Secondary Root Growth Research Articles

Modeling cassava root system architecture and the underlying dynamics in shoot–root carbon allocation during the early storage root bulking stage

Abstract Background and aims Plants store carbohydrates for later use during, e.g., night, drought, and recovery after stress. Carbon allocation presents the plant with tradeoffs, notably between growth and storage. We asked how this tradeoff works for cassava (Manihot esculenta) pre- and post-storage root (SR) formation and if manipulation of the number of storage organs and leaf growth rate might increase yield. Methods We developed a functional-structural plant model, called MeOSR, to simulate carbon partitioning underlying cassava growth and SR formation in conjunction with the root system's three-dimensional (3D) architecture (RSA). We compared the model results to experimental data and simulated phenotypes varying in the number of SR and leaf growth rate. Results The simulated 3D RSA and the root mass closely represented those of field-grown plants. The model simulated root growth and associated carbon allocation across developmental stages. Substantial accumulation of non-structural carbohydrates (NSC) preceded SR formation, suggesting sink-limited growth. SR mass and canopy photosynthesis might be increased by both increasing the number of SR and the leaf growth rate. Conclusion MeOSR offers a valuable tool for simulating plant growth, its associated carbon economy, and 3D RSA over time. In the first month, the specific root length increased due to root branching, but in the third month, it decreased due to secondary root growth. The accumulation of NSC might initiate SR development in cassava. Cassava growth is relatively slow during the first 3 months, and a faster crop establishment combined with a greater SR growth might increase yield.

Complete genome sequence of Bacillus velezensis strain Ag109, a biocontrol agent against plant-parasitic nematodes and Sclerotinia sclerotiorum

Soybean is the main oilseed cultivated worldwide. Even though Brazil is the world’s largest producer and exporter of soybean, its production is severely limited by biotic factors. Soil borne diseases are the most damaging biotic stressors since they significantly reduce yield and are challenging to manage. In this context, the present study aimed to evaluate the potential of a bacterial strain (Ag109) as a biocontrol agent for different soil pathogens (nematodes and fungi) of soybean. In addition, the genome of Ag109 was wholly sequenced and genes related to secondary metabolite production and plant growth promotion were mined. Ag109 showed nematode control in soybean and controlled 69 and 45% of the populations of Meloidogyne javanica and Pratylenchus brachyurus, respectively. Regarding antifungal activity, these strains showed activity against Macrophomia phaseolina, Rhizoctonia solani, and Sclerotinia sclerotiorum. For S. sclerotiorum, this strain increased the number of healthy plants and root dry mass compared to the control (with inoculation). Based on the average nucleotide identity and digital DNA-DNA hybridization, this strain was identified as Bacillus velezensis. Diverse clusters of specific genes related to secondary metabolite biosynthesis and root growth promotion were identified, highlighting the potential of this strain to be used as a multifunctional microbial inoculant that acts as a biological control agent while promoting plant growth in soybean.

Correction to: New insight into secondary growth in roots of monocotyledons using the example of the dragon tree, Dracaena draco L.

Correction to: New insight into secondary growth in roots of monocotyledons using the example of the dragon tree, Dracaena draco L.

Apo-siderophores promote growth of iron-deficient Arabidopsis plants by mobilizing iron from roots to shoots and reducing oxidative stress in roots

