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Bacterial plant diseases are difficult to control as the durability of deployed control measures is thwarted by continuous and rapid changing of bacterial populations. Although application of copper compounds to plants is the most widespread and inexpensive control measure, it is often partially efficacious for the frequent appearance of copper-resistant bacterial strains and it is raising concerns for the harmful effects of copper on environment and human health. Consequently, European Community included copper compounds in the list of substances candidates for substitution. Nanotechnologies and the application of nanoparticles seem to respond to the need to find new very effective and durable measures. We believe that Argirium - SUNCs ®, silver ultra nanoclusters with an average size of 1.79 nm and characterized by rare oxidative states (Ag 2+/3+ ), represent a valid candidate as a nano-bactericide in the control of plant bacterial diseases. Respect to the many silver nanoparticles described in the literature, Argirium - SUNCs have many strengths due to the reproducibility of the synthesis method, the purity and the stability of the preparation, the very strong (less than 1 ppm) antimicrobial, and anti-biofilm activities. In this mini-review, we provide information on this nanomaterial and on the possible application in agriculture. Key points • Argirium-SUNCs have strong antimicrobial activities against phytopathogenic bacteria. • Argirium-SUNCs are a possible plant protection product. • Argirium-SUNCs protect tomato plants against bacterial speck disease. Graphical Abstract

Banana Xanthomonas wilt (BXW) caused by Xanthomonas campestris pv. musacearum ( Xcm ) is a severe bacterial disease affecting banana production in East and Central Africa, where banana is cultivated as a staple crop. Classical breeding of banana is challenging because the crop is clonally propagated and has limited genetic diversity. Thus, genetic engineering serves as a viable alternative for banana improvement. Studies have shown that transfer of the elongation factor Tu receptor gene ( AtEFR ) from Arabidopsis thaliana to other plant species can enhance resistance against bacterial diseases. However, AtEFR activity in banana and its efficacy against Xcm has not been demonstrated. In this study, transgenic events of banana ( Musa acuminata ) cultivar dwarf Cavendish expressing the AtEFR gene were generated and evaluated for resistance against Xcm under greenhouse conditions. The transgenic banana events were responsive to the EF-Tu-derived elf18 peptide and exhibited enhanced resistance to BXW disease compared to non-transgenic control plants. This study suggests that the functionality of AtEFR is retained in banana with the potential of enhancing resistance to BXW under field conditions.

Background Calmodulins ( CaMs )/CaM-like proteins (CMLs) are crucial Ca 2+ -binding sensors that can decode and transduce Ca 2+ signals during plant development and in response to various stimuli. The CaM/CML gene family has been characterized in many plant species, but this family has not yet been characterized and analyzed in peanut, especially for its functions in response to Ralstonia solanacearum . In this study, we performed a genome-wide analysis to analyze the CaM/CML genes and their functions in resistance to R. solanacearum . Results Here, 67, 72, and 214 CaM/CML genes were identified from Arachis duranensis , Arachis ipaensis , and Arachis hypogaea , respectively. The genes were divided into nine subgroups (Groups I-IX) with relatively conserved exon‒intron structures and motif compositions. Gene duplication, which included whole-genome duplication, tandem repeats, scattered repeats, and unconnected repeats, produced approximately 81 pairs of homologous genes in the AhCaM/CML gene family. Allopolyploidization was the main reason for the greater number of AhCaM/CML members. The nonsynonymous (Ka) versus synonymous (Ks) substitution rates (less than 1.0) suggested that all homologous pairs underwent intensive purifying selection pressure during evolution. AhCML69 was constitutively expressed in different tissues of peanut plants and was involved in the response to R. solanacearum infection. The AhCML69 protein was localized in the cytoplasm and nucleus. Transient overexpression of AhCML69 in tobacco leaves increased resistance to R. solanacearum infection and induced the expression of defense-related genes, suggesting that AhCML69 is a positive regulator of disease resistance. Conclusions This study provides the first comprehensive analysis of the AhCaM/CML gene family and potential genetic resources for the molecular design and breeding of peanut bacterial wilt resistance.

Key messageThe bs5 resistance gene against bacterial spot was identified by map-based cloning.The recessive bs5 gene of pepper (Capsicum annuum L.) conditions a non-hypersensitive resistance trait, characterized by a slightly swollen, pale green, photosynthetically active leaf tissue, following Xanthomonas euvesicatoria infection. The isolation of the bs5 gene by map-based cloning revealed that the bs5 protein was shorter by 2 amino acids as compared to the wild type Bs5 protein. The natural 2 amino acid deletion occurred in the cysteine-rich transmembrane domain of the tail-anchored (TA) protein, Ca_CYSTM1. The protein products of the wild type Bs5 and mutant bs5 genes were shown to be located in the cell membrane, indicating an unknown function in this membrane compartment. Successful infection of the Bs5 pepper lines was abolished by the 6 bp deletion in the TM encoding domain of the Ca_CYSTM1 gene in bs5 homozygotes, suggesting, that the resulting resistance might be explained by the lack of entry of the Xanthomonas specific effector molecules into the plant cells.

