Apple Roots Research Articles

A root system architecture measurement pipeline for apple rootstocks

AbstractA robust root system architecture (RSA) is vital for tree health and fruit production of perennial fruit crops across diverse environments over many years. Consequently, RSA holds significant importance for fruit crop breeding programs. However, phenotyping tree roots presents a significant challenge due to their size, complexity, and lack of an existing efficient root phenotyping system. This study aimed to address this gap by developing and validating a root phenotyping pipeline for large, complex, apple root systems. Root traits of both greenhouse and field‐grown apple trees were captured using either a camera or by imaging shaved roots with a flatbed scanner. These images were then analyzed with five root phenotyping software, RhizoVision, ImageJ, DIRT, RootGraph, and PlantCV, as well as visually ranked. Afterward, all these measurements were compared to hand‐measured root traits to evaluate their accuracy. RhizoVision accurately (p < 0.05) measured all traits for both greenhouse and field‐grown apple root systems. RhizoVision was able to accurately measure surface area and volume of intact crowns in as little as three photos. RootGraph and PlantCV showed varying degrees of accuracy. RhizoVision emerged as the most efficient and accurate method, providing root trait data without requiring extensive preprocessing of images, thus offering a reliable approach for phenotyping large apple root systems.

The Expression and Sequence Analysis of MdMATE52 in Apple Roots During Activation of Defense Against Pythium ultimum Infection

To understand the molecular regulation of host defense responses in the pathosystem between apple roots and a necrotrophic oomycete pathogen Pythium ultimum, a series of transcriptome analyses have revealed a multi-phase and multi-layer defense tactic in apple root tissues. Among the most notable transcriptome changes during defense activation in apple roots, upregulation of genes involved in phenylpropanoid biosynthesis, transport of secondary metabolites, and lignin formation appeared to be the key defense themes which may crucially impact the outcome of plant–pathogen interactions. From our transcriptome datasets, the MdMATE52 gene, which encodes a MATE transporter, was shown to be differentially expressed between a resistant and a susceptible apple rootstock genotype in response to P. ultimum infection. The cis elements at promoter regions and sequence variations within coding regions of MdMATE52 were compared among several resistant and susceptible apple rootstock genotypes as well as various Malus species. The stronger upregulated expression patterns of MdMATE52 appeared to be correlated with the observed resistance traits among various genotypes. Our results suggested that minimal but clearly identifiable sequence variations may contribute to the genotype-specific expression and function of MdMATE52. The findings from this study should facilitate future experiments such as site-specific mutation and Crispr-based genome editing to define the regulation mechanisms of MdMATE52 and function during defense activation in apple roots.

The MdERF61-mdm-miR397b-MdLAC7b module regulates apple resistance to Fusarium solani via lignin biosynthesis.

Apple replant disease (ARD) is a worldwide problem that threatens the industry. However, the genetic mechanism underlying plant disease resistance against ARD remains unclear. In this study, a negative regulatory microRNA in Malus domestica, mdm-miR397b \, and its direct target MdLAC7b (Laccase) was selected for examination based on our previous small RNA and degradome sequencing results. Overexpressing the mdm-miR397b-MdLAC7b module altered the lignin deposition and JA contents in apple roots, which also led to increased resistance to Fusarium solani. Additionally, Y1H library screening using mdm-miR397b promoter recombinants identified a transcription factor, MdERF61, that represses mdm-miR397b transcriptional activity by directly binding to two GCC-boxes in the mdm-miR397b promoter. In summary, our results suggest that the MdERF61-mdm-miR397b-MdLAC7b module plays a crucial role in apple resistance to F. solani and offers insights for enhancing plant resistance to soilborne diseases in apple.

Effect of fertilization in drill-holes on soil gas exchange, apple root, and fruit characteristics

Effect of fertilization in drill-holes on soil gas exchange, apple root, and fruit characteristics

MdSINA2-MdNAC104 Module Regulates Apple Alkaline Resistance by Affecting γ-Aminobutyric Acid Synthesis and Transport.

