Transcription factor LBD16 targets cell wall modification/ion transport genes in peach lateral root formation.

LATERAL ORGAN BOUNDARIES DOMAIN/ASYMMETRIC LEAVES2-LIKEs (LBDs/ASLs) are plant-specific transcription factors that function downstream of auxin-regulated lateral root (LR) formation. Our previous research found that PpLBD16 positively regulates peach (Prunus persica) LR formation. However, the downstream regulatory network and target genes of PpLBD16 are still largely unknown. Here, we constructed a PpLBD16 homologous overexpression line and a PpLBD16 silenced line. We found that overexpressing PpLBD16 promoted peach root initiation, while silencing PpLBD16 inhibited peach root formation. Through RNA sequencing (RNA-seq) analysis of roots from PpLBD16 overexpression and silenced lines, we discovered that genes positively regulated by PpLBD16 were closely related to cell wall synthesis and degradation, ion/substance transport, and ion binding and homeostasis. To further detect the binding motifs and potential target genes of PpLBD16, we performed DNA-affinity purification sequencing (DAP-seq) analysis in vitro. PpLBD16 preferentially bound to CCNGAAANNNNGG (MEME-1), [C/T]TTCT[C/T][T/C] (MEME-2), and GCGGCGG (ABR1) motifs. By combined analysis of RNA-seq and DAP-seq data, we screened candidate target genes for PpLBD16. We demonstrated that PpLBD16 bound and activated the cell wall modification-related genes EXPANSIN-B2 (PpEXPB2) and SUBTILISIN-LIKE PROTEASE 1.7 (PpSBT1.7), the ion transport-related gene CYCLIC NUCLEOTIDE-GATED ION CHANNEL 1 (PpCNGC1) and the polyphenol oxidase (PPO)-encoding gene PpPPO, thereby controlling peach root organogenesis and promoting LR formation. Moreover, our results displayed that PpLBD16 and its target genes are involved in peach LR primordia development. Overall, this work reveals the downstream regulatory network and target genes of PpLBD16, providing insights into the molecular network of LBD16-mediated LR development.

Genome-wide identification of nucleotide-binding domain leucine-rich repeat (NLR) genes and their association with green peach aphid (Myzus persicae) resistance in peach.

Resistance genes (R genes) are a class of genes that are immune to a wide range of diseases and pests. In planta, NLR genes are essential components of the innate immune system. Currently, genes belonging to NLR family have been found in a number of plant species, but little is known in peach. Here, 286 NLR genes were identified on peach genome by using their homologous genes in Arabidopsis thaliana as queries. These 286 NLR genes contained at least one NBS domain and LRR domain. Phylogenetic and N-terminal domain analysis showed that these NLRs could be separated into four subfamilies (I-IV) and their promoters contained many cis-elements in response to defense and phytohormones. In addition, transcriptome analysis showed that 22 NLR genes were up-regulated after infected by Green Peach Aphid (GPA), and showed different expression patterns. This study clarified the NLR gene family and their potential functions in aphid resistance process. The candidate NLR genes might be useful in illustrating the mechanism of aphid resistance in peach.

Lipid Metabolomic and Transcriptomic Analyses Reveal That Phosphatidylcholine Enhanced the Resistance of Peach Seedlings to Salt Stress through Phosphatidic Acid.

Soil salinity is a major conlinet limiting sustainable agricultural development in peach tree industry. In this study, lipid metabolomic pathway analysis indicated that phosphatidic acid is essential for root resistance to salt stress in peach seedlings. Through functional annotation analysis of differentially expressed genes in transcriptomics, we found that MAPK signaling pathway is closely related to peach tree resistance to salt stress, wherein PpMPK6 expression is significantly upregulated. Under salt conditions, the OE-PpMPK6 Arabidopsis thaliana (L.) Heynh. line showed higher resistance to salt stress than WT and KO-AtMPK6 lines. Furthermore, we found that the Na+ content in OE-PpMPK6 roots was significantly lower than that in WT and KO-AtMPK6 roots, indicating that phosphatidic acid combined with PpMPK6 activated the SOS1 (salt-overly-sensitive 1) protein to enhance Na+ efflux, thus alleviating the damage caused by NaCl in roots; these findings provide insight into the salt stress-associated transcriptional regulation.

