In a search for differentially expressed genes in peel pitting of ‘Navel’ orange fruit (Citrus sinensis L. Osbeck), a cDNA subtraction library was constructed and a sequence encoding expansin-like gene was isolated and identified as pitting related gene. Based on sequence information derived from this fragment, a full-length cDNA (CsEXP, GenBank accession no. FJ769424) of 1,083 nucleotides encoding expansin was isolated from ‘Navel’ orange by RACE approaches. CsEXP encoded a protein of 254 amino acid residues with an open reading frame located in the region between 52 and 816 bp. The calculated molecular weight of the mature protein was 27.05 kDa and theoretical isoelectric point was 7.93. The deduced protein contained conserved domains of expansin: the histidine-phenylalanine-aspartate motif in central portion, cysteine residues in N-terminus, and tryptophan residues in C-terminal region. The expression of CsEXP was higher in pitting than the control. Exposure of fruit to stresses, including wounding, anoxia, low temperature (4°C), and treatment with ethylene, increased CsEXP mRNA levels in comparison with the control untreated fruit, whereas high temperature (40°C) decreased its mRNA levels. Since low temperature, low oxygen and wounding were suspected factors inducing peel pitting of citrus fruit. The present results provided us a clue that CsEXP may play a role in response to peel pitting related stresses.
Expansin Stress Gene expression Citrus sinensis L. Osbeck Fruit
Expressed sequence tags
Open reading frame
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We thank Dr. John Yang critically reading this manuscript. This work was supported by grants (No. 30371006; No. 30471214) from National Nature science Foundation of China, and from the Committee of Science and Technology of China (No. 2006BAD22B01) and Chongqing (CSTC, 2007AA1018), Chinese-Greek Cooperative Program (2003-63).
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