Soil alkalization is an adverse factor limiting plant growth and yield. As a signaling molecule and secondary metabolite, γ-aminobutyric acid (GABA) responds rapidly to alkaline stress and enhances the alkaline resistance of plants. However, the molecular mechanisms by which the GABA pathway adapts to alkaline stress remain unclear. In this study, a transcription factor, MdNAC104 is identified, from the transcriptome of the alkaline-stressed roots of apple, which effectively reduces GABA levels and negatively regulates alkaline resistance. Nevertheless, applying exogenous GABA compensates the negative regulatory mechanism of overexpressed MdNAC104 on alkaline resistance. Further research confirms that MdNAC104 repressed the GABA biosynthetic gene MdGAD1/3 and the GABA transporter gene MdALMT13 by binding to their promoters. Here, MdGAD1/3 actively regulates alkaline resistance by increasing GABA synthesis, while MdALMT13 promotes GABA accumulation and efflux in roots, resulting in an improved resistance to alkaline stress. This subsequent assays reveal that MdSINA2 interacts with MdNAC104 and positively regulates root GABA content and alkaline resistance by ubiquitinating and degrading MdNAC104 via the 26S proteasome pathway. Thus, the study reveals the regulation of alkaline resistance and GABA homeostasis via the MdSINA2-MdNAC104-MdGAD1/3/MdALMT13 module in apple. These findings provide novel insight into the molecular mechanisms of alkaline resistance in plants.

A holistic cure for cancer and survival from the indirect effects of nuclear attack

Background: The global search for a safe, irreversible cure after lethal radiation exposure and cancer has not been successful since World War II. Nuclear warfare cannot be recreated in a laboratory. Simulation experiments require highly classified, expensive, and approved infrastructure. Chemotherapy and radiotherapy affect both healthy and damaged cells and often lead to cancer recurrence. A lethal dose of ionizing radiation (IR) is devastating because of instant, massive, and diffuse DNA breaks, chromosomal aberrations, tissue oxidation, and the cascading generation of free radicals, and it can cause cancer. People exposed to a nuclear attack directly cannot be cured. Methods: A formulation comprising aqueous extracts of leaves of Indian bael (Aegle marmelos) and Oxalis corniculate, roots of ginseng (Panax ginseng), custard apple (Annona squamosa) or sitaphal cotyledons, methi (Fenugreek) seeds, and lytic Newcastle disease virus (nonhuman) was used. A few doses of the formulation were injected intraperitoneally into lethally gamma-irradiated mice; mice were also injected with Ehrlich ascites carcinoma cells. Breast and cervical cancer cells were treated with this formulation in vitro. Results: We have developed a solution to the lasting problem. The formulation induced apoptosis in IR-damaged cancer cells by the developed formulation in vivo and in vitro, with no subsequent regrowth. No adverse effects were observed. The control ‘DF1’ Fibroblast cells did not exhibit any change after the drug administration. A possible explanation is the loss of defense responses in damaged cells, allowing the multiplication of the killer virus. Thus, people with cancer and those who escape the direct impacts of nuclear accidents may be saved. The lyophilized components can be stored at room temperature under field conditions. Conclusion: Successful treatment with herbs and virotherapy (a nanomedicine) can be delivered as tablets (a stable formulation) to remote areas, which may be a permanent solution to the prolonged search for the treatment of radiation exposure.

Four glycosyltransferase genes are responsible for synthesis and accumulation of different flavonol glycosides in apple tissues.

