha × piperita L.) induces lignin accumulation in leaves by consuming phenolic acids and thus potentially deteriorates quality

Irrational use of pesticides may lead to physiological and metabolic disorders in different crops. However, there are limited investigations on impacts of insecticides on physiology and biochemistry, secondary metabolic pathways, and associated quality of medicinal plants such as peppermint (Mentha × piperita L.). In this study, target metabolites in peppermint were monitored following foliar spraying of five insecticides: imidacloprid, pyriproxyfen, acetamiprid, chlorantraniliprole, and chlorfenapyr. Compared with the control, all insecticide treatments caused a significant loss of soluble protein (decreased by 22.3–38.7%) in peppermint leaves. Insecticides induced an increase in the levels of phytohormones jasmonic acid and abscisic acid in response to these chemical stresses. Among them, imidacloprid increased jasmonic acid by 388.3%, and pyriproxyfen increased abscisic acid by 98.8%. The contents of phenylpropanoid metabolites, including rutin, quercetin, apigenin, caffeic acid, 4-hydroxybenzoic acid, ferulic acid, syringic acid, and sinapic acid showed a decreasing trend, with pyriproxyfen decreasing the levels of quercetin and 4-hydroxybenzoic acid by 78.8% and 72.6%, respectively. Combined with correlation analysis, the content of lignin in leaves shows different degrees of negative correlations with several phenolic acids. It could be inferred that insecticides may trigger plant defense mechanisms that accumulate lignin (increased by 24.6–49.1%) in leaves by consuming phenolic acids to barricade absorption of insecticides. Through constructing networks between phytohormones and secondary metabolites, peppermint may regulate the contents of caffeic acid, 4-hydroxybenzoic acid, and sinapic acid by the antagonistic effect between salicylic acid and abscisic acid in response to insecticidal stresses. Principal component analysis and systemic cluster analysis revealed that the most pronounced changes in physiological indexes and metabolites were caused by the pyriproxyfen treatment. In conclusion, this study improves our understanding of the mechanism by which insecticides affect plant physiological and metabolic processes, thus potentially altering the quality and therapeutic value of peppermint as an example.

Abscisic acid regulates stomatal production by imprinting a SnRK2 kinase-mediated phosphocode on the master regulator SPEECHLESS.

Stomata, the epidermal pores for gas exchange between plants and the atmosphere, are the major sites of water loss. During water shortage, plants limit the formation of new stoma via the phytohormone abscisic acid (ABA) to conserve water. However, how ABA suppresses stomatal production is largely unknown. Here, we demonstrate that three core SnRK2 kinases of ABA signaling inhibit the initiation and proliferation of the stomatal precursors in Arabidopsis. We show that the SnRK2s function within the precursors and directly phosphorylate SPEECHLESS (SPCH), the master transcription factor for stomatal initiation. We identify specific SPCH residues targeted by the SnRK2s, which mediate the ABA/drought-induced suppression of SPCH and stomatal production. This SnRK2-specific SPCH phosphocode connects stomatal development with ABA/drought signals and enables the independent control of this key water conservation response. Our work also highlights how distinct signaling activities can be specifically encoded on a master regulator to modulate developmental plasticity.

Abscisic Acid Signaling in the Regulation of Postharvest Physiological Deterioration of Sliced Cassava Tuberous Roots.

Phytohormone abscisic acid (ABA) influences the shelf life of fruit, vegetables, and tubers after harvest. However, little is known about the core signaling module involved in ABA's control of the postharvest physiological process. Exogenous ABA alleviated postharvest physiological deterioration (PPD) symptoms of sliced cassava tuberous roots, increased endogenous ABA levels, and reduced endogenous H2O2 content. The specific ABA signaling module during the PPD process was identified as MePYL6-MePP2C16-MeSnRK2.1-MebZIP5/34. MebZIP5/MebZIP34 directly binds to and activates the promoters of MeGRX6/MeMDAR1 through ABRE elements. Exogenous ABA significantly induced the expression of genes involved in this module, glutaredoxin content, and monodehydroascorbate reductase activity. We presented a hypothesis suggesting that MePYL6-MePP2C16-MeSnRK2.1-MebZIP5/34-MeGRX6/MeMDAR1 is involved in ABA-induced antioxidative capacity, thus alleviating PPD symptoms in cassava tuberous roots. The identification of the specific signaling module involved in ABA's control of PPD provides a basis and potential targets for extending the shelf life of cassava tuberous roots.

The exodomain of the impaired oomycete susceptibility 1 receptor mediates both endoplasmic reticulum stress responses and abscisic acid signalling during downy mildew infection of Arabidopsis

The phytohormone abscisic acid (ABA) regulates cell growth and plant development, and contributes to defence responses to pathogens. We previously showed that the Arabidopsis malectin-like domain leucine-rich repeat receptor-like kinase (MLD-LRR-RLK) impaired oomycete susceptibility 1 (IOS1) attenuates ABA signalling during infection with the oomycete downy mildew pathogen Hyaloperonospora arabidopsidis. The exodomain of IOS1 with its MLD retains the receptor in the endoplasmic reticulum (ER), where it interacts with the ribophorin HAP6 to dampen a pathogen-induced ER stress response called the unfolded protein response (UPR). The down-regulation of both ABA and UPR signalling probably provides the pathogen with an advantage for infection. Here, we show that ABA-related phenotypes of the ios1-1 mutant, such as up-regulated expression of ABA-responsive genes and hypersensitivity to exogenous ABA application, were reverted by expression of the IOS1 exodomain in the mutant background. Furthermore, knockdown mutants for ER-resident HAP6 showed similarly reduced UPR and ABA signalling, indicating that HAP6 positively regulates both pathways. Our data suggest that the IOS1 exodomain and HAP6 contribute in the ER to the IOS1-mediated interference with ABA and UPR signalling.

