The present study investigates ameliorative effect of nitric oxide (NO) against zinc oxide nanoparticles (ZnONPs) phytotoxicity in wheat seedlings. ZnONPs exposure hampered growth of wheat seedlings which was coincided with reduced photosynthetic efficiency (Fv/Fm and qP) due to increased accumulation of zinc (Zn) in xylem and phloem saps. However, SNP supplementation has partially mitigated the ZnONPs-mediated toxicity by modulation of photosynthetic activity and Zn accumulation in xylem and phloem sap. Further, the results reveal that ZnONPs treatments enhanced level of hydrogen peroxide (H2O2) and hence lipid peroxidation (as malondialdehyde; MDA) due to severely inhibited activities of the ascorbate-glutatione cycle (AsA-GSH) enzymes: ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), and its associated metabolites: reduced ascorbate and glutathione. In contrast to this, the addition of SNP together with ZnONPs maintained the cellular functioning of the AsA-GSH cycle properly, hence lesser damage was noticed in comparison to ZnONPs treatments alone. The protective effect of SNP against ZnONPs toxicity on fresh weight (growth) can be reversed by 2-(4carboxy-2-phenyl)-4,4,5,5-tetramethyl- imidazoline-1-oxyl-3-oxide, a NO scavenger, suggesting role of NO released from SNP in ameliorating ZnONPs toxicity. Overall the results of the present study have shown about implication of NO in the reducing ZnONPs toxicity through the regulation of accumulation of Zn, and functioning of the AsA-GSH cycle.

/pdf/nitric-oxide-ameliorates-zinc-oxide-nanoparticles-38emdrgen8.pdf

Nitric Oxide Ameliorates Zinc Oxide Nanoparticles Phytotoxicity in Wheat Seedlings: Implication of the Ascorbate-Glutathione Cycle.

Role of nanomaterials in plants under challenging environments.

Over the past decade, incorporation of nanomaterials into agricultural practices like nanofertilizers and nanopesticides has gained a lot of attention. Progress and application of fertilizers in nanoforms are one of the effective options for considerable improvement of the agricultural yield worldwide. Zinc oxide nanoparticles (ZnO NPs) are considered as a biosafe material for biological species. Earlier studies have shown the potential of ZnO NPs in stimulation of seed germination and plant growth as well as disease suppression and plant protection by its antimicrobial activity. However, both positive and negative effects of ZnO NPs on plant growth and metabolism at various developmental periods have been documented. Uptake, translocation and accumulation of ZnO NPs by plants depend upon the features of NPs as well as the anatomy of the host plant. This review summarizes the applications of ZnO NPs as nanofertilizer in crop production and also attempts to examine and record the possible mechanism of antimicrobial activity of ZnO NPs. Biological synthesis of ZnO NPs and their uptake, translocation and biotransformation in plants via various routes have also been examined.

Zinc oxide nanoparticles: a review of their biological synthesis, antimicrobial activity, uptake, translocation and biotransformation in plants

Zinc-oxide nanoparticles are being used in a wide range of commercial applications and are therefore expected to find their way into the soil ecosystem. Problems concerning Zinc-oxide nanoparticle toxicity, in-vitro and in-vivo testing methods for living organisms, the development of environmental health criteria and the acceptance of toxicity limits of metal nanoparticles, are topical. This review will contribute to understanding the fate and behaviour of Zinc-oxide nanoparticles in soil, their uptake and distribution within plants, animals, and microbes as well as their interactions with other pollutants. It is an essential prerequisite to environmentally realistic studies of the ecotoxicology of nanoparticles. Increased application of nanoparticles threatens communities as well as plants, terrestrial and aquatic animals. Thus, it is important to explore whether nanoparticles could compromise soil biodiversity and the important functions maintained by soil communities.

