Phytohormone priming elevates the accumulation of defense-related gene transcripts and enhances bacterial blight disease resistance in cassava

Unveiling exogenous potential of phytohormones as sustainable arsenals against plant pathogens: molecular signaling and crosstalk insights

Plants frequently confront pathogens that disrupt physiological and molecular functions, ultimately reducing agricultural yields. To counter these challenges, plants activate sophisticated defense mechanisms to recognize stress signals while optimizing growth. Phytohormones signaling pathways and their crosstalk are central to regulating plant growth, development and defense. Numerous proteins associated with phytohormone signaling pathways have been identified, including receptors for several vital hormones. Previous studies indicate that defense phytohormones, like salicylic acid (SA), jasmonic acid (JA) and ethylene (ET), are crucial to pathogen defense. SA specifically mediates systemic acquired resistance against biotrophic pathogens, while induced systemic resistance relies on JA and ET signaling in response to necrotrophic pathogens. Other hormones, typically associated with growth and development, such as ethylene, abscisic acid, brassinosteroids, melatonin, gibberellins, auxin, and cytokinin, also interact in a complex network of synergistic and antagonistic relationships with defense phytohormones. Moreover, they can achieve effects that surpass conventional pathogen control methods, suggesting their potential as exogenous biocontrol agents. During the past decade, our knowledge of hormone signaling and stress response has become immense. Thus, this review is an attempt to summarize some of the advances in plant signaling and crosstalk mechanisms as well as their potential to be a future arsenal in biotic stress mitigation strategies. Ultimately, this work emphasizes using exogenous phytohormones as a viable alternative for controlling pathogens to enhance crop productivity in pathogen-affected regions.

Effects of ultrasonic treatment on the surface bacteria of Lyophyllum decastes during storage

This study explores the relationship between the storage quality and bacterial microflora in the mushroom Lyophyllum decastes. The surface bacteria of L. decastes were separated by combining the traditional culture plate separation and 16S rRNA sequencing method, to study the effects of ultrasonic (US) treatment on the surface bacteria of L. decastes during storage. The results demonstrated that Pantoea agglomerans and Pseudomonas fluorescens were among the 15 culturable bacteria isolated with traditional plate method during storage, belonging to 2 phyla and 7 genera. US treatment could inhibit the growth and significantly increase cell membrane permeability, and contents extravasation in P. agglomerans, though its inhibitory effect on P. fluorescens was less. The 16S rRNA sequencing revealed, bacteria from 9 phyla and 35 genera were isolated, and P. fluorescens was the dominant species throughout the storage time. These results indicated that the composition of mushroom surface microflora of Control (CK) and US groups are similar, and the bacterial microflora networks analysis also showed a positive correlation. The KEGG annotation for the functional classification of the bacteria showed that a total of 328 pathways were acquired at the KEGG l3 level, and the relative abundance of membrane transport, amino acid metabolism, carbohydrate metabolism, and energy metabolism pathway was high. Moreover, the relative abundance of the surface bacteria of L. decastes also decreased. Hence, the US treatment had a better bacteriostatic effect, maintained the whiteness index and firmness, and improved the sensory quality of L. decastes during storage.

Rhizosphere Signaling: Insights into Plant-Rhizomicrobiome Interactions for Sustainable Agronomy

Rhizospheric plant-microbe interactions have dynamic importance in sustainable agriculture systems that have a reduced reliance on agrochemicals. Rhizosphere signaling focuses on the interactions between plants and the surrounding symbiotic microorganisms that facilitate the development of rhizobiome diversity, which is beneficial for plant productivity. Plant-microbe communication comprises intricate systems that modulate local and systemic defense mechanisms to mitigate environmental stresses. This review deciphers insights into how the exudation of plant secondary metabolites can shape the functions and diversity of the root microbiome. It also elaborates on how rhizosphere interactions influence plant growth, regulate plant immunity against phytopathogens, and prime the plant for protection against biotic and abiotic stresses, along with some recent well-reported examples. A holistic understanding of these interactions can help in the development of tailored microbial inoculants for enhanced plant growth and targeted disease suppression.