Physiological and Transcriptomic Analyses of the Effects of Exogenous Lauric Acid on Drought Resistance in Peach (Prunus persica (L.) Batsch).

Peach (Prunus persica (L.) Batsch) is a fruit tree of economic and nutritional importance, but it is very sensitive to drought stress, which affects its growth to a great extent. Lauric acid (LA) is a fatty acid produced in plants and associated with the response to abiotic stress, but the underlying mechanism remains unclear. In this study, physiological analysis showed that 50 ppm LA pretreatment under drought stress could alleviate the growth of peach seedlings. LA inhibits the degradation of photosynthetic pigments and the closing of pores under drought stress, increasing the photosynthetic rate. LA also reduces the content of O2-, H2O2, and MDA under drought stress; our results were confirmed by Evans Blue, nitroblue tetrazolium (NBT), and DAB(3,3-diaminobenzidine) staining experiments. It may be that, by directly removing reactive oxygen species (ROS) and improving enzyme activity, i.e., catalase (CAT) activity, peroxidase (POD) activity, superoxide dismutase (SOD) activity, and ascorbate peroxidase (APX) activity, the damage caused by reactive oxygen species to peach seedlings is reduced. Peach seedlings treated with LA showed a significant increase in osmoregulatory substances compared with those subjected to drought stress, thereby regulating osmoregulatory balance and reducing damage. RNA-Seq analysis identified 1876 DEGs (differentially expressed genes) in untreated and LA-pretreated plants under drought stress. In-depth analysis of these DEGs showed that, under drought stress, LA regulates the expression of genes related to plant-pathogen interaction, phenylpropanoid biosynthesis, the MAPK signaling pathway, cyanoamino acid metabolism, and sesquiterpenoid and triterpenoid biosynthesis. In addition, LA may activate the Ca2+ signaling pathway by increasing the expressions of CNGC, CAM/CML, and CPDK family genes, thereby improving the drought resistance of peaches. In summary, via physiological and transcriptome analyses, the mechanism of action of LA in drought resistance has been revealed. Our research results provide new insights into the molecular regulatory mechanism of the LA-mediated drought resistance of peach trees.

Waterlogging resistance and evaluation of physiological mechanism of three peach (Prunus persica) rootstocks.

Waterlogging occurs due to poor soil drainage or excessive rainfall. It is a serious abiotic stress factor that negatively affects crop growth. Waterlogging often causes plants to shed leaves, fruits, and, ultimately, to die. Peach (Prunus persica) trees are generally intolerant to waterlogging, and the primary peach rootstock used in Chinais "Maotao," which has very poor resistance to sensitivity. Therefore, waterlogging has become a restriction on the development of the peach industry in many regions. In this experiment, we tested the waterlogging resistance of "Maotao (Prunus persica (L.) Batsch)" (MT), "Shannong1 (GF677 × Cadaman)" (SN1), and "Mirabolano 29C (Prunus cerasifera)" (M29C) rootstocks. Using a simulated waterlogging method, the effects of waterlogging on the photosynthetic system, leaf pigments, osmotic adjustment, lipid membrane peroxidation, and antioxidant system of these three peach rootstocks were studied, and the changes of chlorophyll fluorescence parameters and fluorescence imaging were observed. The results showed that, with prolonged waterlogging, the photosynthetic pigment content and photosynthesis of the three peach rootstocks decreased rapidly, but the decomposition rate of SN1 and M29C chlorophyll was slower, and it still had high light energy absorption and energy transfer capabilities under waterlogging stress, which reduced the damage caused by waterlogging stress; under the stress of flooding, the osmoregulatory substances of the three rootstocks increased to varying degrees compared with normal conditions. At the same time, the enzyme activity of superoxide dismutase (SOD) activity, peroxidase (POD) activity, and catalase (CAT) activity in the leaves of the three rootstocks under flooding stress all increased and then decreased; during this period, malondialdehyde (MDA) continued to increase, and SN1 and M29C were significantly lower than MT; and chlorophyll fluorescence parameters, including the maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), photochemical quenching coefficient (qP), non-photochemical quenching (NPQ), and electron transfer rate (ETR) decreased significantly. The tolerance of SN1 and M29C to waterlogging was significantly better than that of MT rootstocks. The rootstock and grafted seedlings of SN1 have good waterlogging tolerance.