Flavonols are widely synthesized throughout the plant kingdom, playing essential roles in plant physiology and providing unique health benefits for humans. Their glycosylation plays significant role in improving their stability and solubility, thus their accumulation and function. However, the genes encoding the enzymes catalyze this glycosylation remain largely unknown in apple. This study utilized a combination of methods to identify genes encoding such enzymes. Initially, candidate genes were selected based on their potential to encode UDP-dependent glycosyltransferases (UGTs) and their expression patterns in response to light induction. Subsequently, through testing the in vitro enzyme activity of the proteins produced in Escherichia coli cells, four candidates were confirmed to encode a flavonol 3-O-galactosyltransferase (UGT78T6), flavonol 3-O-glucosyltransferase (UGT78S1), flavonol 3-O-xylosyltransferase/arabinosyltransferase (UGT78T5), and flavonol 3-O-rhamnosyltransferase (UGT76AE22), respectively. Further validation of these genes' functions was conducted by modulating their expression levels in stably transformed apple plants. As anticipated, a positive correlation was observed between the expression levels of these genes and the content of specific flavonol glycosides corresponding to each gene. Moreover, overexpression of a flavonol synthase gene, MdFLS, resulted in increased flavonol glycoside content in apple roots and leaves. These findings provide valuable insights for breeding programs aimed at enriching apple flesh with flavonols and for identifying flavonol 3-O-glycosyltransferases of other plant species.

Apple MdZAT5 mediates root development under drought stress

Root plays an important role in plant drought tolerance, especially in horticultural crops like apples. However, the crucial regulator and molecular mechanism in root development of apple trees under drought are not well unknown. Cys2/His2-type Zinc-finger proteins are essential for plant response to drought, while the members of C2H2 Zinc-finger proteins in apple are largely unknown. In this study, we identified the members of the C1-2i subclass family of C2H2 Zinc-finger proteins in apple (Malus × domestica). Among them, MdZAT5 is significantly induced in apple roots under drought conditions and positively regulates apple root development under drought. Further investigation revealed that MdZAT5 positively regulates root development and root hydraulic conductivity by mediating the transcription level of MdMYB88 under drought stress. Taken together, our results demonstrate the importance of MdZAT5 in root development under drought in apple trees. This finding provides a new candidate direction for apple breeding for drought resistance.

Effect of solution pH on root architecture of four apple rootstocks grown in an aeroponics nutrient misting system.

The pH of the solution in the rhizosphere is an important factor that determines the availability and mobility of nutrients for plant uptake. Solution pH may also affect the root distribution and architecture of apple rootstocks. In this study, we evaluated the effect of solution pH on root system development of apple rootstocks using an aeroponics system designed and developed at Cornell AgriTech Geneva, USA. Four Geneva® apple rootstocks (G.210, G.214, G.41, and G.890) were grown in an aeroponic system under nutrient solution misting featuring continuously adjusted pH levels to three pH treatments (5.5, 6.5, and 8.0). Root development was monitored for 30 days and evaluated regularly for distribution and root mass. Images of the developed roots grown in the aeroponic system were collected at the end of the experiment using a high-resolution camera and analyzed using GiA Roots® software, which generates root architecture parameter values in a semi-automated fashion. The resulting root architecture analysis showed that the Geneva® rootstocks were significantly different for two architecture parameters. The length-to-width ratio analysis represented by two GiA Roots parameters (minor-to-major ellipse ratio and network width-to-depth ratio) showed that G.210 was flatter than G.890, which had a greater tendency to grow downward. Rootstocks G.214 and G.41 displayed similar growth values. The solution pH affected most root architecture parameter measurements where overall root growth was higher at pH 8 than at pH 5.5 and 6.5, which showed similar growth. In general, the average root width tended to decrease at higher pH values. While there were no significant differences in the leaf nutrient concentrations of P, K, Ca, Mg, S, B, Zn, Cu, and Fe within the four rootstocks, the pH level of the solution had a significant effect on P, Ca, and Mn. This study is the first of its kind to investigate the effect of pH on root architecture in a soil-free (aeroponic) environment and may have implications for apple root behavior under field conditions where pH levels are different.

Apple-arbuscular mycorrhizal symbiosis confers resistance to Fusarium solani by inducing defense response and elevating nitrogen absorption.