The Cassava NBS-LRR Genes Confer Resistance to Cassava Bacterial Blight

Cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam) seriously affects cassava yield. Genes encoding nucleotide-binding site (NBS) and leucine-rich repeat (LRR) domains are among the most important disease resistance genes in plants that are specifically involved in the response to diverse pathogens. However, the in vivo roles of NBS-LRR remain unclear in cassava (Manihot esculenta). In this study, we isolated four MeLRR genes and assessed their expression under salicylic acid (SA) treatment and Xam inoculation. Four MeLRR genes positively regulate cassava disease general resistance against Xam via virus-induced gene silencing (VIGS) and transient overexpression. During cassava-Xam interaction, MeLRRs positively regulated endogenous SA and reactive oxygen species (ROS) accumulation and pathogenesis-related gene 1 (PR1) transcripts. Additionally, we revealed that MeLRRs positively regulated disease resistance in Arabidopsis. These pathogenic microorganisms include Pseudomonas syringae pv. tomato, Alternaria brassicicola, and Botrytis cinerea. Our findings shed light on the molecular mechanism underlying the regulation of cassava resistance against Xam inoculation.

Cassava diseases caused by Xanthomonas phaseoli pv. manihotis and Xanthomonas cassavae

Xanthomonas phaseoli pv. manihotis (Xpm) and X. cassavae (Xc) are two bacterial pathogens attacking cassava. Cassava bacterial blight (CBB) is a systemic disease caused by Xpm, which might have dramatic effects on plant growth and crop production. Cassava bacterial necrosis is a nonvascular disease caused by Xc with foliar symptoms similar to CBB, but its impacts on the plant vigour and the crop are limited. In this review, we describe the epidemiology and ecology of the two pathogens, the impacts and management of the diseases, and the main research achievements for each pathosystem. Because Xc data are sparse, our main focus is on Xpm and CBB.

Enhancing of anthracnose disease resistance indicates a potential role of antimicrobial peptide genes in cassava

Cassava (Manihot esculenta Crantz.) is an important economic crop in tropical countries. Demands for using cassava in food, feed and biofuel industries have been increasing worldwide. Cassava anthracnose disease, caused by Colletotrichum gloeosporioides f.sp. manihotis (CAD), is considered a major problem in cassava production. To minimize the effects of such disease, this study investigated the response of cassava to attack by CAD and how the plants defend themselves against this threat. Genome-wide identification of antimicrobial peptide genes (AMPs) and their expression in response to fungal infection was performed in the resistant cassava cultivar (Huay Bong 60; HB60) in comparison with the highly susceptible cultivar (Hanatee; HN). A total of 114 gene members of AMP were identified in the cassava genome database. Fifty-six gene members were selected for phylogenetic tree construction and analysis of putative cis-acting elements in their promoter regions. Differential expression profiles of six candidate genes were observed in response to CAD infection of both cassava cultivars. Upregulation of snakins, MeSN1 and MeSN2 was found in HB60, whereas MeHEL, Me-AMP-D2 and MeLTP2 were highly induced in HN. The MeLTP1 gene was not expressed in either cultivar. HB60 showed a reduced severity rating in comparison to HN after CAD infection. The biomembrane permeability test of fungal CAD was strongly affected after treatment with protein extract derived from CAD-infected HB60. Altogether, these findings suggest that snakins have a potential function in the CAD defense response in cassava. These results could be useful for cassava improvement programs to fight fungal pathogen.

CaLRR-RLK1, a novel RD receptor-like kinase from Capsicum annuum and transcriptionally activated by CaHDZ27, act as positive regulator in Ralstonia solanacearum resistance

BACKGROUND

Bacterial wilt caused by Ralstonia solanacearum is one of the most important diseases in pepper worldwide, however, the molecular mechanism underlying pepper resistance to bacterial wilt remains poorly understood.

