Activation of salicylic acid metabolism and signal transduction can enhance resistance to Fusarium wilt in banana (Musa acuminata L. AAA group, cv. Cavendish)

Unlocking nature's secrets: The pivotal role of WRKY transcription factors in plant flowering and fruit development

The WRKY transcription factor family is a key player in the regulatory mechanisms of flowering plants, significantly influencing both their biotic and abiotic response systems as well as being vital to numerous physiological and biological functions. Over the past two decades, the functionality of WRKY proteins has been the subject of extensive research in over 50 plant species, with a strong focus on their roles in responding to various stresses. Despite this extensive research, there remains a notable gap in comprehensive studies aimed at understanding how specific WRKY genes directly influence the timing of flowering and fruit development. This review offers an up-to-date look at WRKY family genes and provides insights into the key genes of WRKY to control flowering, enhance fruit ripening and secondary metabolism synthesis, and maintain fruit quality of various plants, including annuals, perennials, medicinal, and crop plants. The WRKY transcription factors serve as critical regulators within the transcriptional regulatory network, playing a crucial role in the precise enhancement of flowering processes. It is also involved in the up-regulation of fruit ripening was strongly demonstrated by combined transcriptomics and metabolomic investigation. Therefore, we speculated that the WRKY family is known to be a key regulator of flowering and fruiting in plants. This detailed insight will enable the identification of the series of molecular occurrences featuring WRKY proteins throughout the stages of flowering and fruiting.

Secondary Metabolites and Antioxidant Activity against Moko Disease as a Defense Mechanism of Musa spp. from the Ecuadorian Coast Area

The Musa spp. represents the most commonly produced, transitioned, and consumed fruit around the globe, with several important applications in the biotechnology, pharmaceutical, and food industries. Moko disease is produced by Ralstonia solanacearum-a factor with a high impact on all crops in Ecuador, representing one of the biggest phytosanitary problems. Four of the most common varieties of Musa spp. were tested to identify the metabolic reaction of plants facing Moko disease. The phenolic and flavonoid content has been evaluated as a defense system, and the α-diphenyl-α-picrylhydrazyl free-radical-scavenging method (DPPH), free-radical-scavenging activity (ABTS), ferric-reducing antioxidant power (FRAP) assays, and liquid chromatography and mass spectrometry (LC-MS) have been adapted to analyze the active compounds with the antioxidant capacity necessary to counteract the pathogenic attack. Our results indicate that all the studied varieties of Musa spp. react in the same way, such that the diseased samples showed a higher accumulation of secondary metabolites with antioxidant capacity compared with the healthy ones, with high active compound synthesis identified during the appearance of Moko disease symptoms. More than 40 compounds and their derivatives (from kaempferol and quercetin glycosides) with protective roles demonstrate the implication of the Musa spp. defense system against R. solanacearum infection.

Secreted in Xylem (SIX) genes in Fusarium oxysporum f.sp. cubense (Foc) unravels the potential biomarkers for early detection of Fusarium wilt disease

Secreted in Xylem (SIX) are small effector proteins released by Fusarium oxysporum f.sp. cubense (Foc) into the plant's xylem sap disrupting the host's defence responses causing Fusarium wilt disease resulting in a significant decline in banana crop yields and economic losses. Notably, different races of Foc possess unique sets of SIX genes responsible for their virulence, however, these genes remain underutilized, despite their potential as biomarkers for early disease detection. Herein, we identified seven SIX genes i.e. SIX1, SIX2, SIX4, SIX6, SIX8a, SIX9a and SIX13 present in Foc Tropical Race 4 (FocTR4), while only SIX9b in Foc Race 1 (Foc1). Analysis of SIX gene expression in infected banana roots revealed differential patterns during infection providing valuable insights into host-pathogen interactions, virulence level, and early detection time points. Additionally, a comprehensive analysis of virulent Foc1_C2HIR and FocTR4_C1HIR isolates yielded informative genomic insights. Hence, these discoveries contribute to our comprehension of potential disease control targets in these plants, as well as enhancing plant diagnostics and breeding programs.

The effects of chemical fungicides and salicylic acid on the apple microbiome and fungal disease incidence under changing environmental conditions

Epiphytic and endophytic micro-organisms associated with plants form complex communities on or in their host plant. These communities influence physiological traits, development, and host susceptibility to abiotic and biotic stresses, and these communities are theorized to have evolved alongside their hosts, forming a unit of selection known as the holobiont. The microbiome is highly variable and can be influenced by abiotic factors, including applied exogenous agents. In this study, we compared the impact of chemical fungicide and salicylic acid treatments on the fungal communities of "Honeycrisp" apples at harvest over two consecutive growing years. We demonstrated variations in fungal community structure and composition by tissue type, growing season, and treatment regimes and that fungicide treatments were associated with reduced network complexity. Finally, we show that the inclusion of salicylic acid with 50% less chemical fungicides in an integrated spray program allowed a reduction in fungicide use while maintaining effective control of disease at harvest and following storage.