Fusarium solani exerts detrimental effects on plant growth, which is one of the reasons for the incidence of apple replant disease. Arbuscular mycorrhizal fungi (AMF) enhance plant resistance to Fusarium wilt; however, the mechanism remains poorly understood. Therefore, the present study investigated the symbiosis between apple and AMF and explored the physiology, especially nitrate metabolism, antioxidant defense, and photosynthetic performance, when infected by F. solani. The experiment was carried out with four treatments, namely -AMF - F. solani, -AMF + F. solani, -AMF + F. solani, and + AMF + F. solani. In this study, the -AMF + F. solani treatment increased the activity of enzymes associated with nitrogen metabolism, such as the nitrate and nitrite reductases, in the apple root system. The +AMF + F. solani treatment showed higher antioxidant enzyme activities than the -AMF + F. solani by F. solani infection. The apple seedlings of the +AMF + F. solani treatment decreased reactive oxygen accumulation and reduced the oxidative damages triggered by F. solani infection. The improvement in antioxidant capacity due to the +AMF + F. solani treatment was closely associated with the upregulation of genes related to the antioxidant system. The F. solani infection greatly damaged the photosynthetic process, while the +AMF + F. solani treatment significantly improved it compared to the -AMF + F. solani treatment. In conclusion, the study demonstrated that the apple-AMF symbiosis plays an active role in regulating the resistance against F. solani infection by enhancing defense response and nitrogen metabolism.

Assessment of genetic homogeneity of in-vitro propagated apple root stock MM 104 using ISSR and SCoT primers

Apple is an important fruit crop that is always in demand due to its commercial and nutraceutical value. Also, the requirement for quality planting material for this fruit crop for new plantations is increasing continuously. In-vitro propagation is an alternative approach, which may help to produce genetically identical high grade planting material. In this study, for the first time, an efficient and reproducible propagation protocol has been established for apple root stock MM 104 via axillary bud. Culturing axillary buds on Murashige and Skoog apple rootstock (MM 104) resulted in better in-vitro propagation. (MS) basal medium supplemented with 3.0% (w/v) sucrose and 0.8% (w/v) agar. The axillary buds were established in MS basal medium with BA (5.0 µM), NAA (1.0 µM) and further used to establish invitro propagation protocol. Plant Growth Regulators (PGRs), BA (1.0 µM) in combination with NAA (1.0 µM) was found most efficient for shoot multiplication (100%) and produced 9.8 shoots/explants with an average shoot length of (2.4 ± cm). All the shoots produced roots in 0.1 µM IBA with a 5-day dark period. Acclimatization of in-vitro raised plantlets was obtained with vermiculite: perlite: sand: soil (2:2:1:1) resulting in 76% survival under field conditions. The study showed that the use of axillary bud is efficient for multiple-shoot production of apple rootstock (MM 104). This is the first comprehensive report on in-vitro growth of apple root stock MM 104 with an assessment of genetic stability using DNA fingerprinting profiles based on Inter Simple Sequence Repeats (ISSR) and Start Codon Targeted (SCoT). The genetic stability of in-vitro-produced plants, as determined by SCoT and ISSR primers, demonstrated genetic closeness to the mother plant.

MiR164-MhNAC1 regulates apple root nitrogen uptake under low nitrogen stress.

Nitrogen is an essential nutrient for plant growth and serves as a signaling molecule to regulate gene expression inducing physiological, growth and developmental responses. An excess or deficiency of nitrogen may have adverse effects on plants. Studying nitrogen uptake will help us understand the molecular mechanisms of utilization for targeted molecular breeding. Here, we identified and functionally validated an NAC (NAM-ATAF1/2-CUC2) transcription factor based on the transcriptomes of two apple rootstocks with different nitrogen uptake efficiency. NAC1, a target gene of miR164, directly regulates the expression of the high-affinity nitrate transporter (MhNRT2.4) and citric acid transporter (MhMATE), affecting root nitrogen uptake. To examine the role of MhNAC1 in nitrogen uptake, we produced transgenic lines that overexpressed or silenced MhNAC1. Silencing MhNAC1 promoted nitrogen uptake and citric acid secretion in roots, and enhanced plant tolerance to low nitrogen conditions, while overexpression of MhNAC1 or silencing miR164 had the opposite effect. This study not only revealed the role of the miR164-MhNAC1 module in nitrogen uptake in apple rootstocks but also confirmed that citric acid secretion in roots affected nitrogen uptake, which provides a research basis for efficient nitrogen utilization and molecular breeding in apple.

