Molecular cloning and functional characterization of NtWRKY41a in the biosynthesis of phenylpropanoids in Nicotiana tabacum

Response of bacterial community metabolites to bacterial wilt caused by Ralstonia solanacearum: a multi-omics analysis

The soil microbial community plays a critical role in promoting robust plant growth and serves as an effective defence mechanism against root pathogens. Current research has focused on unravelling the compositions and functions of diverse microbial taxa in plant rhizospheres invaded by Ralstonia solanacearum, however, the specific mechanisms by which key microbial groups with distinct functions exert their effects remain unclear. In this study, we employed a combination of amplicon sequencing and metabolomics analysis to investigate the principal metabolic mechanisms of key microbial taxa in plant rhizosphere soil. Compared to the healthy tobacco rhizosphere samples, the bacterial diversity and co-occurrence network of the diseased tobacco rhizosphere soil were significantly reduced. Notably, certain genera, including Gaiella, Rhodoplanes, and MND1 (Nitrosomonadaceae), were found to be significantly more abundant in the rhizosphere of healthy plants than in that of diseased plants. Eight environmental factors, including exchangeable magnesium, available phosphorus, and pH, were found to be crucial factors influencing the composition of the microbial community. Ralstonia displayed negative correlations with pH, exchangeable magnesium, and cation exchange flux, but showed a positive correlation with available iron. Furthermore, metabolomic analysis revealed that the metabolic pathways related to the synthesis of various antibacterial compounds were significantly enriched in the healthy group. The correlation analysis results indicate that the bacterial genera Polycyclovorans, Lysobacter, Pseudomonas, and Nitrosospira may participate in the synthesis of antibacterial compounds. Collectively, our findings contribute to a more in-depth understanding of disease resistance mechanisms within healthy microbial communities and provide a theoretical foundation for the development of targeted strategies using beneficial microorganisms to suppress disease occurrence.

The transcription factor NtERF13a enhances abiotic stress tolerance and phenylpropanoid compounds biosynthesis in tobacco

The AP2/ERF (APETALA2/ETHYLENE RESPONSE FACTOR) transcription factors play multiple roles in modulating the biosynthesis of diverse specialized metabolites in response to various environmental stresses. ERF13 has been shown to participate in plant resistance to biotic stress as well as in repressing the synthesis of fatty acid. However, its full roles in regulating plant metabolism and stress resistance still remains to be further studied. In this study, we identified two NtERF genes from N. tabacum genome that belong to Ⅸa subgroup of ERF family. Over-expression and knock-out of NtERF13a showed that NtERF13a could enhance plant resistance to salt and drought stresses, as well as promoted the biosynthesis of chlorogenic acid (CGA), flavonoids, and lignin in tobacco. Transcriptome analysis between WT and NtERF13a-OE plants revealed 6 differentially expressed genes (DEGs) that encode enzymes catalyzing the key steps of phenylpropanoid pathway. Chromatin immunoprecipitation, Y1H, and Dual-Luc assays further clarified that NtERF13a could directly bind to the fragments containing GCC box or DRE element in the promoters of NtHCT, NtF3'H, and NtANS genes to induce the transcription of these genes. Knock-out of NtHCT, NtF3'H, or NtANS in the NtERF13a-OE background significantly repressed the increase of phenylpropanoid compound contents caused by over-expression of NtERF13a, indicating that the promotion of NtERF13a on the phenylpropanoid compound contents depends on the activity of NtHCT, NtF3'H, and NtANS. Our study demonstrated new roles of NtERF13a in promoting plant resistance to abiotic stresses, and provided a promising target for modulating the biosynthesis of phenylpropanoid compounds in tobacco.