RESULTS

Herein, a novel RD leucine-rich repeat receptor-like kinase, CaLRR-RLK1, was functionally characterized in immunity against R. solanacearum. CaLRR-RLK1 was targeted exclusively to plasma membrane and was up-regulated by R. solanacearum inoculation (RSI) as well as by the exogenous application of salicylic acid (SA), methyl jasmonate (MeJA) or ethephon (ETH). The silencing of CaLRR-RLK1 led to enhanced susceptibility of pepper plants to RSI, accompanied by down-regulation of immunity-related genes including CaACO1, CaHIR1, CaPR4 and CaPO2. In contrast, transient overexpression of CaLRR-RLK1 triggered hypersensitive response (HR)-like cell death and H2O2 accumulation in pepper leaves, manifested by darker trypan blue and DAB staining respectively. In addition, the ectopic overexpression of CaLRR-RLK1 in tobacco plants enhanced resistance R. solanacearum, accompanied with the immunity associated marker genes including NtPR2, NtPR2, NtHSR203 and NtHSR515. Furthermore, it was found that CaHDZ27, a positive regulator in pepper response to RSI in our previous study, transcriptionally activated CaLRR-RLK1 by direct targeting its promoter probably in a CAATTATTG dependent manner.

CONCLUSION

The study revealed that CaLRR-RLK1 confers pepper resistance to R. solanacearum as the direct targeting of CaHDZ27.

The impact of microbes in the orchestration of plants' resistance to biotic stress: a disease management approach

The struggle for survival is a natural and a continuous process. Microbes are struggling to survive by depending on plants for their nutrition while plants on the other hand are resisting the attack of microbes in order to survive. This interaction is a tug of war and the knowledge of microbe-plant relationship will enable farmers/agriculturists improve crop health, yield, sustain regular food supply, and minimize the use of agrochemicals such as fungicides and pesticides in the fight against plant pathogens. Although, these chemicals are capable of inhibiting pathogens, they also constitute an environmental hazard. However, certain microbes known as plant growth-promoting microbes (PGPM) aid in the sensitization and priming of the plant immune defense arsenal for it to conquer invading pathogens. PGPM perform this function by the production of elicitors such as volatile organic compounds, antimicrobials, and/or through competition. These elicitors are capable of inducing the expression of pathogenesis-related genes in plants through induced systemic resistance or acquired systemic resistance channels. This review discusses the current findings on the influence and participation of microbes in plants' resistance to biotic stress and to suggest integrative approach as a better practice in disease management and control for the achievement of sustainable environment, agriculture, and increasing food production.

Estudio de la expresión de genes que codifican para putativas proteínas PR en yuca (<i>Manihot esculenta</i> Crantz)

Posterior al reconocimiento de agentes patógenos las plantas activan una serie de cascadas de señalización que culminan con la activación de factores de transcripción. Esto genera una concomitante reprogramación de la expresión génica que incluye la activación de la transcripción de los genes PR (relacionados con patogenicidad). Las proteínas PR son conocidas por poseer actividad antimicrobiana y evitan la posterior colonización del patógeno. En este estudio se empleó una aproximación bioinformática para identificar el repertorio de posibles proteínas PR en el genoma de yuca. Adicionalmente, se evaluó la expresión de nueve genes PR a lo largo del tiempo en variedades de yuca resistentes y susceptibles en respuesta a la inoculación con la bacteria Xanthomonas axonopodis pv. manihotis (Xam) mediante RT-PCR. Se encontró que varios genes PR fueron inducidos producto de la herida que se realiza durante el proceso de inoculación. Con el fin de evaluar cuantitativamente la contribución real de la infección bacteriana en la expresión de estos genes, se llevó a cabo una RT-PCR en tiempo real (QRT, Quantitative Real-Time PCR). Se encontró que en la variedad resistente el gen que codifica para MePR1 (Manes06G026900.1) presentó una inducción en su expresión a diferentes tiempos post-inoculación, lo cual no se observó en la variedad susceptible. De esta manera, este gen se constituye en un excelente marcador para evaluar la respuesta molecular de resistencia en plantas de yuca.