Background The BAG gene family, encoding Bcl-2-associated anti-apoptotic proteins, plays pivotal roles in regulating plant growth, development, and stress responses. Peanut ( Arachis hypogaea L.), a globally significant oilseed and cash crop, is highly valued for its economic importance. However, systematic genome-wide analysis and functional characterization of the BAG gene family in peanut remain largely unexplored. Results In this study, we identified 13 AhBAG genes in the peanut genome, which are unevenly distributed across 11 chromosomes. Phylogenetic analysis revealed that these AhBAG genes, together with BAG family members from other plant species, are classified into four distinct clades, underscoring their evolutionary conservation. Segmental duplication was identified as a major driver of the expansion of the AhBAG gene family. Notably, AhYSVF0U exhibited significant upregulation under Ralstonia solanacearum infection and abscisic acid treatment, suggesting its potential involvement in mediating peanut resistance to bacterial wilt. Conclusions This study provides comprehensive insights into the evolutionary and functional characteristics of the peanut BAG gene family and offers valuable genetic resources for molecular breeding programs aimed at improving stress tolerance in peanut.

Background DNA demethylases regulate the levels of genomic DNA methylation in plants. The demethylase REPRESSOR OF SILENCING 1 (ROS1) is a crucial factor for modulating gene expression in plant disease responses. Bacterial leaf streak (BLS), caused by Xanthomonas oryzae pv. Oryzicola ( Xoc ), is a highly destructive disease in rice. BLS resistance in rice is known to be quantitatively inherited, but the mechanisms by which DNA methylation controls BLS resistance remain poorly understood. Results In this study, we knocked down OsROS1a expression in the rice variety Nipponbare using RNA interference (RNAi). The average BLS lesion length in the transgenic (T2) OsROS1a -RNAi (RS) lines was significantly reduced compared to that in wild-type Nipponbare plants (NP). Using whole-genome bisulfite sequencing (WGBS) and RNA-sequencing (RNA-seq), we analyzed the DNA methylations and transcriptomes of RS lines in comparison with NP at 0 (control), 5, 10, and 24 h post-inoculation with Xoc . A total of 1080 differentially expressed genes (DEGs) related to Xoc infection between the NP and RS lines were identified, which could be grouped into 8 clusters by K-means analysis. The DEGs in cluster 1 were enriched in the biological process related to defense response, response to stress, oxidation-reduction, etc. Integration of the methylome and transcriptome data revealed 112 overlapping differentially methylated and expressed genes (DMEGs). Gene Ontology (GO) analysis showed that the DMEGs were mainly involved in biological processes, such as metabolic process, cellular process, responses to stimulus, signaling, and immune system processes. KEGG pathway enrichment analysis revealed that these DMEGs were enriched in pathways related to glutathione metabolism, plant-pathogen interaction, cysteine and methionine, diterpenoid biosynthesis, photosynthesis, and starch and sucrose. Additionally, LOC_Os09g12660 , encoding the glucose-1-phosphate adenylyl transferase large subunit, a chloroplast precursor involved in synthesizing activated glycosyl donor, showed strong potential to contribute to BLS resistance. Conclusion OsROS1a plays a crucial role in modulating rice resistance to bacterial leaf streak (BLS) caused by Xanthomonas oryzae pv. oryzicola ( Xoc ). These findings provide valuable insights into the role of OsROS1a in BLS resistance.

Background and aims This research investigates the biocontrol mechanisms of Gluconacetobacter diazotrophicus against the harmful bacterium Ralstonia pseudosolanacearum , causal agent of bacterial wilt disease. Given the ongoing need for effective control strategies, our focus lies in understanding the hormonal pathways, particularly the salicylic acid (SA) and jasmonic acid/ethylene (JA/Et) signaling pathways, involved in plant defense. Methods SA signalization deficiencies effects in plant-endophyte-pathogen interactions were observed through colonization ability, morpho-anatomical, physiological and disease severity parameters of sid2 (unable to produce SA via isochorismate synthase 1) and NahG (unable to accumulate SA) compared to wild-type Col0 plants treated with G. diazotrophicus , R. pseudosolanacearum or both bacteria. Additionally, pr1 , pr5, myc2, pdf1.2 (associated with SA or JA/Et defense response), and fitness (linked to redox homeostasis) relative expression were analyzed in Col0. Results G. diazotrophicus increased root hairs in Col0 and NahG. This correlated with a higher endophytic colonization frequency and enhanced lignification and xylem expansion. However, chlorophyll content and bacterial counts indicated an endophyte-NahG imbalance. Disease index, R. pseudosolanacearum bacterial counts and H 2 O 2 accumulation were lower in G. diazotrophicus inoculated Col0 and expression analysis revealed up-regulation of pr1 and myc2 . In co-inoculated plants, R. pseudosolanacearum increased pdf1.2 levels by 15.2-times, which was significantly higher than in those inoculated solely with pathogenic bacteria. G. diazotrophicus managed to maintain fitness low levels even after R. pseudosolanacearum infection. Conclusions The interplay G. diazotrophicus -Arabidopsis, mediated by the expression of pr , myc2 and fitness primes for subsequent infection with R. pseudosolanacearum , triggering the expression of JA/Et pathway genes.