Why Do We Need Alternative Methods for Fungal Disease Management in Plants?

Fungal pathogens pose a major threat to food production worldwide. Traditionally, chemical fungicides have been the primary means of controlling these pathogens, but many of these fungicides have recently come under increased scrutiny due to their negative effects on the health of humans, animals, and the environment. Furthermore, the use of chemical fungicides can result in the development of resistance in populations of phytopathogenic fungi. Therefore, new environmentally friendly alternatives that provide adequate levels of disease control are needed to replace chemical fungicides-if not completely, then at least partially. A number of alternatives to conventional chemical fungicides have been developed, including plant defence elicitors (PDEs); biological control agents (fungi, bacteria, and mycoviruses), either alone or as consortia; biochemical fungicides; natural products; RNA interference (RNAi) methods; and resistance breeding. This article reviews the conventional and alternative methods available to manage fungal pathogens, discusses their strengths and weaknesses, and identifies potential areas for future research.

Efficient strategies for controlled release of nanoencapsulated phytohormones to improve plant stress tolerance

Climate change due to different human activities is causing adverse environmental conditions and uncontrolled extreme weather events. These harsh conditions are directly affecting the crop areas, and consequently, their yield (both in quantity and quality) is often impaired. It is essential to seek new advanced technologies to allow plants to tolerate environmental stresses and maintain their normal growth and development. Treatments performed with exogenous phytohormones stand out because they mitigate the negative effects of stress and promote the growth rate of plants. However, the technical limitations in field application, the putative side effects, and the difficulty in determining the correct dose, limit their widespread use. Nanoencapsulated systems have attracted attention because they allow a controlled delivery of active compounds and for their protection with eco-friendly shell biomaterials. Encapsulation is in continuous evolution due to the development and improvement of new techniques economically affordable and environmentally friendly, as well as new biomaterials with high affinity to carry and coat bioactive compounds. Despite their potential as an efficient alternative to phytohormone treatments, encapsulation systems remain relatively unexplored to date. This review aims to emphasize the potential of phytohormone treatments as a means of enhancing plant stress tolerance, with a specific focus on the benefits that can be gained through the improved exogenous application of these treatments using encapsulation techniques. Moreover, the main encapsulation techniques, shell materials and recent work on plants treated with encapsulated phytohormones have been compiled.

Identification and analysis of lignin biosynthesis genes related to fruit ripening and stress response in banana (Musa acuminata L. AAA group, cv. Cavendish)

BACKGROUND

Lignin is a key component of the secondary cell wall of plants, providing mechanical support and facilitating water transport as well as having important impact effects in response to a variety of biological and abiotic stresses.

RESULTS

In this study, we identified 104 genes from ten enzyme gene families related to lignin biosynthesis in Musa acuminata genome and found the number of MaCOMT gene family was the largest, while MaC3Hs had only two members. MaPALs retained the original members, and the number of Ma4CLs in lignin biosynthesis was significantly less than that of flavonoids. Segmental duplication existed in most gene families, except for MaC3Hs, and tandem duplication was the main way to expand the number of MaCOMTs. Moreover, the expression profiles of lignin biosynthesis genes during fruit development, postharvest ripening stages and under various abiotic and biological stresses were investigated using available RNA-sequencing data to obtain fruit ripening and stress response candidate genes. Finally, a co-expression network of lignin biosynthesis genes was constructed by weighted gene co-expression network analysis to elucidate the lignin biosynthesis genes that might participate in lignin biosynthesis in banana during development and in response to stresses.

CONCLUSION

This study systematically identified the lignin biosynthesis genes in the Musa acuminata genome, providing important candidate genes for further functional analysis. The identification of the major genes involved in lignin biosynthesis in banana provides the basis for the development of strategies to improve new banana varieties tolerant to biological and abiotic stresses with high yield and high quality.