Effects of Valine and Urea on Carbon and Nitrogen Accumulation and Lignin Content in Peach Trees.

Nitrogen availability and uptake levels can affect nutrient accumulation in plants. In this study, the effects of valine and urea supplementation on the growth of new shoots, lignin content, and carbon and the nitrogen metabolism of 'Ruiguang 39/peach' were investigated. Relative to fertilization with urea, the application of valine inhibited shoot longitudinal growth, reduced the number of secondary shoots in autumn, and increased the degree of shoot lignification. The application of valine also increased the protein level of sucrose synthase (SS) and sucrose phosphate synthase (SPS) in plant leaves, phloem, and xylem, thereby increasing the soluble sugar and starch content. It also resulted in an increase in nitrate reductase (NR), glutamine synthase (GS), and glutamate synthase (GOGAT) protein levels, with an increase in plant contents of ammonium nitrogen, nitrate nitrogen, and soluble proteins. Although urea application increased the protein level of carbon- and nitrogen-metabolizing enzymes, the increase in plant growth reduced the overall nutrient accumulation and lignin content per unit tree mass. In conclusion, the application of valine has a positive effect on increasing the accumulation of carbon and nitrogen nutrients in peach trees and increasing the lignin content.

Dynamic Monitoring of Nutrition Inputs and Fertility Evaluation during a Decade in the Main Peach-Producing Areas of Shandong Province, China.

The main peach-producing area in Shandong is an important peach fruit-producing area in China. Understanding the nutritional properties of the soil in peach orchards helps us to understand the evolution of soil properties and adjust management methods in a timely manner. This study focuses on 52 peach orchards in the main peach-producing area in Shandong as the research object. The spatiotemporal changes in soil traits and their influential factors were studied in depth, and the changes in soil fertility were effectively evaluated. The results showed that the input of nitrogen, phosphorus and potassium from organic fertilizer in 2021 was significantly higher than that in 2011, while the input of fertilizer in 2011 was significantly higher than that in 2021. Compared with traditional parks, both organic fertilizer inputs and chemical fertilizer inputs in demonstration parks showed a significant downwards trend. There was no significant change in pH values between 2011 and 2021. In 2021, the soil organic matter (SOM) contents of the 0-20 cm and 20-40 cm layers were 24.17 g·kg-1 and 23.38 g·kg-1, respectively, an increase of 29.3% and 78.47% over the values measured in 2011. Compared with 2011, the content of soil alkaloid nitrogen (AN) decreased significantly in 2021, and the contents of available phosphorus (AP) and available potassium (AK) in the soil increased significantly. According to the calculation results of the comprehensive fertility index (IFI) value, we found that in 2021, compared with 2011, the quality of soil fertility improved, most of which was at the medium and high levels. The research results show that the fertilizer-saving and synergistic approach in peach orchards in China significantly improved the soil nutrition. In the future, research on suitable comprehensive technologies should be strengthened in the management of peach orchards.

Genome-wide identification, bioinformatics and expression analysis of HD-Zip gene family in peach.

BACKGROUND: HD-Zips (Homeodomain-Leucine Zippers) are a class of plant-specific transcription factors that play multiple roles in plant growth and development. Although some functions of HD-Zip transcription factor have been reported in several plants, it has not been comprehensively studied in peach, especially during adventitious root formation of peach cuttings. RESULTS: In this study, 23 HD-Zip genes distributed on 6 chromosomes were identified from the peach (Prunus persica) genome, and named PpHDZ01-23 according to their positions on the chromosomes. These 23 PpHDZ transcription factors all contained a homeomorphism box domain and a leucine zipper domain, were divided into 4 subfamilies(I-IV) according to the evolutionary analysis, and their promoters contained many different cis-acting elements. Spatio-temporal expression pattern showed that these genes were expressed in many tissues with different levels, and they had distinct expression pattern during adventitious root formation and development. CONCLUSION: Our results showed the roles of PpHDZs on root formation, which is helpful to better understand the classification and function of peach HD-Zip genes.