Iron (Fe) is an essential micronutrient for most organisms that is, however, poorly bioavailable in the soil. Acquiring this element is therefore a major issue for both plants and microorganisms. Bacteria acquire Fe by secreting siderophores that chelate the ferric ion with a high affinity and that can contribute to Fe nutrition in plants, under certain conditions including stressful ones. Our previous work has shown that pyoverdine, a siderophore purified from a beneficial Pseudomonas sp., leads to plant growth stimulation when supplied in its Fe-free form (apo-pyoverdine/apopyo) to Arabidopsis thaliana plants grown hydroponically under Fe-deficient conditions. To better understand siderophore-mediated growth promotion, we studied the impact of an apo-siderophore with a different structure from pyoverdine, deferoxamine (DFO), on the same model. Here we show that growth stimulation is linked to the ability of siderophores to chelate Fe, as DFO also promotes growth after 3 to 6 days when provided at 25 µM to 4-week-old A. thaliana plants starved for Fe for 1 to 7 days. The extent to which the siderophore stimulates root and shoot growth depends on the amount of Fe stored in the roots prior to the addition of DFO, and likely involves the remobilization of Fe from the roots to the shoots. The promotion of root growth by DFO does not appear to depend on coumarin production or secretion, but is associated with an increase in the expression of genes of the HOMOLOG OF BEE2 INTERACTING WITH IBH1 (HBI1)-dependent brassinosteroid signaling pathway. DFO stimulates lateral root elongation concomitant with a significant decrease in hydrogen peroxide (H2O2) and oxidized glutathione levels and a decrease in stress-related gene expression in roots. In addition, DFO decreases the expression of the UPBEAT (UPB1) gene involved in H2O2-mediated root growth inhibition, and thus lifts the inhibition of the expression of its target genes, the class III peroxidases that stimulate root growth. Overall, this work indicates that growth promotion by apo-siderophores in an iron-poor environment is likely linked to their ability to induce a stronger response to Fe deficiency while decreasing oxidative stress in roots, thus stimulating Fe remobilization from root Fe pools to shoots and promoting secondary root growth.

New insight into secondary growth in roots of monocotyledons using the example of the dragon tree, Dracaena draco L.

New insight into secondary growth in roots of monocotyledons using the example of the dragon tree, Dracaena draco L.

Low pH stress activates several genes for lateral root formation and detoxification of aluminum ions in Cotton plants

In low pH condition of soils (pH<5), Al is solubilized into a phytotoxic form Al(H2O)63+ and inhibits the plant root growth and development. Precisely, during low pH stress (e.g., pH 4.75), aluminum compound converts into its ionic form and becomes higher in level which is a limiting factor for plant root growth and seedling formation. Under aluminum (Al) toxic conditions, the organic acid transporters for example citrate and malate transporters in plasma membrane are involved in organic acid release and form non phytotoxic stable complexes with Al3+ in the rhizosphere. The study showed that, the cotton seedlings exhibited very sensitive phenotypes to low pH stress conditions due to high accumulation of ionic Al stress, the seedlings displayed retarded primary, secondary root growth and small cotyledons. These results indicated that cotton plants are susceptible to low pH condition.. As a whole without fine divisions the root system becomes corraloid in structure which will be having squat secondary roots. Plant has developed a natural defense mechanism in order to combat this unfavorable environment. Expression profile and Al complexation with organic acid exudates studies clearly revealed that both GhALMT1 and GhALS3 genes are involved in Al3+detoxification mechanisms. The remarkable expression was detected for GhALS3 under both low pH and aluminum stress condition in comparison to wild type untreated control whereas GhALMT1 expression was only activated under Al3+ stress condition. Our study, displayed enhanced citrate and malate excretion values in the wild type plants which are treated with Al and H+ stress. Thus, it can be clearly mentioned that GhALMT1 and GhALS3 is playing a significant role in low pHstress tolerance of cotton plant.

Physiological responses induced by phospholipase C isoform 5 upon heat stress in Arabidopsis thaliana.

Plant's perception of heat stress involves several pathways and signaling molecules, such as phosphoinositide, which is derived from structural membrane lipids phosphatidylinositol. Phospholipase C (PLC) is a well-known signaling enzyme containing many isoforms in different organisms. In the present study, Phospholipase C Isoform 5 (PLC5) was investigated for its role in thermotolerance in Arabidopsis thaliana. Two over-expressing lines and one knock-down mutant of PLC5 were first treated at a moderate temperature (37 °C) and left for recovery. Then again exposed to a high temperature (45 °C) to check the seedling viability and chlorophyll contents. Root behavior and changes in 32Pi labeled phospholipids were investigated after their exposure to high temperatures. Over-expression of PLC5 (PLC5 OE) exhibited quick and better phenotypic recovery with bigger and greener leaves followed by chlorophyll contents as compared to wild-type (Col-0) and PLC5 knock-down mutant in which seedling recovery was compromised. PLC5 knock-down mutant illustrated well-developed root architecture under controlled conditions but stunted secondary roots under heat stress as compared to over-expressing PLC5 lines. Around 2.3-fold increase in phosphatidylinositol 4,5-bisphosphate level was observed in PLC5 OE lines upon heat stress compared to wild-type and PLC5 knock-down mutant lines. A significant increase in phosphatidylglycerol was also observed in PLC5 OE lines as compared to Col-0 and PLC5 knock-down mutant lines. The results of the present study demonstrated that PLC5 over-expression contributes to heat stress tolerance while maintaining its photosynthetic activity and is also observed to be associated with primary and secondary root growth in Arabidopsis thaliana.

