Abscisic Acid as a Dominant Signal in Tomato During Salt Stress Predisposition to Phytophthora Root and Crown Rot

The plant disease triangle facing climate change: a molecular perspective

Variations in climate conditions can dramatically affect plant health and the generation of climate-resilient crops is imperative to food security. In addition to directly affecting plants, it is predicted that more severe climate conditions will also result in greater biotic stresses. Recent studies have identified climate-sensitive molecular pathways that can result in plants being more susceptible to infection under unfavorable conditions. Here, we review how expected changes in climate will impact plant-pathogen interactions, with a focus on mechanisms regulating plant immunity and microbial virulence strategies. We highlight the complex interactions between abiotic and biotic stresses with the goal of identifying components and/or pathways that are promising targets for genetic engineering to enhance adaptation and strengthen resilience in dynamically changing environments.

RNA-seq analysis reveals transcriptome reprogramming and alternative splicing during early response to salt stress in tomato root

Salt stress is one of the dominant abiotic stress conditions that cause severe damage to plant growth and, in turn, limiting crop productivity. It is therefore crucial to understand the molecular mechanism underlying plant root responses to high salinity as such knowledge will aid in efforts to develop salt-tolerant crops. Alternative splicing (AS) of precursor RNA is one of the important RNA processing steps that regulate gene expression and proteome diversity, and, consequently, many physiological and biochemical processes in plants, including responses to abiotic stresses like salt stress. In the current study, we utilized high-throughput RNA-sequencing to analyze the changes in the transcriptome and characterize AS landscape during the early response of tomato root to salt stress. Under salt stress conditions, 10,588 genes were found to be differentially expressed, including those involved in hormone signaling transduction, amino acid metabolism, and cell cycle regulation. More than 700 transcription factors (TFs), including members of the MYB, bHLH, and WRKY families, potentially regulated tomato root response to salt stress. AS events were found to be greatly enhanced under salt stress, where exon skipping was the most prevalent event. There were 3709 genes identified as differentially alternatively spliced (DAS), the most prominent of which were serine/threonine protein kinase, pentatricopeptide repeat (PPR)-containing protein, E3 ubiquitin-protein ligase. More than 100 DEGs were implicated in splicing and spliceosome assembly, which may regulate salt-responsive AS events in tomato roots. This study uncovers the stimulation of AS during tomato root response to salt stress and provides a valuable resource of salt-responsive genes for future studies to improve tomato salt tolerance.

Complexity of responses to ionizing radiation in plants, and the impact on interacting biotic factors

In nature, plants are simultaneously exposed to different abiotic (e.g., heat, drought, and salinity) and biotic (e.g., bacteria, fungi, and insects) stresses. Climate change and anthropogenic pressure are expected to intensify the frequency of stress factors. Although plants are well equipped with unique and common defense systems protecting against stressors, they may compromise their growth and development for survival in such challenging environments. Ionizing radiation is a peculiar stress factor capable of causing clustered damage. Radionuclides are both naturally present on the planet and produced by human activities. Natural and artificial radioactivity affects plants on molecular, biochemical, cellular, physiological, populational, and transgenerational levels. Moreover, the fitness of pests, pathogens, and symbionts is concomitantly challenged in radiologically contaminated areas. Plant responses to artificial acute ionizing radiation exposure and laboratory-simulated or field chronic exposure are often discordant. Acute or chronic ionizing radiation exposure may occasionally prime the defense system of plants to better tolerate the biotic stress or could often exhaust their metabolic reserves, making plants more susceptible to pests and pathogens. Currently, these alternatives are only marginally explored. Our review summarizes the available literature on the responses of host plants, biotic factors, and their interaction to ionizing radiation exposure. Such systematic analysis contributes to improved risk assessment in radiologically contaminated areas.

