Flavones, one of the largest classes of flavonoids in plants, have a variety of bioactivities and participate in the resistance response of plants to biotic and abiotic stresses. However, flavone synthase (FNS), the key enzyme for flavone biosynthesis, has not yet been characterized in mulberry. In this study, we report that the leaves of certain mulberry cultivars, namely BJ7, PS2, and G14, are rich in flavones. We identified a Fe²⁺/2-oxoglutarate-dependent dioxygenase from Morus notabilis (MnFNSI) that shows the typical enzymatic activity of a FNSI-type enzyme, and directly converts eriodictyol and naringenin into their corresponding flavones. Overexpression of MnFNSI in tobacco increased the flavones contents in leaves and enhanced the tolerance of tobacco to ultraviolet-B (UV-B) stress. We found that mulberry cultivars with higher flavones contents exhibit less UV-B induced damage after a UV-B treatment. Accordingly, our findings demonstrate that MnFNSI, a FNSI-type enzyme, is involved in the biosynthesis of flavones, which provide protection against UV-B radiation. These results lay the foundation for obtaining mulberry germplasm resources that are more tolerant to UV-B stress and richer in their nutritional value.

Type III polyketide synthases are important for the biosynthesis of flavonoids and various plant polyphenols. Mulberry plants have abundant polyphenols, but very little is known about the mulberry type III polyketide synthase genes. An analysis of these genes may provide new targets for genetic improvement to increase relevant secondary metabolites and enhance the plant tolerance to biotic and abiotic stresses. Eighteen genes encoding type III polyketide synthases were identified, including six chalcone synthases (CHS), ten stilbene synthases (STS), and two polyketide synthases (PKS). Functional characterization of four genes representing most of the MnCHS and MnSTS genes by coexpression with 4-Coumaroyl-CoA ligase in Escherichia coli indicated that their products were able to catalyze p-coumaroyl-CoA and malonyl-CoA to generate naringenin and resveratrol, respectively. Microsynteny analysis within mulberry indicated that segmental and tandem duplication events contributed to the expansion of the MnCHS family, while tandem duplications were mainly responsible for the generation of the MnSTS genes. Combining the evolution and expression analysis results of the mulberry type III PKS genes indicated that MnCHS and MnSTS genes evolved mainly under purifying selection to maintain their original functions, but transcriptional subfunctionalization occurred during long-term species evolution. Moreover, mulberry leaves can rapidly accumulated oxyresveratrol after UV-C irradiation, suggesting that resveratrol was converted to oxyresveratrol. Characterizing the functions and evolution of mulberry type III PKS genes is crucial for advancing our understanding of these genes and providing the basis for further studies on the biosynthesis of relevant secondary metabolites in mulberry plants.

Tartary buckwheat (Fagopyrum tataricum Gaertn.) is an important pseudocereal crop with excellent edible, nutritional and medicinal values. However, the yield of Tartary buckwheat (TB) is very low due to old-fashioned cultivation techniques, particularly unreasonable application of nitrogen fertilizer. To improve the understanding on the theories of nitrogen use in TB, the effects of nitrogen application on growth, as well as chemical properties and microbial community of rhizosphere soil were investigated in this study. Nitrogen application could promote the plant height, stem diameter, nitrogen accumulation and yield of TB. The relative abundance and diversity of bacteria and fungi in the rhizosphere soil of TB were improved by nitrogen fertilizer. Nitrogen application increased the abundance of beneficial bacteria such as Lysobacter and Sphingomonas in rhizosphere soil, and decreased the abundance of pathogenic fungi such as Fusarium and Plectosphaerella. The results indicated that nitrogen application changed the distribution of microbial communities in TB rhizosphere soil. Furthermore, the specific enriched or depleted microorganisms in the rhizosphere soil of four TB varieties were analyzed at OTU level. 87 specific nitrogen-responsive genes with sequence variation were identified in four varieties by integrating genomic re-sequencing and transcriptome analysis, and these genes may involve in the recruitment of specific rhizosphere microorganisms in different TB varieties. This study provided new insights into the effects of nitrogen application on TB growth and rhizosphere microbial community, and improved the understanding on the mechanisms of TB root–microbe interactions.

Bacterial wilt caused by Ralstonia solanacearum is one of the most severe plant diseases all over the world. Currently, many scientists are using SynCom (s

Tobacco (Nicotiana tabacum L.) is an important economic crop whose production is severely threatened by black shank and bacterial wilt, caused by Phytophthora nicotianae and Ralstonia solanacearum, respectively. Kunitz-type trypsin inhibitors (KTIs), as key components of plant innate immunity, play crucial roles in defense against biotic stress in various plant species. In this study, we systematically identified 22 KTI genes in N. tabacum genome and conducted a comprehensive analysis of their phylogenetic relationships, structural features, and expression patterns. By comparing transcriptomic profiles under colonization by the beneficial endophyte Piriformospora indica versus infection by the pathogenic fungus P. nicotianae, we identified a pathogen-specifically induced gene, NtKTI9. This gene was significantly activated upon infection by both P. nicotianae and R. solanacearum. Functional studies revealed that the NtKTI9 protein possesses trypsin inhibitory activity and exhibits antimicrobial capacity in vitro. Overexpression of NtKTI9 in tobacco activated the phenylpropanoid metabolism pathway, which promoted lignin deposition in the roots and enhanced plant resistance against both pathogens. Further mechanistic analysis showed that the expression of NtKTI9 is induced by jasmonic acid (JA) signaling, while its overexpression, in turn, strengthens JA signaling by regulating α-linolenic acid metabolism, suggesting a potential positive feedback loop that synergistically amplify plant immune responses. Based on gain-of-function evidence, this study indicates that NtKTI9 positively contributes to immune regulation in tobacco, which not only deepens our understanding of how KTI genes participate in plant immunity but also provides a novel candidate gene and theoretical foundation for molecular breeding of disease-resistant tobacco.