Bacterial plant pathogens exploit natural openings, such as pores or wounds, to enter the plant interior and cause disease. Plants guard these openings through defense mechanisms. However, bacteria from the genus Xanthomonas have specialized in that they enter their host via a special entry point, the hydathode—an organ at the leaf margin involved in xylem sap guttation. Hydathodes can mount an immune response against bacteria, including non-adapted and adapted pathogens like X. campestris pv. campestris (Xcc) that cause vascular disease. Previously, it was shown that the RKS1/ZAR1 immune complex confers vascular resistance against Xcc by recognizing XopAC activity, a type III effector (T3E). However, in absence of XopAC recognition, Arabidopsis Col-0 hydathodes still display resistance against Xcc. Here we mapped the causal gene using an inoculation method that promotes Xcc hydathode entry. Using a population of Recombinant Inbred Lines (RILs) of a cross between a susceptible (Oy-0) and resistant accession (Col-0), a major QTL for Xcc resistance was found on the right arm of Chromosome 5 in Col-0. Combining this result with a genome-wide association analysis yielded a single candidate gene encoding a coiled-coil nucleotide-binding leucine-rich repeat (CNL-type) immune receptor protein called SUPPRESSOR OF TOPP4 1 (SUT1). Expression of SUT1 was confirmed in hydathodes. We reveal that RKS1/ZAR1 and SUT1 confer different levels of Xcc resistance in different tissue types. Both RKS1/ZAR1 and SUT1 are alone sufficient for Xcc resistance in Col-0 hydathodes. However, RKS1/ZAR1 resistance is also effective in tissue types that represent late infection stages, i.e., xylem and mesophyll. In contrast, SUT1 resistance is not effective in the xylem, while weakly additive to RKS1/ZAR1 in the mesophyll. We thus identify a novel R gene, SUT1 , that confers Xcc resistance primarily early in the infection during hydathode colonization.

Background Fungal communities around plant roots play crucial roles in maintaining plant health. Nonetheless, the responses of fungal communities to bacterial wilt disease remain poorly understood. Here, the structure and function of fungal communities across four consecutive compartments (bulk soil, rhizosphere, rhizoplane and root endosphere) were investigated under the influence of bacterial wilt disease. Results The results showed that bacterial wilt disease caused different assembly patterns of fungal communities in the bulk soil, rhizosphere, rhizoplane and endosphere. Under the influence of bacterial wilt disease, a decreased fungal diversity was observed in the rhizoplane and endosphere, and completely different kinds of fungal genera were enriched in the four compartments. The complexity and stability of fungal networks were less affected, but the number of key fungal members in networks were significantly reduced in diseased samples. Functional predictions based on FUNGuild suggested that with the pathogen infection, saprotrophic fungi were increased in the bulk soil, but pathotrophic fungi (potential plant and animal pathogens) were increased in the rhizosphere, rhizoplane and endosphere. Conclusion This work provides a deep insight into the effects of bacterial wilt disease on fungal communities along the soil-root continuum, and is helpful to identify plant-associated beneficial fungi to resist plant disease. Clinical trial number Not applicable.

Background Plant responses to biotic and abiotic stresses are complex processes. Previous studies have shown that the LBD gene family plays important roles in plant growth and development as well as in plant defense against biotic and abiotic stresses. The expression of LBD genes was investigated in walnuts under biotic and abiotic stresses, revealing that LBD38-1 may be a key gene in the plant stress response. This study provides new insights into the roles of LBD genes in plant responses to biotic stress. Results Forty-nine members of the JrLBD gene family were identified in the walnut genome and classified into six subfamilies. Comparative homology analysis through phylogenetic trees revealed that the presence of Group I-a and Group VI plays an important role in resistance to stressors. The expression of walnut LBD genes under cold-temperature, high-temperature, mechanical damage, and biotic stresses was analyzed via transcriptome sequencing, and the expression of JrLBD38-1 in the Group VI subfamily was particularly prominent. According to transcriptome profile analysis, JrLBD38-1 is highly expressed in different tissues of walnuts, suggesting that it plays a regulatory role in the growth and development of different tissues. The function of the Gibberellin (GA) response element in the JrLBD38-1 promoter was further analyzed and verified. These findings confirmed that GA regulated JrLBD38-1 expression changes during Xanthomonas arboricola pv. juglandis infestation of walnut leaves. Conclusion Forty-nine walnut JrLBDs were identified and classified into six subfamilies. JrLBD38-1 has GA-inducible expression, is regulated by GA under pathogenic bacterial stress, and is involved in the response to biotic stress. This function of JrLBD38-1 provides new insights into walnut disease resistance mechanisms.