Molecular, Histological and Histochemical Responses of Banana Cultivars Challenged with Fusarium oxysporum f. sp. cubense with Different Levels of Virulence

Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc) is the most limiting factor in the banana agribusiness worldwide. Therefore, studies regarding pathogen attack mechanisms, and especially host defense responses, in this pathosystem are of utmost importance for genetic breeding programs in the development of Foc-resistant banana cultivars. In this study, analysis at the molecular, histological and histochemical levels of the Musa spp. x Foc interaction was performed. Three Foc isolates representative of race 1 (R1), subtropical race 4 (ST4) and isolate 229A, which is a putative ST4, were inoculated in two Prata-type cultivars (Prata-Anã and BRS Platina) and one cultivar of the Cavendish type (Grand Naine). Of seven genes related to plant–pathogen interactions, five were overexpressed in ‘BRS Platina’ 12 h after inoculation (HAI) with Foc R1 and ST4 but had reduced or negative expression after inoculation with Foc 229A, according to RT–qPCR analyses. While hyphae, mycelia and spores of the Foc 229A isolate grow towards the central cylinder of the Grand Naine and Prata-Anã cultivars, culminating in the occlusion of the xylem vessels, the BRS Platina cultivar responds with increased presence of cellulose, phenolic compounds and calcium oxalate crystals, reducing colonization within 30 days after inoculation (DAI). In general, these data indicate that the cultivar BRS Platina has potential for use in banana-breeding programs focused on resistance to Foc tropical race 4 (TR4) and in aggregating information on the virulence relationships of the Foc pathogen and the defense responses of banana plants after infection.

Nitrogen fertilizer rate but not form affects the severity of Fusarium wilt in banana

Nitrogen (N) fertilizers are routinely applied to bananas (Musa spp.) to increase production but may exacerbate plant diseases like Fusarium wilt of banana (FWB), which is the most economically important disease. Here, we characterized the effects of N rate and form on banana plant growth, root proteome, bacterial and fungal diversity in the rhizosphere, the concentration of Fusarium oxysporum f.sp. cubense (Foc) in the soil, and the FWB severity. Banana plants (Musa subgroup ABB) were grown under greenhouse conditions in soil with ammonium or nitrate supplemented at five N rates, and with or without inoculation with Foc. The growth of non-inoculated plants was positively correlated with the N rate. In bananas inoculated with Foc, disease severity increased with the N rate, resulting in the Foc-inoculated plant growth being greatest at intermediate N rates. The abundance of Foc in the soil was weakly related to the treatment conditions and was a poor predictor of disease severity. Fungal diversity was consistently affected by Foc inoculation, while bacterial diversity was associated with changes in soil pH resulting from N addition, in particular ammonium. N rate altered the expression of host metabolic pathways associated with carbon fixation, energy usage, amino acid metabolism, and importantly stress response signaling, irrespective of inoculation or N form. Furthermore, in diseased plants, Pathogenesis-related protein 1, a key endpoint for biotic stress response and the salicylic acid defense response to biotrophic pathogens, was negatively correlated with the rate of ammonium fertilizer but not nitrate. As expected, inoculation with Foc altered the expression of a wide range of processes in the banana plant including those of defense and growth. In summary, our results indicate that the severity of FWB was negatively associated with host defenses, which was influenced by N application (particularly ammonium), and shifts in microbial communities associated with ammonium-induced acidification.

Genome-Wide Analysis of the Banana WRKY Transcription Factor Gene Family Closely Related to Fruit Ripening and Stress

WRKY transcription factors (TFs) play an important role in plant responses to biotic and abiotic stress as well as in plant growth and development. In the present study, bioinformatics methods were used to identify members of the WRKY transcription factor family in the Musa acuminata (DH-Pahang) genome (version 2). A total of 164 MaWRKYs were identified and phylogenetic analysis showed that MaWRKYs could be categorized into three subfamilies. Overall, the 162 MaWRKYs were distributed on 11 chromosomes, and 2 genes were not located on the chromosome. There were 31 collinear genes from segmental duplication and 7 pairs of genes from tandem duplication. RNA-sequencing was used to analyze the expression profiles of MaWRKYs in different fruit development, ripening stages, under various abiotic and biotic stressors. Most of the MaWRKYs showed a variety of expression patterns in the banana fruit development and ripening stages. Some MaWRKYs responded to abiotic stress, such as low temperature, drought, and salt stress. Most differentially expressed MaWRKYs were downregulated during banana's response to Foc TR4 infection, which plays an important role in physiological regulation to stress. Our findings indicate that MaWRKY21 directly binds to the W-box of the MaICS promoter to decrease MaICS transcription and then reduce the enzyme activity. These studies have improved our understanding of the molecular basis for the development and stress resistance of an important banana variety.

Study on the Role of Salicylic Acid in Watermelon-Resistant Fusarium Wilt under Different Growth Conditions

BACKGROUND

Fusarium wilt disease is leading threat to watermelon yield and quality. Different cultivation cropping systems have been reported as safe and efficient methods to control watermelon Fusarium wilt. However, the role of salicylic acid (SA) in watermelon resistance to Fusarium wilt in these different cultivation systems remains unknown.

METHODS

in this experiment, we used RNA-seq and qRT-PCR to study the effect of SA biosynthesis on improving watermelon health, demonstrating how it may be responsible for Fusarium wilt resistance under continuous monocropping and oilseed rape rotation systems.

