Overexpression of a soybean 4-coumaric acid: coenzyme A ligase (GmPI4L) enhances resistance to Phytophthora sojae in soybean

Oomycete Metabolism Is Highly Dynamic and Reflects Lifestyle Adaptations

The selective pressure of pathogen-host symbiosis drives adaptations. How these interactions shape the metabolism of pathogens is largely unknown. Here, we use comparative genomics to systematically analyze the metabolic networks of oomycetes, a diverse group of eukaryotes that includes saprotrophs as well as animal and plant pathogens, with the latter causing devastating diseases with significant economic and/or ecological impacts. In our analyses of 44 oomycete species, we uncover considerable variation in metabolism that can be linked to lifestyle differences. Comparisons of metabolic gene content reveal that plant pathogenic oomycetes have a bipartite metabolism consisting of a conserved core and an accessory set. The accessory set can be associated with the degradation of defense compounds produced by plants when challenged by pathogens. Obligate biotrophic oomycetes have smaller metabolic networks, and taxonomically distantly related biotrophic lineages display convergent evolution by repeated gene losses in both the conserved as well as the accessory set of metabolisms. When investigating to what extent the metabolic networks in obligate biotrophs differ from those in hemibiotrophic plant pathogens, we observe that the losses of metabolic enzymes in obligate biotrophs are not random and that gene losses predominantly influence the terminal branches of the metabolic networks. Our analyses represent the first metabolism-focused comparison of oomycetes at this scale and will contribute to a better understanding of the evolution of oomycete metabolism in relation to lifestyle adaptation. Numerous oomycete species are devastating plant pathogens that cause major damage in crops and natural ecosystems. Their interactions with hosts are shaped by strong selection, but how selection affects adaptation of the primary metabolism to a pathogenic lifestyle is not yet well established. By pan-genome and metabolic network analyses of distantly related oomycete pathogens and their nonpathogenic relatives, we reveal considerable lifestyle- and lineage-specific adaptations. This study contributes to a better understanding of metabolic adaptations in pathogenic oomycetes in relation to lifestyle, host, and environment, and the findings will help in pinpointing potential targets for disease control. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Molecular module of CmMYB15-like-Cm4CL2 regulating lignin biosynthesis of chrysanthemum (Chrysanthemum morifolium) in response to aphid (Macrosiphoniella sanborni) feeding

Lignin is a major component of plant cell walls and a conserved basic defense mechanism in higher plants deposited in response to aphid infection. However, the molecular mechanisms of lignin biosynthesis in response to aphid infection and the effect of lignin on aphid feeding behavior remain unclear. We report that 4-Coumarate:coenzyme A ligase 2 (Cm4CL2), a gene encoding a key enzyme in the lignin biosynthesis pathway, is induced by aphid feeding, resulting in lignin deposition and reduced aphid attack. Upstream regulator analysis showed that the expression of Cm4CL2 in response to aphid feeding was directly upregulated by CmMYB15-like, an SG2-type R2R3-MYB transcription factor. CmMYB15-like binds directly to the AC cis-element in the promoter region of Cm4CL2. Genetic validation demonstrated that CmMYB15-like was induced by aphid infection and contributed to lignin deposition and cell wall thickening, which consequently enhanced aphid resistance in a Cm4CL2-dependent manner. This study is the first to show that the CmMYB15-like-Cm4CL2 module regulates lignin biosynthesis in response to aphid feeding.

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.

Progress and prospectus in genetics and genomics of Phytophthora root and stem rot resistance in soybean (Glycine max L.)