Manufactured Nano-Objects Confer Viral Protection against Cucurbit Chlorotic Yellows Virus (CCYV) Infecting Nicotiana benthamiana.

Nanotechnology has emerged as a new tool to combat phytopathogens in agricultural crops. Cucurbit chlorotic yellows virus (CCYV) mainly infects Solanaceae crops and causes significant crop losses. Nanomaterials (NMs) may have efficacy against plant viruses, but the mechanisms underlying complex nanomaterials-plant-virus interactions remain elusive. We challenged Nicotiana benthamiana plants with GFP-tagged CCYV and observed morphological, physiological, and molecular changes in response to 21-d foliar exposure to nanoscale Fe and Zn and C60 fullerenes at 100 mg/L concentration for 21 days. We observed that in response to C60 (100 mg/L) treatment, plants displayed a normal phenotype while the viral infection was not seen until 5 days post-inoculation. On the contrary, Fe and Zn were unable to suppress viral progression. The mRNA transcriptional analysis for GFP and viral coat protein revealed that the transcripts of both genes were 5-fold reduced in response to C60 treatment. Evaluation of the chloroplast ultrastructure showed that NMs treatment maintained the normal chloroplast structure in the plants as compared to untreated plants. C60 upregulated the defense-related phytohormones (abscisic acid and salicylic acid) by 42–43%. Our results demonstrate the protective function of carbon-based NMs, with suppression of CCYV symptoms via inhibition of viral replication and systemic movement.

NUA and ESD4 negatively regulate ABA signaling during seed germination

The phytohormone abscisic acid (ABA) plays important roles in plant growth, development and adaptative responses to abiotic stresses. SNF1-related protein kinase 2s (SnRK2) are key components that activate the ABA core signaling pathway. NUCLEAR PORE ANCHOR (NUA) is a component of the nuclear pore complex (NPC) that involves in deSUMOylation through physically interacting with the EARLY IN SHORT DAYS 4 (ESD4) SUMO protease. However, it is not clear how NUA functions with SnRK2 and ESD4 to regulate ABA signaling. In our study, we found that nua loss-of-function mutants exhibited pleiotropic ABA-hypersensitive phenotype. We also found that ABA-responsive genes remarkably up-regulated in nua by exogenous ABA. The nua snrk2.2 snrk2.3 triple mutant and nua abi5 double mutant partially rescued the ABA-hypersensitive phenotype of nua, thereby suggesting that NUA is epistatic to SnRK2s. Additionally, we observed that esd4-3 mutant was also ABA-hypersensitive. NUA and ESD4 were further demonstrated to physically interact with SnRK2s and negatively regulate ABA signaling by reducing SnRK2s stability. Taken together, our findings uncover a new regulatory mechanism that can modulate ABA signaling.

The Plastidial DIG5 Protein Affects Lateral Root Development by Regulating Flavonoid Biosynthesis and Auxin Transport in Arabidopsis.

To reveal the mechanisms underlying root adaptation to drought stress, we isolated and characterized an Arabidopsis mutant, dig5 (drought inhibition of lateral root growth 5), which exhibited increased sensitivity to the phytohormone abscisic acid (ABA) for the inhibition of lateral root growth. The dig5 mutant also had fewer lateral roots under normal conditions and the aerial parts were yellowish with a lower level of chlorophylls. The mutant seedlings also displayed phenotypes indicative of impaired auxin transport, such as abnormal root curling, leaf venation defects, absence of apical hook formation, and reduced hypocotyl elongation in darkness. Auxin transport assays with [3H]-labeled indole acetic acid (IAA) confirmed that dig5 roots were impaired in polar auxin transport. Map-based cloning and complementation assays indicated that the DIG5 locus encodes a chloroplast-localized tRNA adenosine deaminase arginine (TADA) that is involved in chloroplast protein translation. The levels of flavonoids, which are naturally occurring auxin transport inhibitors in plants, were significantly higher in dig5 roots than in the wild type roots. Further investigation showed that flavonoid biosynthetic genes were upregulated in dig5. Introduction of the flavonoid biosynthetic mutation transparent testa 4 (tt4) into dig5 restored the lateral root growth of dig5. Our study uncovers an important role of DIG5/TADA in retrogradely controlling flavonoid biosynthesis and lateral root development. We suggest that the DIG5-related signaling pathways, triggered likely by drought-induced chlorophyll breakdown and leaf senescence, may potentially help the plants to adapt to drought stress through optimizing the root system architecture.