Lili Deng

Effects of postharvest oligochitosan treatment on anthracnose disease in citrus (Citrus sinensis L. Osbeck) fruit

Citrus fruit (Citrus sinensis L. Osbeck) is susceptible to infection by Colletotrichum gloeosporioides during poststorage, which rapidly decreases sensory and nutritional quality of the fruit. The ability of oligochitosan treatment to control C. gloeosporioides of citrus fruit during storage was examined, and possible underlying mechanisms were discussed. Disease incidence and lesion diameter were lower in oligochitosan-treated fruits compared with their respective controls. The fruits dipped in oligochitosan showed increased contents of lignin, hydroxyproline-rich glycoprotein (HRGP), hydrogen peroxide (H2O2), ascorbate, glutathione, total phenol, and flavonoid compounds. In addition, enzymatic activities of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7), polyphenoloxidase (PPO, EC 1.14.18.1), ascorbate peroxidase (APX, EC 1.11.1.11), and β-1, 3-glucanase (GLU, EC 3.2.1.39) also increased in citrus fruit peels, all of which were correlated with the onset of induced disease resistance. These results indicated that oligochitosan treatment can induce disease resistance of citrus fruit to C.gloeosporioides Penz. Oligochitosan can be a potential alternative to conventional control methods of postharvest anthracnose in citrus fruit.

Analysis of changes in volatile constituents and expression of genes involved in terpenoid metabolism in oleocellosis peel

Oleocellosis is a serious physiological disorder in citrus fruit that mainly results in appearance and quality deterioration. It has been well established that the occurrence of oleocellosis is highly correlated with the release of peel oil from citrus fruit, while there is little information on the dynamic changes in the content of the volatile constituents and the expression of genes involved in terpenoid metabolism during oleocellosis development. In the present research, large changes in the volatile profiles and gene expression in terpenoid metabolism were observed in oleocellosis peels compared to healthy ones. Among volatiles, the decreased contents of α-pinene, d-limonene, β-myrcene, linalool, β-caryophyllene, α-terpineol, nonanal, neryl acetate and (-)-carvone played a major role in these changes. For gene expressions in terpenoid metabolism, the up-regulated genes aldehyde dehydrogenase (NAD+) (ALDH) and the down-regulated genes β-caryophyllene synthase 1 (BCS1), α-terpineol synthase 2 (TES2) and myrcene synthase (MS) were the main differences in oleocellosis peels.

Sensitivity to Ethephon Degreening Treatment Is Altered by Blue LED Light Irradiation in Mandarin Fruit

Although citrus fruits are not climacteric, exogenous ethylene is widely used in the degreening treatment of citrus fruits. Irradiation with blue light-emitting diode (LED) light (450 nm) for 10 h can promote the formation of good coloration of ethephon-degreened fruit. This study evaluated the effect of blue LED light irradiation on the pigments contents of ethephon-degreened fruit and evaluated whether the blue LED light irradiation could influence the sensitivity of mandarin fruit to ethylene. The results indicated that blue light can accelerate the color change of ethephon-degreened fruit, accompanied by changes in plastid ultrastructure and chlorophyll and carotenoid contents. Ethephon-induced expressions of CitACS1, CitACO, CitETR1, CitEIN2, CitEIL1, and CitERF2 were enhanced by blue LED light irradiation, which increased the sensitivity to ethylene in ethephon-degreened fruits. These results indicate that blue LED light-induced changes in sensitivity to ethylene in mandarin fruit may be responsible for the improved coloration of ethephon-degreened mandarin fruits.

Optimization of a protective medium for freeze‐dried Pichia membranifaciens and application of this biocontrol agent on citrus fruit

To optimize a protective medium for freeze‐dried Pichia membranifaciens and to evaluate biocontrol efficacies of agents against blue and green mould and anthracnose in citrus fruit.

Control of Citrus Post-harvest Green Molds, Blue Molds, and Sour Rot by the Cecropin A-Melittin Hybrid Peptide BP21

In this study, the activity of the cecropin A-melittin hybrid peptide BP21 (Ac-FKLFKKILKVL-NH2) in controlling of citrus post-harvest green and blue molds and sour rot and its involved mechanism was studied. The minimum inhibitory concentrations of BP21 against Penicillium digitatum, Penicillium italicum, and Geotrichum candidum were 8, 8, and 4 μmol L-1, respectively. BP21 could inhibit the growth of mycelia, the scanning electron microscopy results clearly showed that the mycelia treated with BP21 shrank, formed a rough surface, became distorted and collapsed. Fluorescent staining with SYTOX Green (SG) indicated that BP21 could disintegrate membranes. Membrane permeability parameters, including extracellular conductivity, the leakage of potassium ions, and the release of cellular constituents, visibly increased as the BP21 concentration increased. Gross and irreversible damage to the cytoplasm and membranes was observed. There was a positive correlation between hemolytic activity and the concentration of BP21. These results suggest peptide BP21 could be used to control citrus post-harvest diseases.

Genome-wide in silico identification of membrane-bound transcription factors in plant species

Membrane-bound transcription factors (MTFs) are located in cellular membranes due to their transmembrane domains. In plants, proteolytic processing is considered to be the main mechanism for MTF activation, which ensures the liberation of MTFs from membranes and further their translocation into the nucleus to regulate gene expression; this process skips both the transcriptional and translational stages, and thus it guarantees the prompt responses of plants to various stimuli. Currently, information concerning plant MTFs is limited to model organisms, including Arabidopsis thaliana and Oryza sativa, and little is known in other plant species at the genome level. In the present study, seven membrane topology predictors widely used by the research community were employed to establish a reliable workflow for MTF identification. Genome-wide in silico analysis of MTFs was then performed in 14 plant species spanning the chlorophytes, bryophytes, gymnosperms, monocots and eudicots. A total of 1,089 MTFs have been identified from a total of 25,850 transcription factors in these 14 plant species. These MTFs belong to 52 gene family, and the top six most abundant families are the NAC (128), SBP (77), C2H2 (70), bZIP (67), MYB-related (65) and bHLH (63) families. The MTFs have transmembrane spans ranging from one to thirteen, and 71.5% and 21.1% of the MTFs have one and two transmembrane motifs, respectively. Most of the MTFs in this study have transmembrane motifs located in either N- or C-terminal regions, indicating that proteolytic cleavage could be a conserved mechanism for MTF activation. Additionally, approximately half of the MTFs in the genome of either Arabidopsis thaliana or Gossypium raimondii could be potentially regulated by alternative splicing, indicating that alternative splicing is another conserved activation mechanism for MTFs. The present study performed systematic analyses of MTFs in plant lineages at the genome level, and provides invaluable information for the research community.