Apple Roots Research Articles

Genome-wide analysis of the MdZR gene family revealed MdZR2.2-induced salt and drought stress tolerance in apple rootstock

The DNL-type zinc finger protein constitutes a zinc ribbon protein (ZR) family, which belongs to a branch of zinc finger protein and plays an essential role in response to abiotic stress. Here, we identified six apple (Malus domestica) MdZR genes. Based on their phylogenetic relationship and gene structure, the MdZR genes were divided into three categories, including MdZR1, MdZR2, and MdZR3. Subcellular results showed that the MdZRs are located on the nuclear and membrane. The transcriptome data showed that MdZR2.2 is expressed in various tissues. The expression analysis results showed that MdZR2.2 was significantly upregulated under salt and drought treatments. Thus, we selected MdZR2.2 for further research. Overexpression of MdZR2.2 in apple callus improved their tolerance to drought and salt stress and ability to scavenge reactive oxygen species (ROS). In contrast, transgenic apple roots with silenced MdZR2.2 grew more poorly than the wild type when subjected to salt and drought stress, which reduced their ability to scavenge ROS. To our knowledge, this is the first study to analyze the MdZR protein family. This study identified a gene that responds to drought and salt stress. Our findings lay a foundation for a comprehensive analysis of the MdZR family members.

Overexpression of MdFRK2 enhances apple drought resistance by promoting carbohydrate metabolism and root growth under drought stress

Soluble sugars function not only as the energy and structural blocks supporting plants, but also as osmoregulators and signal molecules during plant adaptation to water deficit. Here, we investigated drought resistance in transgenic apple (Malus × domestica) overexpressing MdFRK2, a key gene regulating fructose content and sugar metabolism. There is no obvious phenotypic difference between MdFRK2-overexpressing transgenic plants and WT plants under the well-watered condition. However, the transgenic plants and the grafted plants using MdFRK2-overexpressing rootstock exhibited improved tolerance to drought stress. Overexpression of MdFRK2 significantly promoted the growth of root system under drought stress. RNA sequencing showed that under drought stress, genes involved in sugar metabolism, transcription regulation, signal transduction or hormone metabolism were differentially expressed in MdFRK2 transgenic plants. Consistent with the gene expression profile, the activities of enzyme (SDH, FRK and NI) involved in sugar metabolism in the roots of MdFRK2 transgenic plants were significantly higher than those of untransformed control plants after drought stress. Under drought stress, overexpression of MdFRK2 promoted the accumulation of IAA, and decreased the contents of ABA and CK in apple root system. In conclusion, these results suggest that MdFRK2 can promote the growth of apple roots under drought stress by regulating sugar metabolism and accumulation, hormone metabolism and signal transduction, and then resist drought stress.

Rho of plant GTPase MxROP1 regulates the responses to Fe deficiency by targeting Zinc Ribbon 3 in apple rootstocks

The Rho-related GTPase of plants (ROPs) is a multifunctional molecular switch that can regulate plant growth, development, and responses to the environment. However, how the ROPs regulate the response to Fe deficiency has not been thoroughly clarified. In this study, we found that Fe deficiency induced MxROP1 in apple (Malus xiaojinensis) at both the transcriptional and translational levels. The overexpression of MxROP1, MxROP1DN (inactive form), and MxROP1CA (active form) in apple roots increased the activity of ferric chelate reductase and the ability to acidify the rhizosphere, and the lines that overexpressed MxROP1DN exhibited the strongest reaction to enhanced Fe uptake. Yeast two-hybrid library screening indicated that MxROP1 interacted with MxZR3.1, a DNL zinc finger protein that negatively regulates the responses to Fe deficiency. We identified their interaction in vitro and in vivo in more detail using pull-down and bimolecular fluorescence complementation assays, respectively, and MxROP1DN-MxZR3.1 interacted the most strongly. Furthermore, MxROP1 negatively affected the stability of MxZR3.1 protein in vitro as shown by a cell semi-degradation assay, and the application of MG132 inhibited the degradation of MxZR3.1-HIS proteins. This indicated that MxROP1 caused the degradation of MxZR3.1 protein through the 26 S proteasome pathway. Similar results were found in OE-MxROP1+OE-MxZR3.1 transgenic apple calli compared with those in the OE-MxZR3.1 calli. We also demonstrated that MxZR3.1 interacted with MxbHLH39, a known positive transcription factor and core component of Fe deficiency, and MxROP1 affected the interaction of MxZR3.1-MxbHLH39 as shown in a competitive binding assay. Τhis clarified one MxROP1-MxZR3.1-MxbHLH39 pathway that maintains Fe homeostasis in M. xiaojinensis.