Abscisic acid and regulation of the sugar transporter gene MdSWEET9b promote apple sugar accumulation.

Enhancing fruit sugar contents, especially for high-flavonoid apples with a sour taste, is one of the main goals of horticultural crop breeders. This study analyzed sugar accumulation and the underlying mechanisms in the F2 progenies of a hybridization between the high-sugar apple (Malus × domestica) variety "Gala" and high-flavonoid apple germplasm "CSR6R6". We revealed that MdSWEET9b (sugars will eventually be exported transporter) helps mediate sugar accumulation in fruits. Functional characterization of MdSWEET9b in yeast mutants lacking sugar transport as well as in overexpressing and CRISPR/Cas9 knockdown apple calli revealed MdSWEET9b could transport sucrose specifically, ultimately promoting normal yeast growth and accumulation of total sugar contents. Moreover, MdWRKY9 bound to the MdSWEET9b promoter and regulated its activity, which responded to abscisic acid (ABA) signaling. Furthermore, MdWRKY9 interacted with MdbZIP23 (basic leucine zipper) and MdbZIP46, key ABA signal transducers, at the protein and DNA levels to enhance its regulatory effect on MdSWEET9b expression, thereby influencing sugar accumulation. Based on the contents of ABA in lines with differing sugar contents and the effects of ABA treatments on fruits and calli, we revealed ABA as one of the main factors responsible for the diversity in apple fruit sugar content. The results of this study have clarified how MdSWEET9b influences fruit sugar accumulation, while also further elucidating the regulatory effects of the ABA-signaling network on fruit sugar accumulation. This work provides a basis for future explorations of the crosstalk between hormone and sugar metabolism pathways.

MdMYB305-MdbHLH33-MdMYB10 regulates sugar and anthocyanin balance in red-fleshed apple fruits.

Sugar and anthocyanin are important indicators of fruit quality, and understanding the mechanism underlying their accumulation is essential for breeding high-quality fruit. We identified an R2R3-MYB transcription factor MdMYB305 in the red-fleshed apple progeny, which was positively correlated with fruit sugar content but negatively correlated with anthocyanin content. Transient injection, stable expression [overexpressing and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)], and heterologous transformation of tomato confirmed that MdMYB305 promotes the accumulation of sugar and inhibits the synthesis of anthocyanin. A series of molecular experiments (such as electrophoretic mobility shift and luciferase assays) confirmed that MdMYB305 combines with sugar-related genes (MdCWI1/MdVGT3/MdTMT2) and anthocyanin-related genes (MdF3H/MdDFR/MdUFGT), promoting and inhibiting their activities, and finally regulating the sugar and anthocyanin content of fruits. In addition, the study also found that MdMYB305 competes with MdMYB10 for the MdbHLH33 binding site to balance sugar and anthocyanin accumulation in the fruits, which provides a reference value for exploring more functions of the MYB-bHLH-MYB complex and the balance relationship between sugar and anthocyanin in the future.

Genome-Wide Identification of Trehalose-6-phosphate Synthase (TPS) Gene Family Reveals the Potential Role in Carbohydrate Metabolism in Peach.

Trehalose-6-phosphate synthase (TPS) is essential for plant growth and development, linking trehalose-6-phosphate (T6P) to carbon metabolism. However, little is known about the TPS gene family in peaches and their potential roles in regulating carbohydrates in peach fruit. In this study, nine TPS genes were identified in the peach genome and named according to the homologous genes in Arabidopsis. Phylogenetic analysis showed that three subfamilies were identified, including TPSI, TPSII-1, and TPSII-2, which were also consistent with gene structure analysis. Considerable cis-elements were enriched in the promoters, including plant hormone-related elements. Tissue-specific analysis showed that these TPS genes were mainly expressed in leaves, stems, and fruit, showing different expression patterns for each gene. In addition, during fruit development, the content of trehalose-6-phosphate (T6P) was positively correlated with the expression of PpTPS7a and negatively with sucrose non-fermenting-1-related kinase 1 (SnRK1) activity. Transient overexpression and silencing of PpTPS7a in peach fruit validated its function in regulating T6P content and SnRK1 activity.

