JXB Advance Access originally published online on October 10, 2007
Journal of Experimental Botany 2007 58(13):3645-3656; doi:10.1093/jxb/erm214
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Characterization of phloem-sap transcription profile in melon plants
1The Institute of Plant Sciences and Genetics in Agriculture and the Otto Warburg Minerva Center for Agricultural Biotechnology, The Hebrew University of Jerusalem, Faculty of Agricultural, Food and Environmental Quality Sciences, PO Box 12, Rehovot 76100, Israel
2The Hebrew University Bioinformatics Unit, Faculty of Agricultural, Food and Environmental Quality Sciences, PO Box 12, Rehovot 76100, Israel
* To whom correspondence should be addressed. E-mail: swolf{at}agri.huji.ac.il
The phloem's role as a tissue responsible for the distribution of photoassimilates and nutrients among the various organs of higher plants has long been recognized. Recent studies have established that numerous proteins and mRNA molecules are also present in the phloem translocation stream; however, limited information is available on the identity of transcripts present within the phloem sap. In this study, a genomic approach was taken to produce a transcription profile of melon phloem sap. A cDNA library was constructed from mRNAs extracted from melon phloem sap and 1900 clones were randomly selected for sequencing. Selection of high-quality sequences resulted in 986 unique transcripts corresponding to 1830 ESTs. A comparison between the phloem-sap library and publicly available libraries from leaves and fruits indicated that the transcript profile of phloem sap is unique, with a substantially higher proportion of genes associated with biotic stimulus, response to stress, and metal-ion binding. Manual functional analyses revealed that over 40% of the transcripts are related to stress and defence responses, while over 15% of them are related to signal transduction. Out of the 1830 ESTs, only three were characterized as coding for chlorophyll-binding protein or ribulose bisphosphate carboxylase. Heterografting experiments established that six out of 43 examined transcripts are capable of long-distance trafficking from melon stocks to pumpkin scions. Annotation of these six transcripts revealed that three of them are associated with auxin-signal transduction while the other three were not identified. The potential role of the expressed transcripts in the phloem sap is discussed.
Key words: cDNA library, companion cells, Cucumis melo, Curcurbitaceae, ESTs, sieve-element
Received 19 June 2007; Revised 13 August 2007 Accepted 14 August 2007
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