Apple Root Microbiome as Indicator of Plant Adaptation to Apple Replant Diseased Soils.

The tree fruit industry in Nova Scotia, Canada, is dominated by the apple (Malus domestica) sector. However, the sector is faced with numerous challenges, including apple replant disease (ARD), which is a well-known problem in areas with intensive apple cultivation. A study was performed using 16S rRNA/18S rRNA and 16S rRNA/ITS2 amplicon sequencing to assess soil- and root-associated microbiomes, respectively, from mature apple orchards and soil microbiomes alone from uncultivated soil. The results indicated significant (p < 0.05) differences in soil microbial community structure and composition between uncultivated soil and cultivated apple orchard soil. We identified an increase in the number of potential pathogens in the orchard soil compared to uncultivated soil. At the same time, we detected a significant (p < 0.05) increase in relative abundances of several potential plant-growth-promoting or biocontrol microorganisms and non-fungal eukaryotes capable of promoting the proliferation of bacterial biocontrol agents in orchard soils. Additionally, the apple roots accumulated several potential PGP bacteria from Proteobacteria and Actinobacteria phyla, while the relative abundances of fungal taxa with the potential to contribute to ARD, such as Nectriaceae and plant pathogenic Fusarium spp., were decreased in the apple root microbiome compared to the soil microbiome. The results suggest that the health of a mature apple tree can be ascribed to a complex interaction between potential pathogenic and plant growth-promoting microorganisms in the soil and on apple roots.

Draft Genome Sequence of the Bacterial Endophyte Priestia megaterium B1, Isolated from Roots of Apple (Malus domestica).

Over the past years, a number of important traits supporting plant growth have been shown for different strains of Priestia megaterium (formerly known as Bacillus megaterium). Here, we report the draft genome sequence of the endophytic bacterial strain Priestia megaterium B1, which was isolated from surface-sterilized roots of apple plants.

Root 1-aminocyclopropane-l-carboxylic acid (ACC) and rhizosphere ACC deaminase-producing bacteria affect apple root architecture under soil compaction stress

Root 1-aminocyclopropane-l-carboxylic acid (ACC) and rhizosphere ACC deaminase-producing bacteria affect apple root architecture under soil compaction stress

Uptake of glucose from the rhizosphere, mediated by apple MdHT1.2, regulates carbohydrate allocation.

Plant roots can absorb sugars from the rhizosphere, which reduces the consumption of carbon derived from photosynthesis. However, the underlying mechanisms that roots use to control sugar absorption from soil are poorly understood. Here, we identified an apple (Malus × domestica Borkh.) hexose transporter, MdHT1.2, that functions on the root epidermis to absorb glucose (Glc) from the rhizosphere. Based on RNA-seq data, MdHT1.2 showed the highest expression level among 29 MdHT genes in apple roots. Biochemical analyses demonstrated that MdHT1.2 was mainly expressed in the epidermal cells of fine roots, and its protein was located on the plasma membrane. The roots of transgenic apple and Solanum lycopersicum lines overexpressing MdHT1.2 had an increased capability to absorb Glc when fed with [13C]-labeled Glc or 2-NBDG, whereas silencing MdHT1.2 in apple showed the opposite results. Further studies established that MdHT1.2-mediated Glc absorption from the rhizosphere changed the carbon assimilate allocation between apple shoot and root, which regulated plant growth. Additionally, a grafting experiment in tomato confirmed that increasing the Glc uptake capacity in the root overexpressing MdHT1.2 could facilitate carbohydrate partitioning to the fruit. Collectively, our study demonstrated that MdHT1.2 functions on the root epidermis to absorb rhizospheric Glc, which regulates the carbohydrate allocation for plant growth and fruit sugar accumulation.