The Arabidopsis transcription factor TCP9 modulates root architectural plasticity, reactive oxygen species-mediated processes, and tolerance to cyst nematode infections.

Infections by root-feeding nematodes have profound effects on root system architecture and consequently shoot growth of host plants. Plants harbor intraspecific variation in their growth responses to belowground biotic stresses by nematodes, but the underlying mechanisms are not well understood. Here, we show that the transcription factor TEOSINTE BRANCHED/CYCLOIDEA/PROLIFERATING CELL FACTOR-9 (TCP9) modulates root system architectural plasticity in Arabidopsis thaliana in response to infections by the endoparasitic cyst nematode Heterodera schachtii. Young seedlings of tcp9 knock-out mutants display a significantly weaker primary root growth inhibition response to cyst nematodes than wild-type Arabidopsis. In older plants, tcp9 reduces the impact of nematode infections on the emergence and growth of secondary roots. Importantly, the altered growth responses by tcp9 are most likely not caused by less biotic stress on the root system, because TCP9 does not affect the number of infections, nematode development, and size of the nematode-induced feeding structures. RNA-sequencing of nematode-infected roots of the tcp9 mutants revealed differential regulation of enzymes involved in reactive oxygen species (ROS) homeostasis and responses to oxidative stress. We also found that root and shoot growth of tcp9 mutants is less sensitive to exogenous hydrogen peroxide and that ROS accumulation in nematode infection sites in these mutants is reduced. Altogether, these observations demonstrate that TCP9 modulates the root system architectural plasticity to nematode infections via ROS-mediated processes. Our study further points at a novel regulatory mechanism contributing to the tolerance of plants to root-feeding nematodes by mitigating the impact of belowground biotic stresses.

Prolonged Exposure to High Temperature Inhibits Shoot Primary and Root Secondary Growth in Panax ginseng.

High temperature is one of the most significant abiotic stresses reducing crop yield and quality by inhibiting plant growth and development. Global warming has recently increased the frequency of heat waves, which negatively impacts agricultural fields. Despite numerous studies on heat stress responses and signal transduction in model plant species, the molecular mechanism underlying thermomorphogenesis in Panax ginseng remains largely unknown. Here, we investigated the high temperature response of ginseng at the phenotypic and molecular levels. Both the primary shoot growth and secondary root growth of ginseng plants were significantly reduced at high temperature. Histological analysis revealed that these decreases in shoot and root growth were caused by decreases in cell elongation and cambium stem cell activity, respectively. Analysis of P. ginseng RNA-seq data revealed that heat-stress-repressed stem and root growth is closely related to changes in photosynthesis, cell wall organization, cell wall loosening, and abscisic acid (ABA) and jasmonic acid (JA) signaling. Reduction in both the light and dark reactions of photosynthesis resulted in defects in starch granule development in the storage parenchymal cells of the main tap root. Thus, by combining bioinformatics and histological analyses, we show that high temperature signaling pathways are integrated with crucial biological processes that repress stem and root growth in ginseng, providing novel insight into the heat stress response mechanism of P. ginseng.

Effects of low phosphorus availability on root cambial activity, biomass production and root morphological pattern in two clones of Chinese fir

