In the present study, the fruit physiology and sugar-acid ratio of 24 pomelo cultivars grown in ten different locations of the subtropical region of China were measured. The contents of soluble sugars and organic acids were quantified using high-performance (HPLC-MS) and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS), respectively. The results revealed that the physiological and basic quality attributes of 24 pomelo cultivars, including fruit weight, fruit width, fruit length, peel thickness, number of segments, pulp weight, pulp color, soluble solids, and Vitamin C, ranged between 264.63–1945.85 g, 8.60–19.56 g, 7.40–20.70 g, 0.46–3.33 mm, 11–18.66, 210.25–1351.66 g, 8.59–15.14 Brix°, and 34.79–84.58 mg/100 g, respectively. Soluble sugars, i.e., fructose, glucose, and sucrose, ranged between 16.25–24.25, 16.17–24.22, and 19.90–55.28 mg/g, respectively. Similarly, Organic acids, i.e., pyruvate, fumaric acids, succinic acid, tartaric acid, quinic acid, citric acid, malic acid, and cis-aconitic acid, in 24 pomelo cultivars ranged between 0.48–1.84, 0.02–0.45, 0–0.05, 0.01–0.1, 0–0.14, 3.01–11.85, 0.18–1.42, and 0.01–0.16 mg/g, respectively. The pomelo cultivars ‘Hongzuanmi’, ‘Minihong’, and ‘Hangwanmi’ exhibited maximum contents of citric acid and pyruvate and showed ultimately excessive organic acids. Overall, the ‘Guanximi’ and its budding cultivars, i.e., ‘Hongroumi’, ‘Huangjinmi’, and ‘Sanhongmi’, had the best quality fruits having maximum sugar-acid ratio. Correlation analysis showed that total soluble sugars had a significantly positive correlation with sucrose contents, while citric acids, malic acid, and pyruvate were positively correlated with total organic acids. The determined sugar-acid profile of pomelo cultivars provides the basis for future elucidation of key mechanisms regulating sugars and acids biosynthesis in pomelo.

Chalcone synthase gene (BaCHS) from Brunfelsia acuminata flowers was isolated using RT-PCR and RACE. The coding region of the gene is 1425-bp with an open reading frame of 1170-bp, 73-bp 5′UTR, and 172-bp 3′UTR. Its deduced protein does not have a signal peptide but does contain a cond_enzyme superfamily domain, and consists of 389 amino acids with a predicted molecular mass of 42,699 Da and a pI of 6.57. The deduced amino acid sequence of BaCHS shares 90%, 88%, 85%, 84% and 79% identity with CHS from Petunia hybrida, Nicotiana tabacum, Solanum lycopersicum, Capsicum annuum and Camellia sinensis, respectively. The striking color change from dark purple to light purple and ultimately lead to pure white resulted from a decline in anthocyanin content of the petals and was preceded by a decrease in the expression of BaCHS. Its gene expression was positively correlated with the contents of anthocyanin (p ≤ 0.01).

Overaccumulation of lignin (a physiological disorder known as granulation) often occurs during fruit ripening and postharvest storage in pomelo (Citrus grandis). It causes an unpleasant fruit texture and taste. Previous studies have shown that lignin metabolism is closely associated with the process of juice sacs granulation. At present, the underlying transcriptional regulatory mechanisms remain unclear. In this study, we identified and isolated a candidate NAC transcription factor, CgNAC043, that is involved in the regulation of lignin biosynthesis in Citrus grandis, which has homologs in Arabidopsis and other plants. We used the fruit juice sacs of ‘San hong’ as the material, the staining for lignin with HCl−phloroglucinol of fruit juice sacs became dark red from the various developmental stages at 172 to 212 days post anthesis (DPA). The RT-qPCR was used to analyze the gene expression of CgNAC043 and its target gene CgMYB46 in fruit sacs, it was found that the expression trend of CgNAC043 was basically same as CgMYB46, which increased gradually and peaked at 212 DPA. The expression level of CgNAC043 in juice sacs obtained away from the core was the lowest, while those near the core and granulated area were highly expressed. The transcriptional activation activity of CgNAC043 and CgMYB46 was analyzed by a yeast two-hybrid system, with only CgNAC043 showing transcriptional activation activity in Y2H Gold yeast. A transformation vector, p1301- CgNAC043, was transformed into the mesocarp of ‘San hong’ by Agrobacterium-mediated transformation. Results showed that the expression of transcription factors CgMYB58 and CgMYB46 are all upregulated. Further experiments proved that CgNAC043 not only can directly trans-activate the promoter of CgMYB46 but also trans-activate the promoters for the lignin biosynthesis-related genes CgCCoAOMT and CgC3H by dual luciferase assay. We isolated the CgNAC043 gene in pomelo and found CgNAC043 regulates target genes conferring the regulation of juice sacs granulation.