Molecular characterization of two new alternaviruses identified in members of the fungal family Nectriaceae

Since the first report in 2009, at least ten additional viruses have been identified and assigned to the proposed virus family Alternaviridae. Here we report two new mycoviruses tentatively assigned to this family, both identified as members of the fungal family Nectriaceae, which were isolated from surface-disinfected apple roots (Malus x domestica, Borkh.) affected by apple replant disease (ARD). ARD is a highly complex, worldwide-occurring disease resulting from plant reactions to a disturbed (micro)-biome and leads to high economic losses every year. The first alternavirus characterized in this study was identified in a Dactylonectria torresensis isolate. The virus was tentatively named dactylonectria torresensis alternavirus 1 (DtAV1) as the first member of the proposed new species Alternavirus dactylonectriae. The second virus was identified in an isolate of Ilyonectria robusta and was tentatively named ilyonectria robusta alternavirus 1 (IrAV1) as the first member of the proposed new species Alternavirus ilyonectriae. Full genomic sequences of the viruses were determined and are presented. Further, we found hints for putative components of a methyl transferase machinery using in silico approaches. This putative protein domain is encoded by segment 2. However, this result only establishes the basis for subsequent studies in which the function must be confirmed experimentally in vitro. Thus, this is the first study where a function is predicted to all three genomic segments within the group of the alternaviruses. These findings provide further insights into the virome of ARD-associated fungi and are therefore another brick in the wall of understanding the complexity of the disease.

The Effect of Drip Irrigation on the Length and Distribution of Apple Tree Roots

In a three-year experiment (2019–2021), the roots of 7-year-old apple trees (Malus domestica cv. ‘Red Jonaprince’) grown under drip irrigation were studied. The aim of the study was to determine the effect of irrigation on root density at different depths and distances from the trunk. The working hypothesis assumed that irrigation significantly affects the total length of apple roots. The irrigation treatments corresponding to the calculated water evapotranspiration (ET100), 50% of the calculated ET (ET50), a control (ET0, no irrigation, under rainfed conditions), and a treatment using double-drip lines (2Drops) were monitored. Soil cores were collected in spring and autumn. The total length of the roots (TRLt) and the length of new vital roots (TRLv) to a depth of 80 cm were evaluated. The effects of treatments were mostly insignificant for the TRLt; only in the dry season in 2019 were the TRLt values of the irrigated treatments (ET50 and ET100) significantly higher, 18.67 km·m−2 and 17.45 km·m−2, in comparison to 11.16 km·m−2 for the ET0, at a 10 cm distance from the tree trunk. The irrigation treatments had a statistically significant effect on the TRLv values near the trunk in 2019 and 2020, while in autumn 2020 and 2021, irrigation significantly affected the TRLv at greater distances from the tree trunk. In summary, the irrigation treatments mostly had no significant effect on the total root length. However, an effect of irrigation on the root length of new vital roots was observed at certain sampling dates and distances from the trunk.

Ectopic expression of MmSERT, a mouse serotonin transporter gene, regulates salt tolerance and ABA sensitivity in apple and Arabidopsis

5-hydroxytryptamine (5-HT) is ubiquitously present in animals and plants, playing a vital regulatory role. SERT, a conserved serotonin reuptake transporter in animals, regulates intracellular and extracellular concentrations of 5-HT. Few studies have reported 5-HT transporters in plants. Hence, we cloned MmSERT, a serotonin reuptake transporter, from Mus musculus. Ectopic expression of MmSERT into apple calli, apple roots and Arabidopsis. Because 5-HT plays a momentous role in plant stress tolerance, we used MmSERT transgenic materials for stress treatment. We found that MmSERT transgenic materials, including apple calli, apple roots and Arabidopsis, exhibited a stronger salt tolerance phenotype. The reactive oxygen species (ROS) produced were significantly lower in MmSERT transgenic materials compared with controls under salt stress. Meanwhile, MmSERT induced the expression of SOS1, SOS3, NHX1, LEA5 and LTP1 in response to salt stress. 5-HT is the precursor of melatonin, which regulates plant growth under adversity and effectively scavenges ROS. Detection of MmSERT transgenic apple calli and Arabidopsis revealed higher melatonin levels than controls. Besides, MmSERT decreased the sensitivity of apple calli and Arabidopsis to abscisic acid (ABA). In summary, these results demonstrated that MmSERT plays a vital role in plant stress resistances, which perhaps serves as a reference for the application of transgenic technology to improve crops in the future.

