Ankyrin-Like Protein AnkB Interacts with CatB, Affects Catalase Activity, and Enhances Resistance of Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola to Phenazine-1-Carboxylic Acid

Noninvasive Raman spectroscopy for the detection of rice bacterial leaf blight and bacterial leaf streak

Plant diseases pose significant threats to agricultural yields and are responsible for nearly 20 % of losses in total food production. Therefore, the rapid detection of plant pathogens is critically important for preventing the rapid development of plant diseases and minimizing crop damage. Raman spectroscopy (RS) has been shown to be effective for detecting living biological samples. Compared with traditional detection methods, RS is fast, sensitive, and non-destructive; it also does not require sample labeling. In this study, we used Laser tweezers Raman spectroscopy combined with convolutional neural networks to detect two closely related strains of bacteria, Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc), exuded from bacteria-infected rice leaves. The accuracy of this technique was 97.5 %. For the application of RS in the field, we used the portable Raman spectrometer to detect mock-inoculated as well as Xoo- and Xoc-infected rice leaves at different disease courses. The identification accuracy via this technique was 87.02 % in the early stage, in which no obvious symptoms were apparent. This method also revealed spectral differences in rice leaves caused by the two bacteria, which could be leveraged for subsequent analysis of the molecular mechanism of infection. Our results indicate that RS is a promising approach for the early detection of bacterial diseases in rice in the field, as well as for in-depth single-cell analysis in laboratory settings.

Genetic-based dissection of resistance to bacterial leaf streak in rice by GWAS

BACKGROUND

Rice is the second-largest food crop in the world and vulnerable to bacterial leaf streak disease. A thorough comprehension of the genetic foundation of agronomic traits was essential for effective implementation of molecular marker-assisted selection.

RESULTS

Our study aimed to evaluate the vulnerability of rice to bacterial leaf streak disease (BLS) induced by the gram-negative bacterium Xanthomonas oryzae pv. oryzicola (Xoc). In order to accomplish this, we first analyzed the population structure of 747 accessions and subsequently assessed their phenotypes 20 days after inoculation with a strain of Xoc, GX01. We conducted genome-wide association studies (GWAS) on a population of 747 rice accessions, consisting of both indica and japonica subpopulations, utilizing phenotypic data on resistance to bacterial leaf streak (RBLS) and sequence data. We identified a total of 20 QTLs associated with RBLS in our analysis. Through the integration of linkage mapping, sequence analysis, haplotype analysis, and transcriptome analysis, we were able to identify five potential candidate genes (OsRBLS1-OsRBLS5) that possess the potential to regulate RBLS in rice. In order to gain a more comprehensive understanding of the genetic mechanism behind resistance to bacterial leaf streak, we conducted tests on these genes in both the indica and japonica subpopulations, ultimately identifying superior haplotypes that suggest the potential utilization of these genes in breeding disease-resistant rice varieties.

CONCLUSIONS

The findings of our study broaden our comprehension of the genetic mechanisms underlying RBLS in rice and offer significant insights that can be applied towards genetic improvement and breeding of disease-resistant rice in rapidly evolving environmental conditions.

The Arsenal of Leptospira Species against Oxidants

Reactive oxygen species (ROS) are byproducts of oxygen metabolism produced by virtually all organisms living in an oxic environment. ROS are also produced by phagocytic cells in response to microorganism invasion. These highly reactive molecules can damage cellular constituents (proteins, DNA, and lipids) and exhibit antimicrobial activities when present in sufficient amount. Consequently, microorganisms have evolved defense mechanisms to counteract ROS-induced oxidative damage. Leptospira are diderm bacteria form the Spirochaetes phylum. This genus is diverse, encompassing both free-living non-pathogenic bacteria as well as pathogenic species responsible for leptospirosis, a widespread zoonotic disease. All leptospires are exposed to ROS in the environment, but only pathogenic species are well-equipped to sustain the oxidative stress encountered inside their hosts during infection. Importantly, this ability plays a pivotal role in Leptospira virulence. In this review, we describe the ROS encountered by Leptospira in their different ecological niches and outline the repertoire of defense mechanisms identified so far in these bacteria to scavenge deadly ROS. We also review the mechanisms controlling the expression of these antioxidants systems and recent advances in understanding the contribution of Peroxide Stress Regulators in Leptospira adaptation to oxidative stress.

Exploiting the antibacterial mechanism of phenazine substances from Lysobacter antibioticus 13-6 against Xanthomonas oryzae pv. oryzicola

Bacterial leaf streak caused by Xanthomonas oryzae pv. oryzicola (Xoc) is one of the most destructive diseases affecting rice production worldwide. In this study, we extracted and purified phenazine substances from the secondary metabolites of Lysobacter antibioticus 13-6. The bacteriostatic mechanism of phenazine substances against Xoc was investigated through physiological response and transcriptomic analysis. Results showed that phenazine substances affects the cell membrane permeability of Xoc, which causes cell swelling and deformation, blockage of flagellum synthesis, and imbalance of intracellular environment. The changes in intracellular environment affect the physiological and metabolic functions of Xoc, which reduces the formation of pathogenic factors and pathogenicity. Through transcriptomic analysis, we found that among differentially expressed genes, the expression of 595 genes was induced significantly (275 up-regulated and 320 down-regulated). In addition, we observed that phenazine substances affects three main functions of Xoc, i.e., transmembrane transporter activity, DNA-mediated transposition, and structural molecular activity. Phenazine substances also inhibits the potassium ion transport system that reduces Xoc resistance and induces the phosphate ion transport system to maintain the stability of the internal environment. Finally, we conclude that phenazine substances could retard cell growth and reduce the pathogenicity of Xoc by affecting cell structure and physiological metabolism. Altogether, our study highlights latest insights into the antibacterial mechanism of phenazine substances against Xoc and provides basic guidance to manage the incidence of bacterial leaf streak of rice.

