Glycine rich proline rich protein from Sorghum bicolor serves as an antimicrobial protein implicated in plant defense response

Proline-rich protein PRPL1 enhances Panax notoginseng defence against Fusarium solani by regulating reactive oxygen species balance and strengthening the cell wall barrier

The root rot mainly caused by Fusarium solani is a bottleneck in the cultivation of Panax notoginseng. In this study, we reported a gene encoding a plant cell wall structural protein, P. notoginseng proline-rich protein (PnPRPL1), whose transcription was upregulated by F. solani and induced by some hormone signals. The PnPRPL1 recombinant protein significantly inhibited the growth and conidial germination of the root rot pathogens. Downregulation of PnPRPL1 by RNA interference (RNAi) in P. notoginseng leaves increased the susceptibility to F. solani, whereas overexpression of PnPRPL1 in tobacco (Nicotiana tabacum) enhanced the resistance to F. solani. Compared with wild-type tobacco, the PnPRPL1-overexpressing transgenic tobacco had higher reactive oxygen species (ROS)-scavenging enzyme activities, lower ROS levels, and more lignin and callose deposition. The opposite results were obtained for the P. notoginseng expressing PnPRPL1 RNAi fragments. Furthermore, the PnPRPL1 promoter transcription activity was induced by several plant hormones and multiple stress stimuli. In addition, the transcription factor PnWRKY27 activated the expression of PnPRPL1 by directly binding to the promoter region. Thus, PnPRPL1, which is positively regulated by a WRKY transcription factor, encodes an antimicrobial protein that also mediates ROS homoeostasis and callose/lignin deposition during the response to F. solani infection.

Exogenous application of 5-azacitidin, royal jelly and folic acid regulate plant redox state, expression level of DNA methyltransferases and alleviate adverse effects of salinity stress on Vicia faba L. plants

DNA methylation is one of induced changes under salinity stress causing reduction in the expression of several crucial genes required for normal plant's operation. Potential use of royal jelly (RJ), folic acid (FA) and 5-azacitidine (5-AZA) on two Egyptian faba bean varieties (Sakha-3 and Giza-716) grown under saline conditions was investigated. Salinity stress affects negatively on seeds germination (G %), mitotic index, membrane stability and induced a significant increase in chromosomal abnormalities (CAs). DNA methyltransferases genes (MT1 and MT2) were highly up-regulated (∼23 and 8 folds for MT1 and MT2 in shoots of Giza-716 stressed plants). On the other hand, down regulation of other studied stress related genes: superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), heat shock protein (HSP-17.9) and proline-rich protein (GPRP) were detected in stressed plants of both studied varieties. Treating plants with RJ and FA increase G%, chlorophyll content, improves membrane properties and reduces CAs compared to non-treated stressed plants. Exogenous application of 5-AZA, RJ and FA on salinity stressed plants was associated with a significant reduction in the transcription of MT1 and MT2 which was associated with significant up regulation in the expression of Cu/Zn-SOD, CAT, GR, GPRP and HSP-17.9 encoding genes. The Lowest expression of MT1 and MT2 were induced with 5-AZA treatment in both studied varieties. Exogenous application of the FA, RJ and 5-AZA modified the methylation state of stressed plants by regulation the expression of DNA methyltransferases, subsequently, modulated the expression of studied genes and could be proposed as a promising treatment to ameliorate hazardous effects of salt stress on different plants.

Comparative transcriptome profiling reveals differential defense responses among Alternaria brassicicola resistant Sinapis alba and susceptible Brassica rapa

Alternaria blight is a devastating disease that causes significant crop losses in oilseed Brassicas every year. Adoption of conventional breeding to generate disease-resistant varieties has so far been unsuccessful due to the lack of suitable resistant source germplasms of cultivated Brassica spp. A thorough understanding of the molecular basis of resistance, as well as the identification of defense-related genes involved in resistance responses in closely related wild germplasms, would substantially aid in disease management. In the current study, a comparative transcriptome profiling was performed using Illumina based RNA-seq to detect differentially expressed genes (DEGs) specifically modulated in response to Alternaria brassicicola infection in resistant Sinapis alba, a close relative of Brassicas, and the highly susceptible Brassica rapa. The analysis revealed that, at 48 hpi (hours post inoculation), 3396 genes were upregulated and 23239 were downregulated, whereas at 72 hpi, 4023 genes were upregulated and 21116 were downregulated. Furthermore, a large number of defense response genes were detected to be specifically regulated as a result of Alternaria infection. The transcriptome data was validated using qPCR-based expression profiling for selected defense-related DEGs, that revealed significantly higher fold change in gene expression in S. alba when compared to B. rapa. Expression of most of the selected genes was elevated across all the time points under study with significantly higher expression towards the later time point of 72 hpi in the resistant germplasm. S. alba activates a stronger defense response reaction against the disease by deploying an array of genes and transcription factors involved in a wide range of biological processes such as pathogen recognition, signal transduction, cell wall modification, antioxidation, transcription regulation, etc. Overall, the study provides new insights on resistance of S. alba against A. brassicicola, which will aid in devising strategies for breeding resistant varieties of oilseed Brassica.