Nitrogen Application Timing and Levels Affect the Fate and Budget of Fertilizer Nitrogen in the Apple-Soil System.

This study aimed to determine the effects of the nitrogen (N) application period and level on the fate of fertilizer N and the contribution of N absorption and translocation to apple organ N. Two N application periods (labeled by the 15N tracer technique in spring and summer, represented by SP and SU, respectively) and three N levels (N0, MN, and HN) were used to determine the physiological indexes and aboveground, root, and soil 15N content of 4-year-old dwarf ('Red Fuji'/M9T337) and arborized ('Red Fuji'/Malus hupehensis Rehd.) apple trees. The results showed that HN led to shoot overgrowth, which was not conducive to the growth of the apple root system (root length, root tips, root surface area, and root volume) or the improvement of root activity. The contribution of soil N to apple organ N accounted for more than 50%, and the contribution of N application in summer to fruit N was higher than that in spring. Under HN treatment, the proportion of soil N absorbed by trees decreased, while that of fertilizer N increased; however, the highest proportion was still less than 50%, so apple trees were highly dependent on soil N. Under MN treatment, fertilizer N residue was similar to soil N consumption, and soil N fertility maintained a basic balance. Under HN treatment, fertilizer N residue was significantly higher than soil N consumption, indicating that excessive N application increased fertilizer N residue in the soil. Overall, the 15N utilization rate of arborized trees (17.33-22.38%) was higher than that of dwarf trees (12.89-16.91%). A total of 12.89-22.38% of fertilizer 15N was absorbed by trees, 30.37-35.41% of fertilizer 15N remained in the soil, and 44.65-54.46% of fertilizer 15N was lost. The 15N utilization rate and 15N residual rate of summer N application were higher than those of spring N application, and the 15N loss rate was lower than that of spring N application. High microbial biomass N (MBN) may be one of the reasons for the high N utilization rate and the low loss rate of N application in summer.

Differential accumulation of phenolics and phytoalexins in seven Malus genotypes cultivated in apple replant disease-affected soil

Apple replant disease (ARD) is a globally recognised soil-borne disease, which affects apple orchards and tree nurseries. Biotic factors are considered to be the main causal agent of ARD. Phenolics and phytoalexins were induced in apple roots grown in ARD soil compared to roots grown in disinfested ARD soil. However, the relationship between ARD susceptibility and production of phenolics and phytoalexins in apple roots is still unclear. To answer this question, we cultivated seven Malus genotypes with varying levels of ARD susceptibility (M.26, EMR 2, M.200, G.214, G.935, Selection 4, and MAL0739) in both ARD soil from Heidgraben, Germany, and the same soil after disinfestation by gamma-irradiation (γ-ARD). Despite the overall growth reduction observed for all seven genotypes, three of them, EMR 2, G.935 and MAL0739, showed better performance, as indicated by the ARD susceptibility index (ASI) and differences in their root structure. Phenolics and phytoalexins were differentially induced in the roots grown for four weeks (T4) and eight weeks (T8) in ARD soil compared to γ-ARD soil. Moreover, differences in the total phenolics content (TPC) and the total phytoalexin content among the evaluated Malus genotypes were observed. The biochemical data from the early time point (T4) separated Malus genotypes more effectively compared to that from the late time point (T8). Among the six ARD-induced phytoalexins, 3-hydroxy-5-methoxybiphenyl at T4 can serve as an early biomarker for ARD. Although TPC and total phytoalexin content of the Malus genotypes exhibited no or weak correlation with root and shoot growth reduction, some individual phenolics and phytoalexins showed higher coefficients, suggesting that they might influence the ARD susceptibility of apple rootstocks.

