A Lipid Transfer Protein has Antifungal and Antioxidant Activity and Suppresses Fusarium Head Blight Disease and DON Accumulation in Transgenic Wheat

Lipid transfer protein StLTPa enhances potato disease resistance against different pathogens by binding and disturbing the integrity of pathogens plasma membrane

Potato is the third most important food crop worldwide. Potato production suffers from severe diseases caused by multiple detrimental plant pathogens, and broad-spectrum disease resistance genes are rarely identified in potato. Here we identified the potato non-specific lipid transfer protein StLTPa, which enhances species none-specific disease resistance against various pathogens, such as the oomycete pathogen Phytophthora infestans, the fungal pathogens Botrytis cinerea and Verticillium dahliae, and the bacterial pathogens Pectobacterium carotovorum and Ralstonia solanacearum. The StLTPa overexpression potato lines do not show growth penalty. Furthermore, we provide evidence that StLTPa binds to lipids present in the plasma membrane (PM) of the hyphal cells of P. infestans, leading to an increased permeability of the PM. Adding of PI(3,5)P2 and PI(3)P could compete the binding of StLTPa to pathogen PM and reduce the inhibition effect of StLTPa. The lipid-binding activity of StLTPa is essential for its role in pathogen inhibition and promotion of potato disease resistance. We propose that StLTPa enhances potato broad-spectrum disease resistance by binding to, and thereby promoting the permeability of the PM of the cells of various pathogens. Overall, our discovery illustrates that increasing the expression of a single gene in potato enhances potato disease resistance against different pathogens without growth penalty.

Fusarium mycotoxins: The major food contaminants

Mycotoxins, which are secondary metabolites produced by toxicogenic fungi, are natural food toxins that cause acute and chronic adverse reactions in humans and animals. The genus Fusarium is one of three major genera of mycotoxin-producing fungi. Trichothecenes, fumonisins, and zearalenone are the major Fusarium mycotoxins that occur worldwide. Fusarium mycotoxins have the potential to infiltrate the human food chain via contamination during crop production and food processing, eventually threatening human health. The occurrence and development of Fusarium mycotoxin contamination will change with climate change, especially with variations in temperature, precipitation, and carbon dioxide concentration. To address these challenges, researchers have built a series of effective models to forecast the occurrence of Fusarium mycotoxins and provide guidance for crop production. Fusarium mycotoxins frequently exist in food products at extremely low levels, thus necessitating the development of highly sensitive and reliable detection techniques. Numerous successful detection methods have been developed to meet the requirements of various situations, and an increasing number of methods are moving toward high-throughput features. Although Fusarium mycotoxins cannot be completely eliminated, numerous agronomic, chemical, physical, and biological methods can lower Fusarium mycotoxin contamination to safe levels during the preharvest and postharvest stages. These theoretical innovations and technological advances have the potential to facilitate the development of comprehensive strategies for effectively managing Fusarium mycotoxin contamination in the future.

Oomycete pathogen pectin acetylesterase targets host lipid transfer protein to reduce salicylic acid signaling

During initial stages of microbial invasion, the extracellular space (apoplast) of plant cells is a vital battleground between plants and pathogens. The oomycete plant pathogens secrete an array of apoplastic carbohydrate active enzymes, which are central molecules for understanding the complex plant-oomycete interactions. Among them, pectin acetylesterase (PAE) plays a critical role in the pathogenesis of plant pathogens including bacteria, fungi, and oomycetes. Here, we demonstrated that Peronophythora litchii (syn. Phytophthora litchii) PlPAE5 suppresses litchi (Litchi chinensis) plant immunity by interacting with litchi lipid transfer protein 1 (LcLTP1). The LcLTP1-binding activity and virulence function of PlPAE5 depend on its PAE domain but not on its PAE activity. The high expression of LcLTP1 enhances plant resistance to oomycete and fungal pathogens, and this disease resistance depends on BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1 (BAK1) and Suppressor of BIR1 (SOBIR1) in Nicotiana benthamiana. LcLTP1 activates the plant salicylic acid (SA) signaling pathway, while PlPAE5 subverts the LcLTP1-mediated SA signaling pathway by destabilizing LcLTP1. Conclusively, this study reports a virulence mechanism of oomycete PAE suppressing plant LTP-mediated SA immune signaling and will be instrumental for boosting plant resistance breeding.

