Myelocytomatosis (MYC) transcription factors are crucial mediators of the jasmonate signaling pathway, which mediates the growth and developmental processes of plants. However, the function of MYC genes in tomato, Solanum lycopersicum (SlMYC), remains poorly understood. In this study, we have identified 14 non-redundant SlMYC genes across the genome of tomatoes. Six of the twelve chromosomes included these genes, and four syntenic pairs of SlMYC were identified. According to the results of phylogenetic analysis, 14 SlMYC genes were clustered into classes I, II, III, and IV, and their functional domains were predicted. The SlMYC upstream promoter region contained a variety of light-, stress-, and hormone-response regulatory elements. The expression of the 14 SlMYC genes differed significantly across organs. SlMYCs primarily showed an upregulation trend after methyl jasmonate (MeJA) treatment. In contrast, after treatment with sodium chloride (NaCl), SlMYCs showed a trend of downregulation. However, there were differences in the expression patterns of SlMYCs after mannitol treatment. Using clustered regularly interspaced short palindromic repeats/Cas 9 (CRISPR/Cas 9) technology, the loss-of-function of SlMYC1 (slmyc1) was obtained. The slmyc1 tomato plants demonstrated reduced resistance to NaCl and mannitol stress compared to wild-type plants due to their shorter root length and higher reactive oxygen species (ROS) content. In brief, this study provides valuable information about the taxonomy of the SlMYC genes in tomato. It establishes a foundation for future research on the mechanism by which SlMYC influences plant development and stress response.

Nitric oxide (NO) is a redox-dependent signaling molecule that plays a crucial role in regulating a wide range of biological processes in plants. It functions by post-translationally modifying proteins, primarily through S-nitrosation. Thioredoxin (Trx), a small and ubiquitous protein with multifunctional properties, plays a pivotal role in the antioxidant defense system. However, the regulatory mechanism governing the response of tomato Trxh (SlTrxh) to excessive nitrate stress remains unknown. In this study, overexpression or silencing of SlTrxh in tomato led to increased or decreased nitrate stress tolerance, respectively. The overexpression of SlTrxh resulted in a reduction in levels of reactive oxygen species (ROS) and an increase in S-nitrosothiol (SNO) contents; conversely, silencing SlTrxh exhibited the opposite trend. The level of S-nitrosated SlTrxh was increased and decreased in SlTrxh overexpression and RNAi plants after nitrate treatment, respectively. SlTrxh was found to be susceptible to S-nitrosation both in vivo and in vitro, with Cysteine 54 potentially being the key site for S-nitrosation. Protein interaction assays revealed that SlTrxh physically interacts with SlGrx9, and this interaction is strengthened by S-nitrosation. Moreover, a combination of yeast one-hybrid (Y1H), electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR), and transient expression assays confirmed the direct binding of SlMYB86 to the SlTrxh promoter, thereby enhancing its expression. SlMYB86 is located in the nucleus and SlMYB86 overexpressed and knockout tomato lines showed enhanced and decreased nitrate stress tolerance, respectively. Our findings indicate that SlTrxh functions downstream of SlMYB86 and highlight the potential significance of S-nitrosation of SlTrxh in modulating its function under nitrate stress.

Nitric oxide (NO) modulates plant response by post-translationally modifying proteins, mainly through S-nitrosylation. Ascorbate peroxidase (APX) in the ascorbate-glutathione (AsA-GSH) cycle participates in the removal of hydrogen peroxide (H₂O₂). However, the relationship between S-nitrosylation and the role of tomato APX (SlAPX) under nitrate stress is still unclear. In this study, the enzyme activity, mRNA expression, and S-nitrosylation level of SlAPX were significantly increased in tomato roots after nitrate treatment. SlAPX protein could be S-nitrosylated by S-nitrosoglutathione in vitro, and APX activity was significantly increased after S-nitrosylation. The SlAPX overexpressed tobacco plants grew better than the wild type (WT) plants under nitrate stress. Meanwhile, the transgenic plants showed lower reactive oxygen species and malondialdehyde content, higher APX, monodehydroascorbate reductase, glutathione reductase activities, ascorbic acid/dehydroascorbic acid, and reduced glutathione/oxidized glutathione ratio, proline, and soluble sugar contents than those in the WT plants under nitrate treatment. Moreover, overexpressed transgenic seeds showed higher tolerance to methyl viologen induced oxidative stress compared with the WT. The NO accumulation and S-nitrosylation APX level were higher in transgenic plants than in WT plants after nitrate stress treatment. Our results provide novel insights into the mechanism of SlAPX modulation excess nitrate stress tolerance involving the S-nitrosylation modification.

Aconitum vilmorinianum (A. vilmorinianum) is an important medicinal plant in the Aconitum genus that is known for its diterpenoid alkaloids, which exhibit significant pharmacological activity and toxicity, thus making it valuable for both medicinal use and as a biopesticide. Although the biosynthesis of terpenoids is well characterized, the potential gene regulatory role of microRNAs (miRNAs) in terpenoid biosynthesis in A. vilmorinianum remains unclear, and further research is needed to explore this aspect in this species. In this study, miRNA sequencing was conducted to analyze the miRNA population and its targets in A. vilmorinianum. A total of 22,435 small RNAs were identified across the nine samples. Through miRNA target gene association analysis, 356 target genes from 54 known miRNAs and 977 target genes from 151 novel miRNAs were identified. Target identification revealed that miR6300 targets the hydroxymethylglutaryl-CoA reductase (HMGR) gene, which is involved in the formation of the terpenoid backbone and regulates the synthesis of diterpenoid alkaloids. Additionally, preliminary findings suggest that miR4995 and miR5021 may be involved in the regulation of terpenoid biosynthesis, although further biochemical analysis is needed to confirm these potential roles. This study provides a foundational understanding of the molecular mechanisms by which miRNAs regulate terpenoid biosynthesis in A. vilmorinianum and offers scientific evidence for further research on the biosynthesis of diterpenoid alkaloids in this medicinal plant.