Characterization of caEG2, a Pepper Endo-β-1,4-Glucanase Gene Involved in the Abscission of Leaves and Flowers

Abstract

In pepper high amounts of endo-ß-1,4-glucanase (EGase; E.C. 3.2.1.4) activity are expressed during the abscission of leaves and flowers. Like in other plants, also in pepper this enzyme is encoded by a multigene family and the cCel2 mRNA is the transcript of the EGase gene specifically expressed at very high levels in leaf and flower abscission zones (AZ) following activation by ethylene treatments [3]. Very low amounts of cCel2 mRNA can also be detected in flowers and in roots. In order to understand the regulation of cCel2 expression, we have isolated its cognate gene, named caEG2 (Capsicum annuum EndoGlucanase 2, EMBL accession no.: AJ010950), and we have started its characterization. The sequence of a 6632 bp fragment of pepper genomic DNA revealed that it contains the whole coding region and flanking sequences at both 5′ and 3′ ends. After determining the transcription start site at position 3257 by means of 5′ primer extension, the caEG2 coding region was positioned between 59 bp of 5′ untranslated region (UTR) and 272 bp of 3′ UTR. The coding region is 100 % identical to that of the cCel2 cDNA [3] used to isolate this gene, and it appears to be spaced by 5 introns, the biggest of which is 216 bp long (intron 5) while the smallest (intron 4) is 81 bp long. The 6 exons are different in size ranging from 93 bp (exon 3) to 769 bp (exon 6). Intron-exon boundaries follow the Hanley and Schuler [1] rule. They are conserved among caEG2 and the other two abscission EGase genes known so far in higher plants (peach ppEG1 [4] and bean BAC 10 [2]) but for exon 2 which corresponds to the sum of exons 2 and 3 of the other two genes (Fig. 1).