Hd3a and OsFD1 negatively regulate rice resistance to Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola

Drug repurposing strategy part 1: from approved drugs to agri-bactericides leads

Phytopathogenic bacteria are a major cause of crop mortality and yield reduction, especially in field cultivation. The lack of effective chemistry agri-bactericides is responsible for challenging field prevention and treatment, prompting the development of long-lasting solutions to prevent, reduce, or manage some of the most devastating plant diseases facing modern agriculture today and in the future. Therefore, there is an urgent need to find lead drugs preventing and treating phytopathogenic bacterial infection. Drug repurposing, a strategy used to identify novel uses for existing approved drugs outside of their original indication, takes less time and investment than Traditional R&D Strategies in the process of drug development. Based on this method, we conduct a screen of 700 chemically diverse and potentially safe drugs against Xanthomonas oryzae PV. oryzae ACCC 11602 (Xoo), Xanthomonas axonopodis PV. citri (Xac), and Pectobacterium atrosepticum ACCC 19901 (Pa). Furthermore, the structure-activity relationship and structural similarity analysis of active drugs classify potent agri-bactericides into 8 lead series: salicylanilides, cationic nitrogen-containing drugs, azole antifungals, N-containing group, hydroxyquinolines, piperazine, kinase inhibitor and miscellaneous groups. MIC values were evaluated as antibacterial activities in this study. Identifying highly active lead compounds from the screening of approved drugs and comparison with the currently applied plant pathogenic bactericide to validate the bactericidal activity of the best candidates and assess if selected molecules or scaffolds lead to develop new antibacterial agents in the future. In conclusion, this study provides a possibility for the development of potent and highly selective agri-bactericides leads.

Alanine-mediated P cycle boosting enhances the killing efficiency of kasugamycin on antibiotic-resistant Xanthomonas oryzae

The outbreak of Bacterial blight (BB) caused by Xanthomonas oryzae (Xoo) generates substantial economic losses to agricultural production. Antibiotics application is a valuable measure to control this bacterial disease. However, microbial antibiotic resistance dramatically reduced antibiotic effectiveness. Identifying the resistance mechanism of Xoo to antibiotics and restoring antibiotic susceptibility is one of the crucial ways to solve this problem. This study employed a GC-MS-based metabolomic approach to reveal the differential metabolomics between a kasugamycin-susceptible Xoo strain (Z173-S) and a kasugamycin-resistant strain (Z173-R_KA). The metabolic mechanism of kasugamycin (KA) resistance in Xoo by GC-MS showed that the downregulation of the pyruvate cycle (P cycle) is a crucial feature of Z173-R_KA resistance to KA. This conclusion was confirmed by the decreased enzyme activities and the related gene transcriptional level in the P cycle. Furfural (an inhibitor of pyruvate dehydrogenase) can effectively inhibit the P cycle and increase the resistance of Z173-R_KA to KA. Moreover, exogenous alanine can reduce the resistance of Z173-R_KA to KA by promoting the P cycle. Our work seems to be the first exploration of the mechanism of KA resistance in Xoo by GC-MS-based metabonomics approach. These results provide a new idea for developing metabolic regulation to address KA resistance in Xoo.

Exogenous Alanine Reverses the Bacterial Resistance to Zhongshengmycin with the Promotion of the P Cycle in Xanthomonas oryzae

Microbial antibiotic resistance has become a worldwide concern, as it weakens the efficiency of the control of pathogenic microbes in both the fields of medicine and plant protection. A better understanding of antibiotic resistance mechanisms is helpful for the development of efficient approaches to settle this issue. In the present study, GC-MS-based metabolomic analysis was applied to explore the mechanisms of Zhongshengmycin (ZSM) resistance in Xanthomonas oryzae (Xoo), a bacterium that causes serious disease in rice. Our results show that the decline in the pyruvate cycle (the P cycle) was a feature for ZSM resistance in the metabolome of ZSM-resistant strain (Xoo-ZSM), which was further demonstrated as the expression level of genes involved in the P cycle and two enzyme activities were reduced. On the other hand, alanine was considered a crucial metabolite as it was significantly decreased in Xoo-ZSM. Exogenous alanine promoted the P cycle and enhanced the ZSM-mediated killing efficiency in Xoo-ZSM. Our study highlights that the depressed P cycle is a feature in Xoo-ZSM for the first time. Additionally, exogenous alanine is a candidate enhancer and can be applied with ZSM to improve the antibiotic-mediated killing efficiency in the control of infection caused by Xoo.

