Capsicum frutescens, one of the domesticated species of pepper grown worldwide, is thought to be highly advantageous due to its strong resistance against plant pathogenesis, high productivity, and intense aroma. However, a shortage of molecular markers limits the efficiency and accuracy of genetic breeding for pepper. With the newly developed next-generation sequencing technology, genome sequences of C. frutescens can be generated, which are now available for identifying SSR markers via data mining. In this study, a total of 278,425 SSRs were detected from the pepper genome using MISA software. It was observed that trinucleotides were the dominant repeat motif. This was followed by dinucleotides, tetranucleotides, pentanucleotides, and the hexanucleotides repeat types. (AT)n (TTG)n (AAAT)n (AAATA)n (TATAGA)n is known to be the most common repeat motifs corresponding to dinucleotide to hexanucleotide repeats, respectively. In addition, a total of 240 SSR primers evenly distributed over all 12 chromosomes were designed and screened against 8 C. frutescens cultivars. Of these, 33 SSR markers that have high polymorphism, have been scrutinized for 147 accessions from 25 countries. The dendrogram constructed clustered these accessions into seven major groups. The groups were found to be consistent with their origins. The results obtained in this study provided resources of SSR molecular markers and insight into genetic diversity of the C. frutescens.

Melatonin plays an important role in plant growth, development, and environmental stress. In this study, a systematic analysis of tomato tryptophan decarboxylase (SlTrpDC), which is the first enzyme of melatonin biosynthesis, was conducted by integrating structural features, phylogenetic relationships, an exon/intron feature, and a divergent expression profile. The results determined that the tomato genome encoded five members (SlTrpDC1-SlTrpDC5). The phylogenetic relationships indicated that gene expansion was proposed as the major mode of evolution of the TrpDC genes from the different plant algae species to the higher plants species. The analyses of the exon/intron configurations revealed that the intron loss events occurred during the structural evolution of the TrpDCs in plants. Additionally, the RNA-seq and qRT-PCR analysis revealed that the expression of the SlTrpDC3 was high in all of the tested tissues, while the SlTrpDC4 and SlTrpDC5 were not expressed. The expression patterns of the remaining two (SlTrpDC1 and SlTrpDC2) were tissue-specific, which indicated that these genes may play important roles within the different tissues. No expression difference was observed in the tomato plants in response to the biotic stresses. This study will expand the current knowledge of the roles of the TrpDC genes in tomato growth and development.

Fungal wilt and root rot diseases affecting tomato have become prevalent in China in recent years and have caused considerable damage. In 2016 to 2018, symptoms of putative wilt and root rot diseases were observed in several locations in tomato cultivars with resistance to Fusarium oxysporum f. sp. lycopersici races 1 and 2. The objective of this study was to identify the causative agents of wilt and root rot of tomato in China and provide a basis for disease prevention and resistance breeding programs. Based on DNA sequence analyses of the internal transcribed spacer (ITS) region, 91 isolates from the roots of tomato plants showing symptoms of wilt and root rot were identified, including F. oxysporum (64 isolates), Fusarium solani (11 isolates), Fusarium proliferatum (2 isolates), Fusarium graminearum (2 isolates), Fusarium equiseti (1 isolate), Pythium aphanidermatum (6 isolates), Ascomycota sp. (2 isolates), and Plectosphaerella cucumerina (3 isolates). F. oxysporum accounted for 70.33% of the isolates obtained. In this case, using PCR-based methods for differentiation of F. oxysporum, we identified several formae speciales and races of F. oxysporum: 7 isolates were identified as F. oxysporum f. sp. lycopersici race 1, 2 isolates as F. oxysporum f. sp. lycopersici race 2, 35 isolates as F. oxysporum f. sp. lycopersici race 3, and 13 isolates as F. oxysporum f. sp. radicis-lycopersici. Pathogenicity tests revealed 55 isolates of tomato wilt and root rot pathogens to be virulent. This study demonstrated that F. oxysporum f. sp. lycopersici race 3 was the most widespread and highly virulent race among these tomato pathogens in China, followed by F. oxysporum f. sp. radicis-lycopersici. Therefore, the development of resistant varieties of tomato against F. oxysporum f. sp. lycopersici race 3 and F. oxysporum f. sp. radicis-lycopersici would aid efforts to develop effective disease management strategies.