Tissue-specific proteome profile analysis reveals regulatory and stress responsive networks in passion fruit during storage

Passiflora edulis, commonly known as passion fruit, is a crop with a fragrant aroma and refreshingly tropical flavor that is a valuable source of antioxidants. It offers a unique opportunity for growers because of its adaptability to tropical and subtropical climates. Passion fruit can be sold in the fresh market or used in value-added products, but its postharvest shelf life has not been well-researched, nor have superior cultivars been well-developed. Understanding the proteins expressed at the tissue level during the postharvest stage can help improve fruit quality and extend shelf life. In this study, we carried out comparative proteomics analysis on four passion fruit tissues, the epicarp, mesocarp, endocarp, and pulp, using multiplexed isobaric tandem mass tag (TMT) labeling quantitation. A total of 3352 proteins were identified, including 295 differentially expressed proteins (DEPs). Of these DEPs, 213 showed a fold increase greater than 1.45 (50 proteins) or a fold decrease less than 0.45 (163 proteins) with different patterns among tissue types. Among the DEPs, there were proteins expressed with functions in oxygen scavenging, lipid peroxidation, response to heat stress, and pathogen resistance. Thirty-six proteins were designated as hypothetical proteins were characterized for potential functions in immunity, cell structure, homeostasis, stress response, protein metabolism and miraculin biosynthesis. This research provides insight into tissue-specific pathways that can be further studied within fruit physiology and postharvest shelf life to aid in implementing effective plant breeding programs. Knowing the tissue-specific function of fruit is essential for improving fruit quality, developing new varieties, identifying health benefits, and optimizing processing techniques.

Trichothecenes and Fumonisins: Key Players in Fusarium-Cereal Ecosystem Interactions

Fusarium fungi produce a diverse array of mycotoxic metabolites during the pathogenesis of cereals. Some, such as the trichothecenes and fumonisins, are phytotoxic, acting as non-proteinaceous effectors that facilitate disease development in cereals. Over the last few decades, we have gained some depth of understanding as to how trichothecenes and fumonisins interact with plant cells and how plants deploy mycotoxin detoxification and resistance strategies to defend themselves against the producer fungi. The cereal-mycotoxin interaction is part of a co-evolutionary dance between Fusarium and cereals, as evidenced by a trichothecene-responsive, taxonomically restricted, cereal gene competing with a fungal effector protein and enhancing tolerance to the trichothecene and resistance to DON-producing F. graminearum. But the binary fungal-plant interaction is part of a bigger ecosystem wherein other microbes and insects have been shown to interact with fungal mycotoxins, directly or indirectly through host plants. We are only beginning to unravel the extent to which trichothecenes, fumonisins and other mycotoxins play a role in fungal-ecosystem interactions. We now have tools to determine how, when and where mycotoxins impact and are impacted by the microbiome and microfauna. As more mycotoxins are described, research into their individual and synergistic toxicity and their interactions with the crop ecosystem will give insights into how we can holistically breed for and cultivate healthy crops.

Update on the state of research to manage Fusarium head blight

Fusarium head blight (FHB) is one of the most devastating diseases of cereal crops, causing severe reduction in yield and quality of grain worldwide. In the United States, the major causal agent of FHB is the mycotoxigenic fungus, Fusarium graminearum. The contamination of grain with mycotoxins, including deoxynivalenol and zearalenone, is a particularly serious concern due to its impact on the health of humans and livestock. For the past few decades, multidisciplinary studies have been conducted on management strategies designed to reduce the losses caused by FHB. However, effective management is still challenging due to the emergence of fungicide-tolerant strains of F. graminearum and the lack of highly resistant wheat and barley cultivars. This review presents multidisciplinary approaches that incorporate advances in genomics, genetic-engineering, new fungicide chemistries, applied biocontrol, and consideration of the disease cycle for management of FHB.

Non-specific LIPID TRANSFER PROTEIN 1 enhances immunity against tobacco mosaic virus in Nicotiana benthamiana

Plant non-specific lipid transfer proteins (nsLTPs) are small, cysteine-rich proteins that play significant roles in biotic and abiotic stress responses; however, the molecular mechanism of their functions against viral infections remains unclear. In this study, we employed virus-induced gene-silencing and transgenic overexpression to functionally analyse a type-I nsLTP in Nicotiana benthamiana, NbLTP1, in the immunity response against tobacco mosaic virus (TMV). NbLTP1 was inducible by TMV infection, and its silencing increased TMV-induced oxidative damage and the production of reactive oxygen species (ROS), compromised local and systemic resistance to TMV, and inactivated the biosynthesis of salicylic acid (SA) and its downstream signaling pathway. The effects of NbLTP1-silencing were partially restored by application of exogenous SA. Overexpressing NbLTP1 activated genes related to ROS scavenging to increase cell membrane stability and maintain redox homeostasis, confirming that an early ROS burst followed by ROS suppression at the later phases of pathogenesis is essential for resistance to TMV infection. The cell-wall localization of NbLTP1 was beneficial to viral resistance. Overall, our results showed that NbLTP1 positively regulates plant immunity against viral infection through up-regulating SA biosynthesis and its downstream signaling component, NONEXPRESSOR OF PATHOGENESIS-RELATED 1 (NPR1), which in turn activates pathogenesis-related genes, and by suppressing ROS accumulation at the later phases of viral pathogenesis.