Auxin Participates in the Regulation of the Antioxidant System in Malus baccata Borkh. Roots under Sub-Low Temperature by Exogenous Sucrose Application

Malus baccata Borkh., an apple rootstock, is found to be damaged by oxidation at sub-low root-zone temperature. In previous studies, we have found that exogenous sucrose could alleviate oxidative damage and increase the indole acetic acid (IAA) in roots under sub-low temperature (L). However, the role of IAA in sucrose-induced tolerance to L remains unclear. A pot experiment was conducted to evaluate the effects of exogenous sucrose and IAA synthesis/transport inhibitors (2,3,5-triiodobenzoic acid, TIBA; 4-biphenylboronic acid, BBo) on growth, IAA levels, sugars, and the antioxidant system of M. baccata under L. The results showed that the L treatment decreased IAA contents by 23.69% (48 h) and induced significant increases in root contents of malondialdehyde (MDA) and reactive oxygen (ROS), along with increasing catalase (CAT), ascorbate peroxidase (APX), and glucose-6-phosphate dehydrogenase (G6PDH) activities, while superoxide dismutase (SOD) and monodehydroascorbate reductase (MDHAR) activities first increased (24 h) and then decreased (48 h), and glutathione reductase (GR) and peroxidase (POD) activities significantly decreased. The L treatment also decreased ascorbate/oxidized ascorbate (AsA/DHA), glutathione/oxidized glutathione (GSH/GSSG), and coenzyme II/oxidized coenzyme II (NADPH/NADP+) ratios. Furthermore, the L treatment increased the contents of sucrose, fructose, glucose and sorbitol in the roots and suppressed plant growth. Sucrose pretreatment significantly increased IAA contents (12.42%, 24 h and 14.44%, 48 h) and decreased MDA and ROS contents, which improved the activities of antioxidant enzymes other than APX and increased the contents of AsA, GSH, and NADPH, and increased sucrose, fructose, and sorbitol contents and promoted plant growth. However, the sucrose + TIBA or BBo treatments decreased IAA contents and attenuated or almost abolished the positive effects of exogenous sucrose under sub-low temperature. Our findings indicate that IAA is involved in the sucrose-induced regulation of the antioxidant system in M. baccata roots under sub-low temperature and we provided theoretical references for further study on the adaptability of apple roots to low temperature.

Regulatory Effect of Exogenous γ-Aminobutyric Acid on Respiratory Rate through the γ-Aminobutyric Acid Shunt in Malus baccata (L.) Borkh. Roots under Suboptimal Low Root-Zone Temperature

Malus baccata (L.) Borkh. is one of the most widely used rootstocks in the apple-producing region of Northern China. However, in the early growing season, apple roots are often subjected to suboptimal low root-zone temperatures. The regulatory effects of exogenous γ-aminobutyric acid (GABA) on both the γ-aminobutyric acid shunt (GABA shunt) and the respiratory activity of roots under suboptimal low root-zone temperatures remain unknown. To explore the physiological basis for GABA alleviation of low-temperature stress in M. baccata Borkh. roots, the following treatments were examined: suboptimal low root-zone temperature (potted parts of the seedlings were maintained at 5 ± 0.5 °C; L); suboptimal low root-zone temperature + GABA (LG); and suboptimal low root-zone temperature + vigabatrin (VGB; LV), which is a specific active inhibitor of γ-aminobutyric acid transaminase (GABA-T). Each treatment was matched with a control (18 °C/8 °C day/night; CK) for comparison. Our results showed that the L treatment reduced the root vitality, increased malondialdehyde (MDA) content, promoted the accumulation of GABA, activated the GABA shunt, and inhibited the total root respiration rate (VTotal) by decreasing the respiratory rates of Embden–Meyerhof pathway (VEMP) and tricarboxylic acid cycle (VTCAC). The LG treatment significantly increased the content of endogenous GABA, accelerated the metabolism of the GABA shunt, enhanced root respiratory activity by increasing VTotal, VEMP, VTCAC, and increased the cytochrome pathway respiratory rate (VCP), thus alleviating the damage of low root-zone temperature stress. Meanwhile, contrasting results were observed in the LV treatment. These findings revealed that exogenous GABA improved the tolerance of apple rootstocks to suboptimal low temperatures in early spring by regulating the GABA shunt and root respiratory activity.