Effects of zinc-oxide nanoparticles on soil, plants, animals and soil organisms: A review

Nanoparticles (NPs) are submicron particles with 1- 100 nm lengths in two or three dimensions NPs released as nanomaterial-containing wastes from household, industrial and medical products are emerging as a new threat to the environment Plants, being fixed to the two major environmental sinks where NPs accumulate ¬— namely water and soil, cannot escape the impact of nanopollution Recent studies have shown that plant growth, development and physiology are significantly affected by NPs But, the effect of NPs on plant secondary metabolism is still obscure The induction of reactive oxygen species (ROS) following interactions with NPs has been observed consistently across plant species Taking into account the existing link between ROS and secondary signaling messengers that lead to transcriptional regulation of secondary metabolism, in this perspective we put forward the argument that ROS induced in plants upon their interaction with NPs will likely interfere with plant secondary metabolism As plant secondary metabolites play vital roles in plant performance, communication and adaptation, a comprehensive understanding of plant secondary metabolism in response to NPs is an utmost priority

/pdf/nanoparticles-alter-secondary-metabolism-in-plants-via-ros-1dxuns1m1j.pdf

Nanoparticles Alter Secondary Metabolism in Plants via ROS Burst

Dramatic increase in the use of nanoparticles (NPs) in a variety of applications greatly increased the likelihood of the release of NPs into the environment. Zinc oxide nanoparticles (ZnO NPs) are among the most commonly used NPs, and it has been shown that ZnO NPs were harmful to several different plants. We report here the effects of ZnO NPs exposure on biomass accumulation and photosynthesis in Arabidopsis. We found that 200 and 300 mg/L ZnO NPs treatments reduced Arabidopsis growth by ∼20 and 80%, respectively, in comparison to the control. Pigments measurement showed that Chlorophyll a and b contents were reduced more than 50%, whereas carotenoid contents remain largely unaffected in 300 mg/L ZnO NPs treated Arabidopsis plants. Consistent with this, net rate of photosynthesis, leaf stomatal conductance, intercellular CO2 concentration and transpiration rate were all reduced more than 50% in 300 mg/L ZnO NPs treated plants. Quantitative RT-PCR results showed that expression levels of chlorophyll synthesis genes including CHLOROPHYLL A OXYGENASE (CAO), CHLOROPHYLL SYNTHASE (CHLG), COPPER RESPONSE DEFECT 1 (CRD1), MAGNESIUM-PROTOPORPHYRIN IX METHYLTRANSFERASE (CHLM) and MG-CHELATASE SUBUNIT D (CHLD), and photosystem structure gene PHOTOSYSTEM I SUBUNIT D-2 (PSAD2), PHOTOSYSTEM I SUBUNIT E-2 (PSAE2), PHOTOSYSTEM I SUBUNIT K (PSAK) and PHOTOSYSTEM I SUBUNIT K (PSAN) were reduced about five folds in 300 mg/L ZnO NPs treated plants. On the other hand, elevated expression, though to different degrees, of several carotenoids synthesis genes including GERANYLGERANYL PYROPHOSPHATE SYNTHASE 6 (GGPS6), PHYTOENE SYNTHASE (PSY) PHYTOENE DESATURASE (PDS), and ZETA-CAROTENE DESATURASE (ZDS) were observed in ZnO NPs treated plants. Taken together, these results suggest that toxicity effects of ZnO NPs observed in Arabidopsis was likely due to the inhibition of the expression of chlorophyll synthesis genes and photosystem structure genes, which results in the inhibition of chlorophylls biosynthesis, leading to the reduce in photosynthesis efficiency in the plants.