Microscopic features of lignin deposition patterns in young apple roots using brightfield and fluorescence imaging

Microscopic features of lignin deposition patterns in young apple roots using brightfield and fluorescence imaging

γ-Aminobutyric acid enhances salt tolerance by sustaining ion homeostasis in apples

Soil salinization had become a global ecological problem, which restricts the plant growth, and the quantity and quality of fruits. As a signaling molecule, γ-Aminobutyric acid (GABA) mediates a series of physiological processes and stress responses. Our previous research showed that GABA could alleviate drought, low phosphorus, cadmium stresses in apples, but the further research about its physiological mechanisms under salt stress was even more needed. The present study showed that the inhibition of salt stress on plant growth might be effectively alleviated by the treatment of 0.5 mM GABA, and the osmotic balance and photosynthetic capacity of plants could be maintained. Exogenous GABA could effectively inhibit the enrichment of reactive oxygen species and the uptake of Na+, while maintaining ion homeostasis. The experiment results indicated GABA could markedly promote the expression amount of Na+ and K+ transport-related genes (e.g., HKT1, AKT1, NHX1, SOS1, SOS2, and SOS3) in apples under salt stress. Overexpression and interference (RNAi) of MdGAD1 in apple roots, which is a crucial enzyme in the GABA biosynthesis, affected the salt tolerance of plants. Transgenic apple plants with roots of overexpression MdGAD1 showed less relative electrolyte leakage and more expression level of related ion transport genes than CK group, but RNAi MdGAD1 led to the opposite results. These results indicated that GABA accumulation could effectively strengthen the resistance of apple plants to salt stress and alleviate the injury of apple seedlings resulted from salinity.

ВЛИЯНИЕ ПИТАТЕЛЬНЫХ СРЕД НА МОРФОЛОГО-КУЛЬТУРАЛЬНЫЕ ПРИЗНАКИ ШТАММА PHYTOPHTHORA SP. DE BARY

In the protection of fruit crops from a complex of pathogens, one of the current tasks is to prevent the development of root rot, among the causes of which are the activity of soil micromycetes Phytophthora sp. Selective media play a key role both in identification and subsequent storage in the laboratory, and in the study of morphological and cultural traits, sporulation ability, as well as to obtain a certain amount of inoculum (for example, for in vivo studies) and mycelium (for DNA isolation). Obtaining a pure culture of pathogenic micromycete with certain morphological and cultural characteristics, which may be important for diagnosis by both traditional and modern methods, determines the relevance of studying the influence of various media on these parameters of the pathogenic fungus Phytophthora sp. The studies were carried out by methods of laboratory and comparative analyses. The growth of the pathogen strain of apple root rot Phytophthora sp. on nine nutrient media was studied. The colony growth rate and morphological and cultural characteristics were evaluated. As a result of the research, the strain has been found to vary not only the growth rate of the colony, but also the cultural characteristics depending on the nutrient medium. Of the nine nutrient media, three universal ones were selected that are most suitable for cultivation and identification, namely, tomato, potato-glucose and must agars. They meet the following criteria: ensuring the maximum degree of sporulation, rapid growth and development of the mycelium of the fungus, ease of preparation. It was also noted that Leroux medium can be used to obtain a large amount of inoculum, since it will produce more spores when planted in a lawn than on other media

Inter-row cropping and rootstock genotype selection in a UK cider orchard to combat apple replant disease

Apple rootstock genotypes confer different levels of tolerance to apple replant disease (ARD) and vigour to a newly replanted apple tree. A hybrid management system of rotating the rootstock genotype planted between successive generations and inter-row planting in the alleyways of orchards may minimise the severity of ARD symptoms. High-throughput sequencing of the fungal ITS and bacterial 16S rDNA regions was used to investigate the diversity, and differential taxa present in soils displaying symptoms of ARD. Candidate pathogens and beneficial microorganisms were correlated with the above-ground establishment of each rootstock genotype in a UK cider orchard. Our results suggest that the same rootstock or rootstock with closely related parentage to the previous rootstock had more severe ARD symptoms. Planting in the alleyway appeared an effective strategy to minimise the severity of symptoms irrespective of rootstock genotype. The planting location effect had a higher contribution to the variation in the rhizosphere microbiome than that of the rootstock genotype. No predicted causal agents for ARD could be identified to a taxonomic level to predict their function but two species associated with mycorrhizae, Pteridiospora spinosispora and Paraglomus laccatum were identified as inversely correlated with ARD severity and could be candidate beneficial species for apple, warranting further investigation and research. Our findings suggest that planting in the alleyways and planting rootstocks genetically dissimilar to the previously planted rootstock can be beneficial for tree establishment. We have also identified species inversely associated with ARD severity, making candidates for future research to test the antagonistic effect of the species against ARD pathogens in apple roots.

