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| Superoxide dismutases (SODs) encoded by a multigene family are important antioxidant enzymes that guard against superoxide toxicity. To date, no systematic characterization of this gene family has been conducted and their functions are not completely clear in plant embryos. 20 full-length cDNAs, encoding cytoplasmic CSD1a and DlCSD1b, chloroplast DlCSD2a and DlFSD1a, plastidic DlFSD1b and mitochondrial DlMSD, respectively, were obtained from longan embryogenic callus (EC) by RT-PCR and RACE. Each member contained multiple polyadenylation sites. The genomic structures of DlCSD1a, DlCSD1b, DlCSD2a, DlFSD1a, DlFSD1b and DlMSD genes consisted eight, six, seven, six, seven and five introns, respectively, and their introns lengths varied greatly. In addition, seven variants with different splicing modes were cloned, showing their functional diversity during longan somatic emrbyogenesis (SE). Further, each type of SOD gene had multiple transcription start sites (TSS), and the choice of TSS in SODs only affected the length of the 5'UTR, but not created protein diversity. Meanwhile, the promoters of DlCSD1a, DlCSD2a, DlFSD1a and DlMSD were isolated, which contained lots of cis-acting elements in response to light, GA, auxin, JA, MeJA, dehydration, coldness, wounding, etc. Comprehensive analysis of the expression profiles showed that the different types of SOD showed different spatial and temporal expression modes and played a key role especially at the middle and later developmental stages during longan SE. This study provided the comprehensive analysis of the whole SOD gene family from plants SE for the first time, including cloning of the full-length cDNAs, gene structures, alternatively spliced variants, phylogeny, TSS, isolation of promoters, and expression patterns, and these comparisons could provide a multifaceted view on diverse functions of the SOD isoforms during longan somatic embryos formation. |
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| Keywords: Dimocarpus longan; somatic embryogenesis; SOD gene family; gene structures; splicing; expression |
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