SmWRKY11 acts as a positive regulator in eggplant response to salt stress

Salt stress is one of the most threatening abiotic stresses to plants, which can seriously affect plant growth, development, reproduction, and yield. However, the mechanisms of plant against salt stress largely remain unclear. Herein, SmWRKY11, an assumed WRKY transcription factor, was functionally characterized in eggplant against salt stress. SmWRKY11 was significantly up-regulated by salt, dehydration stress, and ABA treatment. SmWRKY11 located in the nucleus, and the Plant_zn_clust conserved domain exhibited transcriptional activation activity. Silencing of SmWRKY11 enhanced the susceptibility of eggplant to salt stress, accompanied by significantly down-regulation of transcript expression levels of salt stress defense-related genes SmNCED1, SmGSTU10, and positive regulator of salt stress response SmERF1 as well as increase of hydrogen peroxide (H2O2) content and decrease of the enzyme activities of catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX). In addition, silencing of SmERF1 also could significantly down-regulate SmWRKY11 expression in eggplant response to salt stress. By luciferase reporter assay and chromatin immunoprecipitation PCR assay, SmERF1 expression was found to be indirectly activated by SmWRKY11. These data indicate that SmWRKY11 acts as a positive regulator by forming positive feedback loop with SmERF1 via an indirect regulatory manner in eggplant response to salt stress.

Variations in amino acids caused by drought stress mediate the predisposition of Carya cathayensis to Botryosphaeria canker disease

Abiotic stresses can affect the outcome of plant-pathogen interactions, mostly by predisposing the host plant to infection; however, the crosstalk between pathogens and plants related to such predisposition remains unclear. Here, we investigated the predisposition of Carya cathayensis to infection by the fungal pathogen Botryosphaeria dothidea (Bd) caused by drought in the host plant. High levels of drought stress resulted in a significant increase in plant susceptibility to Bd. Drought significantly induced the accumulation of H2O2 and the free amino acids Pro, Leu, and Ile, and in the phloem tissues of plants, and decreased the content of non-structural carbohydrates. In vitro assays showed that Bd was sensitive to H2O2; however, Pro played a protective role against exogenous H2O2. Leu, Ile, and Pro induced asexual reproduction of Bd. Our results provide the first analysis of how drought predisposes C. cathayensis to Botrysphaeria canker via amino acid accumulation in the host plant, and we propose a model that integrates the plant-pathogen interactions involved.

Tomato responses to salinity stress: From morphological traits to genetic changes

Tomato is an essential annual crop providing human food worldwide. It is estimated that by the year 2050 more than 50% of the arable land will become saline and, in this respect, in recent years, researchers have focused their attention on studying how tomato plants behave under various saline conditions. Plenty of research papers are available regarding the effects of salinity on tomato plant growth and development, that provide information on the behavior of different cultivars under various salt concentrations, or experimental protocols analyzing various parameters. This review gives a synthetic insight of the recent scientific advances relevant into the effects of salinity on the morphological, physiological, biochemical, yield, fruit quality parameters, and on gene expression of tomato plants. Notably, the works that assessed the salinity effects on tomatoes were firstly identified in Scopus, PubMed, and Web of Science databases, followed by their sifter according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline and with an emphasis on their results. The assessment of the selected studies pointed out that salinity is one of the factors significantly affecting tomato growth in all stages of plant development. Therefore, more research to find solutions to increase the tolerance of tomato plants to salinity stress is needed. Furthermore, the findings reported in this review are helpful to select, and apply appropriate cropping practices to sustain tomato market demand in a scenario of increasing salinity in arable lands due to soil water deficit, use of low-quality water in farming and intensive agronomic practices.

Study on the Preparation and Effect of Tomato Seedling Disease Biocontrol Compound Seed-Coating Agent