Advances in bread wheat production through CRISPR/Cas9 technology: a comprehensive review of quality and other aspects

MAIN CONCLUSION

This review provides a comprehensive overview of the CRISPR/Cas9 technique and the research areas of this gene editing tool in improving wheat quality. Wheat (Triticum aestivum L.), the basic nutrition for most of the human population, contributes 20% of the daily energy needed because of its, carbohydrate, essential amino acids, minerals, protein, and vitamin content. Wheat varieties that produce high yields and have enhanced nutritional quality will be required to fulfill future demands. Hexaploid wheat has A, B, and D genomes and includes three like but not identical copies of genes that influence important yield and quality. CRISPR/Cas9, which allows multiplex genome editing provides major opportunities in genome editing studies of plants, especially complicated genomes such as wheat. In this overview, we discuss the CRISPR/Cas9 technique, which is credited with bringing about a paradigm shift in genome editing studies. We also provide a summary of recent research utilizing CRISPR/Cas9 to investigate yield, quality, resistance to biotic/abiotic stress, and hybrid seed production. In addition, we provide a synopsis of the laboratory experience-based solution alternatives as well as the potential obstacles for wheat CRISPR studies. Although wheat's extensive genome and complicated polyploid structure previously slowed wheat genetic engineering and breeding progress, effective CRISPR/Cas9 systems are now successfully used to boost wheat development.

Deoxynivalenol accumulation and detoxification in cereals and its potential role in wheat-Fusarium graminearum interactions

Deoxynivalenol (DON) is a prominent mycotoxin showing significant accumulation in cereal plants during infection by the phytopathogen Fusarium graminearum. It is a virulence factor that is important in the spread of F. graminearum within cereal heads, and it causes serious yield losses and significant contamination of cereal grains. In recent decades, genetic and genomic studies have facilitated the characterization of the molecular pathways of DON biosynthesis in F. graminearum and the environmental factors that influence DON accumulation. In addition, diverse scab resistance traits related to the repression of DON accumulation in plants have been identified, and experimental studies of wheat-pathogen interactions have contributed to understanding detoxification mechanisms in host plants. The present review illustrates and summarizes the molecular networks of DON mycotoxin production in F. graminearum and the methods of DON detoxification in plants based on the current literature, which provides molecular targets for crop improvement programs. This review also comprehensively discusses recent advances and challenges related to genetic engineering-mediated cultivar improvements to strengthen scab resistance. Furthermore, ongoing advancements in genetic engineering will enable the application of these molecular targets to develop more scab-resistant wheat cultivars with DON detoxification traits.

The function of plant PR1 and other members of the CAP protein superfamily in plant-pathogen interactions

The pathogenesis-related (PR) proteins of plants have originally been identified as proteins that are strongly induced upon biotic and abiotic stress. These proteins fall into 17 distinct classes (PR1-PR17). The mode of action of most of these PR proteins has been well characterized, except for PR1, which belongs to a widespread superfamily of proteins that share a common CAP domain. Proteins of this family are not only expressed in plants but also in humans and in many different pathogens, including phytopathogenic nematodes and fungi. These proteins are associated with a diverse range of physiological functions. However, their precise mode of action has remained elusive. The importance of these proteins in immune defence is illustrated by the fact that PR1 overexpression in plants results in increased resistance against pathogens. However, PR1-like CAP proteins are also produced by pathogens and deletion of these genes results in reduced virulence, suggesting that CAP proteins can exert both defensive and offensive functions. Recent progress has revealed that plant PR1 is proteolytically cleaved to release a C-terminal CAPE1 peptide, which is sufficient to activate an immune response. The release of this signalling peptide is blocked by pathogenic effectors to evade immune defence. Moreover, plant PR1 forms complexes with other PR family members, including PR5, also known as thaumatin, and PR14, a lipid transfer protein, to enhance the host's immune response. Here, we discuss possible functions of PR1 proteins and their interactors, particularly in light of the fact that these proteins can bind lipids, which have important immune signalling functions.