/pdf/zinc-oxide-nanoparticles-affect-biomass-accumulation-and-52ayxbx77c.pdf

Zinc Oxide Nanoparticles Affect Biomass Accumulation and Photosynthesis in Arabidopsis

The plant hormone abscisic acid (ABA) plays a crucial role in regulating plant responses to environmental stresses. Interplay of several different proteins including the PYR/PYL/RCAR receptors, A-group PP2C protein phosphatases, SnRK2 protein kinases, and downstream transcription factors regulates ABA signalling. We report here the identification of a family of ABA-induced transcription repressors (AITRs) that act as feedback regulators in ABA signalling. We found that the expression of all the 6 Arabidopsis AITR genes was induced by exogenously ABA, and their expression levels were decreased in ABA biosynthesis mutant aba1-5. BLAST searches showed that AITRs are exclusively present in angiosperms. When recruited to the promoter region of a reporter gene by a fused DNA binding domain, all AITRs inhibited reporter gene expression in transfected protoplasts. In Arabidopsis, aitr mutants showed reduced sensitivity to ABA and to stresses such as salt and drought. Quantitative RT-PCR analysis demonstrated that the ABA-induced response of PP2C and some PYR/PYL/RCAR genes was reduced in AITR5 transgenic plants but increased in an aitr2 aitr5 aitr6 triple mutant. These results provide important new insights into the regulation of ABA signalling in plants, and such information may lead to the production of plants with enhanced resistance to environmental stresses.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/pce.13058

A novel family of transcription factors conserved in angiosperms is required for ABA signalling.

Both seed size and abiotic stress tolerance are important agronomic traits in crops. In Arabidopsis, two closely related transcription repressors DPA4 (Development-Related PcG Target in the APEX4)/NGAL3 and SOD7 (Suppressor of da1-1)/NGAL2 (NGATHA-like protein) function redundantly to regulate seed size, which was increased in the dpa4 sod7 double mutants. Whereas ABA-induced transcription repressors (AITRs) are involved in the regulation of ABA signaling and abiotic stress tolerance, Arabidopsis aitr2 aitr5 aitr6 (aitr256) triple mutant showed enhanced tolerance to drought and salt. Here we performed CRISPR/Cas9 genome editing to disrupt DPA4 and SOD7 in aitr256 mutant, trying to integrate seed size and abiotic stress tolerance traits in Arabidopsis, and also to examine whether DPA4 and SOD7 may regulate other aspects of plant growth and development. Indeed, seed size was increased in the dpa4 sod7 aitr256 quintuple mutants, and enhanced tolerance to drought was observed in the mutants. In addition, we found that shoot branching was affected in the dpa4 sod7 aitr256 mutants. The mutant plants failed to produce secondary branches, and flowers/siliques were distributed irregularly on the main stems of the plants. Floral organ number and fertility were also affected in the dpa4 sod7 aitr256 mutant plants. To examine if these phenotypes were dependent on loss-of-function of AITRs, dpa4 sod7 double mutants were generated in Col wild type background, and we found that the dpa4 sod7 mutant plants showed a phenotype similar to the dpa4 sod7 aitr256 quintuple mutants. Taken together, our results indicate that the integration of seed size and abiotic stress tolerance traits by CRISPR/Cas9 editing was successful, and our results also revealed a role of DPA4 and SOD7 in the regulation of inflorescence architecture in Arabidopsis.

https://www.mdpi.com/1422-0067/20/11/2695/pdf

Genome Editing to Integrate Seed Size and Abiotic Stress Tolerance Traits in Arabidopsis Reveals a Role for DPA4 and SOD7 in the Regulation of Inflorescence Architecture.