The C-terminal stretch of glycine-rich proline-rich protein (SbGPRP1) from Sorghum bicolor serves as an antimicrobial peptide by targeting the bacterial outer membrane protein

The C-terminal stretch in SbGPRP1 (Sorghum glycine-rich proline-rich protein) acts as an antimicrobial peptide in the host innate defense mechanism. Cationic antimicrobial proteins or peptides can either bind to the bacterial membrane or target a specific protein on the bacterial membrane thus leading to membrane perturbation. The 197 amino acid polypeptide of SbGPRP1 showed disordered structure at the N-terminal end and ordered conformation at the C-terminal end. In the present study, the expression of N-SbGPRP1, C-SbGPRP1, and ∆SbGPRP1 followed by antimicrobial assays showed potential antimicrobial property of the C-terminal peptide against gram-positive bacteria Bacillus subtilis and phytopathogen Rhodococcus fascians. The SbGPRP1 protein loses its antimicrobial property when the 23 amino acid sequence (GHGGHGVFGGGYGHGGYGHGYGG) from position 136 to 158 is deleted from the protein. Thus, it can be concluded that the 23 amino acid sequence is vital for the said antimicrobial property. NPN assay, SEM analysis, and electrolyte leakage assays showed potent antimicrobial activity for C-SbGPRP1. Overexpression of the C-SbGPRP1 mutant protein in tobacco followed by infection with Rhodococcus fascians inhibited bacterial growth as shown by SEM analysis. To determine if C-SbGPRP1 might target any protein on the bacterial membrane we isolated the bacterial membrane protein from both Bacillus subtilis and Rhodococcus fascians. Bacterial membrane protein that interacted with the column-bound C-SbGPRP1 was eluted and subjected to LC-MS/MS. LC-MS/MS data analysis showed peptide hit with membrane protein YszA from Bacillus subtilis and a membrane protein from Rhodococcus fascians. Isolated bacterial membrane protein from Bacillus subtilis or Rhodococcus fascians was able to reduce the antimicrobial activity of C-SbGPRP1. Furthermore, BiFC experiments showed interactions between C-SbGPRP1 and YszA protein from Bacillus subtilis leading to the conclusion that bacterial membrane protein was targeted in such membrane perturbation leading to antimicrobial activity.

Antimicrobial Activity of Sorghum Phenolic Extract on Bovine Foodborne and Mastitis-Causing Pathogens

Antimicrobial resistance in bacterial pathogens associated with bovine mastitis and human foodborne illnesses from contaminated food and water have an impact on animal and human health. Phenolic compounds have antimicrobial properties and some specialty sorghum grains are high in phenolic compounds, and the grain extract may have the potential as a natural antimicrobial alternative. The study’s objective was to determine antimicrobial effects of sorghum phenolic extract on bacterial pathogens that cause bovine mastitis and human foodborne illnesses. Bacterial pathogens tested included Escherichia coli, Salmonella Typhimurium, Campylobacter jejuni, Campylobacter coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Klebsiella oxytoca, Staphylococcus aureus, and Enterococcus faecalis. Antibacterial activities of sorghum phenolic extracts were determined by agar-well diffusion assay. Sorghum phenolic extract was added to the wells in concentrations of 0, 100, 200, 500, 1000, or 4000 µg/mL. The control wells did not receive phenolic extract. Plates were incubated for 18–24 h, and the diameter of each zone of inhibition was measured. The results indicated that sorghum phenolic extract had inhibitory effects on Staphylococcus aureus, Enterococcus faecalis, Campylobacter jejuni, and Campylobacter coli.

Targeted Metabolic Profiles of the Leaves and Xylem Sap of Two Sugarcane Genotypes Infected with the Vascular Bacterial Pathogen Leifsonia xyli subsp. xyli

Ratoon stunt (RS) is a worldwide disease that reduces biomass up to 80% and is caused by the xylem-dwelling bacterium Leifsonia xyli subsp. xyli. This study identified discriminant metabolites between a resistant (R) and a susceptible (S) sugarcane variety at the early stages of pathogen colonization (30 and 120 days after inoculation—DAI) by untargeted and targeted metabolomics of leaves and xylem sap using gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), respectively. Bacterial titers were quantified in sugarcane extracts at 180 DAI through real-time polymerase chain reaction. Bacterial titers were at least four times higher on the S variety than in the R one. Global profiling detected 514 features in the leaves and 68 in the sap, while 119 metabolites were quantified in the leaves and 28 in the sap by targeted metabolomics. Comparisons between mock-inoculated treatments indicated a greater abundance of amino acids in the leaves of the S variety and of phenolics, flavonoids, and salicylic acid in the R one. In the xylem sap, fewer differences were detected among phenolics and flavonoids, but also included higher abundances of the signaling molecule sorbitol and glycerol in R. Metabolic changes in the leaves following pathogen inoculation were detected earlier in R than in S and were mostly related to amino acids in R and to phosphorylated compounds in S. Differentially represented metabolites in the xylem sap included abscisic acid. The data represent a valuable resource of potential biomarkers for metabolite-assisted selection of resistant varieties to RS.