MxMPK6-2-mediated phosphorylation enhances the responseof apple rootstocks to Fe deficiency by activating PM H+ -ATPase MxHA2.

Iron (Fe) deficiency significantly affects the growth and development, fruit yield and quality of apples. Apple roots respond to Fe deficiency stress by promoting H+ secretion, which acidifies the soil. In this study, the plasma membrane (PM) H+ -ATPase MxHA2 promoted H+ secretion and root acidification of apple rootstocks under Fe deficiency stress. H+ -ATPase MxHA2 is upregulated in Fe-efficient apple rootstock of Malus xiaojinensis at the transcription level. Fe deficiency also induced kinase MxMPK6-2, a positive regulator in Fe absorption that can interact with MxHA2. However, the mechanism involving these two factors under Fe deficiency stress is unclear. MxMPK6-2 overexpression in apple roots positively regulated PM H+ -ATPase activity, thus enhancing root acidification under Fe deficiency stress. Moreover, co-expression of MxMPK6-2 and MxHA2 in apple rootstocks further enhanced PM H+ -ATPase activity under Fe deficiency. MxMPK6-2 phosphorylated MxHA2 at the Ser909 site of C terminus, Thr320 and Thr412 sites of the Central loop region. Phosphorylation at the Ser909 and Thr320 promoted PM H+ -ATPase activity, while phosphorylation at Thr412 inhibited PM H+ -ATPase activity. MxMPK6-2 also phosphorylated the Fe deficiency-induced transcription factor MxbHLH104 at the Ser169 site, which then could bind to the promoter of MxHA2, thus enhancing MxHA2 upregulation. In conclusion, the MAP kinase MxMPK6-2-mediated phosphorylation directly and indirectly regulates PM H+ -ATPase MxHA2 activity at the protein post-translation and transcription levels, thus synergistically enhancing root acidification under Fe deficiency stress.

Inoculation with arbuscular mycorrhizal fungi increase calcium uptake in Malus robusta

Utilization of plants-microbe's interactions to remediate calcium11Ca: calcium (Ca) deficiency soils is effective and practical. A greenhouse pot experiment was conducted to evaluate the effect of arbuscular mycorrhizal fungi22AMF: arbuscular mycorrhizal fungi (AMF) inoculation and the synergy of AMF and Ca fertilizer on physiological and transcriptomic responses in apple rootstock (Malus robusta) roots. AMF and Ca fertilizer synergistically served to elongate root length, surface area, average stem diameter and biomass, such extended the surface area in contact with soil nutrients and water. Symbiosis of AMF with apple seedlings made significantly higher levels of Ca in root tissue and promoted Ca translocation from roots to shoot tissue. GO and KEGG pathway analysis disclosed that gene expression varies in several critical gene families, such as auxin response (MdAux/IAAs, MdGH3 and MdSAUR), TCA cycles (MdCS, MdMDH and MdACO), phosphate transporters (MdPHT1;1, MdPHT1;10 and MdPHT1;3) and Ca2+ signal transduction pathways (MdCa2+/ATPase, MdCML, MdTPC1 and MdCDPK), indicating that apple regulates the expression of genes related to auxin synthesis, organic acid secretion, and calcium transporters and channels, thereby increased the growth of apple roots and promoted the secretion of organic acids, resulting in the increase of calcium effectiveness in soil. AMF promoted the accumulation and utilization of Ca in plants by regulating the expression levels of genes related to these pathways. These results contribute to a better understanding of AMF symbiosis mechanism behind the Ca uptake of apple seedlings under exogenous Ca treatment.