Lijun Song

Eggplant confers prominent nutritional benefits owing to its abundant phenolic compounds and antioxidants. Exogenous melatonin at 100 μmol L-1 sustains postharvest external quality of eggplant fruit via enhancement of antioxidative activity. Herein, effects of 100 μmol L-1 melatonin on nutritional quality and storability of cold-stored eggplant fruits were further investigated during 30 days of storage at 7 °C. Melatonin significantly maintained the fruit commercially acceptable rate, weight, firmness, and density of cold-stored eggplant, while extending its shelf-life by approximately 15 d. Melatonin attenuated the starch degradation by enhancing activity of ADP-glucose pyrophosphorylase (ADGPase) while reducing the activities of α- and β-amylases, these effects were attributed to the upregulation of ADGPase encoding genes AGPL, AGPS, and as well as the downregulation of α- and β-amylase encoding genes AMY1, AMY2, BMY. Melatonin upregulated the key genes in phenylpropanoid pathway, including those involved in the biosynthesis of total anthocyanin and their individual components (MYB1, TT8, TTG1, CHS, F3H, F3′5′H, ANS, 3GT), rutin (F3'H, FLS, 3GT), and chlorogenic acid (HCT, C3H, HQT), thereby promoting the accumulation of these phenolic compounds, resulting in an average 20.84% higher level of total phenolics in melatonin-treated fruits. Collectively, melatonin alleviates the deterioration of nutritional quality in cold-stored eggplant fruit by modulating starch and phenylpropanoid metabolisms, offering a potential strategy for enhancing postharvest fruit quality in eggplant.

Salt stress presents a major environmental constraint to global agricultural productivity and crop yield stability. Eggplant (Solanum melongena L.) is one of the most extensively cultivated Solanaceae crops worldwide, and the characterization of its germplasm for salt tolerance is essential to develop breeding programs to target its abiotic stress resilience. In this study, 200 mmol/L NaCl was identified as the initial screening concentration for the discrimination of salt tolerance levels in eggplant seedlings. Salt tolerance indices derived from 13 descriptors, including the plant height, stem diameter, and leaf number, were used to evaluate 165 germplasm resources (108 inbred lines and 57 commercial cultivars). These 165 germplasms were grouped into five groups, and six highly tolerant and eight highly sensitive germplasms were identified. Importantly, a stepwise multiple linear regression model incorporating the root surface area, leaf number, leaf water content, malondialdehyde content, and stem water content achieved 90.02% predictive accuracy, establishing a high-throughput screening protocol for germplasm selection. This systematic approach provides methodological advancements for precision breeding and identifies key physiological and morphological markers for salt tolerance improvement in eggplant.

Fleshy fruit shape is an important external quality trait influencing the usage of fruits and consumer preference. Thus, modification of fruit shape has become one of the major objectives for crop improvement. However, the underlying mechanisms of fruit shape regulation are poorly understood. In this review we summarize recent progress in the genetic basis of fleshy fruit shape regulation using tomato, cucumber, and peach as examples. Comparative analyses suggest that the OFP-TRM (OVATE Family Protein - TONNEAU1 Recruiting Motif) and IQD (IQ67 domain) pathways are probably conserved in regulating fruit shape by primarily modulating cell division patterns across fleshy fruit species. Interestingly, cucumber homologs of FRUITFULL (FUL1), CRABS CLAW (CRC) and 1-aminocyclopropane-1-carboxylate synthase 2 (ACS2) were found to regulate fruit elongation. We also outline the recent progress in fruit shape regulation mediated by OFP-TRM and IQD pathways in Arabidopsis and rice, and propose that the OFP-TRM pathway and IQD pathway coordinate regulate fruit shape through integration of phytohormones, including brassinosteroids, gibberellic acids, and auxin, and microtubule organization. In addition, functional redundancy and divergence of the members of each of the OFP, TRM, and IQD families are also shown. This review provides a general overview of current knowledge in fruit shape regulation and discusses the possible mechanisms that need to be addressed in future studies.

Purple eggplant fruits often turn brown during maturity stages, severely influencing their market value and shelf life. However, the metabolites and genes accounting for the fruit color changes are largely unknown. Here, metabolites and gene expression analyses were used to explore the candidates underlying the differences in fruit color changes between two eggplant genotypes, ‘14-345’ and ‘CGN23829’, with contrasting fruit color changes during fruit development. We found that flavonoids are the most differentially accumulated metabolites between ‘14-345’ and ‘CGN23829’. Higher contents of D3R and D3G are important for keeping the purple color at the maturity stage. Naringenin chalcone likely accounts for the color changes from purple to brown in ‘14-345’. Notably, at the physiological maturity stage, lower expression of early biosynthetic genes (EBGs) involved in the flavonoid biosynthesis pathway is important to keep lower contents of metabolites upstream of anthocyanins, thus leading to more purple coloring. Taken together, the results indicate that delphinidins and naringenin chalcone play important roles in determining eggplant fruit color changes at maturity stages, which is helpful for further dissecting the mechanisms underlying fruit color differences and changes in eggplants.

Wheat gluten properties can be improved by the application of nitrogen. This study investigates the effects of nitrogen application in the booting stage on glutenin polymerization during grain-filling and structural–thermal properties of gluten based on the high-molecular-weight glutenin subunits (HMW-GSs) using near-isogenic lines (Glu-1Da and Glu-1Dd). The nitrogen rate experiment included rates of 0, 60, 90, and 120 kg N ha⁻¹ applied with three replicates. Nitrogen significantly improved the grain quality traits (wet gluten contents, Zeleny sedimentation values, and maximum resistance) and dough strength (dough development time, dough stability time, and protein weakening), especially in wheat with the Glu-1Da allele. Nitrogen increased the protein composition contents, proportions of glutenins and HMW-GSs, and disulfide bond concentration in the flours of Glu-1Da and Glu-1Dd, and accelerated the polymerization of glutenins (appearing as glutenin macropolymer) during grain-filling, where nitrogen enhanced the accumulation and polymerization of glutenins more for line containing Glu-1Da than Glu-1Dd. The β-sheets, α-helix/β-sheet ratio, microstructures, and thermal stability were also improved to a greater degree by nitrogen for gluten with Glu-1Da compared to Glu-1Dd. Nitrogen treatment was highly effective at improving the gluten structural‒thermal properties of wheat in the booting stage, especially with inferior glutenin subunits.

Absence of high-molecular-weight glutenin subunit (HMW-GS) Dx2 weakens the gluten quality, but it is unclear how the absence of Dx2 has these effects. Thus, we investigated the gluten quality in terms of cytological, physicochemical, and transcriptional characteristics using two near-isogenic lines with Dx2 absent or present at Glu-D1 locus. Cytological observations showed that absence of Dx2 delayed and decreased the accumulation of protein bodies (PBs), where fewer and smaller PBs formed in the endosperm. The activity and gene expression levels of nitrogen assimilation and proteolysis enzymes were lower in HMW-D1a without Dx2 than HMW-D1p with Dx2, and thus less amino acid was transported for protein synthesis in the grains. The expression pattern of genes encoding Glu-1Dx2+1Dy12 was similar to those of three transcription factors, where these genes were significantly down-regulated in HMW-D1a than HMW-D1p. Three genes involving with glutenin polymerization were also down-regulated in HMW-D1a. These results may explain the changes in the glutenin and glutenin macropolymer (GMP) levels during grain development. Therefore, we suggest that the lower nitrogen metabolism capacity and expression levels of glutenin synthesis-related genes in HMW-D1a accounted for the lower accumulation of glutenin, GMP, and PBs, thereby weakening the structural‒thermal properties of gluten.