Soybean is one of the largest sources of protein and oil in the world and is also considered a "super crop" due to several industrial advantages. However, enhanced acreage and adoption of monoculture practices rendered the crop vulnerable to several diseases. Phytophthora root and stem rot (PRSR) caused by Phytophthora sojae is one of the most prevalent diseases adversely affecting soybean production globally. Deployment of genetic resistance is the most sustainable approach for avoiding yield losses due to this disease. PRSR resistance is complex in nature and difficult to address by conventional breeding alone. Genetic mapping through a cost-effective sequencing platform facilitates identification of candidate genes and associated molecular markers for genetic improvement against PRSR. Furthermore, with the help of novel genomic approaches, identification and functional characterization of Rps (resistance to Phytophthora sojae) have also progressed in the recent past, and more than 30 Rps genes imparting complete resistance to different PRSR pathotypes have been reported. In addition, many genomic regions imparting partial resistance have also been identified. Furthermore, the adoption of emerging approaches like genome editing, genomic-assisted breeding, and genomic selection can assist in the functional characterization of novel genes and their rapid introgression for PRSR resistance. Hence, in the near future, soybean growers will likely witness an increase in production by adopting PRSR-resistant cultivars. This review highlights the progress made in deciphering the genetic architecture of PRSR resistance, genomic advances, and future perspectives for the deployment of PRSR resistance in soybean for the sustainable management of PRSR disease.

Impact of Geraniol and Geraniol Nanoemulsions on Botrytis cinerea and Effect of Geraniol on Cucumber Plants’ Metabolic Profile Analyzed by LC-QTOF-MS

In the present study, the bioactive substance geraniol was tested in vitro and in planta against B. cinerea on cucumber plants, and the changes in the metabolic profile of cucumber plants inoculated with the pathogen and/or treated with geraniol were monitored by a novel LC-QTOF-MS method employing target and suspect screening. The aforementioned treatments were also studied for their impact on membrane lipid peroxidation calculated as malondialdehyde (MDA) content. Additionally, geraniol-loaded nanoemulsions (GNEs) were synthesized and tested against B. cinerea as an integrated formulation mode of geraniol application. The EC₅₀ values calculated for geraniol and GNEs against B. cinerea were calculated at 235 μg/mL and 105 μg/mL, respectively. The in planta experiment on cucumber plants demonstrated the ability of geraniol and GNEs to significantly inhibit B. cinerea under greenhouse conditions. The LC-QTOF-MS analysis of the metabolic profile of the cucumber plants treated with geraniol demonstrated an increase in the concentration levels of myricetin, chlorogenic acid, and kaempferol rhamnoside, as compared to control plants and the presence of B. cinerea caused an increase in sinapic acid and genistein. These compounds are part of important biosynthetic pathways mostly related to responses against a pathogen attack.

CRISPRi-Mediated Down-Regulation of the Cinnamate-4-Hydroxylase (C4H) Gene Enhances the Flavonoid Biosynthesis in Nicotiana tabacum

Simple Summary

Flavonoids are natural compounds in plants. They play a critical role in plant growth and pathogen defense. Due to their health benefits, flavonoids have gained much attention as potent therapeutic agents. However, the low abundance of flavonoids in nature has limited their exploitation. Hence, this study aimed to enhance flavonoid production by silencing the cinnamate-4-hydroxylase (C4H) enzyme using the clustered regularly interspaced short palindromic repeats interference (CRISPRi) technology. Our results showed that the C4H-silenced tobacco cells had a lower NtC4H expression level compared to wild-type. This was concurred by the flavonoid analysis, where the accumulation of C4H’s substrate in the C4H-silenced cells was significantly higher than in the wild-type. Our findings provide valuable insight into the future development of CRISPRi to manipulate plant metabolite biosynthesis.

Abstract

Flavonoids are an important class of natural compounds present in plants. However, despite various known biological activities and therapeutic potential, the low abundance of flavonoids in nature limits their development for industrial applications. In this study, we aimed to enhance flavonoid production by silencing cinnamate-4-hydroxylase (C4H), an enzyme involved in the branch point of the flavonoid biosynthetic pathway, using the clustered regularly interspaced short palindromic repeats interference (CRISPRi) approach. We designed three sgRNAs targeting the promoter region of NtC4H and cloned them into a CRISPRi construct. After being introduced into Nicotiana tabacum cell suspension culture, the transformed cells were sampled for qPCR and liquid chromatography-mass spectrometry analyses. Sixteen of 21 cell lines showed PCR-positive, confirming the presence of the CRISPRi transgene. The NtC4H transcript in the transgenic cells was 0.44-fold lower than in the wild-type. In contrast, the flavonoid-related genes in the other branching pathways, such as Nt4CL and NtCHS, in the C4H-silenced cells showed higher expression than wild-type. The upregulation of these genes increased their respective products, including pinostrobin, naringenin, and chlorogenic acid. This study provides valuable insight into the future development of CRISPRi-based metabolic engineering to suppress target genes in plants.

