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Ying Jia, Dianren Xia, and E.S. Louzada

A cDNA coding for a putative terpene synthase (Grtps) was isolated from `Rio Red' grapefruit (Citrus paradisi Macf.) mature fruit by differential display RT-PCR and the corresponding full-length cDNA and genomic clone were subsequently obtained. The isolated cDNA clone was 1644 bp in length encoding a protein of 548 amino acids with a predicted molecular mass of 64 kDa and of pI 5.38. The genomic clone was 3203 bp in length with 6 introns and 7 exons. This Grtps appears to be a sesquiterpene synthase based on molecular weight, genomic organization, and similarity with the other terpene synthases. Both RT-PCR and Northern blot expression analysis indicated that Grtps is not expressed in immature fruits, roots, or leaves, but only in mature fruits. Southern blot analysis of genomic DNA demonstrated that Grtps is one of the members in the family of terpene synthases.

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Eliezer Louzada, Sonia Del Rio, and Dianren Xia

The development of improved orange and grapefruit varieties via conventional breeding is not possible due their high degree of apomixis. The currently available varieties originated through natural or induced mutation. The development of a alternative breeding method is urgently needed for these citrus group. Microprotoplast Mediated Chromosome Transfer (MMCT) provides a direct way to transfer a very limited portion of the genome (one or more chromosome) from a donor species to a recipient species. In mammalian cells this procedure has been a powerful tool for gene mapping and to study the regulation of gene expression. Until recently, no chemical treatment was known for an efficient induction of microprotoplat in plants. Recently, amiprophosmethyl (APM) and cremart was found to be very efficient for the mass production of microprotoplasts in the Solanaceae family enabling a single chromosome to be transferred from potato to tomato and tobacco. To establish this technology in citrus, the efficiency of APM for the mass induction of microprotoplast from Swiglea glutinosa, a wild relative of citrus, was studied. APM ranging from 16 to 32 μmol was effective on promoting the scattering of the chromosomes and to create multinucleated cells. The microprotoplasts will be used in chromosome transfer experiments.