A non-specific lipid transfer protein, NtLTPI.38, positively mediates heat tolerance by regulating photosynthetic ability and antioxidant capacity in tobacco

Non-specific lipid transfer proteins (nsLTPs) play an important role in plant growth and stress resistance; however, their function in tobacco remains poorly understood. Therefore, to explore the function of NtLTP in response to high temperature, we identified an NtLTPI.38 from tobacco, obtained its overexpression and knockout transgenic plants, and further studied their response to heat stress (42 °C). The results showed that NtLTPI.38 overexpression in tobacco reduced chlorophyll degradation, alleviated the high temperature damage to photosynthetic organs, and enhanced the photosynthetic capacity of tobacco under heat stress. NtLTPI.38 overexpression in heat-stressed tobacco increased the contents of soluble sugar and protein, proline, and flavonoid substances, reduced the relative conductivity, and decreased H₂O₂, O₂^•-, and MDA accumulation, and increased the enzymatic antioxidant activities, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), compared to wild type (WT) and knockout mutant plants. RT-PCR confirmed that the expression levels of antioxidant enzymes and thermal stress-related genes were significantly upregulated under thermal stress in overexpression plants. Therefore, NtLTPI.38 enhanced heat tolerance in tobacco by mitigating photosynthetic damage and improving osmoregulation and antioxidant capacity. These results provided the theoretical basis and a potential resource for further breeding projects to improve heat tolerance in plants.

NtLTPI.38, a plasma membrane-localized protein, mediates lipid metabolism and salt tolerance in Nicotiana tabacum

Non-specific lipid transfer proteins (nsLTPs) typically have conserved structural resemblance, low sequence identity, and broad biological functions in plant growth and stress resistance. Here, a plasma membrane-localized nsLTP, NtLTPI.38, was identified in tobacco plants. Multi-omics integrated analysis revealed that NtLTPI.38 overexpression or knock out significantly changed glycerophospholipid and glycerolipid metabolism pathways. NtLTPI.38 overexpression remarkably increased phosphatidylcholine, phosphatidylethanolamine, triacylglycerol, and flavonoid levels, but decreased ceramides compared to wild type and mutant lines. Differentially expressed genes were associated with lipid metabolite and flavonoid synthesis. Many genes related to Ca²⁺ channels, abscisic acid (ABA) signal transduction, and ion transport pathways were upregulated in overexpressing plants. NtLTPI.38 overexpression in salt-stressed tobacco triggered a Ca²⁺ and K⁺ influx in leaves, increased the contents of chlorophyll, proline, flavonoids, and osmotic tolerance, and raised enzymatic antioxidant activities as well as the expression level of related genes. However, mutants accumulated more O₂^- and H₂O_2, exhibited ionic imbalance, gathered excess Na⁺, Cl^-, and malondialdehyde, with more severe ion leakage. Therefore, NtLTPI.38 enhanced salt tolerance in tobacco by regulating lipid and flavonoid synthesis, antioxidant activity, ion homeostasis, and ABA signaling pathways.

Intelligent reprogramming of wheat for enhancement of fungal and nematode disease resistance using advanced molecular techniques

Wheat (Triticum aestivum L.) diseases are major factors responsible for substantial yield losses worldwide, which affect global food security. For a long time, plant breeders have been struggling to improve wheat resistance against major diseases by selection and conventional breeding techniques. Therefore, this review was conducted to shed light on various gaps in the available literature and to reveal the most promising criteria for disease resistance in wheat. However, novel techniques for molecular breeding in the past few decades have been very fruitful for developing broad-spectrum disease resistance and other important traits in wheat. Many types of molecular markers such as SCAR, RAPD, SSR, SSLP, RFLP, SNP, and DArT, etc., have been reported for resistance against wheat pathogens. This article summarizes various insightful molecular markers involved in wheat improvement for resistance to major diseases through diverse breeding programs. Moreover, this review highlights the applications of marker assisted selection (MAS), quantitative trait loci (QTL), genome wide association studies (GWAS) and the CRISPR/Cas-9 system for developing disease resistance against most important wheat diseases. We also reviewed all reported mapped QTLs for bunts, rusts, smuts, and nematode diseases of wheat. Furthermore, we have also proposed how the CRISPR/Cas-9 system and GWAS can assist breeders in the future for the genetic improvement of wheat. If these molecular approaches are used successfully in the future, they can be a significant step toward expanding food production in wheat crops.

Genome-wide characterization, chromosome localization, and expression profile analysis of poplar non-specific lipid transfer proteins

Plant non-specific lipid transfer proteins (nsLTPs) are small and have a broad biological function involved in reproductive development and abiotic stress resistance. Although a small part of plant nsLTPs have been identified, these proteins have not been characterized in poplar at the genomic level. A genome-wide characterization and expression identification of poplar nsLTP members were performed in this study. A total of 42 poplar nsLTP genes were identified from the poplar genome. A comprehensive analysis of poplar nsLTPs was conducted by a phylogenetic tree, duplication events, gene structures, and conserved motifs. The cis-elements of poplar nsLTPs were predicted to respond to light, hormone, and abiotic stress. Many transcription factors (TFs) were identified to interact with poplar nsLTP cis-elements. The tested poplar nsLTPs were expressed in leaves, stems, and roots, but their expression levels differed among tested tissues. Most poplar nsLTP expression levels were changed by abiotic stress, implying that poplar nsLTP may be involved in abiotic stress resistance. Network analysis showed that poplar nsLTPs are putative genes involved in fatty acid (FA) metabolism. This research provides sight into the further study to explain the regulatory mechanism of the poplar nsLTPs.

