Transcriptomic data exploring the effect of agave fructans on the induction of the defense system in avocado fruit.

The effect of 20% high degree polymerized agave fructans (HDPAF) on the induction of the defense system in avocado fruits was investigated by transcriptomic analysis at 1, 24 and 72 h after treatment, and the effect of HDPAF on respiration rate and ethylene production was also analyzed. Transcriptomic profiling revealed 5425 differentially expressed genes (DEGs), 55 of which were involved in the pathways related to plant defense response to pathogens. Key genes were associated with phenylpropanoid biosynthesis, mitogen-activated protein signaling, plant hormone signaling, calcium ion signal decoding, and pathogenesis-related proteins. Dysregulated genes involved in ethylene biosynthesis were also identified, and the reduction in ethylene production by HDPAF was corroborated by gas chromatography, where three days of delayed peak production was observed compared to that in water-treated fruits. These results help to understand the mechanism of induction of the avocado defense system by applying HDPAF and support the application of HDPAF as an efficient postharvest treatment to extend the shelf life of the fruit.

Protein Profiling of Psittacanthus calyculatus during Mesquite Infection.

Psittacanthus calyculatus is a hemiparasite mistletoe that represents an ecological problem due to the impacts caused to various tree species of ecological and commercial interest. Although the life cycle for the Psittacanthus genus is well established in the literature, the development stages and molecular mechanism implicated in P. calyculatus host infection are poorly understood. In this study, we used a manageable infestation of P. laevigata with P. calyculatus to clearly trace the infection, which allowed us to describe five phenological infective stages of mistletoe on host tree branches: mature seed (T1), holdfast formation (T2), haustorium activation (T3), haustorium penetration (T4), and haustorium connection (T5) with the host tree. Proteomic analyses revealed proteins with a different accumulation and cellular processes in infective stages. Activities of the cell wall-degrading enzymes cellulase and ß-1,4-glucosidase were primarily active in haustorium development (T3), while xylanase, endo-glucanase, and peptidase were highly active in the haustorium penetration (T4) and xylem connection (T5). Patterns of auxins and cytokinin showed spatial concentrations in infective stages and moreover were involved in haustorium development. These results are the first evidence of proteins, cell wall-degrading enzymes, and phytohormones that are involved in early infection for the Psittacanthus genus, and thus represent a general infection mechanism for other mistletoe species. These results could help to understand the molecular dialogue in the establishment of P. calyculatus parasitism.

Postharvest application effect of agave fructans on anthracnose disease, defense-related enzyme activities, and quality attributes in avocado fruit.

The postharvest application of high degree of polymerization agave fructans (HDPAF) was tested, evaluating anthracnose disease, defense-related enzyme activities, and quality attributes in avocado fruit. Application of a 20% HDPAF solution showed a reduction in anthracnose severity (60%) and incidence (34%) compared to the other concentrations evaluated and the water-treated control. Polyphenoloxidase activity increased 4.6 times more 24 h after treatment. In addition, peroxidase and phenylalanine ammonia-lyase enzyme activity was 4.34 and 1.7 times higher than the control at 0.5 h after treatment. HDPAF retrieves the deceleration of both firmness loss and physiological weight loss compared to the control. Regarding quality parameters such as color, pH, total soluble solids, and titratable acidity, no significant differences were observed between treatments compared to the control; therefore, these parameters were not negatively affected by HDPAF treatments, but a positive effect on the induction of the defense system is shown.

Transgenic Soybeans Expressing Phosphatidylinositol-3-Phosphate-Binding Proteins Show Enhanced Resistance Against the Oomycete Pathogen Phytophthora sojae.