RESULTS

the results revealed that the expression of the CIPALs genes was key to SA accumulation in watermelon roots. We observed that the NPR family genes may play different roles in responding to the SA signal. Differentially expressed NPRs and WRKYs may interact with other phytohormones, leading to the amelioration of watermelon Fusarium wilt.

CONCLUSIONS

further understanding of gene expression patterns will pave the way for interventions that effectively control the disease.

Study on the Role of Phytohormones in Resistance to Watermelon Fusarium Wilt

Fusarium wilt disease is one of the major diseases causing a decline in watermelon yield and quality. Researches have informed that phytohormones play essential roles in regulating plants growth, development, and stress defendants. However, the molecular mechanism of salicylic acid (SA), jasmonic acid (JA), and abscisic acid (ABA) in resistance to watermelon Fusarium wilt remains unknown. In this experiment, we established the SA, JA, and ABA determination system in watermelon roots, and analyzed their roles in against watermelon Fusarium wilt compared to the resistant and susceptible varieties using transcriptome sequencing and RT-qPCR. Our results revealed that the up-regulated expression of Cla97C09G174770, Cla97C05G089520, Cla97C05G081210, Cla97C04G071000, and Cla97C10G198890 genes in resistant variety were key factors against (Fusarium oxysporum f. sp. Niveum) FON infection at 7 dpi. Additionally, there might be crosstalk between SA, JA, and ABA, caused by those differentially expressed (non-pathogen-related) NPRs, (Jasmonate-resistant) JAR, and (Pyrabactin resistance 1-like) PYLs genes, to trigger the plant immune system against FON infection. Overall, our results provide a theoretical basis for watermelon resistance breeding, in which phytohormones participate.

Identification of MaWRKY40 and MaDLO1 as Effective Marker Genes for Tracking the Salicylic Acid-Mediated Immune Response in Bananas

Bananas are among the world's most important cash and staple crops but are threatened by various devastating pathogens. The phytohormone salicylic acid (SA) plays a key role in the regulation of plant immune response. Tracking the expression of SA-responsive marker genes under pathogen infection is important in pathogenesis elucidation. However, the common SA-responsive marker genes are not consistently induced in different banana cultivars or different organs. Here, we conducted transcriptome analysis for SA response of a banana cultivar, 'Pei-Chiao' (Cavendish, AAA genome), and identified three genes, MaWRKY40, MaWRKY70, and Downy Mildew Resistant 6 (DMR6)-Like Oxygenase 1 (MaDLO1) that are robustly induced upon SA treatment in both the leaves and roots. Consistent induction of these three genes by SA treatment was also detected in both the leaves and roots of bananas belonging to different genome types such as 'Tai-Chiao No. 7' (Cavendish, AAA genome), 'Pisang Awak' (ABB genome), and 'Lady Finger' (AA genome). Furthermore, the biotrophic pathogen cucumber mosaic virus elicited the expression of MaWRKY40 and MaDLO1 in infected leaves of susceptible cultivars. The hemibiotrophic fungal pathogen Fusarium oxysporum f. sp. cubense tropical race 4 (TR4) also consistently induced the expression of MaWRKY40 and MaDLO1 in the infected roots of the F. oxysporum f. sp. cubense TR4-resistant cultivar. These results indicate that MaWRKY40 and MaDLO1 can be used as reliable SA-responsive marker genes for the study of plant immunity in banana. Revealing SA-responsive marker genes provides a stepping stone for further studies in banana resistance to pathogens.

Expression Analysis of MaTGA8 Transcription Factor in Banana and Its Defence Functional Analysis by Overexpression in Arabidopsis

TGA transcription factor is a member of the D subfamily of the basic region-leucine zippers (bZIP) family. It is a type of transcription factor that was first identified in plants and is the main regulator in plant development and physiological processes, including morphogenesis and seed formation in response to abiotic and biotic stress and maintaining plant growth. The present study examined the sequence of the MaTGA8 transcription factor, the sequence of which belonged to subfamily D of the bZIP and had multiple cis-acting elements such as the G-box, TCA-element, TGACG-element, and P-box. Quantitative real time polymerase chain reaction (qRT-PCR) analyses showed that MaTGA8 was significantly down-regulated by the soil-borne fungus Fusarium oxysporum f. sp. cubense race 4 (Foc TR4). Under the induction of salicylic acid (SA), MaTGA8 was down-regulated, while different members of the MaNPR1 family responded significantly differently. Among them, MaNPR11 and MaNPR3 showed an overall upward trend, and the expression level of MaNPR4, MaNPR8, and MaNPR13 was higher than other members. MaTGA8 is a nuclear-localized transcription factor through strong interaction with MaNPR11 or weaker interaction with MaNPR4, and it is implied that the MaPR gene can be activated. In addition, the MaTGA8 transgenic Arabidopsis has obvious disease resistance and higher chlorophyll content than the wild-type Arabidopsis with the infection of Foc TR4. These results indicate that MaTGA8 may enhance the resistance of bananas to Foc TR4 by interacting with MaNPR11 or MaNPR4. This study provides a basis for further research on the application of banana TGA transcription factors in Foc TR4 stress and disease resistance and molecular breeding programs.