Antimycobacterial Activity of Sida hermaphrodita (L.) Rusby (Malvaceae) Seed Extract

The current prevalence of such lifestyle diseases as mycobacteriosis and tuberculosis is a result of the growing resistance of microorganisms to the available antibiotics and their significant toxicity. Therefore, plants can successfully become a source of new therapeutic agents. The aim of this study was to investigate the effect of protein extract from Sida hermaphrodita seeds on the morphology, structure, and viability of Mycobacterium smegmatis and to carry out proteomic characterization of the protein extract. The analyses were carried out using fluorescence and transmission microscopy, atomic force microscopy, and spectroscopy. The proteomic studies were performed using liquid chromatography coupled to tandem mass spectrometry. The studies showed that the seed extract applied at concentrations of 50-150 µg/mL exerted a statistically significant effect on M. smegmatis cells, that is, a reduction of the viability of the bacteria and induction of changes in the structure of the mycobacterial cell wall. Additionally, the SEM analysis confirmed that the extract did not have a cytotoxic or cytopathic effect on fibroblast cells. The proteomic analysis revealed the presence of structural, storage, and enzymatic proteins and peptides in the extract, which are typical for seeds. Proteins and peptides with antimicrobial activity identified as vicillins and lipid-transporting proteins were also determined in the protein profile of the extract.

Engineering plant immune circuit: walking to the bright future with a novel toolbox

Plant pathogens destroy crops and cause severe yield losses, leading to an insufficient food supply to sustain the human population. Apart from relying on natural plant immune systems to combat biological agents or waiting for the appropriate evolutionary steps to occur over time, researchers are currently seeking new breakthrough methods to boost disease resistance in plants through genetic engineering. Here, we summarize the past two decades of research in disease resistance engineering against an assortment of pathogens through modifying the plant immune components (internal and external) with several biotechnological techniques. We also discuss potential strategies and provide perspectives on engineering plant immune systems for enhanced pathogen resistance and plant fitness.

Lipid transfer proteins involved in plant-pathogen interactions and their molecular mechanisms

Nonspecific lipid transfer proteins (LTPs) are small, cysteine-rich proteins that play numerous functional roles in plant growth and development, including cutin wax formation, pollen tube adhesion, cell expansion, seed development, germination, and adaptation to changing environmental conditions. LTPs contain eight conserved cysteine residues and a hydrophobic cavity that provides a wide variety of lipid-binding specificities. As members of the pathogenesis-related protein 14 family (PR14), many LTPs inhibit fungal or bacterial growth, and act as positive regulators in plant disease resistance. Over the past decade, these essential immunity-related roles of LTPs in plant immune processes have been documented in a growing body of literature. In this review, we summarize the roles of LTPs in plant-pathogen interactions, emphasizing the underlying molecular mechanisms in plant immune responses and specific LTP functions.

Systematic and functional analysis of non-specific lipid transfer protein family genes in sugarcane under Xanthomonas albilineans infection and salicylic acid treatment

Plant non-specific lipid transfer proteins (nsLTPs) are small basic proteins that play a significant regulatory role in a wide range of physiological processes. To date, no genome-wide survey and expression analysis of this gene family in sugarcane has been performed. In this study we identified the nsLTP gene family in Saccharum spontaneum and carried out expression profiling of nsLTPs in two sugarcane cultivars (Saccharum spp.) that have different resistance to leaf scald caused by Xanthomonas albilineans (Xa) infection. The effect of stress related to exogenous salicylic acid (SA) treatment was also examined. At a genome-wide level, S. spontaneum AP85-441 had 71 SsnsLTP genes including 66 alleles. Tandem (9 gene pairs) and segmental (36 gene pairs) duplication events contributed to SsnsLTP gene family expansion. Five SsnsLTP proteins were predicted to interact with five other proteins. Expression of ShnsLTPI.8/10/Gb.1 genes was significantly upregulated in LCP85-384 (resistant cultivar), but downregulated in ROC20 (susceptible cultivar), suggesting that these genes play a positive regulatory role in response of sugarcane to Xa infection. Conversely, ShnsLTPGa.4/Ge.3 appears to act as a negative regulator in response Xa infection. The majority (16/17) of tested genes were positively induced in LCP85-384 72 h after SA treatment. In both cultivars, but particularly in LCP85-384, ShnsLTPIV.3/VIII.1 genes were upregulated at all time-points, suggesting that the two genes might act as positive regulators under SA stress. Meanwhile, both cultivars showed downregulated ShnsLTPGb.1 gene expression, indicating its potential negative role in SA treatment responses. Notably, the ShnsLTPGb.1 gene had contrasting effects, with positive regulation of gene expression in response to Xa infection and negative regulation induced by SA stress. Together, our results provide valuable information for elucidating the function of ShnsLTP family members under two stressors and identified novel gene sources for development of sugarcane that are tolerant of environmental stimuli.