Progress in Soybean Genetic Transformation Over the Last Decade

Soybean is one of the important food, feed, and biofuel crops in the world. Soybean genome modification by genetic transformation has been carried out for trait improvement for more than 4 decades. However, compared to other major crops such as rice, soybean is still recalcitrant to genetic transformation, and transgenic soybean production has been hampered by limitations such as low transformation efficiency and genotype specificity, and prolonged and tedious protocols. The primary goal in soybean transformation over the last decade is to achieve high efficiency and genotype flexibility. Soybean transformation has been improved by modifying tissue culture conditions such as selection of explant types, adjustment of culture medium components and choice of selection reagents, as well as better understanding the transformation mechanisms of specific approaches such as Agrobacterium infection. Transgenesis-based breeding of soybean varieties with new traits is now possible by development of improved protocols. In this review, we summarize the developments in soybean genetic transformation to date, especially focusing on the progress made using Agrobacterium-mediated methods and biolistic methods over the past decade. We also discuss current challenges and future directions.

Fraxinus mandshurica 4-coumarate-CoA ligase 2 enhances drought and osmotic stress tolerance of tobacco by increasing coniferyl alcohol content

4-Coumarate-CoA ligase (4CL) is an important branch point in the phenylpropane pathway and plays important roles in plant growth and development. In this study, the 4CL2 gene from Fraxinus mandshurica (designated Fm4CL2) was identified and isolated. Sequence analysis revealed that Fm4CL2 is a type I 4CL gene involved in lignin biosynthesis. Analysis of cell wall components revealed that Fm4CL2-overexpressing (OE-Fm4CL2) tobacco showed increased lignin content (by 58.9%) and decreased hemicellulose content (by 41.2%). Detection of small-molecule metabolites in the lignin pathway revealed that coumaric acid content decreased by 48% and coniferyl alcohol content increased by 250% compared with the control values. Compared with wild type, OE-Fm4CL2 tobacco showed increased xylem cell layer number (by 120%) and cell wall thickness (by 54.5%). Under osmotic stress, transgenic tobacco showed higher growth than wild-type tobacco. The germination rate of transgenic tobacco was higher than that of wild type. Reactive oxygen species accumulation and malondialdehyde content were significantly lower in transgenic tobacco than in wild type. Under drought, the expression of stress-related genes was higher in 35S-Fm4CL2-infected Fraxinus mandshurica plants than in control plants. These results indicate that Fm4CL2 overexpression can enhance drought and osmotic stress tolerance of plants.

The Effects of Domestication on Secondary Metabolite Composition in Legumes

Legumes are rich in secondary metabolites, such as polyphenols, alkaloids, and saponins, which are important defense compounds to protect the plant against herbivores and pathogens, and act as signaling molecules between the plant and its biotic environment. Legume-sourced secondary metabolites are well known for their potential benefits to human health as pharmaceuticals and nutraceuticals. During domestication, the color, smell, and taste of crop plants have been the focus of artificial selection by breeders. Since these agronomic traits are regulated by secondary metabolites, the basis behind the genomic evolution was the selection of the secondary metabolite composition. In this review, we will discuss the classification, occurrence, and health benefits of secondary metabolites in legumes. The differences in their profiles between wild legumes and their cultivated counterparts will be investigated to trace the possible effects of domestication on secondary metabolite compositions, and the advantages and drawbacks of such modifications. The changes in secondary metabolite contents will also be discussed at the genetic level to examine the genes responsible for determining the secondary metabolite composition that might have been lost due to domestication. Understanding these genes would enable breeding programs and metabolic engineering to produce legume varieties with favorable secondary metabolite profiles for facilitating adaptations to a changing climate, promoting beneficial interactions with biotic factors, and enhancing health-beneficial secondary metabolite contents for human consumption.