Improvements in the Resistance of the Banana Species to Fusarium Wilt: A Systematic Review of Methods and Perspectives

The fungus Fusarium oxysporum f. sp. cubense (FOC), tropical race 4 (TR4), causes Fusarium wilt of banana, a pandemic that has threatened the cultivation and export trade of this fruit. This article presents the first systematic review of studies conducted in the last 10 years on the resistance of Musa spp. to Fusarium wilt. We evaluated articles deposited in different academic databases, using a standardized search string and predefined inclusion and exclusion criteria. We note that the information on the sequencing of the Musa sp. genome is certainly a source for obtaining resistant cultivars, mainly by evaluating the banana transcriptome data after infection with FOC. We also showed that there are sources of resistance to FOC race 1 (R1) and FOC TR4 in banana germplasms and that these data are the basis for obtaining resistant cultivars, although the published data are still scarce. In contrast, the transgenics approach has been adopted frequently. We propose harmonizing methods and protocols to facilitate the comparison of information obtained in different research centers and efforts based on global cooperation to cope with the disease. Thus, we offer here a contribution that may facilitate and direct research towards the production of banana resistant to FOC.

Deep RNA-seq analysis reveals key responding aspects of wild banana relative resistance to Fusarium oxysporum f. sp. cubense tropical race 4

Tropical race 4 of Fusarium oxysporum f. sp. cubense (FocTR4) is seriously threatening the banana industry worldwide. Resistant genotypes are present in wild relatives of banana, but little is known about the genetic and molecular mechanisms driving resistance responses. In this work, through in-depth expression analysis, we compared the responses of the resistant wild relative Musa acuminata ssp. burmanicoides (WTB) with the susceptible banana cultivar "Brizilian" (CAV, as it belongs to the Cavendish subgroup) to FocTR4 infection. Our findings showed that 1196 defense-related genes in the resistant WTB were differentially expressed genes (DEGs); only 358 defense-related DEGs were detected in CAV. DEGs related to pattern recognition receptors (PRRs) and disease resistance (R genes) were found in both genotypes, indicating the onset of both basal and specific defenses to FocTR4. Genes associated with cell wall modification exhibited a more remarkable upregulation in WTB than in CAV and might be involved in resistance during penetration steps. Our data also suggested that the high resistance of WTB is quantitatively driven with larger numbers and higher expression levels of defense-related DEGs. Fine-tuning studies to understand the resistance responses of WTB at early stages should be conducted to better support banana breeding programs. Further investigations are also required to validate the role of key genes screened in this study.

Salicylic Acid as a Safe Plant Protector and Growth Regulator

Since salicylic acid (SA) was discovered as an elicitor of tobacco plants inducing the resistance against Tobacco mosaic virus (TMV) in 1979, increasing reports suggest that SA indeed is a key plant hormone regulating plant immunity. In addition, recent studies indicate that SA can regulate many different responses, such as tolerance to abiotic stress, plant growth and development, and soil microbiome. In this review, we focused on the recent findings on SA's effects on resistance to biotic stresses in different plant-pathogen systems, tolerance to different abiotic stresses in different plants, plant growth and development, and soil microbiome. This allows us to discuss about the safe and practical use of SA as a plant defense activator and growth regulator. Crosstalk of SA with different plant hormones, such as abscisic acid, ethylene, jasmonic acid, and auxin in different stress and developmental conditions were also discussed.

Transcriptomic analysis of resistant and susceptible banana corms in response to infection by Fusarium oxysporum f. sp. cubense tropical race 4

Fusarium wilt disease, caused by Fusarium oxysporum f. sp. cubense, especially by tropical race 4 (Foc TR4), is threatening the global banana industry. Musa acuminata Pahang, a wild diploid banana that displays strong resistance to Foc TR4, holds great potential to understand the underlying resistance mechanisms. Microscopic examination reports that, in a wounding inoculation system, the Foc TR4 infection processes in roots of Pahang (resistant) and a triploid cultivar Brazilian (susceptible) were similar by 7 days post inoculation (dpi), but significant differences were observed in corms of both genotypes at 14 dpi. We compare transcriptomic responses in the corms of Pahang and Brazilian, and show that Pahang exhibited constitutive defense responses before Foc TR4 infection and inducible defense responses prior to Brazilian at the initial Foc TR4 infection stage. Most key enzymatic genes in the phenylalanine metabolism pathway were up-regulated in Brazilian, suggesting that lignin and phytotoxin may be triggered during later stages of Foc TR4 infection. This study unravels a few potential resistance candidate genes whose expression patterns were assessed by RT-qPCR assay and improves our understanding the defense mechanisms of Pahang response to Foc TR4.