Potato (Solanum tuberosum L.) non-specific lipid transfer protein StLTP6 promotes viral infection by inhibiting virus-induced RNA silencing

For the first time it is reported that members of the nsLTP protein family could promote viral infection by inhibiting virus-induced RNA silencing. Non-specific lipid transfer proteins (nsLTPs) are a class of soluble proteins with low relative molecular weight and widely present in higher plants. The role of nsLTPs in biotic and abiotic stresses has been studied, but no report has shown that nsLTPs play a role in the process of viral infection. We report the function and mechanism of the classical nsLTP protein StLTP6 in viral infection. We found that StLTP6 expression was remarkably upregulated in potato infected with potato virus Y and potato virus S. The infection efficiency and virus content of StLTP6-overexpressed potato and Nicotiana benthamiana were remarkable increased. Further study found that the overexpression of StLTP6 inhibited the expression of multiple genes in the RNA silencing pathway, thereby inhibiting virus-induced RNA silencing. This result indicated that StLTP6 expression was induced during viral infection to inhibit the resistance of virus-induced RNA silencing and promote viral infection. In summary, we reported the role of StLTP6 in viral infection, broadening the biological function range of the nsLTP family and providing valuable information for the study of viral infection mechanism.

Genome-Wide Identification and Expression Analysis of nsLTP Gene Family in Rapeseed (Brassica napus) Reveals Their Critical Roles in Biotic and Abiotic Stress Responses

Non-specific lipid transfer proteins (nsLTPs) are small cysteine-rich basic proteins which play essential roles in plant growth, development and abiotic/biotic stress response. However, there is limited information about the nsLTP gene (BnLTP) family in rapeseed (Brassica napus). In this study, 283 BnLTP genes were identified in rapeseed, which were distributed randomly in 19 chromosomes of rapeseed. Phylogenetic analysis showed that BnLTP proteins were divided into seven groups. Exon/intron structure and MEME motifs both remained highly conserved in each BnLTP group. Segmental duplication and hybridization of rapeseed’s two sub-genomes mainly contributed to the expansion of the BnLTP gene family. Various potential cis-elements that respond to plant growth, development, biotic/abiotic stresses, and phytohormone signals existed in BnLTP gene promoters. Transcriptome analysis showed that BnLTP genes were expressed in various tissues/organs with different levels and were also involved in the response to heat, drought, NaCl, cold, IAA and ABA stresses, as well as the treatment of fungal pathogens (Sclerotinia sclerotiorum and Leptosphaeria maculans). The qRT-PCR assay validated the results of RNA-seq expression analysis of two top Sclerotinia-responsive BnLTP genes, BnLTP129 and BnLTP161. Moreover, batches of BnLTPs might be regulated by BnTT1 and BnbZIP67 to play roles in the development, metabolism or adaptability of the seed coat and embryo in rapeseed. This work provides an important basis for further functional study of the BnLTP genes in rapeseed quality improvement and stress resistance.

Breeding Tools for Assessing and Improving Resistance and Limiting Mycotoxin Production by Fusarium graminearum in Wheat

The recently adopted conservation and minimum tillage practices in wheat-production systems coupled with the concomitant warming of the Earth are believed to have caused the upsurges in Fusarium head blight (FHB) prevalence in major wheat-producing regions of the world. Measures to counter this effect include breeding for resistance to both initial infection of wheat and spread of the disease. Cases of mycotoxicosis caused by ingestion of wheat by-products contaminated with FHB mycotoxins have necessitated the need for resistant wheat cultivars that can limit mycotoxin production by the dominant causal pathogen, Fusarium graminearum. This manuscript reviews breeding tools for assessing and improving resistance as well as limiting mycotoxin contamination in wheat to reflect on the current state of affairs. Combining these aspects in wheat research and development promotes sustainable quality grain production and safeguards human and livestock health from mycotoxicosis.