Oomycete and fungal pathogens cause billions of dollars of damage to crops worldwide annually. Therefore, there remains a need for broad-spectrum resistance genes, especially ones that target pathogens but do not interfere with colonization by beneficial microbes. Motivated by evidence suggesting that phosphatidylinositol-3-phosphate (PI3P) may be involved in the delivery of some oomycete and fungal virulence effector proteins, we created stable transgenic soybean plants that express and secrete two different PI3P-binding proteins, GmPH1 and VAM7, in an effort to interfere with effector delivery and confer resistance. Soybean plants expressing the two PI3P-binding proteins exhibited reduced infection by the oomycete pathogen Phytophthora sojae compared to control lines. Measurements of nodulation by nitrogen-fixing mutualistic bacterium Bradyrhizobium japonicum, which does not produce PI3P, revealed that the two lines with the highest levels of GmPH1 transcripts exhibited reductions in nodulation and in benefits from nodulation. Transcriptome and plant hormone measurements were made of soybean lines with the highest transcript levels of GmPH1 and VAM7, as well as controls, following P. sojae- or mock-inoculation. The results revealed increased levels of infection-associated transcripts in the transgenic lines, compared to controls, even prior to P. sojae infection, suggesting that the plants were primed for increased defense. The lines with reduced nodulation exhibited elevated levels of jasmonate-isoleucine and of transcripts of a JAR1 ortholog encoding jasmonate-isoleucine synthetase. However, lines expressing VAM7 transgenes exhibited normal nodulation and no increases in jasmonate-isoleucine. Overall, together with previously published data from cacao and from P. sojae transformants, the data suggest that secretion of PI3P-binding proteins may confer disease resistance through a variety of mechanisms.

The effect of benzo[a]pyrene on the gut microbiota of Nile tilapia (Oreochromis niloticus).

Benzo[a]pyrene (BaP) is a highly toxic and carcinogenic polycyclic aromatic hydrocarbon (PAH) whose toxicological effects in the gut microbiota of aquatic organisms have not yet been fully revealed. Therefore, in this study, we used high-throughput 16S rRNA gene sequencing to evaluate the effects of BaP in the gut microbiome of Oreochromis niloticus, including its possible participation in the process of detoxification and its ability to recover. The fish were injected with a single intraperitoneal dose of 20 mg kg-1 of BaP, and the effects in the microbiome were evaluated at 24, 72, and 120 h post-injection. The results indicate a clear dysbiosis (in composition, relative abundance, diversity, and interaction networks) of the gut microbiota during 24 h post-injection, dominated by Fusobacteria and Bacteroidetes and a decrease in Proteobacteria and Spirochaetae. Interestingly, a slight recovery of the microbiome begins at 72 h and stabilises at 120 h post-injection. Pathway analysis revealed the participation of the gut microbiome in PAH degradation mainly at 24 h post-injection. This study provides new insights in the toxicology of BaP in O. niloticus and the first evidence of the ability of the gut microbiome to recovery after a chemical disturbance. KEY POINTS: • Benzo[a]pyrene caused a dysbiosis in the gut microbiota of Oreochromis niloticus. • We observed an enrichment of bacteria involved in the metabolism of xenobiotics. • The gut microbiota was recovered after exposure to benzo[a]pyrene.

Epigenetic insight into regulatory role of chromatin covalent modifications in lifecycle and virulence of Phytophthora.

The Oomycota phylum includes fungi-like filamentous microorganisms classified as plant pathogens. The most destructive genus within oomycetes is Phytophthora, which causes diseases in plants of economic importance in agriculture, forestry and ornamental. Phytophthora species are widespread worldwide and some of them enable adaptation to different hosts and environmental changes. The development of sexual and asexual reproductive structures and the secretion of proteins to control plant immunity are critical for the adaptative lifestyle. However, molecular mechanisms underlying the adaptation of Phytophthora to different hosts and environmental changes are poorly understood. In the last decade, the role of epigenetics has gained attention, and important evidence has demonstrated the potential role of chromatin covalent modifications, such as DNA methylation and histone acetylation/methylation, in the regulation of gene expression during Phytophthora development and plant infection. Here, we review for the first time the evidence of the potential role of chromatin covalent modifications in the lifecycle of the phytopathogenic genus Phytophthora, including virulence, and host and environment adaptation processes.

Cell death in Ustilago maydis: comparison with other fungi and the effect of metformin and curcumin on its chronological lifespan.