Silicon inhibits gummosis by promoting polyamine synthesis and repressing ethylene biosynthesis in peach.

Silicon is a beneficial element for plant growth, as well as for improving plant resistance to multiple biotic and abiotic stresses. Gummosis is a common harmful disease in peach and is induced by many factors. However, the effect of silicon on gummosis of peach has not been determined yet. In this study, we reported that application of silicon significantly reduced gummosis by regulating biosynthesis of ethylene and polyamines in peach. Ethylene promoted the development of gummosis by inducing the expression of genes encoding cell wall degrading enzymes. While application of different types of polyamines, including spermidine and spermine, dramatically inhibited the occurrence of gummosis. Moreover, polyamines inhibited the ethylene biosynthesis by down-regulating expression of ethylene biosynthetic gene PpACS1 (1-aminocyclopropane -1-carboxylic acid synthase), as well as the enzymatic activity of ACS. We further found that application of silicon significantly restricted the development of gummosis in peach. Exogenous silicon dramatically inhibited expression of PpACS1 and the enzymatic activity of its product to reduce ethylene biosynthesis. Simultaneously, the activity of S-adenosylmethionine decarboxylase, a key enzyme in ployamines biosynthesis, was increased by 9.85% under silicon treatment, resulting in elevated accumulation of polyamines. Thus, our data proved that application of silicon restricted gummosis development by activating ployamines biosynthesis and inhibiting ethylene synthesis in peach.

Leucine Contributes to Copper Stress Tolerance in Peach (Prunus persica) Seedlings by Enhancing Photosynthesis and the Antioxidant Defense System.

Heavy metal contamination has a severe impact on ecological health and plant growth and is becoming increasingly serious globally. Copper (Cu) is a heavy metal that is essential for the growth and development of plants, including peach (Prunus persica L. Batsch); however, an excess is toxic. In plants, amino acids are involved in responses to abiotic and biotic stresses, such as water deficit, extreme temperatures, high salinity, and heavy metal stress. However, the role of leucine in the regulation of heavy metal stress is currently unclear. Therefore, we investigated the effects of exogenous leucine on the growth of peach seedlings under Cu stress. Exogenous leucine improved the leaf ultrastructure and ionic balance and increased the chlorophyll content, the net photosynthetic rate, and the maximum photochemical efficiency. Furthermore, it attenuated Cu-stress-induced oxidative damage via a decrease in reactive oxygen species (ROS) and the regulation of the antioxidant and osmotic systems. These effects, in turn, ameliorated the reductions in cell viability, cellular activity, and biomass under Cu stress. Moreover, exogenous leucine increased the activities of nitrate reductase (NR), glutamine synthetase (GS), and glutamic acid synthetase (GOGAT) and thus improved the nitrogen metabolism efficiency of plants. In conclusion, leucine significantly improved the photosynthetic performance and antioxidant capacity, reduced Cu accumulation, and promoted nitrogen metabolism, which in turn improved the resistance of peach seedlings to Cu stress.

Comparison of lauric acid and 12-hydroxylauric acid in the alleviation of drought stress in peach (Prunus persica (L.) Batsch).

Water shortage is a key factor that can restrict peach tree growth. Plants produce fatty acids and the fatty acid derivatives lauric acid (LA) and 12-hydroxylauric acid (LA-OH), which are involved in abiotic stress responses, but the underlying stress response mechanisms remain unclear. In this study, physiological examination revealed that in Prunus persica (L.) Batsch, pretreatment with 50 ppm LA-OH and LA reduced drought stress, efficiently maintained the leaf relative water content, and controlled the relative conductivity increase. Under drought stress, LA-OH and LA treatments prevented the degradation of photosynthetic pigments, increased the degree of leaf stomatal opening and enhanced the net photosynthetic rate. Compared with drought stress, LA-OH and LA treatment effectively increased the net photosynthetic rate by 204.55% and 115.91%, respectively, while increasing the Fv/Fm by 2.75% and 7.75%, respectively, but NPQ decreased by 7.67% and 37.54%, respectively. In addition, the level of reactive oxygen species increased under drought stress. The content of O2 - in LA-OH and LA treatment decreased by 12.91% and 11.24% compared to CK-D, respectively, and the content of H2O2 decreased by 13.73% and 19.94%, respectively. At the same time, the content of malondialdehyde (MDA) decreased by 55.56% and 58.48%, respectively. We believe that the main reason is that LA-OH and LA treatment have improved the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). The application of exogenous LA increased the levels of soluble sugars, soluble proteins, proline and free amino acids under drought stress, and maintained the osmotic balance of cells. Compared with CK-D treatment, it increased by 24.11%, 16.89%, 29.3% and 15.04%, respectively. At the same time, the application of exogenous LA-OH also obtained similar results. In conclusion, exogenous LA-OH and LA can alleviate the damage to peach seedlings caused by drought stress by enhancing the photosynthetic and antioxidant capacities, increasing the activities of protective enzymes and regulating the contents of osmotic regulators, but the molecular mechanism is still in need of further exploration.