Tomato damping-off and root rot are the two most common diseases of tomatoes at the seedling stage. At present, biological compound seed-coating agents are gradually replacing chemical agents in preventing and controlling plant diseases and insect pests, regulating plant growth, and ensuring crop yields. In this study, five biocontrol bacteria (Bacillus amyloliquefaciens (Ba), Bacillus subtilis (Bs wy-1), Bacillus subtilis (WXCDD105), Pseudomonas fluorescens (WXCDD51), and Bacillus velezensis (WZ-37)), with broad antibacterial spectra were mixed with auxiliary factors (inactive components of seed-coating agent) after fermentation to compound a seed-coating agent. In this study, the formula for a compound seed-coating agent was selected through orthogonal experiment. Gaseous silica was used as a thickener, and gum arabic and sodium dodecylbenzene sulfonate were used as a film-forming agent and dispersant, respectively. The mass of fumed silica, gum arabic, sodium dodecylbenzene sulfonate, and pearlescent powder was 1.3 g, 1 g, 0.05 g, and 0.5 g, respectively. Adding gibberellin can improve the ability of seed-coating agents to promote seed germination and plant growth. This showed high efficiency in preventing and controlling seedling diseases and promoting seedling growth. After 6 days of inoculation with Pythium aphanidermatum, which caused tomato damping-off disease, the seedling mortality rate was 26.7% lower than that of the sterile water control, and 20% lower than that of carbendazim. After 21 days of inoculation with Fusarium sp., which caused tomato root rot disease, the seedling mortality rate was 44.31% lower than that of the control, and 22.36% lower than that of carbendazim. The plant height, stem diameter, root length, fresh weight, and dry weight of tomato seeds treated with biological compound seed-coating agent were significantly higher than that of the control. We tested the shelf life of the biological compound seed-coating agent, and found that the effect of seed germination and radicle growth did not decrease. This research provides information on the production technology and application of biological seed-coating agents in tomato production.

Calcium Sensor SlCBL4 Associates with SlCIPK24 Protein Kinase and Mediates Salt Tolerance in Solanum lycopersicum

Soil salinity is one of the major environmental stresses that restrict the growth and development of tomato (Solanum lycopersicum L.) worldwide. In Arabidopsis, the calcium signaling pathway mediated by calcineurin B-like protein 4 (CBL4) and CBL-interacting protein kinase 24 (CIPK24) plays a critical role in salt stress response. In this study, we identified and isolated two tomato genes similar to the Arabidopsis genes, designated as SlCBL4 and SlCIPK24, respectively. Bimolecular fluorescence complementation (BiFC) and pull-down assays indicated that SlCBL4 can physically interact with SlCIPK24 at the plasma membrane of plant cells in a Ca2+-dependent manner. Overexpression of SlCBL4 or superactive SlCIPK24 mutant (SlCIPK24M) conferred salt tolerance to transgenic tomato (cv. Moneymaker) plants. In particular, the SlCIPK24M-overexpression lines displayed dramatically enhanced tolerance to high salinity. It is notable that the transgenic plants retained higher contents of Na+ and K+ in the roots compared to the wild-type tomato under salt stress. Taken together, our findings clearly suggest that SlCBL4 and SlCIPK24 are functional orthologs of the Arabidopsis counterpart genes, which can be used or engineered to produce salt-tolerant tomato plants.

The Effect of Applied Salinity and Water Stress on Chemical Suppression of Phytophthora ramorum from Soilborne Inoculum in Rhododendron

A serious concern for nurseries is the potential for Phytophthora ramorum and other Phytophthora species to colonize roots without inducing aboveground symptoms in plants that then serve as cryptic reservoirs of inoculum. Episodic abiotic stresses that reduce plant water potential can compromise the host resistance to trigger disease development from root and crown infections during many Phytophthora-plant interactions. We conducted a series of experiments with root-inoculated Rhododendron plants in a potting soil mix to assess the influence of excess salt or water deficit on ramorum blight development and the potential for these abiotic stresses to affect the efficacy of oomycete-suppressive chemical soil treatments. During growth chamber trials, P. ramorum colonized roots of both nonsalt-treated and salt-treated plants. However, salt treatment offset the benefit realized from soil treatment with mefanoxam (Subdue Maxx) and mandipropamid (Micora), as evidenced by the enhanced pathogen colonization of roots. A 3-week episode of water stress imposed after chemical treatment but before inoculation eliminated protection against P. ramorum root colonization conferred by fosetyl-Al (Aliette). At an outdoor experimental nursery, foliar symptoms were apparent in 23% of root-inoculated plants during two trials and absent during one trial. However, the majority of inoculated plants in all trials had colonized roots with little or no aboveground symptoms. A single application of Subdue Maxx or Aliette reduced root colonization by P. ramorum in Rhododendron plants. Although salt stress did not enhance ramorum blight symptom expression at the nursery, salt partially offset protection from P. ramorum root colonization obtained by Subdue Maxx.

