Exogenous Application of Harpin Protein Hpa1 onto Pinellia ternata Induces Systemic Resistance Against Tobacco Mosaic Virus.

The harpin protein Hpa1 has various beneficial effects in plants, such as promoting plant growth and inducing pathogen resistance. Our previous study found that Hpa1 could significantly alleviate the mosaic symptoms of tobacco mosaic virus (TMV) in Pinellia ternata, indicating that Hpa1 can effectively stimulate resistance. Here, the potential mechanism of disease resistance and field applicability of Hpa1 against TMV in P. ternata were further investigated. The results showed that 15 µg ml-1 Hpa1 had stronger antiviral activity than the control, and its protective effect was better than its curative effect. Furthermore, Hpa1 could significantly induce an increase in defense-related enzyme activity, including polyphenol oxidase, peroxidase, catalase, and superoxide dismutase, as well as increase the expression of disease resistance-related genes (PR1, PR3, PR5, and PDF1.2). Concurrently, Hpa1 significantly increased the content of some disease resistance-related substances, including hydrogen peroxide, phenolics, and callose, whereas the content of malondialdehyde was reduced. In addition, field application analysis demonstrated that Hpa1 could effectively elicit a defense response against TMV in P. ternata. Our findings propose a mechanism by which Hpa1 can prevent TMV infection in Pinellia by inducing systemic resistance, thereby providing an environmentally friendly approach for the use of Hpa1 in large-scale applications to improve TMV resistance in Pinellia.

Metabolomic and Transcriptomic Profiling Uncover the Underlying Mechanism of Color Differentiation in Scutellaria baicalensis Georgi. Flowers.

Scutellaria baicalensis Georgi. (Chinese skullcap or Huang-qin) is an extremely crucial medicinal plant in the Labiate family, and the color of its flowers naturally appears purple. However, during the long-term cultivation of S. baicalensis, very few plants of S. baicalensis also present white and purple-red flower colors under the same ecological conditions. However, the complex metabolic and transcriptional networks underlying color formation in white, purple-red, and purple flowers of S. baicalensis remain largely unclarified. To gain an insight into this issue, we conducted transcriptome and metabolomic profiling to elucidate the anthocyanin synthesis metabolic pathway in the flowers of S. baicalensis, and to identify the differentially expressed candidate genes potentially involved in the biosynthesis of anthocyanins. The results showed that 15 anthocyanins were identified, among which cyanidin 3-rutinoside and delphin chloride were the primary anthocyanins, and accumulation was significantly related to the flower color changes of S. baicalensis. Furthermore, the down-regulation of SbDFR (Sb02g31040) reduced the anthocyanin levels in the flowers of S. baicalensis. The differential expression of the Sb3GT (Sb07g04780 and Sb01g72290) gene in purple and purple-red flowers affected anthocyanin accumulation, suggesting that anthocyanin levels were closely associated with the expression of SbDFR and Sb3GT, which play important roles in regulating the anthocyanin biosynthesis process of S. baicalensis flowers. Transcriptomic analysis revealed that transcription factors WRKY, bHLH, and NAC were also highly correlated with anthocyanin accumulation, especially for NAC35, which positively regulated SbDFR (Sb02g31040) gene expression and modulated anthocyanin biosynthesis in flower color variation of S. baicalensis. Overall, this study presents the first experimental evidence for the metabolomic and transcriptomic profiles of S. baicalensis in response to flower coloration, which provides a foundation for dynamic metabolic engineering and plant breeding, and to understand floral evolution in S. baicalensis plants.

[Cloning and temporal-spatial expression analysis of dfr gene from Scutellaria baicalensis with different colors].

Dihydroflavanol-4-reductase (Dfr) is a key enzyme that regulates the synthesis of anthocyanin and proanthocyanidin in the flavonoid biosynthesis pathway. To investigate the difference of dfr gene in Scutellaria baicalensis Georgi with different colors in the same ecological environment, three complete full-length sequences of dfr gene were cloned from the cDNA of S. baicalensis with white, purple-red and purple colors using homologous cloning and RACE techniques. The three genes were named Sbdfr1, Sbdfr2 and Sbdfr3, respectively, and their corresponding structures were analyzed. The results showed that all three Dfr proteins have highly conserved NADPH binding sites and substrate-specific binding sites. Phylogenetic analysis showed that they are closely related to that of the known S. viscidula (ACV49882.1). Analysis of key structural domains and 3D models revealed differences in the catalytically active regions on the surface of all three Dfr proteins, and their unique structural characteristics may provide favorable conditions for studying the substrate specificity of different Dfr proteins. qRT-PCR analysis shows that dfr was expressed at different level in all tissues except the roots of S. baicalensis in full-bloom. During floral development, the expression level of dfr in white and purple-flowered Scutellaria showed an overall upward trend. In purple-red-flowered Scutellaria, the expression first slowly increased, followed by a decrease, and then rapidly increased to the maximum. This research provides a theoretical basis for further exploring the mechanism and function of Dfr substrate selectivity, and are of great scientific value for elucidating the molecular mechanism of floral color variation in S. baicalensis.