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  • Author or Editor: Kunsong Chen x
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Two complementary DNA fragments encoding expansin genes Ad-EXP1 and Ad-EXP2 were isolated from ripening kiwifruit (Actinidia deliciosa cv. Bruno) by reverse transcription–polymerase chain reaction amplification using a pair of degenerate primers. The homology between these two expansin family members was 50% in nucleotide sequence and 74% in amino acid sequence. It was revealed that Ad-EXP1 and Ad-EXP2 belong to subgroups A and B of an expansin gene family respectively. However, gene expression of these two members shared similar patterns. Both were upregulated by ethylene treatment and downregulated by acetylsalicylic acid treatment. The study suggests that members of both subgroups A and B of the expansin family are involved in kiwifruit fruit ripening.

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Peach (Prunus persica) is an important fruit crop worldwide with several thousand cultivars. Cultivar discrimination and hybrid authentication are often required in peach breeding and can be achieved by applying various molecular markers including simple sequence repeat (SSR). In this study a total of 2146 expressed sequence tag (EST)–SSR loci were detected with the 10,737 EST sequences retrieved from the NCBI. A total of 49 EST-SSR markers, including 24 simple ones with a motif comprising of tri-, tetra-, penta-, hexanucleotides, and 25 compound ones, were selected and then primers were designed. Following conventional polymerase chain reaction (PCR) specificity control and sequence authentication, as well as fluorescence-based PCR product size and stutter band evaluation, 37 EST-SSR markers with correct amplification and without stutter band interference were validated. Among them, 14 were polymorphic in 18 closely related peach accessions, with polymorphism information content (PIC) ranging from 0.0994 to 0.3750. The 18 peach accessions can be distinguished using nine polymorphic markers, with the exception of ‘Shangshandayulu’ and ‘Xipu 1’, both being bud sports from ‘Yulu’. The clustering of the accessions as well as the fingerprint profiles supported the authentication of the hybrids. These EST-SSR markers are useful for peach breeding research.

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Amplified fragment length polymorphism (AFLP) was used to analyze genetic diversity of 100 accessions of Chinese bayberry (Myrica rubra Sieb. et Zucc.), one of the widely cultivated fruit tree crops in southern China. Six E-NN/M-NNN primer combinations were selected and a total of 236 bands were obtained, of which 177 were polymorphic (75.01%). An unweighted pair-group method of the arithmetic averages (UPGMA) was used to analyze the genetic relationships. The Dice's similarity coefficient among the Chinese bayberry accessions ranged from 0.75 to 1.00 and was 0.49 between Chinese bayberry and wax myrtle (M. cerifera L.). The 100 accessions of Chinese bayberry were clustered into two groups and seven subgroups. Subgrouping of Chinese bayberry was not related to the sex of the plant and color or size of the ripe fruit, but to some extent the region where the accession originated. However, the accessions from the same region did not necessarily belong to the same group or subgroup, which suggested the presence of extensive gene flow among different regions. Furthermore, close relationships between some morphologically similar accessions were found.

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The relationship between lipoxygenase (LOX) pathway-derived volatiles and LOX gene expression was evaluated in kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. deliciosa cv. Bruno] during postharvest ripening at 20 °C. The C6 aldehydes n-hexanal and (E)-2-hexenal were abundant in peel compared with flesh tissue and declined as kiwifruit ripened. Esters such as ethyl butanoate and methyl butanoate were lower in the peel than flesh and accumulated when the fruit underwent a climacteric rise in ethylene production. Total LOX activity was higher in the peel than in the flesh and increased as kiwifruit ripened. Expression of AdLox2, AdLox3, AdLox4 and AdLox6 was high in the peel, whereas AdLox1 and AdLox5 showed similar levels in the peel and flesh at the ethylene climacteric. AdLox1 and AdLox5 transcript levels increased and AdLox2, AdLox3, AdLox4 and AdLox6 levels decreased during postharvest fruit ripening. Principal component analysis showed that n-hexanal and (E)-2-hexenal were grouped with LOX genes that were downregulated as kiwifruit ripened. The possible roles of LOX genes in relation to kiwifruit volatile formation during fruit ripening are discussed.

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Chinese bayberry (Morella rubra) is an economically important subtropical evergreen fruit crop native to China and other Asian countries. For facilitating cultivar discrimination and genetic diversity analysis, a total of 38 high-quality and highly polymorphic expressed sequence tags-simple sequence repeat (EST-SSR) markers, with little or no polymerase chain reaction (PCR) stutter bands, including 21 screened from those obtained previously and 17 newly developed markers, were developed. The average number of alleles (N a ) per locus was 5.6, and polymorphism information content varied from 0.34 to 0.86, with a mean value of 0.57. With these markers, all 42 Chinese bayberry accessions analyzed were successfully discriminated and the phylogenetic relationship between accessions was revealed. The accessions can be separated into two groups with six subgroups. The grouping of four main cultivars in three subgroups and 12 white-fruited accessions, each with little or no anthocyanin accumulation in ripe fruit, into five subgroups suggested the preservation of broad diversity among cultivated populations. These EST-SSR markers and the findings obtained in this study can assist the discrimination of cultivars and lines and contribute to genetic and breeding studies in Chinese bayberry.

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Loquat (Eriobotrya japonica) is a model fruit for investigating flesh lignification during storage and response to chilling injury. However, the investigations of enzymes and coding genes and loquat fruit lignification under low-temperature storage are still limited. Here, the activity and transcript levels of up-stream enzymes of the phenylpropanoid pathway, including l-phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-coumarate:coenzyme A ligase (4CL), were investigated. The results indicated that activity of these enzymes was positively correlated with loquat fruit lignification and suppression of these increases by heat treatment (HT) and low-temperature conditioning (LTC) significantly alleviated loquat fruit lignification. Coding genes for these enzymes were subsequently isolated based on information from an RNA-seq database and expression of Ej4CL1 was found to be the most responsive to low temperature and inhibition by HT and LTC treatment, whereas the other genes were less responsive to these treatments. Furthermore, function of Ej4CL1 was analyzed by transient overexpression in tobacco leaves, where it stimulated lignin accumulation. Ej4CL1 may be a key candidate that involved in CI-related loquat fruit lignification.

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