Dynamics of lipid displacement inside the hydrophobic cavity of a nonspecific lipid transfer protein from Solanum melongena

Nonspecific lipid transfer proteins are multifunctional and multispecific seed proteins with a characteristic hydrophobic cavity that runs form N-terminal to the C-terminal end. They are capable of binding and transferring different lipid molecules by means of their hydrophobic cavity. Apart from the cavity, lipid molecules bind and interact at key positions on the nsLTP surface as well. The plasticity of the hydrophobic cavity is an unusual property, considered as the primary lipid binding site. Here, we report a crystal structure of nsLTP from Solanum melongena with two lauric acid molecules bound inside the cavity. It has been observed that the extent of the N-terminal entry point and plasticity of the cavity can be extended, upon binding of one or two lipid molecules inside the cavity. The MD simulation further revealed that the lipid molecule shows high mobility inside the cavity and interestingly, was able to change its orientation. An alternate lipid entry site adjacent to the N-terminal end was uncovered during simulation and Arg-84 was implicated to be a potential regulatory residue aside from Tyr-59. Collectively, this study helps to understand that changes in orientation of the lipid inside the cavity could occur intermittently besides entering the cavity via tail-in-mechanism.Communicated by Ramaswamy H. Sarma.

Biocontrol Methods in Avoidance and Downsizing of Mycotoxin Contamination of Food Crops

By increasing the resistance of seeds against abiotic and biotic stress, the possibility of cereal mold contamination and hence the occurrence of secondary mold metabolites mycotoxins decreases. The use of biological methods of seed treatment represents a complementary strategy, which can be implemented as an environmental-friendlier approach to increase the agricultural sustainability. Whereas the use of resistant cultivars helps to reduce mold growth and mycotoxin contamination at the very beginning of the production chain, biological detoxification of cereals provides additional weapons against fungal pathogens in the later stage. Most efficient techniques can be selected and combined on an industrial scale to reduce losses and boost crop yields and agriculture sustainability, increasing at the same time food and feed safety. This paper strives to emphasize the possibility of implementation of biocontrol methods in the production of resistant seeds and the prevention and reduction in cereal mycotoxin contamination.

Biallelic Editing of the LOB1 Promoter via CRISPR/Cas9 Creates Canker-Resistant 'Duncan' Grapefruit

Citrus canker caused by Xanthomonas citri subsp. citri is one of the most devastating citrus diseases worldwide. Generating disease-resistant citrus varieties is considered one of the most efficient and environmentally friendly measures for controlling canker. X. citri subsp. citri causes canker symptoms by inducing the expression of canker susceptibility gene LOB1 via PthA4, a transcription activator-like (TAL) effector, by binding to the effector binding element (EBE) in the promoter region. In previous studies, canker-resistant plants were generated by mutating the coding region or the EBE of LOB1. However, homozygous or biallelic canker-resistant plants have not been generated for commercial citrus varieties, such as grapefruit (Citrus paradisi), which usually contain two alleles of LOB1 and thus, have two types of LOB1 promoter sequences: TI LOBP and TII LOBP. Two different sgRNAs were used to target both EBE types. Both 35S promoter and Yao promoter were used to drive the expression of SpCas9p to modify EBE_PthA4-LOBP in grapefruit. Using 'Duncan' grapefruit epicotyls as explants, 19 genome-edited grapefruit plants were generated with one biallelic mutant line (#Dun_Yao7). X. citri subsp. citri caused canker symptoms on wild-type and nonbiallelic mutant plants but not on #Dun_Yao7. XccPthA4 mutant containing the designer TAL effector dLOB1.5, which recognizes a conserved sequence in both wild-type and #Dun_Yao7, caused canker symptoms on both wild-type and #Dun_Yao7. No off-target mutations were detected in #Dun_Yao7. This study represents the first time that CRISPR-mediated genome editing has been successfully used to generate disease-resistant plants for 'Duncan' grapefruit, paving the way for using disease-resistant varieties to control canker.

Systematic analysis of the non-specific lipid transfer protein gene family in Nicotiana tabacum reveal its potential roles in stress responses