Identification and characterization of miRNA169 family members in banana (Musa acuminata L.) that respond to fusarium oxysporum f. sp. cubense infection in banana cultivars

MicroRNAs (miRNAs) play an important role in plant resistance to pathogen infections. However, little is known about the role of miRNAs in banana Fusarium wilt, which is the most economically devastating disease in banana production. In the present study, we identified and characterized a total of 18 miR169 family members in banana (Musa acuminata L.) based on small RNA sequencing. The banana miR169 family clustered into two groups based on miRNA evolutionary analysis. Multiple sequence alignment indicated a high degree of sequence conservation in miRNA169 family members across 28 plant species. Computational target prediction algorithms were used to identify 25 targets of miR169 family members in banana. These targets were enriched in various metabolic pathways that include the following molecules: glycine, serine, threonine, pentose, glycerolipids, nucleotide sugars, starch, and sucrose. Through miRNA transcriptomic analysis, we found that ma-miR169a and ma-miR169b displayed high expression levels, whereas the other 16 ma-miR169 members exhibited low expression in the HG and Baxi banana cultivars. Further experiments indicate that there were negative relationships between ma-miR169a, ma-miR169b and their targets basing on their expression levels to Foc4 (Fusarium oxysporum f. sp. cubense tropical race 4) infection in resistant cultivars. But they were low expressed in susceptive cultivars. These results suggested that the expression levels of ma-miR169a and ma-miR169b were consistent with the resistance degree of the banana cultivars to Foc4. The analysis presented here constitutes a starting point to understand ma-miR169-mediated Fusarium wilt resistance at the transcriptional level in banana and predicts possible candidate targets for the genetic improvement of banana resistance to Foc4.

Genome-wide transcriptome analysis and identification of benzothiadiazole-induced genes and pathways potentially associated with defense response in banana

Background

Bananas (Musa spp.) are the most important fruit crops worldwide due to their high nutrition value. Fusarium wilt of banana, caused by fungal pathogen Fusarium oxysporum f. sp. cubense tropical race 4 (Foc 4), is considered as the most destructive disease in the world and results in extensive damage leading to productivity loss. The widespread use of plant resistance inducers (PRIs), such as benzothiadiazole (BTH), is a novel strategy to stimulate defense responses in banana plants to protect against pathogens infection. The recent focus on the crop defense against fungal infections has led to a renewed interest on understanding the molecular mechanisms of specific PRIs-mediated resistance. This transcriptome study aimed to identify genes that are associated with BTH-induced resistance. Patterns of gene expression in the leaves and roots of BTH-sprayed banana plants were studied using RNA-Seq.

Results

In this study, 18 RNA-Seq libraries from BTH-sprayed and untreated leaves and roots of the Cavendish plants, the most widely grown banana cultivar, were used for studying the transcriptional basis of BTH-related resistance. Comparative analyses have revealed that 6689 and 3624 differentially expressed genes were identified in leaves and roots, respectively, as compared to the control. Approximately 80% of these genes were differentially expressed in a tissue-specific manner. Further analysis showed that signaling perception and transduction, transcription factors, disease resistant proteins, plant hormones and cell wall organization-related genes were stimulated by BTH treatment, especially in roots. Interestingly, the ethylene and auxin biosynthesis and response genes were found to be up-regulated in leaves and roots, respectively, suggesting a choice among BTH-responsive phytohormone regulation.

Conclusions

Our data suggests a role for BTH in enhancing banana plant defense responses to Foc 4 infection, and demonstrates that BTH selectively affect biological processes associated with plant defenses. The genes identified in the study could be further studied and exploited to develop Foc 4-resistant banana varieties.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4830-7) contains supplementary material, which is available to authorized users.