Epidermal cell fate determination—including trichome initiation, root hair formation, and flavonoid and mucilage biosynthesis in Arabidopsis (Arabidopsis thaliana)—are controlled by a similar transcriptional regulatory network. In the network, it has been proposed that the MYB-bHLH-WD40 (MBW) activator complexes formed by an R2R3 MYB transcription factor, a bHLH transcription factor and the WD40-repeat protein TRANSPARENT TESTA GLABRA1 (TTG1) regulate the expression of downstream genes required for cell fate determination, flavonoid or mucilage biosynthesis, respectively. In epidermal cell fate determination and mucilage biosynthesis, the MBW activator complexes activate the expression of GLABRA2 (GL2). GL2 is a homeodomain transcription factor that promotes trichome initiation in shoots, mucilage biosynthesis in seeds, and inhibits root hair formation in roots. The MBW activator complexes also activate several R3 MYB genes. The R3 MYB proteins, in turn, competing with the R2R3 MYBs for binding bHLH transcription factors, therefore inhibiting the formation of the MBW activator complexes, lead to the inhibition of trichome initiation in shoots, and promotion of root hair formation in roots. In flavonoid biosynthesis, the MBW activator complexes activate the expression of the late biosynthesis genes in the flavonoid pathway, resulting in the production of anthocyanins or proanthocyanidins. Research progress in recent years suggests that the transcriptional regulatory network that controls epidermal cell fate determination and anthocyanin biosynthesis in Arabidopsis is far more complicated than previously thought. In particular, more regulators of GL2 have been identified, and GL2 has been shown to be involved in the regulation of anthocyanin biosynthesis. This review focuses on the research progress on the regulation of GL2 expression, and the roles of GL2 in the regulation of epidermal cell fate determination and anthocyanin biosynthesis in Arabidopsis.

https://www.mdpi.com/1422-0067/20/20/4997/pdf

GLABRA2, A Common Regulator for Epidermal Cell Fate Determination and Anthocyanin Biosynthesis in Arabidopsis

Environmental stresses including abiotic stresses and biotic stresses limit yield of plants. Stress-tolerant breeding is an efficient way to improve plant yield under stress conditions. Genome editing by CRISPR/Cas9 can be used in molecular breeding to improve agronomic traits in crops, but in most cases, with fitness costs. The plant hormone ABA regulates plant responses to abiotic stresses via signaling transduction. We previously identified AITRs as a family of novel transcription factors that play a role in regulating plant responses to ABA and abiotic stresses. We found that abiotic stress tolerance was increased in the single, double and triple aitr mutants. However, it is unclear if the increased abiotic stress tolerance in the mutants may have fitness costs. We report here the characterization of AITRs as suitable candidate genes for CRISPR/Cas9 editing to improve plant stress tolerance. By using CRISPR/Cas9 to target AITR3 and AITR4 simultaneously in the aitr256 triple and aitr1256 quadruple mutants respectively, we generated Cas9-free aitr23456 quintuple and aitr123456 sextuple mutants. We found that reduced sensitivities to ABA and enhanced tolerance to drought and salt were observed in these mutants. Most importantly, plant growth and development was not affected even in the aitr123456 sextuple mutants, in whom the entire AITR family genes have been knocked out, and the aitr123456 sextuple mutants also showed a wild type response to the pathogen infection. Our results suggest that knockout of the AITR family genes in Arabidopsis enhanced abiotic stress tolerance without fitness costs. Considering that knock-out a few AITRs will lead to enhanced abiotic stress tolerance, that AITRs are widely distributed in angiosperms with multiple encoding genes, AITRs may be targeted for molecular breeding to improve abiotic stress tolerance in plants including crops.

/pdf/knockout-of-the-entire-family-of-aitr-genes-in-arabidopsis-1xcqicr7y3.pdf

Siyu Chen

Papers

Zinc Oxide Nanoparticles Affect Biomass Accumulation and Photosynthesis in Arabidopsis

A novel family of transcription factors conserved in angiosperms is required for ABA signalling.

Genome Editing to Integrate Seed Size and Abiotic Stress Tolerance Traits in Arabidopsis Reveals a Role for DPA4 and SOD7 in the Regulation of Inflorescence Architecture.

GLABRA2, A Common Regulator for Epidermal Cell Fate Determination and Anthocyanin Biosynthesis in Arabidopsis

Knockout of the entire family of AITR genes in Arabidopsis leads to enhanced drought and salinity tolerance without fitness costs.