Abstract Phosphorous (P) is a crucial limiting nutrient for plant growth and development in terrestrial ecosystems. As one of the most important subtropical coniferous tree species, Chinese fir (Cunninghamia lanceolata) plays a major role in timber supply, climate mitigation and forest recreation. In this study, two Chinese fir clones (020 and 061) with a high growth rate were subjected to two levels of P supply in a greenhouse pot experiment: P-deficient P0 (no P supply) and P-replete P1 (1.0 mmol L−1 KH2PO4). Our objectives were to study the differences in morphology and growth patterns, cambial development mechanism and secondary root growth. Root sampling was performed at 40, 80 and 120 days after treatment initiation. Results indicated that the P-replete condition produced more root cambial cells (RCCs) in third class (larger) roots of clone-061 than in those of clone-020; concomitantly, clone-061 showed significantly greater stem height (42.87 ± 1.33 cm), root collar diameter (5.45 ± 0.126 mm), root average diameter (RAD, third class = 1.27 ± 0.04 mm) in different root classes and whole-plant biomass (7.55 ± 0.69 g) compared with clone-020 under the P-replete condition. Root diameter and biomass increase due to higher cambial activity resulted in greater seedling quality. In addition, a significant positive correlation was observed between the number of RCCs and root morphological traits (root length, root surface area, RAD and root volume). Root development was significantly promoted by cambium activity in the P-replete environment, thereby enhancing plant secondary growth. Based on these outcomes, we suggest that clone-061 would be more useful for enhancing production. Regarding commercial purposes, these findings will contribute to the improvement of P fertilization efficiency.

Nitrate enhances the secondary growth of storage roots in Panax ginseng

BackgroundNitrogen (N) is an essential macronutrient for plant growth and development. To support agricultural production and enhance crop yield, two major N sources, nitrate and ammonium, are applied as fertilizers to the soil. Although many studies have been conducted on N uptake and signal transduction, the molecular genetic mechanisms of N-mediated physiological roles, such as the secondary growth of storage roots, remain largely unknown. MethodsOne-year-old P. ginseng seedlings treated with KNO3 were analyzed for the secondary growth of storage roots. The histological paraffin sections were subjected to bright and polarized light microscopic analysis. Genome-wide RNA-seq and network analysis were carried out to dissect the molecular mechanism of nitrate-mediated promotion of ginseng storage root thickening. ResultsHere, we report the positive effects of nitrate on storage root secondary growth in Panax ginseng. Exogenous nitrate supply to ginseng seedlings significantly increased the root secondary growth. Histological analysis indicated that the enhancement of root secondary growth could be attributed to the increase in cambium stem cell activity and the subsequent differentiation of cambium-derived storage parenchymal cells. RNA-seq and gene set enrichment analysis (GSEA) revealed that the formation of a transcriptional network comprising auxin, brassinosteroid (BR)-, ethylene-, and jasmonic acid (JA)-related genes mainly contributed to the secondary growth of ginseng storage roots. In addition, increased proliferation of cambium stem cells by a N-rich source inhibited the accumulation of starch granules in storage parenchymal cells. ConclusionThus, through the integration of bioinformatic and histological tissue analyses, we demonstrate that nitrate assimilation and signaling pathways are integrated into key biological processes that promote the secondary growth of P. ginseng storage roots.

Effects of soil biotic and abiotic properties on the growth and mycorrhization of Cedrus atlantica Manetti cedars

Cedrus atlantica Manetti is an emblematic species of great ecological, economic and social value. However, its weak root architecture seriously compromises (re)afforestation and regeneration of the species. Although it is known that mycorrhization is beneficial to cedars growing in unfavourable conditions, our knowledge on the mycorrhization of cedar seedlings is remains patchy. These difficulties show a need to study the interactions between the roots and the soil biotic and abiotic factors and to seek solutions to promote the mycorrhization of cedar seedlings. For this purpose, we studied the responses of cedar seedlings to the physico-chemical, textural, hydromechanical and microbiological factors of the soil and mycorrhization success in juvenile cedars. The response of C. atlantica seedlings to the textural and physico-chemical properties of soils in cedar woods shows that they are highly dependent on organic carbon, nitrogen and phosphorus contents and on the soil's granulometry. These factors stimulate the growth of secondary roots in some soils while in others, they cause seedling growth to predominate. The provenances of C. atlantica show a high nitrogen requirement and different preferences for nitrogen forms. Variations in the cotyledons also reveal different patterns of adaptation to nitrogen nutrition. The hydromechanical properties of the culture medium profoundly affect C. atlantica seedlings, so that in extreme cases, they either over-stimulate the elongation of unbranched main roots or completely inhibit their elongation, producing a great many reduced lateral roots. On the anatomical scale, these responses are more apparent around the cortex. Interactions with the native soil microflora have a determining effect on the growth of C. atlantica seedlings, since the microbial composition of the soil can stimulate growth and decrease the density of roots. The nutrient depletion of 6 soils allowed the trapping of 15 species of ectomycorrhizal fungi of young C. atlantica seedlings. This indicates the crucial importance of this new range of mycorrhizal fungi, characterized for the first time in C. atlantica seedlings, especially for work aiming to improve the health status of cedar seedlings.