The invertase gene family in plants is composed of two subfamilies of enzymes, namely, acid- and neutral/alkaline invertases (cytosolic invertase, CIN). Both can irreversibly cleave sucrose into fructose and glucose, which are thought to play key roles in carbon metabolism and plant growth. CINs are widely found in plants, but little is reported about this family. In this paper, a comparative genomic approach was used to analyze the CIN gene family in Solanum, including Solanum tuberosum, Solanum lycopersicum, Solanum pennellii, Solanum pimpinellifolium, and Solanum melongena. A total of 40 CINs were identified in five Solanum plants, and sequence features, phylogenetic relationships, motif compositions, gene structure, collinear relationship, and expression profile were further analyzed. Sequence analysis revealed a remarkable conservation of CINs in sequence length, gene number, and molecular weight. The previously verified four amino acid residues (D188, E414, Arg430, and Ser547) were also observed in 39 out of 40 CINs in our study, showing to be deeply conserved. The CIN gene family could be distinguished into groups α and β, and α is further subdivided into subgroups α1 and α2 in our phylogenetic tree. More remarkably, each species has an average of four CINs in the α and β groups. Marked interspecies conservation and collinearity of CINs were also further revealed by chromosome mapping. Exon–intron configuration and conserved motifs were consistent in each of these α and β groups on the basis of in silico analysis. Expression analysis indicated that CINs were constitutively expressed and share similar expression profiles in all tested samples from S. tuberosum and S. lycopersicum. In addition, in CIN genes of the tomato and potato in response to abiotic and biotic stresses, phytohormones also performed. Overall, CINs in Solanum were encoded by a small and highly conserved gene family, possibly reflecting structural and functional conservation in Solanum. These results lay the foundation for further expounding the functional characterization of CIN genes and are also significant for understanding the evolutionary profiling of the CIN gene family in Solanum.

Histone methylation plays important roles in plant development and adaptation to multiple stresses. SET domain group (SDG) proteins are identified as plant histone lysine methyltransferases in Arabidopsis and other crops. However, the SDG gene family and its functional roles in tomato remain unknown. In this research, 48 tomato SDG (SlSDG) gene family members were identified, and their chromosomal locations and conserved motifs were determined. According to phylogenetic analysis, the SlSDGs are divided into seven groups, which is consistent with Arabidopsis and rice. Promoter analysis indicated that the SlSDGs may be associated with biotic and abiotic stress responses. The expression pattern of SlSDGs illustrates that heat and cold stress significantly influence the transcript abundance of SDG14/19/21/23/48. The results of a VIGS assay showed that silencing SlSDG19 and SlSDG48 decreases tomato heat tolerance, while silencing SlSDG14 improves the heat tolerance of tomato plants. The analysis of downstream regulating genes indicated that heat shock proteins (HSPs), especially HSP70 and HSP90, act as critical effectors. Similarly, the experimental assay and expression analysis suggest that SDG21 and SDG23 positively and negatively regulate tomato cold tolerance through the CBF-COR pathway, respectively. These findings clarify the function of tomato SDG proteins and provide insight for the genetic improvement of tomato for temperature stress tolerance.

Seed germination is the first critical transition in the plant life cycle, strongly influencing seedling establishment, crop uniformity, and subsequent productivity. However, the genetic basis of seed germination in tomato remains incompletely understood. Here, we performed a genome-wide association study (GWAS) using 319 diverse tomato accessions to identify new loci and candidate genes associated with seed germination. Five significant variants were detected across the genome. Among them, SNP_59508294 on chromosome 3 was consistently associated with the seed germination index (SGI), and accessions carrying the GG haplotype exhibited a significantly higher SGI than those carrying the TT haplotype. Seven α-expansin (EXPA) genes were located within or near the associated interval. Integration of transcriptomic data from contrasting accessions and expression profiles across tomato tissues showed SlEXPA10 to be the most plausible candidate gene. The InDels in the SlEXPA10 promoter were highly associated with its low expression level in low SGI varieties. CRISPR/Cas9-mediated disruption of SlEXPA10 significantly reduced the rate and speed of seed germination relative to the wild type. Collectively, these results identify SlEXPA10 as a positive regulator of tomato seed germination and provide a candidate locus for improving seed vigor and emergence uniformity.