Metabolomic, Biochemical, and Gene Expression Analyses Reveal the Underlying Responses of Resistant and Susceptible Banana Species during Early Infection with Fusarium oxysporum f. sp. cubense

Banana (Musa spp.) is an important staple and economic fruit crop, especially in Africa, Southeast Asia, and Latin America. The wilt disease caused by Fusarium oxysporum f. sp. cubense, especially F. oxysporum f. sp. cubense strain TR4, is disastrous for banana production. Banana plants infected by F. oxysporum f. sp. cubense TR4 gradually die from leaf blight or vascular rot. There is no efficient method to control this disease, and the underlying response of banana plants to F. oxysporum f. sp. cubense remains unknown. In this study, the responses of an economically important banana cultivar, the F. oxysporum f. sp. cubense-susceptible 'BX', and a wild banana relative, the F. oxysporum f. sp. cubense-resistant Musa yunnanensis ('YN'), to F. oxysporum f. sp. cubense infection were investigated using metabolomic, biochemical, and molecular biological methods. Numerous metabolomic compounds, including defense-responsive signaling molecules, phytohormones, phenolics, and antioxidants, were identified through metabolomic analysis. Changes in salicylic acid (SA), methyl-jasmonic acid, abscisic acid (ABA), cytokinin, 3-indoleacetic acid, gibberellic acid, and total phenolic levels were detected using liquid chromatography-mass spectrometry and the Folin-Ciocalteu method. The expression levels of genes involved in the biosynthesis of some defense-responsive compounds were studied through quantitative real-time polymerase chain reaction. The results revealed that the resistant YN had a larger change in SA content and a lower ABA level throughout the early infection period, compared with the levels in BX. The susceptible BX had a lower phenolic content. The resistant YN also expressed pathogenesis-related (PR) genes, especially PR1, PR4, PR5-1, and PDF2.2, at higher levels than the susceptible BX. These dynamic metabolic and gene-expression profiles from susceptible and resistant banana during the early stage of F. oxysporum f. sp. cubense infection increase our understanding of the complex interaction response between this crop and its pathogen.

Paenibacillus polymyxa NSY50 suppresses Fusarium wilt in cucumbers by regulating the rhizospheric microbial community

Paenibacillus polymyxa (P. polymyxa) NSY50, isolated from vinegar residue substrate, suppresses the growth of Fusarium oxysporum in the cucumber rhizosphere and protects the host plant from pathogen invasion. The aim of the present study was to evaluate the effects of NSY50 application on cucumber growth, soil properties and composition of the rhizospheric soil microbial community after exposure to Fusarium oxysporum. Bacterial and fungal communities were investigated by Illumina sequencing of the 16S rRNA gene and the internal transcribed spacer (ITS) regions (ITS1 and ITS2). The results showed that NSY50 effectively reduced the incidence of Fusarium wilt (56.4%) by altering the soil physico-chemical properties (e.g., pH, Cmic, Rmic, total N and Corg) and enzyme activities, especially of urease and β-glucosidase, which were significantly increased by 2.25- and 2.64-fold, respectively, relative to the pathogen treatment condition. More specifically, NSY50 application reduced the abundance of Fusarium and promoted potentially beneficial groups, including the Bacillus, Actinobacteria, Streptomyces, Actinospica, Catenulispora and Pseudomonas genera. Thus, our results suggest that NSY50 application can improve soil properties, shift the microbial community by increasing beneficial strains and decreasing pathogen colonization in the cucumber rhizosphere, and reduce the occurrence of cucumber Fusarium wilt, thereby promoting cucumber growth.

Exploring drought stress-regulated genes in senna (Cassia angustifolia Vahl.): a transcriptomic approach

De novo assembly of reads produced by next-generation sequencing (NGS) technologies offers a rapid approach to obtain expressed gene sequences for non-model organisms. Senna (Cassia angustifolia Vahl.) is a drought-tolerant annual undershrub of Caesalpiniaceae, a subfamily of Fabaceae. There are insufficient transcriptomic and genomic data in public databases for understanding the molecular mechanism underlying the drought tolerance of senna. Therefore, the main purpose of this study was to know the transcriptome profile of senna, with special reference to drought stress. RNA from two different stages of leaf development was extracted and sequenced separately using the Illumina technology. A total of 200 million reads were generated, and a de novo assembly of processed reads in the pooled transcriptome using Trinity yielded 43,413 transcripts which were further annotated using NCBI BLAST with "green plant database (txid 33090)," Swiss Prot, Kyoto Encyclopedia of Genes and Genomes (KEGG), Clusters of Orthologous Groups (COG), and Gene Ontology (GO). Out of the total transcripts, 42,280 (95.0 %) were annotated by BLASTX against the green plant database of NCBI. Senna transcriptome showed the highest similarity to Glycine max (41 %), followed by Phaseolus vulgaris (16 %), Cicer arietinum (15 %), and Medicago trancatula (5 %). The highest number of GO terms were enriched for the molecular functions category; of these "catalytic activity" (GO: 0003824) (25.10 %) and "binding activity" (GO: 0005488) (20.10 %) were most abundantly represented. We used InterProscan to see protein similarity at domain level; a total of 33,256 transcripts were annotated against the Pfam domains. The transcripts were assigned with various KEGG pathways. Coding DNA sequences (CDS) encoding various drought stress-regulated pathways such as signaling factors, protein-modifying/degrading enzymes, biosynthesis of phytohormone, phytohormone signaling, osmotically active compounds, free radical scavengers, chlorophyll metabolism, leaf cuticular wax, polyamines, and protective proteins were identified through BLASTX search. The lucine-rich repeat kinase family was the most abundantly found group of protein kinases. Orphan, bHLH, and bZIP family TFs were the most abundantly found in senna. Six genes encoding MYC2 transcription factor, 9-cis-epoxycarotenoid dioxygenase (NCED), l -ascorbate peroxidase (APX), aminocyclopropane carboxylate oxidase (ACO), abscisic acid 8'-hydroxylase (ABA), and WRKY transcription factor were confirmed through reverse transcriptase-PCR (RT-PCR) and Sanger sequencing for the first time in senna. The potential drought stress-related transcripts identified in this study provide a good start for further investigation into the drought adaptation in senna. Additionally, our transcriptome sequences are the valuable resource for accelerated genomics-assisted genetic improvement programs and facilitate manipulation of biochemical pathways for developing drought-tolerant genotypes of crop plants.