MdERF114 enhances the resistance of apple roots to Fusarium solani by regulating the transcription of MdPRX63.

As the main fungal etiologic agent of apple (Malus domestica) replant disease (ARD), Fusarium solani seriously damages apple roots. Ethylene response factors (ERFs) play an important role in plant resistance to biotic stress. Here, we show that MdERF114 is expressed during F. solani infections and positively regulates the resistance of apple roots to F. solani. Yeast one-hybrid, dual-luciferase, electrophoretic mobility shift assays and determinations of lignin content indicated that MdERF114 directly binds the GCC-box of the MdPEROXIDASE63 (MdPRX63) promoter and activates its expression, resulting in lignin deposition in apple roots and increased resistance to F. solani. We identified a WRKY family transcription factor, MdWRKY75, that binds to the W-box of the MdERF114 promoter. Overexpression of MdWRKY75 enhanced resistance of apple roots to F. solani. MdMYB8 interacted with MdERF114 to enhance resistance to F. solani by promoting the binding of MdERF114 to the MdPRX63 promoter. In summary, our findings reveal that the MdWRKY75-MdERF114-MdMYB8-MdPRX63 module is required for apple resistance to F. solani and the application of this mechanism by Agrobacterium rhizogenes-mediated root transformation provides a promising strategy to prevent ARD.

A framework for the targeted recruitment of crop-beneficial soil taxa based on network analysis of metagenomics data

BackgroundThe design of ecologically sustainable and plant-beneficial soil systems is a key goal in actively manipulating root-associated microbiomes. Community engineering efforts commonly seek to harness the potential of the indigenous microbiome through substrate-mediated recruitment of beneficial members. In most sustainable practices, microbial recruitment mechanisms rely on the application of complex organic mixtures where the resources/metabolites that act as direct stimulants of beneficial groups are not characterized. Outcomes of such indirect amendments are unpredictable regarding engineering the microbiome and achieving a plant-beneficial environment.ResultsThis study applied network analysis of metagenomics data to explore amendment-derived transformations in the soil microbiome, which lead to the suppression of pathogens affecting apple root systems. Shotgun metagenomic analysis was conducted with data from ‘sick’ vs ‘healthy/recovered’ rhizosphere soil microbiomes. The data was then converted into community-level metabolic networks. Simulations examined the functional contribution of treatment-associated taxonomic groups and linked them with specific amendment-induced metabolites. This analysis enabled the selection of specific metabolites that were predicted to amplify or diminish the abundance of targeted microbes functional in the healthy soil system. Many of these predictions were corroborated by experimental evidence from the literature. The potential of two of these metabolites (dopamine and vitamin B12) to either stimulate or suppress targeted microbial groups was evaluated in a follow-up set of soil microcosm experiments. The results corroborated the stimulant’s potential (but not the suppressor) to act as a modulator of plant beneficial bacteria, paving the way for future development of knowledge-based (rather than trial and error) metabolic-defined amendments. Our pipeline for generating predictions for the selective targeting of microbial groups based on processing assembled and annotated metagenomics data is available at https://github.com/ot483/NetCom2.ConclusionsThis research demonstrates how genomic-based algorithms can be used to formulate testable hypotheses for strategically engineering the rhizosphere microbiome by identifying specific compounds, which may act as selective modulators of microbial communities. Applying this framework to reduce unpredictable elements in amendment-based solutions promotes the development of ecologically-sound methods for re-establishing a functional microbiome in agro and other ecosystems.E7XdzHk-x_xNr6tGiZLY1VVideo

Granulometric composition and moisture capacity of the soil in old-age apple orchards of the Lipetsk region

