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Pectins are synthesized and secreted to the cell wall as highly methyl-esterified polymers and demethyl-esterified by pectin methylesterases (PMEs), which are regulated by pectin methylesterase inhibitors (PMEIs). PMEs and PMEIs are involved in pectin degradation during fruit softening; however, the roles of the PME and PMEI gene families during fruit softening remain unclear. Here, 71 PME and 30 PMEI genes were identified in the peach (Prunus persica) genome and shown to be unevenly distributed on all eight chromosomes. The 71 PME genes comprised 36 Type-1 PMEs and 35 Type-2 PMEs. Transcriptome analysis showed that 11 PME and 15 PMEI genes were expressed during fruit ripening in melting flesh (MF) and stony-hard (SH) peaches. Three PME and five PMEI genes were expressed at higher levels in MF than in SH fruit and exhibited softening-associated expression patterns. Upstream regulatory cis elements of these genes related to hormone response, especially naphthaleneacetic acid and ethylene, were investigated. One PME (Prupe.7G192800) and two PMEIs (Prupe.1G114500 and Prupe.2G279800), and their promoters were identified as potential targets for future studies on the biochemical metabolism and regulation of fruit ripening. The comprehensive data generated in this study will improve our understanding of the PME and PMEI gene families in peach. However, further detailed investigation is necessary to elucidate the biochemical function and regulation mechanism of the PME and PMEI genes during peach fruit ripening.
Efficient nitrogen (N) fertilizer management is crucial for ensuring the maximum economic yield and reducing the risk of environmental pollution. The objective of this study was to determine the effect of N fertilizer management on root yield and N uptake of radish in southern China by using 15N isotope tracing. A 2-year field experiment was conducted with three N rates (0, 60, and 120 kg N/ha) and two different application proportions, viz, A [50% at basal, 20% at 15 days after seeding (DAS), 30% at 30 DAS] and B (30% at basal, 20% at 15 DAS, 50% at 30 DAS) for each N rate, which were expressed as N0, N60A, N60B, N120A, and N120B, respectively. The results showed that root yields were significantly increased with N rates increasing from 0 to 120 kg N/ha. The root yields for N120A and N120B were 67.60 t·ha−1 and 72.50 t·ha−1 at harvest, 64.07% and 66.67% higher than those for the treatments of N60A and N60B, respectively. Mean radish recovery of N fertilizer ranged from 25.90% at N120A to 32.60% at N60B, and N fertilizer residual rate in the soil ranged from 11.50% at N120A to 14.90% at N60B. About 17.50% to 35.70% of total uptake of 15N derived from basal fertilizer was absorbed at seeding stage. However, 61.87% to 80.18% of total uptake of 15N derived from topdressing fertilizer absorbed at root expanding stage. Therefore, appropriate nitrogen application with increasing topdressing nitrogen amount could increase root yield of radish and the nitrogen recovery efficiency. Nitrogen fertilizer application recommended was 120 kg N/ha with 30% for basal, 20% for 15 DAS and 50% for 30 DAS in this study.
Cultivated peach (Prunus persica) is an important fruit species worldwide. The wild relatives in Prunus, such as P. mira, P. davidiana, P. kansuensis, P. ferganensis, and P. persica, are valuable for peach breeding, and early and accurate identification of parental and hybrid genotypes is critical. In this study, 20 representative accessions of peach germplasm from the National Germplasm Repository of Peach in China were used to select a set of 18 simple sequence repeat (SSR) markers for accurate species discrimination. Eight unknown peach samples were successfully identified using the SSR panel and species genotype database. Interspecific hybrid genotypes of P. persica × P. davidiana, P. persica × P. kansuensis, and P. persica × P. ferganensis were also analyzed reliably. The markers were amenable to high-throughput fluorescent labeling and capillary electrophoresis (CE) analysis, allowing rapid and efficient species identification. The practical method described in this study will facilitate peach breeding and germplasm management.
Stony hard (SH) peach (Prunus persica) fruits produce no ethylene and clingstone-type SH peaches have a crispy flesh texture; however, freestone-type SH peach fruits ripen to a soft, mealy state. During this study, we compared and analyzed changes in the microstructure, cell wall polysaccharides, and candidate cell wall-related genes of freestone-type SH ‘Zhongtao 14’ (‘CP14’), ‘Zhongtao White Jade 2’ (‘CPWJ2’), clingstone-type SH ‘Zhongtao 13’ (‘CP13’), and ‘Zhongtao 9’ (‘CP9’) during fruit ripening. The parenchyma cells of mealy freestone-type SH peaches became detached, were single, dried, and irregularly arranged, and remained intact in comparison with the nonmealy clingstone-type SH peaches. Methyl-esterified homogalacturonan was strongly immunolabeled in the cell wall of clingstone SH peaches; however, nonmethylated homogalacturonan was weakly immunolabeled in freestone SH peaches. A transcriptome analysis was performed to investigate the molecular mechanism of the mealiness process. A principal component analysis indicated that ‘CP14’ S4 III (mealy) could be distinguished from the samples of ‘CP13’ (S4 I, S4 II, S4 III) and ‘CP14’ (S4 I, S4 II). The highly coexpressed gene modules linked with firmness were found using a weighted gene coexpression network analysis; 189 upregulated genes and 817 downregulated genes were identified. Six upregulated cell wall-related genes (PpPG1, PpPG2, PpAGP1, PpAGP2, PpEXT1, and PpEXP1) and one downregulated cell wall-related gene (PpXET2) were involved in the mealiness process during freestone-type SH fruit ripening. These findings will improve our understanding of the relationship between clingstone, freestone, and stony hard fruits and lay the foundation for further exploration of the mechanisms underlying the softening of peach fruits.