The herbaceous peony transcription factor WRKY41a promotes secondary cell wall thickening to enhance stem strength

Stem bending or lodging caused by insufficient stem strength is an important limiting factor for plant production. Secondary cell walls play a crucial role in plant stem strength, but whether WRKY transcription factors can positively modulate secondary cell wall thickness are remain unknown. Here, we characterized a WRKY transcription factor PlWRKY41a from herbaceous peony (Paeonia lactiflora), which was highly expressed in stems. PlWRKY41a functioned as a nucleus-localized transcriptional activator and enhanced stem strength by positively modulating secondary cell wall thickness. Moreover, PlWRKY41a bound to the promoter of the XYLOGLUCAN ENDOTRANSGLUCOSYLASE/HYDROLASE4 (PlXTH4) and activated the expression of PlXTH4. PlXTH4-overexpressing tobacco (Nicotiana tabacum) had thicker secondary cell walls, resulting in enhanced stem strength, while PlXTH4-silenced P. lactiflora had thinner secondary cell walls, showing decreased stem strength. Additionally, PlWRKY41a directly interacted with PlMYB43 to form a protein complex, and their interaction induced the expression of PlXTH4. These data support that the PlMYB43-PlWRKY41a protein complex can directly activate the expression of PlXTH4 to enhance stem strength by modulating secondary cell wall thickness in P. lactiflora. The results will enhance our understanding of the formation mechanism of stem strength and provide a candidate gene to improve stem straightness in plants.

Transcription factor NtWRKY33a modulates the biosynthesis of polyphenols by targeting NtMYB4 and NtHCT genes in tobacco

There are abundant polyphenols in tobacco leaves mainly including chlorogenic acid (CGA), rutin, and scopoletin, which not only influence plant growth, development, and environmental adaptation, but also have a great impact on the industrial utilization of tobacco leaves. Few transcription factors regulating the biosynthesis of polyphenols have been identified in tobacco so far. In this study, two NtWRKY33 genes were identified from N. tabacum genome. NtWRKY33a showed higher transcriptional activity than NtWRKY33b, and encoded a nuclear localized protein. Overexpression and knock-out of NtWRKY33a gene revealed that NtWRKY33a inhibited the accumulation of rutin, scopoletin, and total polyphenols, but meanwhile promoted the biosynthesis of CGA. Chromatin immunoprecipitation and Dual-Luc assays indicated that NtWRKY33a could directly bind to the promoters of NtMYB4 and NtHCT, and thus induced the transcription of these two genes. The contents of polyphenols in ntwrky33a, ntmy4, and ntwrky33a/ntmyb4 mutants further confirmed that the repression of NtWRKY33a on the biosynthesis of rutin, scopoletin, and total polyphenols depends on the activity of NtMYB4. Moreover, the promotion of NtHCT by NtWRKY33a modulates the distribution of metabolism flux into the synthesis of CGA. Ectopic expression of NtWRKY33a inhibit the expression of NtSAUR14, NtSAUR59, NtSAUR66, NtIAA4, NtIAA17, and NtIAA19 genes, indicating that NtWRKY33a might be involved in the regulation of plant auxin response. Our study revealed new functions of NtWRKY33a in regulating the synthesis of polyphenols, and provided a promising target for manipulating polyphenols contents in tobacco.

Overexpression of Myrothamnus flabellifolia MfWRKY41 confers drought and salinity tolerance by enhancing root system and antioxidation ability in Arabidopsis

Myrothamnus flabellifolia is the only woody resurrection plant discovered so far and could recover from extreme desiccation condition. However, few genes related to its strong drought tolerance have been characterized, and the underlying molecular mechanisms remains mysterious. Members of WRKY transcription factor family are effective in regulating abiotic stress responses or tolerance in various plants. An early dehydration-induced gene encoding a WRKY transcription factor namely MfWRKY41 was isolated from M. flabellifolia, which is homologous to AtWRKY41 of Arabidopsis. It contains a typical WRKY domain and zinc finger motif, and is located in the nucleus. Comparing to wild type, the four transgenic lines overexpressing MfWRKY41 showed better growth performance under drought and salt treatments, and exhibited higher chlorophyll content, lower water loss rate and stomatal aperture and better osmotic adjustment capacity. These results indicated that MfWRKY41 of M. flabellifolia positively regulates drought as well as salinity responses. Interestingly, the root system architecture, including lateral root number and primary root length, of the transgenic lines was enhanced by MfWRKY41 under both normal and stressful conditions, and the antioxidation ability was also significantly improved. Therefore, MfWRKY41 may have potential application values in genetic improvement of plant tolerance to drought and salinity stresses. The molecular mechanism involving in the regulatory roles of MfWRKY41 is worthy being explored in the future.