As the abundant phenolic substance in peach fruit, chlorogenic acid (CGA) has various biological activities and is an important target for improving the nutritional and resistance qualities. Nevertheless, the gene functions and regulatory mechanisms of CGA biosynthesis in peach fruit are poorly understood. Using gene expression patterns from different developmental stages and different peach cultivars, one structural gene PpHCT5 was identified as being involved in CGA biosynthesis. An in vitro enzyme activity assay confirmed that the PpHCT5 protein catalyzed the biosynthesis of caffeoyl CoA and quinic acid into CGA. The in vivo functional validation confirmed that PpHCT5 overexpression increased CGA accumulation in transgenic plants, including peach, tomato, and tobacco. Furthermore, upstream transcription factors of PpHCT5 were identified. PpMYB62 and PpbHLH14 activated PpHCT5 expression by directly binding promoter MBS or G-box elements, thereby inducing CGA accumulation in peach fruit. Additionally, PpMYB308 interactions with PpbHLH14 promoted the activating effect of PpbHLH14 on PpHCT5, thereby positively regulating CGA biosynthesis. Thus, a regulatory network of PpMYB and PpbHLH transcription factors to modulate the PpHCT5-mediated CGA biosynthesis pathway was constructed. It will be useful for elucidating the complex mechanisms underlying CGA biosynthesis and provide a theoretical basis for the development of resistance and increased CGA content breeding in peach.
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Weed control is an important step for fruit tree production. To investigate the safety of different herbicides, suitable herbicides for peach nurseries and orchards were screened in peach production, which can provide theoretical basis for the application of chemical herbicides in the peach industry.
To preliminarily screen the safety of 13 herbicides, the peach seedlings combined with Lolium perenne, Cynodon dactylon, Alternanthera philoxeroides, Trifolium repens and Medicago falcata were evaluated in pot. Based on the results of the phytotoxicity index of each herbicide, 10% quizalofop-p-ethyl and 60% quinclorac were mixed. According to the effective doses of 25, 50, and 75 mL·hm-2 of quizalofop-p-ethyl and 150, 300, 450 g·hm-2 of quinclorac, a total of 9 herbicide mixtures were established. After 7, 14, and 21 d of stem and leaf spraying treatment, the weed inhibition rate was investigated. After 30 d of the treatment, the plant height, stem diameter, aboveground and underground biomass, electrolyte permeability of the leaf and root tip cells, total root length, total root surface area, root volume and root tip number of peach seedlings were also measured. Based on principal component analysis, the safety of different treatments was comprehensively evaluated.
After spraying on the stems and leaves of peach seedlings, 11 herbicides caused phytotoxicity in peach seedlings, resulting in varying degrees of symptoms such as chlorosis, wilting, and withering. However, quizalofop-p-ethyl and quinclorac had no significant effect on the growth of peach seedlings. After spraying weeds with a single agent of quizalofop-p-ethyl for 21 d, the inhibition rate of quizalofop-p-ethyl on gramineous weeds was 100%. However, it had no effect on broad-leaved weeds. On the contrary, the inhibition rate of spraying quinclorac on gramineous weeds was 0, and the inhibition rate range of M. falcata, T. repens and A. philoxeroides was 80% to 100%. After being mixed with quizalofop-p-ethyl and quinclorac, the total weed inhibition rate under 9 compound preparations could reach over 90% after 21 d. Meanwhile, each formulation had no significant effect on the height of peach seedlings, aboveground and underground biomass, electrolyte permeability of the leaf and root tip cells. The comprehensive analysis showed that the effective dose of quizalofop-p-ethyl had a significant impact on the comprehensive evaluation D value of the mixed formulation. When the effective dose of quizalofop-p-ethyl increased to 75 mL·hm-2, the comprehensive evaluation D value of the mixed formulation exceeded 0.563, but there was no trend between the increasing D value and the increase of the effective dose of quinclorac.
Peach seedlings are sensitive to most herbicides, and mixing is an effective measure to improve the comprehensive weed inhibition rate of quizalofop-p-ethyl and quinclorac. After mixing an effective dose of 75 mL·hm-2 quizalofop-p-ethyl with 300 g·hm-2 quinclorac, the comprehensive evaluation D value of the formulation is the highest, which can achieve the best weed inhibition rate while ensuring the safety of peach seedlings.
Open Access
Research paper
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Shikimic acid/quinic acid hydroxy cinnamyl transferase (HCT) is one of the key enzymes in the phenylpropanoid pathway. However, the role of the HCT gene in chlorogenic acid (CGA) biosynthesis in peach fruit remains unclear. For this, we identified the accumulation pattern of CGA in four peach cultivars, cloned and characterized 11 PpHCT gene members, and further analyzed the expression patterns of these PpHCT genes during fruit development. The contents of CGAs in the four peach cultivars all exhibited a trend of increasing and then decreasing during the fruit growth and development. Moreover, the contents of CGAs in the peel and flesh were tissue-specific. Gene structure analysis indicated that the PpHCT genes were highly conserved, containing two exons and one intron. The protein structure analysis demonstrated that the PpHCT proteins contained two conserved motifs (HXXXD, DFGWG) and a transferase domain (PF02458), which belonged to the BAHD acyltransferase family. The cis-acting element analysis suggested that the promoters of PpHCT genes contained many light-related, hormone-related, stress-related, tissue-specific, and circadian-related elements, and they could participate in a variety of biological processes. Phylogenetic analysis showed that the HCT proteins of peach were closely related to the HCT proteins of plum and had a close evolutionary relationship. The qRT-PCR analysis indicated that the expression levels of PpHCT1 and PpHCT2 showed an opposite trend to the accumulation of CGA, whereas the expression levels of PpHCT4, PpHCT5, PpHCT7, PpHCT8, and PpHCT11 demonstrated the same trend as CGA accumulation. It was worth noting that only PpHCT4 and PpHCT5 were highly expressed in the two high-CGA cultivars but showed low levels of expression in the two low-CGA cultivars. Therefore, it was hypothesized that these two genes might be key genes to the synthesis of CGA in peach fruit. Those findings provide a theoretical basis for further study on the biological functions of the HCT gene and help to reveal the molecular mechanism of CGA.
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