Genome-wide identification, characterization and expression analysis of BES1 gene family in tomato

BACKGROUND

As the key regulators in BR signaling, BES1 family genes regulate thousands of target genes involved in various development processes. So far, the functions of BES1 family are poorly understood in tomato, and a comprehensive genomic and expressional analysis is worth to conduct for this family.

RESULTS

Here, nine SlBES1 family members were identified in tomato and classified into five groups based on the conserved motif, gene structure and phylogenetic analysis. Synteny among tomato, Arabidopsis, pepper and rice were further analyzed to obtain insights into evolutionary characteristics. Several cis-elements related to hormone, stress and plant development were exhibited in the promoter regions of SlBES1 family genes. Subcellular localization showed seven members localized both in the nucleus and cytoplasm, implying the presence of dephosphorylated and phosphorylated form of these seven proteins, furthermore, five of them possessed transcription activation activity whereas the left two functioned as transcriptional repressors. Another two members, however, neither localized in the nucleus nor had transactivation activity. Besides, SlBES1.8 showed flower-specific expression while other members expressed ubiquitously in all organs. Moreover, SlBES1 genes exhibited variational expression in response to nine principal plant hormones. Notably, the expression levels of SlBES1 genes presented a dominant downregulated trend in response to stresses.

CONCLUSIONS

In this study, we systematically analyzed the genomic characterization of SlBES1 family, together with the analyses of protein functional features and expression patterns, our results lay a foundation for the functional research of SlBES1 family.

Systemic propagation of immunity in plants

Systemic immunity triggered by local plant-microbe interactions is studied as systemic acquired resistance (SAR) or induced systemic resistance (ISR) depending on the site of induction and the lifestyle of the inducing microorganism. SAR is induced by pathogens interacting with leaves, whereas ISR is induced by beneficial microbes interacting with roots. Although salicylic acid (SA) is a central component of SAR, additional signals exclusively promote systemic and not local immunity. These signals cooperate in SAR- and possibly also ISR-associated signaling networks that regulate systemic immunity. The non-SA SAR pathway is driven by pipecolic acid or its presumed bioactive derivative N-hydroxy-pipecolic acid. This pathway further regulates inter-plant defense propagation through volatile organic compounds that are emitted by SAR-induced plants and recognized as defense cues by neighboring plants. Both SAR and ISR influence phytohormone crosstalk towards enhanced defense against pathogens, which at the same time affects the composition of the plant microbiome. This potentially leads to further changes in plant defense, plant-microbe, and plant-plant interactions. Therefore, we propose that such inter-organismic interactions could be combined in potentially highly effective plant protection strategies.

The Effect of Endogenous Hormones, Total Antioxidant and Total Phenol Changes on Regeneration of Barley Cultivars

Background

Barley (Hordeum vulgar L.) is a valuable platform for producing recombinant proteins. Before using different barley cultivars as an efficient platform for molecular farming, optimization of cultural conditions and studying the effective factors on the tissue culture are critical.

Objectives

In this study, we evaluated callus induction, plant regeneration and changes in the levels of total antioxidant, total phenol and endogenous hormones of three Iranian barley cultivars (Reyhan, Yousef and Bahman) and Golden Promise cultivar.

Materials and Methods

We used immature embryos as explants on MS-based medium containing 3 mg.L^-1 2,4-D for callus induction. Calluses were transferred to regeneration media with 2 mg.L^-1 BAP. The levels of endogenous hormones were measured using High-Performance Liquid Chromatography system and total antioxidant and total phenols were determined using a spectrophotometer.

Results

We demonstrated that callus formation was very high in all cultivars (about 91%) and all immature embryo explants had the potential to produce embryogenic calluses. The present study also showed that the regeneration rates among the studied cultivars were very different and the Iranian cultivars showed lower regeneration percentages (about 1.4%) compared to Golden Promise cultivar (about 72.5%). The levels of endogenous hormones in Iranian cultivars and Golden Promise varied distinctly and significant differences in terms of total antioxidants and total phenols were found in the two groups.

Conclusions

Accumulated evidence suggests that for successful regeneration of recalcitrant cultivars, external treatments should be done in a way to reduce the inhibitory effects of internal factors.

