JXB Advance Access originally published online on June 18, 2004
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Journal of Experimental Botany, Vol. 55, No. 402, pp. 1483-1490, July 2004
Journal of Experimental Botany, Vol. 55, No. 402, © Society for Experimental Biology 2004; all rights reserved
RESEARCH PAPER |
A ß-galactosidase gene is expressed during mature fruit abscission of ‘Valencia’ orange (Citrus sinensis)
University of Florida, IFAS, Horticultural Sciences Department, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, Florida 33850-2299, USA
* To whom correspondence should be addressed. Fax: +1 863 956 4631. E-mail: jkbu{at}crec.ifas.ufl.edu
ß-galactosidases have been detected in a wide range of plants and are characterized by their ability to hydrolyse terminal non-reducing ß-D-galactosyl residues from ß-D-galactosides. These enzymes have been detected in a wide range of plant organs and tissues. In a search for differentially expressed genes during the abscission process in citrus, sequences encoding ß-galactosidase were identified. Three cDNA fragments of a ß-galactosidase gene were isolated from a cDNA subtraction library constructed from mature fruit abscission zones 48 h after the application of a mature fruit-specific abscission agent, 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMN-pyrazole). Based on sequence information derived from these fragments, a full-length cDNA of 2847 nucleotides (GenBank accession number AY029198) encoding ß-galactosidase was isolated from mature fruit abscission zones by 5'- and 3'-RACE approaches. The ß-galactosidase cDNA encoded a protein of 737 amino acid residues with a calculated molecular weight of 82 kDa. The deduced protein was highly homologous to plant ß-galactosidases expressed in fruit ripening. Southern blot analysis demonstrated that at least two closely related ß-galactosidase genes were present in ‘Valencia’ orange. Temporal expression patterns in mature fruit abscission zones indicated ß-galactosidase mRNA was detected 48 h after treatment of CMN-pyrazole and ethephon in mature fruit abscission zones. ß-galactosidase transcripts were detected in leaf abscission zones only after ethephon application. The citrus ß-galactosidase was expressed in stamens and petals of fully opened flowers and young fruitlets. The results suggest that this ß-galactosidase may play a role during abscission as well as early growth and development processes in flowers and fruitlets.
Key words: Abscission zone, cell wall hydrolase, 5-chloro-3-methyl-4-nitro-1H-pyrazole, ethephon, fruitlet, petal, stamen
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