Ustilago maydis is a Basidiomycota fungus, in which very little is known about its mechanisms of cell survival and death. To date, only the role of metacaspase1, acetate and hydrogen peroxide as inducers of cell death has been investigated. In the present work, we analyzed the lifespan of U. maydis compared with other species like Sporisorium reilianum, Saccharomyces cerevisiae and Yarrowia lipolytica, and we observed that U. maydis has a minor lifespan. We probe the addition of low concentrations metformin and curcumin to the culture media, and we observed that both prolonged the lifespan of U. maydis, a result observed for the first time in a phytopathogen fungus. However, higher concentrations of curcumin were toxic for the cells, and interestingly induced the yeast-to-mycelium dimorphic transition. The positive effect of metformin and curcumin appears to be related to an inhibition of the mechanistic Target of Rapamycin (mTOR) pathway, increase expression of autophagy genes and reducing of reactive oxygen species. These data indicate that U. maydis may be a eukaryotic model organism to elucidate the molecular mechanism underlying apoptotic and necrosis pathways, and the lifespan increase caused by metformin and curcumin.

EffHunter: A Tool for Prediction of Effector Protein Candidates in Fungal Proteomic Databases.

Pathogens are able to deliver small-secreted, cysteine-rich proteins into plant cells to enable infection. The computational prediction of effector proteins remains one of the most challenging areas in the study of plant fungi interactions. At present, there are several bioinformatic programs that can help in the identification of these proteins; however, in most cases, these programs are managed independently. Here, we present EffHunter, an easy and fast bioinformatics tool for the identification of effectors. This predictor was used to identify putative effectors in 88 proteomes using characteristics such as size, cysteine residue content, secretion signal and transmembrane domains.

Differential Accumulation of Innate- and Adaptive-Immune-Response-Derived Transcripts during Antagonism between Papaya Ringspot Virus and Papaya Mosaic Virus.

Papaya ringspot virus (PRSV), a common potyvirus infecting papaya plants worldwide, can lead to either antagonism or synergism in mixed infections with Papaya mosaic virus (PapMV), a potexvirus. These two unrelated viruses produce antagonism or synergism depending on their order of infection in the plant. When PRSV is inoculated first or at the same time as PapMV, the viral interaction is synergistic. However, an antagonistic response is observed when PapMV is inoculated before PRSV. In the antagonistic condition, PRSV is deterred from the plant and its drastic effects are overcome. Here, we examine differences in gene expression by high-throughput RNA sequencing, focused on immune system pathways. We present the transcriptomic expression of single and mixed inoculations of PRSV and PapMV leading to synergism and antagonism. Upregulation of dominant and hormone-mediated resistance transcripts suggests that the innate immune system participates in synergism. In antagonism, in addition to innate immunity, upregulation of RNA interference-mediated resistance transcripts suggests that adaptive immunity is involved.

Draft Genome Sequence of Paenibacillus polymyxa 3A-25AI, a Strain Antagonist to Root Rot Causal Phytopathogens.

Here, we report the draft genome sequence of the Paenibacillus polymyxa 3A-25AI strain, isolated from the rhizosphere of wild grass. This strain inhibits Phytophthora capsici and Rhizoctonia solani phytopathogens. The genome size is 5.6 Mb, with a G+C content of 45.59%, and contains 5,079 genes, 4,968 coding DNA sequences (CDSs), 35 tRNAs, 3 rRNAs, and 72 unexpected miscellaneous RNA (miscRNA) features.

Complete Genome Sequence of XaF13, a Novel Bacteriophage of Xanthomonas vesicatoria from Mexico.

The phytopathogenic bacterium Xanthomonas vesicatoria is the causative agent of bacterial spot disease in various Solanaceae family members. Here, we describe the complete genome sequence of XaF13, a novel filamentous phage that infects the phytopathogenic bacterium X. vesicatoria The 7,045-bp genome is predicted to encode 14 open reading frames, 7 of which are related to those of other filamentous Xanthomonas phages.

Autophagosomes accumulation in the vacuoles of the fungus Ustilago maydis and the role of proteases in their digestion.

In the present study we determined whether Ustilago maydis accumulates autophagosomes within vacuoles when the cells are exposed to nutritional stress conditions. We investigated whether proteinase B and proteinase A are involved in their degradation. To this effect, wild type and Δpep4 mutant were incubated in minimal medium lacking a carbon source. It was observed that after incubation in nutrient-deficient media, spherical bodies appeared within the Δpep4 mutant strains vacuoles. In addition, autophagosomes were accumulated in U. maydis WT cells incubated in the presence of the serine protease inhibitor PMSF and accumulation of large autophagosomes and electrodense structures in the Δpep4 mutant cell vacuoles took place. These results demonstrate that the homologues of both, the proteinase B and the protease A, are involved in the autophagosomes degradation process in U. maydis.

