Browsing by Author "Zhang N"

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    Analysis of the Antioxidant Mechanism of Ozone Treatment to Extend the Shelf Life and Storage Quality of ‘Korla’ Fragrant Pears Based on Label-Free Proteomics
    (MDPI (Basel, Switzerland), 2024-05-01) Lin S; Zhang X; Li M; Zhang N; Dong C; Ji H; Zheng P; Ban Z; Mei X; Gu C; Chen C; Antunes MDC
    In this study, the physiological indicators, reactive oxygen species (ROS) levels, and activities and expressions of key enzymes related to ROS metabolism were monitored to explore the mechanism of ozone treatment on the shelf life of postharvest Korla fragrant pears. The results show that postharvest fragrant pears treated with ozone had a higher firmness and lower weight loss rate and decay rate during their shelf life, especially in the late stage. Ozone treatment could also delay the occurrence of the respiratory peak and reduce the peak value. The generation rate of superoxide anion (O2−), the hydrogen peroxide (H2O2) content, and the malondialdehyde (MDA) level were reduced in the ozone-treated group, while the activities of key enzymes, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), related to ROS metabolism in postharvest fragrant pears were stimulated by ozone treatment, especially in the middle and late stages of shelf life. Analysis of the proteomics results indicates that the POD family enzymes were the main target protein in postharvest fragrant pears treated by ozone during the middle and late stages of shelf life. The activity and expression of antioxidant-related enzymes in postharvest fragrant pears were stimulated by ozone to accelerate the metabolism of ROS and maintain high quality, especially in the middle and late shelf lives.
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    Impact of genetic background on allele selection in a highly mutable Candida albicans gene, PNG2
    (PLoS ONE, 2010) Zhang N; Cannon RD; Holland BR; Patchett ML; Schmid J
    In many microbes rapid mutation of highly mutable contingency genes continually replenishes a pool of variant alleles from which the most suitable are selected, assisting in rapid adaptation and evasion of the immune response. In some contingency genes mutability is achieved through DNA repeats within the coding region. The fungal human pathogen Candida albicans has 2600 repeat-containing ORFs. For those investigated (ALS genes, HYR1, HYR2, CEK1, RLM1) many protein variants with differing amino acid repeat regions exist, as expected for contingency genes. However, specific alleles dominate in different clades, which is unexpected if allele variation is used for short-term adaptation. Generation of new alleles of repeat-containing C. albicans ORFs has never been observed directly. Here we present evidence for restrictions on the emergence of new alleles in a highly mutable C. albicans repeat-containing ORF, PNG2, encoding a putative secreted or cell surface glycoamidase. In laboratory cultures new PNG2 alleles arose at a rate of 2.8x10(-5) (confidence interval 3.3x10(-6)-9. 9x10(-5)) per cell per division, comparable to rates measured for contingency genes. Among 80 clinical isolates 17 alleles of different length and 23 allele combinations were distinguishable; sequence differences between repeat regions of identical size suggest the existence of 36 protein variants. Specific allele combinations predominated in different genetic backgrounds, as defined by DNA fingerprinting and multilocus sequence typing. Given the PNG2 mutation rate, this is unexpected, unless in different genetic backgrounds selection favors different alleles. Specific alleles or allele combinations were not preferentially associated with C. albicans isolates from particular body sites or geographical regions. Our results suggest that the mutability of PNG2 is not used for short-term adaptation or evasion of the immune system. Nevertheless the large number of alleles observed indicates that mutability of PNG2 may assist C. albicans strains from different genetic backgrounds optimize their interaction with the host in the long term.