Prediction and Analysis in silico of Genomic Islands in Aeromonas hydrophila

Aeromonas are Gram-negative rods widely distributed in the environment. They can cause severe infections in fish related to financial losses in the fish industry, and are considered opportunistic pathogens of humans causing infections ranging from diarrhea to septicemia. The objective of this study was to determine in silico the contribution of genomic islands to A. hydrophila. The complete genomes of 17 A. hydrophila isolates, which were separated into two phylogenetic groups, were analyzed using a genomic island (GI) predictor. The number of predicted GIs and their characteristics varied among strains. Strains from group 1, which contains mainly fish pathogens, generally have a higher number of predicted GIs, and with larger size, than strains from group 2 constituted by strains recovered from distinct sources. Only a few predicted GIs were shared among them and contained mostly genes from the core genome. Features related to virulence, metabolism, and resistance were found in the predicted GIs, but strains varied in relation to their gene content. In strains from group 1, O Ag biosynthesis clusters OX1 and OX6 were identified, while strains from group 2 each had unique clusters. Metabolic pathways for myo-inositol, L-fucose, sialic acid, and a cluster encoding QueDEC, tgtA5, and proteins related to DNA metabolism were identified in strains of group 1, which share a high number of predicted GIs. No distinctive features of group 2 strains were identified in their predicted GIs, which are more diverse and possibly better represent GIs in this species. However, some strains have several resistance attributes encoded by their predicted GIs. Several predicted GIs encode hypothetical proteins and phage proteins whose functions have not been identified but may contribute to Aeromonas fitness. In summary, features with functions identified on predicted GIs may confer advantages to host colonization and competitiveness in the environment.

Differential proteomic analyses of green microalga Ettlia sp. at various dehydration levels

Water deprivation could be a lethal stress for aquatic and aero-terrestrial organisms. Ettlia sp. is a unicellular photosynthetic freshwater microalga. In the present study, proteomic alterations and physiological characteristics of Ettlia sp. were analyzed to comprehend the molecular changes in dehydrated conditions. Varying levels of dehydration were achieved by incubating drained Ettlia sp. in different relative humidity environments for 24  hours. Using a comparative proteomic analysis, 52 differentially expressed protein spots were identified that could be divided into eight functional groups. The PCA analysis of normalized protein expression values demonstrated a clear segregation of protein expression profiles among different dehydration levels. Identified proteins could be grouped into four clusters based on their expression profiles. Proteins relating to photosynthesis comprised the largest group with 25% of the identified proteins that were decreased in dehydrated samples and belonged to cluster I. The photosynthetic activities were measured with rehydrated Ettlia sp. These results revealed that photosynthesis remained inhibited over extended time in response to dehydration. The expressions of reactive oxygen species (ROS) scavenger proteins increased in strong dehydration and were assigned to cluster III. Carbon metabolism proteins were suppressed, which might limit energy consumption, whereas glycolysis was activated at mild dehydration. The accumulation of desiccation-associated late embryogenesis proteins might inhibit the aggregation of housekeeping proteins. DNA protective proteins were expressed higher in the dehydrated state, which might reduce DNA damage, and membrane-stabilizing proteins increased in abundance in desiccation. These findings provide an understanding of Ettlia's adaptation and survival capabilities in a dehydrated state.

Synthesis and bioactivities of phenazine-1-carboxylic piperazine derivatives

Phenazine-1-carboxylic acid (PCA) as a natural product which has significant inhibition effects against many soil-borne fungal phytopathogens in agricultural application and has been registered in China as the fungicide against rice sheath blight. In order to find new higher fungicidal activities lead compounds and develop new eco-friendly agrochemicals, we introduced substructure piperazines which also have high biological activity into PCA, designed and synthesized a series of phenazine-1-carboxylic piperazine derivatives, and their structures were confirmed by ¹H NMR and HRMS. Most compounds exhibited certain in vitro fungicidal activities. In particular, Compounds 5r exhibited the activity against all the tested pathogenic fungi, such as Rhizoctonia solani, Alternaria solani, Fusarium oxysporum, Fusarium graminearum, Pyricularia oryzac Cavgra, with the EC₅₀ value of 24.6μM, 42.9μM, 73.7μM, 73.8μM, 34.2μM, respectively, more potent activities than PCA (33.2μM, 81.5μM, 186.5μM, 176.4μM, 37.3μM). This result provided a highly active lead compound for the further structure optimization design.