Gibberellin Signaling Promotes the Secondary Growth of Storage Roots in Panax ginseng.

Gibberellins (GAs) are an important group of phytohormones associated with diverse growth and developmental processes, including cell elongation, seed germination, and secondary growth. Recent genomic and genetic analyses have advanced our knowledge of GA signaling pathways and related genes in model plant species. However, functional genomics analyses of GA signaling pathways in Panax ginseng, a perennial herb, have rarely been carried out, despite its well-known economical and medicinal importance. Here, we conducted functional characterization of GA receptors and investigated their physiological roles in the secondary growth of P. ginseng storage roots. We found that the physiological and genetic functions of P. ginseng gibberellin-insensitive dwarf1s (PgGID1s) have been evolutionarily conserved. Additionally, the essential domains and residues in the primary protein structure for interaction with active GAs and DELLA proteins are well-conserved. Overexpression of PgGID1s in Arabidopsis completely restored the GA deficient phenotype of the Arabidopsis gid1a gid1c (atgid1a/c) double mutant. Exogenous GA treatment greatly enhanced the secondary growth of tap roots; however, paclobutrazol (PCZ), a GA biosynthetic inhibitor, reduced root growth in P. ginseng. Transcriptome profiling of P. ginseng roots revealed that GA-induced root secondary growth is closely associated with cell wall biogenesis, the cell cycle, the jasmonic acid (JA) response, and nitrate assimilation, suggesting that a transcriptional network regulate root secondary growth in P. ginseng. These results provide novel insights into the mechanism controlling secondary root growth in P. ginseng.

The multi metal-resistant bacterium Cupriavidus metallidurans CH34 affects growth and metal mobilization in Arabidopsis thaliana plants exposed to copper.

Copper (Cu) is important for plant growth, but high concentrations can lead to detrimental effects such as primary root length inhibition, vegetative tissue chlorosis, and even plant death. The interaction between plant-soil microbiota and roots can potentially affect metal mobility and availability, and, therefore, overall plant metal concentration. Cupriavidus metallidurans CH34 is a multi metal-resistant bacterial model that alters metal mobility and bioavailability through ion pumping, metal complexation, and reduction processes. The interactions between strain CH34 and plants may affect the growth, metal uptake, and translocation of Arabidopsis thaliana plants that are exposed to or not exposed to Cu. In this study, we looked also at the specific gene expression changes in C. metallidurans when co-cultured with Cu-exposed A. thaliana. We found that A. thaliana’s rosette area, primary and secondary root growth, and dry weight were affected by strain CH34, and that beneficial or detrimental effects depended on Cu concentration. An increase in some plant growth parameters was observed at copper concentrations lower than 50 µM and significant detrimental effects were found at concentrations higher than 50 µM Cu. We also observed up to a 90% increase and 60% decrease in metal accumulation and mobilization in inoculated A. thaliana. In turn, copper-stressed A. thaliana altered C. metallidurans colonization, and cop genes that encoded copper resistance in strain CH34 were induced by the combination of A. thaliana and Cu. These results reveal the complexity of the plant-bacteria-metal triad and will contribute to our understanding of their applications in plant growth promotion, protection, and phytoremediation strategies.

Herbivore‐induced plant volatiles mediate defense regulation in maize leaves but not in maize roots

Plant leaves that are exposed to herbivore‐induced plant volatiles (HIPVs) respond by increasing their defenses, a phenomenon referred to as priming. Whether this phenomenon also occurs in the roots is unknown. Using maize plants, Zea mays, whose leaves respond strongly to leaf HIPVs, we measured the impact of belowground HIPVs, emanating from roots infested by the banded cucumber beetle, Diabrotica balteata, on constitutive and herbivore‐induced levels of defense‐related gene expression, phytohormones, volatile and non‐volatile primary and secondary metabolites, growth and herbivore resistance in roots of neighbouring plants. HIPV exposure did not increase constitutive or induced levels of any of the measured root traits. Furthermore, HIPV exposure did not reduce the performance or survival of D. balteata on maize or its ancestor teosinte. Cross‐exposure experiments between HIPVs from roots and leaves revealed that maize roots, in contrast to maize leaves, neither emit nor respond strongly to defense‐regulating HIPVs. Together, these results demonstrate that volatile‐mediated defense regulation is restricted to the leaves of maize. This finding is in line with the lower diffusibility of volatiles in the soil and the availability of other, potentially more efficient, information conduits below ground.