Comparative Transcriptome Analysis of Two Peach Rootstocks Uncovers the Effect of Gene Differential Expression on Nitrogen Use Efficiency.

Nitrogen is an important nutrient element that limits plant growth and yield formation, but excessive nitrogen has negative effects on plants and the environment. It is important to reveal the molecular mechanism of high NUE (nitrogen use efficiency) for breeding peach rootstock and variety with high NUE. In this study, two peach rootstocks, Shannong-1 (S) and Maotao (M), with different NUE were used as materials and treated with 0.1 mM KNO3 for transcriptome sequencing together with the control group. From the results of comparison between groups, we found that the two rootstocks had different responses to KNO3, and 2151 (KCL_S vs. KCL_M), 327 (KNO3_S vs. KCL_S), 2200 (KNO3_S vs. KNO3_M) and 146 (KNO3_M vs. KCL_M) differentially expressed genes (DEGs) were identified, respectively, which included multiple transcription factor families. These DEGs were enriched in many biological processes and signal transduction pathways, including nitrogen metabolism and plant hormone signal transduction. The function of PpNRT2.1, which showed up-regulated expression under KNO3 treatment, was verified by heterologous expression in Arabidopsis. The plant height, SPAD (soil and plant analyzer development) of leaf and primary root length of the transgenic plants were increased compared with those of WT, indicating the roles of PpNRT2.1 in nitrogen metabolism. The study uncovered for the first time the different molecular regulatory pathways involved in nitrogen metabolism between two peach rootstocks and provided gene reserve for studying the molecular mechanism of nitrogen metabolism and theoretical basis for screening peach rootstock or variety with high NUE.

Effects of Root Zone Aeration on Soil Microbes Species in a Peach Tree Rhizosphere and Root Growth.

The oxygen content in the root zone considerably affects the growth and development of peach trees. However, few studies have been conducted on the effects of the oxygen content in the root zones of peach trees on soil microbes and root growth. Four-year-old Ruiguang 33/Prunus persica (L.) Batsch trees were used to study the effects of root-zone aeration on soil microbes in a peach orchard, as well as on the soil nutrient contents, peach tree root systems, and plant potassium-to-nitrogen ratios. The results showed that the root-zone aeration substantially increased the soil oxygen content in the root zone and changed the soil microbial community structure. Compared with the control, the relative abundances of soil nitrogen-fixing microorganisms (Beta proteobacteria and Bradyrhizobium elkanii) and potassium-solubilizing microorganisms (Bacillus circulans) under the root-zone aeration conditions were greatly enhanced. Root-zone aeration increased the soil's alkaline nitrogen content, available potassium content, and organic matter content, as well as the number and thickness of new white roots of peach trees, and root activity was increased significantly. At the same time, root-zone aeration changed the relative contents of total potassium and total nitrogen in the plants and considerably increased the potassium-nitrogen ratio in the shoots. The results indicate that aeration in the root zone can change the soil microbial community structure, increase the abundances of nitrogen-fixing and potassium-solubilizing microorganisms, and increase the plant potassium-to-nitrogen ratio, which are conducive to peach fruit quality.

Silicon enhances the drought resistance of peach seedlings by regulating hormone, amino acid, and sugar metabolism.