Proteomic Responses to Alkali Stress in Oats and the Alleviatory Effects of Exogenous Spermine Application

Alkali stress limits plant growth and yield more strongly than salt stress and can lead to the appearance of yellow leaves; however, the reasons remain unclear. In this study, we found that (1) the down-regulation of coproporphyrinogen III oxidase, protoporphyrinogen oxidase, and Pheophorbide a oxygenase in oats under alkali stress contributes to the appearance of yellow leaves (as assessed by proteome and western blot analyses). (2) Some oat proteins that are involved in the antioxidant system, root growth, and jasmonic acid (JA) and indole-3-acetic acid (IAA) synthesis are up-regulated in response to alkalinity and help increase alkali tolerance. (3) We added exogenous spermine to oat plants to improve their alkali tolerance, which resulted in higher chlorophyll contents and plant dry weights than in plants subjected to alkaline stress alone. This was due to up-regulation of chitinase and proteins related to chloroplast structure, root growth, and the antioxidant system. Spermine addition increased sucrose utilization efficiency, and promoted carbohydrate export from leaves to roots to increase energy storage in roots. Spermine addition also increased the IAA and JA contents required for root growth.

Abscisic Acid Mediates Drought and Salt Stress Responses in Vitis vinifera-A Review

The foreseen increase in evaporative demand and reduction in rainfall occurrence are expected to stress the abiotic constrains of drought and salt concentration in soil. The intensification of abiotic stresses coupled with the progressive depletion in water pools is a major concern especially in viticulture, as most vineyards rely on water provided by rainfall. Because its economical relevance and its use as a model species for the study of abiotic stress effect on perennial plants, a significant amount of literature has focused on Vitis vinifera, assessing the physiological mechanisms occurring under stress. Despite the complexity of the stress-resistance strategy of grapevine, the ensemble of phenomena involved seems to be regulated by the key hormone abscisic acid (ABA). This review aims at summarizing our knowledge on the role of ABA in mediating mechanisms whereby grapevine copes with abiotic stresses and to highlight aspects that deserve more attention in future research.

Xanthomonas translucens commandeers the host rate-limiting step in ABA biosynthesis for disease susceptibility

Pathogenic bacteria acquire new virulence strategies for exploiting their hosts. This work reveals that the bacterial wheat pathogen Xanthomonas translucens uses a transcription activation-like (TAL) effector to promote virulence by directly activating the host gene 9-cis-epoxycarotenoid dioxygenase, the rate-limiting enzyme in biosynthesis of abscisic acid that is normally involved in water management within the host plant. Evolutionarily, TAL effectors are a relatively new class of virulence factors limited to a few species of pathogenic bacteria, and this work adds to the diversity of host susceptibility genes that can be exploited by pathogens through TAL effector gene function.

Plants are vulnerable to disease through pathogen manipulation of phytohormone levels, which otherwise regulate development, abiotic, and biotic responses. Here, we show that the wheat pathogen Xanthomonas translucens pv. undulosa elevates expression of the host gene encoding 9-cis-epoxycarotenoid dioxygenase (TaNCED-5BS), which catalyzes the rate-limiting step in the biosynthesis of the phytohormone abscisic acid and a component of a major abiotic stress-response pathway, to promote disease susceptibility. Gene induction is mediated by a type III transcription activator-like effector. The induction of TaNCED-5BS results in elevated abscisic acid levels, reduced host transpiration and water loss, enhanced spread of bacteria in infected leaves, and decreased expression of the central defense gene TaNPR1. The results represent an appropriation of host physiology by a bacterial virulence effector.

Plant Host-Associated Mechanisms for Microbial Selection

Plants serve as host to numerous microorganisms. The members of these microbial communities interact among each other and with the plant, and there is increasing evidence to suggest that the microbial community may promote plant growth, improve drought tolerance, facilitate pathogen defense and even assist in environmental remediation. Therefore, it is important to better understand the mechanisms that influence the composition and structure of microbial communities, and what role the host may play in the recruitment and control of its microbiome. In particular, there is a growing body of research to suggest that plant defense systems not only provide a layer of protection against pathogens but may also actively manage the composition of the overall microbiome. In this review, we provide an overview of the current research into mechanisms employed by the plant host to select for and control its microbiome. We specifically review recent research that expands upon the role of keystone microbial species, phytohormones, and abiotic stress, and in how they relate to plant driven dynamic microbial structuring.