Plant non-specific lipid transfer proteins (nsLTPs) are characterized by an eight-cysteine motif backbone stabilized by four disulfide bonds; these proteins can bind or transfer lipids. NsLTPs play important roles in plant growth and development, and in the responses to abiotic and biotic stresses. In this study, 50, 51, and 100 nsLTPs from Nicotiana sylvestris, N. tomentosiformis, and their descendant N. tabacum, respectively, were identified and classified into six types (I, II, IV, V, VII, and VIII). The phylogeny, gene structures, motifs, tertiary structures, gene duplications and expression patterns were systematically analyzed. The intron/exon patterns and the conserved motifs were highly similar among the same types of nsLTP genes. Purifying selection and segmental duplication dominated the expansion of the nsLTPs family during evolution. Cis-regulatory elements of the NtLTP promoters were involved in light responsiveness, abiotic stress, and phytohormone responsiveness. Expression pattern analysis using RNA-seq and qPCR revealed that NtLTP family genes exhibited tissue-specific expression patterns and they have potential roles in response to abiotic and biotic stresses, especially drought stress, and resistance to black shank and bacterial wilt. Furthermore, overexpression of NtLTPI.38 in tobacco increased drought tolerance by improving the antioxidant defense ability, through reducing O2•- and H2O2 accumulation and increasing the number of lateral roots. These results provide a comprehensive overview of this gene family and provide valuable insights for the functional characterization of nsLTP family genes.

Plant non-specific lipid transfer proteins: An overview

Plant non-specific lipid transfer proteins (nsLTPs) are usually defined as small, basic proteins, with a wide distribution in all orders of higher plants. Structurally, nsLTPs contain a conserved motif of eight cysteines, linked by four disulphide bonds, and a hydrophobic cavity in which the ligand is housed. This structure confers stability and enhances the ability to bind and transport a variety of hydrophobic molecules. Their highly conserved structural resemblance but low sequence identity reflects the wide variety of ligands they can carry, as well as the broad biological functions to which they are linked to, such as membrane stabilization, cell wall organization and signal transduction. In addition, they have also been described as essential in resistance to biotic and abiotic stresses, plant growth and development, seed development, and germination. Hence, there is growing interest in this family of proteins for their critical roles in plant development and for the many unresolved questions that need to be clarified, regarding their subcellular localization, transfer capacity, expression profile, biological function, and evolution.

Overexpression of chitinase in the endophyte Phomopsis liquidambaris enhances wheat resistance to Fusarium graminearum

Fusarium head blight (FHB) is a disease that affects wheat crops worldwide and is caused by Fusarium graminearum. Effective and safe strategies for the prevention and treatment of the disease are very limited. Phomopsis liquidambaris, a universal endophyte, can colonize wheat. Two engineered strains, Phomopsis liquidambaris OE-Chi and IN-Chi, were constructed by transformation with a plasmid and integration of a chitinase into the genome, respectively. The OE-Chi and IN-Chi strains could inhibit the expansion of Fusarium sp. in plate confrontation assays in vitro. Colonization of the OE-Chi strain in wheat showed better effects than colonization of the IN-Chi strain and alleviated the inhibition of wheat growth caused by F. graminearum. The shoot length, root length and fresh weight of infected wheat increased by 164.9%, 115.4%, and 190.7%, respectively, when the plants were inoculated with the OE-Chi strain. The peroxidase (POD) activity in the wheat root increased by 38.0%, and it was maintained at a high level in the shoot, which suggested that the OE-Chi strain could enhance the resistance of wheat to F. graminearum. The root and shoot superoxide dismutase (SOD) activities were decreased by 11.8% and 19.0%, respectively, which may be helpful for colonization by the OE-Chi strain. These results suggested that the Phomopsis liquidambaris OE-Chi strain may be a potential endophyte in the biocontrol of FHB.

Wheat Apoplast-Localized Lipid Transfer Protein TaLTP3 Enhances Defense Responses Against Puccinia triticina

Plant apoplast serves as the frontier battlefield of plant defense in response to different types of pathogens. Many pathogenesis-related (PR) proteins are accumulated in apoplastic space during the onset of plant-pathogen interaction, where they act to suppress pathogen infection. In this study, we found the expression of Triticum aestivum lipid transfer protein 3 (TaLTP3) gene was unregulated during incompatible interaction mediated by leaf rust resistance genes Lr39/41 at the early infection stage. Stable transgenic wheat lines overexpressing TaLTP3 exhibited enhanced resistance to leaf rust pathogen Puccinia triticina. Transcriptome analysis revealed that overexpression of TaLTP3 specifically activated the transcription of pathogenesis-related protein 1a (TaPR1a) and multiple plant hormone pathways, including salicylic acid (SA), jasmonic acid (JA), and auxin, in response to the infection of the model bacterial pathogen Pseudomonas syringae pv. tomato DC3000. Further investigation indicated that TaLTP3 physically associated with wheat TaPR1a protein in the apoplast. Transgenic wheat lines overexpressing TaLTP3 and TaPR1a showed higher accumulations of reactive oxygen species (ROS) during plant defense responses. All these findings suggested that TaLTP3 is involved in wheat resistance against leaf rust pathogen infection and forming a TaLTP3-TaPR1a complex in apoplast against this pathogen, which provides new insights into the functional roles of PR proteins.