Auxin signaling and vascular cambium formation enable storage metabolism in cassava tuberous roots.

Cassava storage roots are among the most important root crops worldwide, and represent one of the most consumed staple foods in sub-Saharan Africa. The vegetatively propagated tropical shrub can form many starchy tuberous roots from its stem. These storage roots are formed through the activation of secondary root growth processes. However, the underlying genetic regulation of storage root development is largely unknown. Here we report distinct structural and transcriptional changes occurring during the early phases of storage root development. A pronounced increase in auxin-related transcripts and the transcriptional activation of secondary growth factors, as well as a decrease in gibberellin-related transcripts were observed during the early stages of secondary root growth. This was accompanied by increased cell wall biosynthesis, most notably increased during the initial xylem expansion within the root vasculature. Starch storage metabolism was activated only after the formation of the vascular cambium. The formation of non-lignified xylem parenchyma cells and the activation of starch storage metabolism coincided with increased expression of the KNOX/BEL genes KNAT1, PENNYWISE, and POUND-FOOLISH, indicating their importance for proper xylem parenchyma function.

Anatomical patterns of condensed tannin in fine roots of tree species from a cool-temperate forest

Condensed tannin (CT) is an important compound in plant biological structural defence and for tolerance of herbivory and environmental stress. However, little is known of the role and location of CT within the fine roots of woody plants. To understand the role of CT in fine roots across diverse species of woody dicot, we evaluated the localization of CT that accumulated in root tissue, and examined its relationships with the stele and cortex tissue in cross-sections of roots in 20 tree species forming different microbial symbiotic groups (ectomycorrhiza and arbuscular mycorrhiza). In a cool-temperate forest in Japan, cross-sections of sampled roots in different branching order classes, namely, first order, second to third order, fourth order, and higher than fourth order (higher order), were measured in terms of the length-based ratios of stele diameter and cortex thickness to root diameter. All root samples were then stained with ρ-dimethylaminocinnamaldehyde solution and we determined the ratio of localized CT accumulation area to the root cross-section area (CT ratio). Stele ratio tended to increase with increasing root order, whereas cortex ratio either remained unchanged or decreased with increasing order in all species. The CT ratio was significantly positively correlated to the stele ratio and negatively correlated to the cortex ratio in second- to fourth-order roots across species during the shift from primary to secondary root growth. Ectomycorrhiza-associated species mostly had a higher stele ratio and lower cortex ratio than arbuscular mycorrhiza-associated species across root orders. Compared with arbuscular mycorrhiza species, there was greater accumulation of CT in response to changes in the root order of ectomycorrhiza species. Different development patterns of the stele, cortex and CT accumulation along the transition from root tip to secondary roots could be distinguished between different mycorrhizal associations. The CT in tissues in different mycorrhizal associations could help with root protection in specific branching orders during shifts in stele and cortex development before and during cork layer formation.

English

β-expansin 2 (EXPB2) gene induces drought tolerance in different plant species including maize. Different epigenetic mechanisms like DNA methylation, histone modification and RNA interference affect the gene activities under stress conditions. DNA methylation, an important epigenetic mechanism, could be involved in the regulation of ZmEXPB2 gene under drought stress in maize. Plants of drought sensitive variety „Jalal‟ were grown till 4th leaf stage under well-watered conditions. At 5th leaf stage, plants were divided in two groups i.e., well-watered (100% water holding capacity) or drought stress (0% water holding capacity for 15 days). Plants subjected to drought stress showed clear signs of stress by significant decrease in fresh weight of whole plant, 6th leaf length, stunted secondary root growth and increased primary root length. DNA methylation profile of three regions (denoted as -1.7 k, -1.3 k and -0.8 k) in the promoter of ZmEXPB2 gene, of root DNA, were evaluated. Under well-watered conditions, heterogeneity in DNA methylation profile along the promoter sequence was observed. Regions -1.7 k and -1.3 k were methylated whereas the region -0.8 k was nonmethylated. After the comparison of DNA methylation profile of well-watered and drought stress plants, no change in -1.7 k and -0.8 k regions was observed. However, the -1.3k region had significant decrease in the DNA methylation at symmetric cytosine sites i.e., cytosine-guanine (CG) dinucleotides and cytosine-adenine/cytosine/thymine-guanine (CHG where H = A, C or T) trinucleotide and significant increase at asymmetric cytosine sites (CHH) under the stress condition. In addition, significant increase in the gene expression of ZmEXPB2 under drought was also observed. In conclusion, drought stress conditions induce DNA hypomethylation at CG, and CHG sites and DNA hypermethylation at CHH sites in the middle region of the promoter of ZmEXPB2 gene. This shift can be associated with the up regulation of ZmEXPB2 gene which in turn increased primary root length as a plant stress response mechanism. © 2021 Friends Science Publishers