The research was carried out in 2018-2021 in the old fruit-bearing, but not yet uprooted apple orchards of the Lipetsk region. The lowest moisture capacity was determined by the method of gypsum casts, the granulometric composition was determined by the pyrophosphate method. In old age (40-98 years) in apple orchards on chernozems leached in a layer of 10-40 cm of trunk strips, the granulometric composition changes: the proportion of physical sand increases, but the percentage of physical clay decreases. An increase in the proportion of physical sand in the trunk strips occurs mainly due to an increase in the proportion of fine sand (0.05-0.25 mm), and in the aisles an increase in the amount of physical clay occurs due to an increase in the proportion of medium dust (0.001-0.05 mm). With the age of the garden, the decrease in the proportion of physical clay in the trunk strips occurs due to the removal of medium dust (0.001-0.05 mm) and coarse silt (less than 0.001 mm) down the profile. The lowest moisture capacity increases with an increase in the proportion of coarse silt in the soil (r = 0.5), but decreases with an increase in the percentage of medium (r=-0.65) and coarse (r=-0.53) sand. A decrease in the percentage of physical clay in the trunk strips leads to a decrease in the lowest moisture capacity in a layer of 10-40 cm only by the age of the garden of 98 years. The change of the granulometric composition to a lighter one and the reduction of the lowest moisture capacity of the soil in the trunk strips of old apple orchards are evidence of the podzol–forming activity of apple roots.

Optimization of critical determinants for efficient transformation in M7 apple root stock

Optimization of critical determinants for efficient transformation in M7 apple root stock

Kinase MxMPK4-1 and calmodulin-binding protein MxIQM3 enhance apple root acidification during Fe deficiency.

Iron (Fe) deficiency is a long-standing issue in plant mineral nutrition. Ca2+ signals and the mitogen-activated protein kinase (MAPK) cascade are frequently activated in parallel to perceive external cues, but their interplay under Fe deficiency stress remains largely unclear. Here, the kinase MxMPK4-1, which is induced during the response to Fe deficiency stress in apple rootstock Malus xiaojinensis, cooperates with IQ-motif containing protein3 (MxIQM3). MxIQM3 gene expression, protein abundance, and phosphorylation level increased under Fe deficiency stress. The overexpression of MxIQM3 in apple calli and rootstocks mitigated the Fe deficiency phenotype and improved stress tolerance, whereas RNA interference or silencing of MxIQM3 in apple calli and rootstocks, respectively, worsened the phenotype and reduced tolerance to Fe deficiency. MxMPK4-1 interacted with MxIQM3 and subsequently phosphorylated MxIQM3 at Ser393, and co-expression of MxMPK4-1 and MxIQM3 in apple calli and rootstocks enhanced Fe deficiency responses. Furthermore, MxIQM3 interacted with the central-loop region of the plasma membrane (PM) H+-ATPase MxHA2. Phospho-mimicking mutation of MxIQM3 at Ser393 inhibited binding to MxHA2, but phospho-abolishing mutation promoted interaction with both the central-loop and C terminus of MxHA2, demonstrating phosphorylation of MxIQM3 caused dissociation from MxHA2 and therefore increased H+ secretion. Moreover, Ca2+/MxCAM7 (Calmodulin7) regulated the MxMPK4-1-MxIQM3 module in response to Fe deficiency stress. Overall, our results demonstrate that MxMPK4-1-MxIQM3 forms a functional complex and positively regulates PM H+-ATPase activity in Fe deficiency responses, revealing a versatile mechanism of Ca2+/MxCAM7 signaling and MAPK cascade under Fe deficiency stress.

Exogenous Dopamine and MdTyDC Overexpression Enhance Apple Resistance to Fusarium solani.

Fusarium solani, one of the main pathogenic fungi involved in apple replant disease (ARD), is a serious threat to apple growth and development. Dopamine and tyrosine decarboxylase (TyDC), a key enzyme in the dopamine synthesis pathway, have been reported to play an active role in plant responses to biotic and abiotic stresses, but little is known about the functions of dopamine and Malus domestica TyDC (MdTyDC) in the interaction between F. solani and apple roots. In this study, seedlings treated with exogenous dopamine and apple plants overexpressing MdTyDC were inoculated with F. solani; both treatments reduced the root system damage caused by F. solani. After inoculation with F. solani, exogenous dopamine increased dopamine content in the seedlings; alleviated the inhibition of biomass accumulation; increased root metabolic activity, photosynthetic efficiency, and antioxidant enzyme activities; reduced reactive oxygen species accumulation; and upregulated the expression of genes encoding chitinase, β-1,3-glucanase, and pathogenesis-related proteins. Similar results were observed in MdTyDC-overexpressing apple plants. In addition, the overexpression of MdTyDC increased tyramine content and the deposition of cell wall-bound amines in roots. Overall, our results reveal that exogenous dopamine and overexpression of MdTyDC enhance apple resistance to F. solani, which is an important application for the prevention of ARD.