Activation of the phenylpropanoid biosynthesis pathway reveals a novel action mechanism of the elicitor effect of chitosan on avocado fruit epicarp.

Secondary metabolites play an important role in the avocado fruit defense system. Phenolic compounds are the main biosynthesized metabolites of this system response. Our objective in this investigation was to evaluate the induction of specific metabolic pathways using chitosan as an elicitor. Extracts obtained from avocado in intermediate and consumption maturity stages treated with chitosan exhibited an increase in antifungal activity, which caused inhibition of mycelial growth and a decrease in sporulation as well as spore germination of Colletotrichum gloeosporioides. Additionally, RNA from epicarp of the fruits treated and untreated with chitosan was obtained in order to evaluate the expression of genes related to phenylpropanoids and the antifungal compound 1-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene biosynthesis. An increased in gene expression of genes that participates in the phenylpropanoids route was observed during the stage of physiological fruit maturity, others genes such as Flavonol synthase (Fls), increased only in samples obtained from fruit treated with chitosan at consumption maturity. Our results reveal a new molecular mechanism where chitosan induces a specific accumulation of phenylpropanoids and antifungal diene; this partially explains avocado's resistance against fungal pathogens. Finally, we discuss the molecular connections between chitosan induction and gene expression to explain the biological events that orchestrate the resistance pathways in fruits.

Genome Sequence of Bacillus halotolerans Strain MS50-18A with Antifungal Activity against Phytopathogens, Isolated from Saline Soil in San Luís Potosí, Mexico.

Bacillus halotolerans strain MS50-18A, isolated from saline soil, possesses antifungal activity toward root rot causal phytopathogens and has friendly interactions with the chili pepper plant. The draft genome sequence is 4.06 Mb in length and contains 4,215 genes. Genes related to glycine/betaine uptake and bacilysin biosynthesis are present, supporting its saline stress tolerance and antifungal activity.

Draft Genome Sequence of Bacillus subtilis 2C-9B, a Strain with Biocontrol Potential against Chili Pepper Root Pathogens and Tolerance to Pb and Zn.

Bacillus subtilis 2C-9B, obtained from the rhizosphere of wild grass, exhibits inhibition against root rot causal pathogens in Capsicum annuum, Pb and Zn tolerance, and plant growth promotion in medium supplemented with Pb. The genome of B. subtilis 2C-9B was sequenced and the draft genome assembled, with a length of 4,215,855 bp and 4,723 coding genes.

Draft genome sequence of Bacillus velezensis 2A-2B strain: a rhizospheric inhabitant of Sporobolus airoides (Torr.) Torr., with antifungal activity against root rot causing phytopathogens.

A Bacillus velezensis strain from the rhizosphere of Sporobolus airoides (Torr.) Torr., a grass in central-north México, was isolated during a biocontrol of phytopathogens scrutiny study. The 2A-2B strain exhibited at least 60% of growth inhibition of virulent isolates of phytopathogens causing root rot. These phytopathogens include Phytophthora capsici, Fusarium solani, Fusarium oxysporum and Rhizoctonia solani. Furthermore, the 2A-2B strain is an indolacetic acid producer, and a plant inducer of PR1, which is an induced systemic resistance related gene in chili pepper plantlets. Whole genome sequencing was performed to generate a draft genome assembly of 3.953 MB with 46.36% of GC content, and a N50 of 294,737. The genome contains 3713 protein coding genes and 89 RNA genes. Moreover, comparative genome analysis revealed that the 2A-2B strain had the greatest identity (98.4%) with Bacillus velezensis.

Draft Genome Sequence of Bacillus velezensis 3A-25B, a Strain with Biocontrol Activity against Fungal and Oomycete Root Plant Phytopathogens, Isolated from Grassland Soil.