Juice sac granulation (a physiological disorder) leads to large postharvest losses of pomelo (Citrus maxima). Previous studies have shown that juice sac granulation is closely related to lignin accumulation, while the molecular mechanisms underlying this disorder remain elusive in pomelo. Our results showed that the lignin content in NC (near the core) and FC (far away from the core) juice sacs overall increased from 157 DPA (days post anthesis) to 212 DPA and reached a maximum at 212 DPA. Additionally, the lignin content of NC juice sacs was higher than that of FC juice sacs. In this study, we used transcriptome-based weighted gene co-expression network analysis (WGCNA) to address how lignin formation in NC and FC juice sacs is generated during the development of pomelo. After data assembly and bioinformatic analysis, we found a most correlated module (black module) to the lignin content, then we used the 11 DEGs in this module as hub genes for lignin biosynthesis. Among these DEGs, PAL (phenylalanine ammonia lyase), HCT (hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferase), 4CL2 (4-coumarate: CoA ligase), C4H (cinnamate 4-hydroxylase), C3′H (p-coumarate 3-hydroxylase), and CCoAOMT1 (caffeoyl CoA 3-Omethyltransferase) were the most distinct DEGs in granulated juice sacs. Co-expression analysis revealed that the expression patterns of several transcription factors such as MYB, NAC, OFP6, and bHLH130 are highly correlated with lignin formation. In addition, the expression patterns of the DEGs related to lignin biosynthesis and transcription factors were validated by qRT-PCR, and the results were highly concordant with the RNA-seq results. These results would be beneficial for further studies on the molecular mechanism of lignin accumulation in pomelo juice sacs and would help with citrus breeding.

Postharvest decay is a major factor causing strawberry losses. Florida produced strawberries (Fragaria × ananassa Duch., var. Pilgrim or Radiance) were obtained from a total of 4 harvests in 2018 a...

Phenolics in the Chinese olive (Canarium album (Lour.) Raeusch) fruit significantly affect its flavor and quality. The shikimate pathway is a bridge connecting primary metabolism and secondary metabolism through which fixed carbon can be transformed into phenolics. In this study, we aimed to reveal the relationship between the shikimate pathway and phenolic compound biosynthesis. Three Chinese olive fruits (cv. Tanxiang (TX), Changying (CY) and Lingfeng (LF)) with distinct flavor were utilized as materials. The results of this study showed that the synthesis and accumulation of quinate and gallate were active in the Chinese olive fruit. The accumulation amount of phenolic compounds was significantly different among the three cultivars. TX contained the highest content of ellagate, (iso)corilagin, conjugated quercetin and conjugated kaempferol; CY contained the highest content of conjugated luteolin; and LF contained the lowest content of ellagate, conjugated gallate, hyperin, conjugated quercetin, conjugated kaempferol and conjugated luteolin during fruit development. The expression of 3-dehydroquinate/shikimate dehydrogenase gene-4 (DHD/SDH-4), 3-dehydroquinate synthase gene (DHQS), chorismate synthase gene (CS) and Chorismate mutase gene-1 (CM-1) and shikimate content increased with the maturing of fruit. The gene 3-Deoxy-D-arabino-heptulosonate-7-phosphate synthase gene-1 (DAHPS-1) was most expressed in TX, while barely expressed in LF during fruit development. The expression of CM-1 was highest in CY. Chorismate mutase gene-2 (CM-2) expression was higher in TX and CY during late fruit development. The cultivars with higher expression of DAHPS-1 and Chorismate mutase genes (CMs) accumulated more phenolic compounds in fruit. DAHPS-1 and CMs are proposed as key genes for polyphenolic synthesis in the Chinese olive fruit. These results proved that shikimate metabolism had a positive effect on the phenols’ synthesis. Our study provides new insight into the regulatory mechanism of the biosynthesis and accumulation of phenolic compounds in the fruit of Chinese olive.