Influence of Nano-silicon Treatment on Growth Behavior of ‘Sukkary’ and ‘Gahrawy’ Mango Root-stocks Under Salinity Stress

The experiment was carried out in two consecutive seasons (2017/18 and 2018/19) on ‘Sukkary’ and ‘Gahrawy’ mango root-stocks seedlings and the purpose of the research was to investigate the effectiveness of applying Nano-silica to increase the tolerance of ‘Gahrawy’ and ‘Sukkary’ mango rootstocks. The tested treatments were tap water irrigation (TWI),TWI and spraying Nano silicon (SNSi) at 1.0g/L,Sea water irrigation (SWI) at 1750ppm, SWI at 1750ppm and SNSi, SWI at 3500ppm, and SWI at 3500ppm and SNSi. Foliar sprays of Nano-silicon were done four times;the first at the beginning of the experiment, and then three times at 45-days intervals.The effect of treatments on the behavior of the seedlings of the two rootstocks including vegetative characteristics (new leaf area, seedling height increase%, seedling stem diameter increase, root length and width, number of lateral and secondary roots and root growth coefficient), physiological parameter Leaf pigments, total phenols and soluble carbohydrates contents,leaf mineral contents N, P, K, Na, Ca and Mg and Non-enzymatic antioxidantsproline content and DPPH” as well as salinity symptoms parameters were studied. Increasing levels of salinity caused a decrease in most parameters and an increase in the sodium and proline content, and salinity symptoms of the leaves. Irrigation with salty water at 1750ppm together with foliar spraying Nano-silicon enhanced leaf content of pigments, soluble carbohydrate and total phenols, Mg, N, P, K and decreasing of salinity symptoms parameters.The results confirmed that the effects of Nano-silicon on the behavior of treated seedlings differ according to the variety under salinity conditions.

A de novo transcriptome analysis revealed that photomorphogenic genes are required for carotenoid synthesis in the dark-grown carrot taproot.

Carotenoids are terpenoid pigments synthesized by all photosynthetic and some non-photosynthetic organisms. In plants, these lipophilic compounds are involved in photosynthesis, photoprotection, and phytohormone synthesis. In plants, carotenoid biosynthesis is induced by several environmental factors such as light including photoreceptors, such as phytochromes (PHYs) and negatively regulated by phytochrome interacting factors (PIFs). Daucus carota (carrot) is one of the few plant species that synthesize and accumulate carotenoids in the storage root that grows in darkness. Contrary to other plants, light inhibits secondary root growth and carotenoid accumulation suggesting the existence of new mechanisms repressed by light that regulate both processes. To identify genes induced by dark and repressed by light that regulate carotenoid synthesis and carrot root development, in this work an RNA-Seq analysis was performed from dark- and light-grown carrot roots. Using this high-throughput sequencing methodology, a de novo transcriptome model with 63,164 contigs was obtained, from which 18,488 were differentially expressed (DEG) between the two experimental conditions. Interestingly, light-regulated genes are preferably expressed in dark-grown roots. Enrichment analysis of GO terms with DEGs genes, validation of the transcriptome model and DEG analysis through qPCR allow us to hypothesize that genes involved in photomorphogenesis and light perception such as PHYA, PHYB, PIF3, PAR1, CRY2, FYH3, FAR1 and COP1 participate in the synthesis of carotenoids and carrot storage root development.