Here, we present the draft genome of Bacillus velezensis 3A-25B, which totaled 4.01 Mb with 36 contigs, 3,948 genes, and a GC content of 46.34%. This strain, which demonstrates biocontrol activity against root rot causal phytopathogens in horticultural crops and friendly interactions in roots of pepper plantlets, was obtained from grassland soil in Zacatecas Province, Mexico.

Transcriptomic Analysis of Avocado Hass (Persea americana Mill) in the Interaction System Fruit-Chitosan-Colletotrichum.

Avocado (Persea americana) is one of the most important crops in Mexico as it is the main producer, consumer, and exporter of avocado fruit in the world. However, successful avocado commercialization is often reduced by large postharvest losses due to Colletotrichum sp., the causal agent of anthracnose. Chitosan is known to have a direct antifungal effect and acts also as an elicitor capable of stimulating a defense response in plants. However, there is little information regarding the genes that are either activated or repressed in fruits treated with chitosan. The aim of this study was to identify by RNA-seq the genes differentially regulated by the action of low molecular weight chitosan in the avocado-chitosan-Colletotrichum interaction system. The samples for RNA-seq were obtained from fruits treated with chitosan, fruits inoculated with Colletotrichum and fruits both treated with chitosan and inoculated with the fungus. Non-treated and non-inoculated fruits were also analyzed. Expression profiles showed that in short times, the fruit-chitosan system presented a greater number of differentially expressed genes, compared to the fruit-pathogen system. Gene Ontology analysis of differentially expressed genes showed a large number of metabolic processes regulated by chitosan, including those preventing the spread of Colletotrichum. It was also found that there is a high correlation between the expression of genes in silico and qPCR of several genes involved in different metabolic pathways.

Non-host Plant Resistance against Phytophthora capsici Is Mediated in Part by Members of the I2 R Gene Family in Nicotiana spp.

The identification of host genes associated with resistance to Phytophthora capsici is crucial to developing strategies of control against this oomycete pathogen. Since there are few sources of resistance to P. capsici in crop plants, non-host plants represent a promising source of resistance genes as well as excellent models to study P. capsici - plant interactions. We have previously shown that non-host resistance to P. capsici in Nicotiana spp. is mediated by the recognition of a specific P. capsici effector protein, PcAvr3a1 in a manner that suggests the involvement of a cognate disease resistance (R) genes. Here, we have used virus-induced gene silencing (VIGS) and transgenic tobacco plants expressing dsRNA in Nicotiana spp. to identify candidate R genes that mediate non-host resistance to P. capsici. Silencing of members of the I2 multigene family in the partially resistant plant N. edwardsonii and in the resistant N. tabacum resulted in compromised resistance to P. capsici. VIGS of two other components required for R gene-mediated resistance, EDS1 and SGT1, also enhanced susceptibility to P. capsici in N. edwardsonii, as well as in the susceptible plants N. benthamiana and N. clevelandii. The silencing of I2 family members in N. tabacum also compromised the recognition of PcAvr3a1. These results indicate that in this case, non-host resistance is mediated by the same components normally associated with race-specific resistance.

Transcriptional dynamics of Phytophthora infestans during sequential stages of hemibiotrophic infection of tomato.

Hemibiotrophic plant pathogens, such as the oomycete Phytophthora infestans, employ a biphasic infection strategy, initially behaving as biotrophs, where minimal symptoms are exhibited by the plant, and subsequently as necrotrophs, feeding on dead plant tissue. The regulation of this transition and the breadth of molecular mechanisms that modulate plant defences are not well understood, although effector proteins secreted by the pathogen are thought to play a key role. We examined the transcriptional dynamics of P. infestans in a compatible interaction with its host tomato (Solanum lycopersicum) at three infection stages: biotrophy; the transition from biotrophy to necrotrophy; and necrotrophy. The expression data suggest a tight temporal regulation of many pathways associated with the suppression of plant defence mechanisms and pathogenicity, including the induction of putative cytoplasmic and apoplastic effectors. Twelve of these were experimentally evaluated to determine their ability to suppress necrosis caused by the P. infestans necrosis-inducing protein PiNPP1.1 in Nicotiana benthamiana. Four effectors suppressed necrosis, suggesting that they might prolong the biotrophic phase. This study suggests that a complex regulation of effector expression modulates the outcome of the interaction.