BACKGROUND: Drought is one of the main concerns worldwide and restricts the development of agriculture. Silicon improves the drought resistance of plants, but the underlying mechanism remains unclear. RESULTS: We sequenced the transcriptomes of both control and silicon-treated peach seedlings under drought stress to identify genes or gene networks that could be managed to increase the drought tolerance of peach seedlings. Peach (Prunus persica) seedlings were used to analyse the effects of silicon on plant growth and physiological indexes related to drought resistance under drought stress. The results showed that silicon addition improved the water use efficiency, antioxidant capacity, and net photosynthetic rate, inhibition of stomatal closure, promoted the development of roots, and further regulated the synthesis of hormones, amino acids and sugars in peach seedlings. A comparative transcriptome analysis identified a total of 2275 genes that respond to silicon under drought stress. These genes were mainly involved in ion transport, hormone and signal transduction, biosynthetic and metabolic processes, stress and defence responses and other processes. We analysed the effects of silicon on the modulation of stress-related hormonal crosstalk and amino acid and sugar metabolism. The results showed that silicon promotes zeatin, gibberellin, and auxin biosynthesis, inhibits the synthesis of abscisic acid, then promote lateral root development and inhibit stomatal closure, and regulates the signal transduction of auxin, cytokinin, gibberellin and salicylic acid. Silicon also regulates the metabolism of various amino acids and promotes the accumulation of sucrose and glucose to improve drought resistance of peach seedlings. CONCLUSIONS: Silicon enhanced the drought resistance of peach seedlings by regulating stress-related hormone synthesis and signal transduction, and regulating amino acid and sugar metabolism.

Silicon inhibits gummosis in peach via ethylene and PpERF-PpPG1 pathway.

Silicon (Si) is abundant in nature, and it has been proved to be beneficial for the healthy growth and development of many plant species, improve plant stress resistance. Gummosis in peach is an invasive disease that causes widespread and serious damage. Mechanical damage and ethylene (ETH) can induce gummosis in peach shoots in the field. In this research, we found that Si as a chemical substance or signal to enhance plant resistance can reduce the synthesis of ETH, thereby inhibiting gummosis in peach. The results showed that Si can decrease the rate of gummosis, reduce the expression level of PpACS1 (1-aminocyclopropane -1-carboxylate synthase gene) and reduce the enzyme activity of polygalacturonase (PG). It was further discovered that Si can regulate the gene expression of PpERF21 and PpERF27. Yeast one-hybrid and dual-luciferase reporter assays showed that PpERF21 and PpERF27, through direct interaction with the promoter of PpPG1, inhibited the transcriptional activation of PpPG1. Overexpression of PpERF21 and PpERF27 effectively reduced fruit colloid production when bacterial cells harbouring the expression vector were used to instantaneously infect peach fruit. These results show that Si can inhibit the synthesis of ETH and mediate PpERF21 and PpERF27 expression to inhibit the expression of PpPG1, thereby inhibiting gummosis in peach.

Overexpression of PpSnRK1α in Tomato Increased Autophagy Activity under Low Nutrient Stress.

Plants suffer from a variety of environmental stresses during their growth and development. The evolutionarily conserved sucrose nonfermenting kinase 1-related protein kinase 1 (SnRK1) plays a central role in the regulation of energy homeostasis in response to stresses. In plant cells, autophagy is a degradation process occurring during development or under stress, such as nutrient starvation. In recent years, SnRK1 signaling has been reported to be an upstream activator of autophagy. However, these studies all focused on the regulatory effect of SnRK1 on TOR signaling and the autophagy-related gene 1 (ATG1) complex. In this study, overexpression of the gene encoding the Prunus persica SnRK1 α subunit (PpSnRK1α) in tomato improved the photosynthetic rates and enhanced the resistance to low nutrient stress (LNS). Overexpression of PpSnRK1α increased autophagy activity and upregulated the expression of seven autophagy-related genes (ATGs). The transcriptional levels of SlSnRK2 family genes were altered significantly by PpSnRK1α, signifying that PpSnRK1α may be involved in the ABA signaling pathway. Further analysis showed that PpSnRK1α not only activated autophagy by inhibiting target of rapamycin (TOR) signaling but also enhanced ABA-induced autophagy. This indicates that PpSnRK1α regulates the photosynthetic rate and induces autophagy, and then responds to low nutrient stress.