The Feasibility of Using Autofluorescence to Detect Lignin Deposition Pattern during Defense Response in Apple Roots to Pythium ultimum Infection

The molecular mechanisms underpinning apple root resistance to infection by Pythium ultimum have not been carefully investigated until recently. A panoramic and high-resolution picture of genome-wide transcriptional networks regulating the defense activation in apple roots was obtained recently from a comprehensive transcriptome analysis. Among the most notable transcriptome changes are the upregulation of phenylpropanoid and flavonoid biosynthesis, transportation of secondary metabolites, and laccase-directed lignin formation. However, assessing cellular responses and anatomical changes in young roots of apple as a woody species of the Rosacea family remains challenging. Taking advantage of the autofluorescence of lignin and the specific staining by Wiesner reagent, the feasibility of using microscopy to detect lignin deposition in apple roots was evaluated. The preliminary results indicated that a combination of brightfield and fluorescence images may provide the opportunity to reveal the location and degree of lignification in sectioned roots. The procedure represents a proof-of-concept of using fluorescence microscopy to examine cellular features relevant to apple root resistance traits. The ability to detect subtle phenotypic variations, such as lignin deposition patterns, is critically needed to bridge the gap between genomic data and macro-level plant resistance phenotypes and to further identify the resistance mechanisms of apple root.

Screening of antagonistic strains &lt;i&gt;Trichoderma&lt;/i&gt; Pers. towards causative agent of root rot in apples of genus Fusarium Link.

In recent years, in the south of Russia, fungi of the genus Fusarium Link (1809) constitute a special danger to such important agricultural perennial crops as the apple tree. Тhese fungi cause root rot, a harmful disease, which weakens the vascular organs, leading to a significant decrease in yield and even death of the plant. A literature review showed that the genus Trichoderma has great potential for the integrated protection of apple trees. In this regard, due to the lack of registered microbiological agents for the control of fusarium root rot in apple trees, the search for antagonistic strains for biotechnological control of this disease becomes relevant. In this work, the parasitic activity of strains of the genus Trichoderma against the causative agents of root rot in apple trees, namely Fusarium sporotrichioides and Fusarium oxysporum, was studied in vitro. Тhe research was carried out in 2020–2021 in the Laboratory of biotechnological control of phytopathogens and phytophages of the FGBSO “North Caucasian Federal Scientific Center of Horticulture, Viticulture and Winemaking”. Тhe research was focused on monoconidial strains of the causative agent of apple root rot: F. sporotrichioides (strain RR20XXIV/4.3) and F. oxysporum (strain RR20XXV/6.2), as well as 7 strains of the genus Trichoderma having expected antagonistic activity. Тhe activity of strains of the genus Trichoderma against fungi of the genus Fusarium was determined by the dual culture method using joint splicing on the PGA medium (potato-glucose agar). Тhe Trichocin, SP (titer 1010 CFU/g Trichoderma harzianum, strain G-30 VISR), registered against root rot for a number of crops, was used as a standard. A monoculture of the test object (strains of the genus Fusarium) was used as a control. Out of the 7 strains of antagonistic fungi, strains 20I/1 and 20II/2 showed the greatest activity against F. sporotrichioides by a dual mechanism of action, which involves competition for a nutrient medium and fungicidal parasitic antagonism; the latter strain showed hyperparasitism. Antibiotic (strain 20XIV/5) and alimentary antagonisms (strain 20II/3.2) were also detected. Strain 20XIV/5 showed antibiotic antagonism against F. oxysporum, having higher activity than the standard; strain 20I/1 showed alimentary antagonism. Тhe remaining antagonist strains showed competitive interactions for the environment.