The emerging role of jasmonate in the control of flowering time

Plants dynamically synchronize their flowering time with changes in the internal and external environments through a variety of signaling pathways to maximize fitness. In the last two decades, the major pathways associated with flowering, including the photoperiod, vernalization, age, autonomous, gibberellin, and ambient temperature pathways, have been extensively analyzed. In recent years, an increasing number of signals, such as sugar, thermosensory, stress, and certain hormones, have been shown to be involved in fine-tuning flowering time. Among these signals, the jasmonate signaling pathway has a function in the determination of flowering time that has not been systematically summarized. In this review, we present an overview of current knowledge of jasmonate control of flowering and discuss jasmonate crosstalk with other signals (such as gibberellin, defense, and touch) during floral transition.

OsVQ1 links rice immunity and flowering via interaction with a mitogen-activated protein kinase OsMPK6

Knocking out OsVQ1 in rice released OsMPK6 for activation and in turn promoted H₂O₂ accumulation, which repressed the expression of flowering-promoting genes, thus delaying rice flowering but enhancing disease resistance. The valine-glutamine (VQ) protein family, which contains the conserved motif FxxxVQxLTG ("x" represents any amino acid), plays a crucial role in plant growth and immunity along with mitogen-activated protein kinase (MAPK) cascades. However, only a few rice VQ proteins have been functionally characterized, and the roles of the MAPK-VQ module in rice biological processes are not fully understood. Here, we investigated the role of OsVQ1 in rice disease resistance and the control of flowering time. The OsVQ1-knock out (KO) mutants exhibited increased resistance to Xanthomonas oryzae pathovars, accumulated high levels of hydrogen peroxide (H₂O₂), and showed a late flowering phenotype under natural long-day conditions, while the OsVQ1-overexpressing plants showed phenotypes similar to that of the wild type. Further studies revealed that OsVQ1 physically interacted with and inhibited OsMPK6 activity. In addition, OsVQ1 expression was downregulated by the pathogen-induced OsMPKK10.2-OsMPK6-OsWRKY45 cascade, suggesting a feedback loop between OsVQ1 and OsMPK6. Moreover, the OsVQ1-KO/osmpk6 double-mutant exhibited increased susceptibility to X. oryzae infection and showed an early flowering phenotype, which may partially be attributed to the reduced accumulation of H₂O₂ and the consequent up-expression of flowering-promoting genes. These results suggested that the OsVQ1-OsMPK6 module was involved in rice immunity and flowering.

Elevation of Fatty Acid Biosynthesis Metabolism Contributes to Zhongshengmycin Resistance in Xanthomonas oryzae

Xanthomonas oryzae severely impacts the yield and quality of rice. Antibiotics are the most common control measure for this pathogen; however, the overuse of antibiotics in past decades has caused bacterial resistance to these antibiotics. The agricultural context is of particular importance as antibiotic-resistant bacteria are prevalent, but the resistance mechanism largely remains unexplored. Herein, using gas chromatography-mass spectrometry (GC-MS), we demonstrated that zhongshengmycin-resistant X. oryzae (Xoo-Rzs) and zhongshengmycin-sensitive X. oryzae (Xoo-S) have distinct metabolic profiles. We found that the resistance to zhongshengmycin (ZS) in X. oryzae is related to increased fatty acid biosynthesis. This was demonstrated by measuring the Acetyl-CoA carboxylase (ACC) activity, the expression levels of enzyme genes involved in the fatty acid biosynthesis and degradation pathways, and adding exogenous materials, i.e., triclosan and fatty acids. Our work provides a basis for the subsequent control of the production of antibiotic-resistant strains of X. oryzae and the development of coping strategies.

Photostable 1-Trifluoromethyl Cinnamyl Alcohol Derivatives Designed as Potential Fungicides and Bactericides

In the current work, a series of 1-trifluoromethyl cinnamyl alcohol derivatives were designed and synthesized and their antifungal activities were evaluated. The bioassay result showed that most compounds exhibited excellent antifungal activity in vitro at 10 μg mL^-1. Next, photostable and easily synthesized compound 2 with broad-spectrum antifungal activity in vitro was selected as a potential candidate to evaluate its antibacterial and antifungal activities. The EC₅₀ values of compound 2 against eight fungal plant pathogens in vitro ranged from 3.806 to 17.981 μg mL^-1; at the same time, compound 2 could effectively control Podosphaera xanthii, Odium heveae Steinm, Puccinia striiformis West, and Puccinia sorghi in pot experiments. In addition, compound 2 exhibited excellent antibacterial activities in vitro and in vivo against Xanthomonas oryzae pv. oryzae. Furthermore, the absorption and translocation of compound 2 in wheat plants were determined by the high-performance liquid chromatography method. The result showed that compound 2 could be translocated acropetally as well as basipetally in wheat plants. Finally, it was found that compound 2 had no cross-resistance with carbendazim, azoxystrobin, and boscalid.