Phenylphenalenones protect banana plants from infection by Mycosphaerella fijiensis and are deactivated by metabolic conversion

Phenylphenalenones, polycyclic aromatic natural products from some monocotyledonous plants, are known as phytoalexins in banana (Musa spp.). In this study, (1) H nuclear magnetic resonance (NMR)-based metabolomics along with liquid chromatography and mass spectrometry were used to explore the chemical responses of the susceptible 'Williams' and the resistant 'Khai Thong Ruang' Musa varieties to the ascomycete fungus Mycosphaerella fijiensis, the agent of the black leaf Sigatoka disease. Principal component analysis discriminated strongly between infected and non-infected plant tissue, mainly because of specialized metabolism induced in response to the fungus. Phenylphenalenones are among the major induced compounds, and the resistance level of the plants was correlated with the progress of the disease. However, a virulent strain of M. fijiensis was able to overcome plant resistance by converting phenylphenalenones to sulfate conjugates. Here, we report the first metabolic detoxification of fungitoxic phenylphenalenones to evade the chemical defence of Musa plants.

The wheat homolog of putative nucleotide-binding site-leucine-rich repeat resistance gene TaRGA contributes to resistance against powdery mildew

Powdery mildew, one of the most destructive wheat diseases worldwide, is caused by Blumeria graminis f. sp. tritici (Bgt), a fungal species with a consistently high mutation rate that makes individual resistance (R) genes ineffective. Therefore, effective resistance-related gene cloning is vital for breeding and studying the resistance mechanisms of the disease. In this study, a putative nucleotide-binding site-leucine-rich repeat (NBS-LRR) R gene (TaRGA) was cloned using a homology-based cloning strategy and analyzed for its effect on powdery mildew disease and wheat defense responses. Real-time reverse transcription-PCR (RT-PCR) analyses revealed that a Bgt isolate 15 and salicylic acid stimulation significantly induced TaRGA in the resistant variety. Furthermore, the silencing of TaRGA in powdery mildew-resistant plants increased susceptibility to Bgt15 and prompted conidia propagation at the infection site. However, the expression of TaRGA in leaf segments after single-cell transient expression assay highly increased the defense responses to Bgt15 by enhancing callose deposition and phenolic autofluorogen accumulation at the pathogen invading sites. Meanwhile, the expression of pathogenesis-related genes decreased in the TaRGA-silenced plants and increased in the TaRGA-transient-overexpressing leaf segments. These results implied that the TaRGA gene positively regulates the defense response to powdery mildew disease in wheat.

Fusarium Wilt of Banana

Banana (Musa spp.) is one of the world's most important fruits. In 2011, 145 million metric tons, worth an estimated $44 billion, were produced in over 130 countries. Fusarium wilt (also known as Panama disease) is one of the most destructive diseases of this crop. It devastated the 'Gros Michel'-based export trades before the mid-1900s, and threatens the Cavendish cultivars that were used to replace it; in total, the latter cultivars are now responsible for approximately 45% of all production. An overview of the disease and its causal agent, Fusarium oxysporum f. sp. cubense, is presented below. Despite a substantial positive literature on biological, chemical, or cultural measures, management is largely restricted to excluding F. oxysporum f. sp. cubense from noninfested areas and using resistant cultivars where the pathogen has established. Resistance to Fusarium wilt is poor in several breeding targets, including important dessert and cooking cultivars. Better resistance to this and other diseases is needed. The history and impact of Fusarium wilt is summarized with an emphasis on tropical race 4 (TR4), a 'Cavendish'-killing variant of the pathogen that has spread dramatically in the Eastern Hemisphere.