The Glycine- and Proline-Rich Protein AtGPRP3 Negatively Regulates Plant Growth in Arabidopsis

Glycine- and proline-rich proteins (GPRPs) comprise a small conserved family that is widely distributed in the plant kingdom. GPRPs are relatively short peptides (<200 amino acids) that contain three typical domains, including an N-terminal XYPP-repeat domain, a middle hydrophobic domain rich in alanine, and a C-terminal HGK-repeat domain. These proteins have been proposed to play fundamental roles in plant growth and environmental adaptation, but their functions remain unknown. In this study, we selected an Arabidopsis GPRP (AtGPRP3) to profile the physiological role of GPRPs. Transcripts of AtGPRP3 could be detected in the whole Arabidopsis plant, but greater amounts were found in the rosette, followed by the cauline. The AtGPRP3::GFP fusion protein was mainly localized in the nucleus. The overexpression and knockout of AtGPRP3, respectively, retarded and accelerated the growth of Arabidopsis seedlings, while the increase in the growth rate of atgprp3 plants was offset by the complementary expression of AtGPRP3. CAT2 and CAT3, but not CAT1, interacted with AtGPRP3 in the nuclei of Arabidopsis protoplasts. The knockout of CAT2 by CRISPR-Cas9 retarded the growth of the Arabidopsis seedlings. Together, our data suggest that AtGPRP3 negatively regulates plant growth, potentially through CAT2 and CAT3.

Glycine- and Proline-Rich Protein OsGPRP3 Regulates Grain Size and Quality in Rice

The grain size and shape of rice are limited by the growth of the spikelet hulls and are important selective target during domestication and breeding. In this study, we identified a glycine- and proline-rich protein (OsGPRP3), which belongs to a conserved family rarely studied. We found that OsGPRP3 was highly expressed in the seed at 10 days after pollination (DAP) using qRT-PCR, pOsGPRP3::GUS and in situ hybridization. Knockout and knockdown of OsGPRP3 led to significant decrease of 1000-grain weight, grain width, and grain thickness. We further found that the content of storage protein and total lipid were decreased in osgprp3 lines. In particular, the contents of C14:0 (myristic acid), C16:0 (palmitic acid), C18:1 (oleic acid), and C18:2 (linoleic acid) were reduced in osgprp3 lines. Cytological experiments revealed that the cell width of spikelet hull in osgprp3 lines was significantly reduced than that in WT. Taken together, our results reveal that OsGPRP3 regulates the grain size and shape of rice by influencing the cell width of spikelet hulls and the accumulation of storage protein and lipids.

Prediction and Characterization of Cationic Arginine-Rich Plant Antimicrobial Peptide SM-985 From Teosinte (Zea mays ssp. mexicana)

Antimicrobial peptides (AMPs) are effective against different plant pathogens and newly considered as part of plant defense systems. From prokaryotes to eukaryotes, AMPs can exist in all forms of life. SM-985 is a cationic AMP (CAMP) isolated from the cDNA library of Mexican teosinte (Zea mays ssp. mexicana). A computational prediction server running with different algorithms was used to screen the teosinte cDNA library for AMPs, and the SM-985 peptide was predicted as an AMP with high probability prediction values. SM-985 is an arginine-rich peptide and composed of 21 amino acids (MW: 2671.06 Da). The physicochemical properties of SM-985 are very promising as an AMP, including the net charge (+8), hydrophobicity ratio of 23%, Boman index of 5.19 kcal/mol, and isoelectric point of 12.95. The SM-985 peptide has amphipathic α-helix conformations. The antimicrobial activity of SM-985 was confirmed against six bacterial plant pathogens, and the MIC of SM-985 against Gram-positive indicators was 8 μM, while the MIC of SM-985 against Gram-negative indicators was 4 μM. The SM-985 interacting with the bacterial membrane and this interaction were examined by treatment of the bacterial indicators with FITC-SM-985 peptide, which showed a high binding affinity of SM-985 to the bacterial membrane (whether Gram-positive or Gram-negative). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the treated bacteria with SM-985 demonstrated cell membrane damage and cell lysis. In vivo antimicrobial activity was examined, and SM-985 prevented leaf spot disease infection caused by Pst DC3000 on Solanum lycopersicum. Moreover, SM-985 showed sensitivity to calcium chloride salt, which is a common feature of CAMPs.