2 DIVERGENT ENDO-BETA-1,4-GLUCANASE GENES EXHIBIT OVERLAPPING EXPRESSION IN RIPENING FRUIT AND ABSCISING FLOWERS

Two structurally divergent endo-beta-1,4-glucanase (EGase) cDNAs were cloned from tomato. Although both cDNAs (Cell and Cel2) encode potenti ally glycosylated, basic proteins of 51 to 53 kD and possess multiple amino acid domains conserved in both plant and microbial EGases, Cel1 and Cel2 exhibit only 50% amino acid identity at the overall sequence level. Amino acid sequence comparisons to other plant EGases indicate that tomato Cell is most similar to bean abscission zone EGase (68%), whereas Cel2 exhibits greatest sequence identity to avocado fruit EGas e (57%). Sequence comparisons suggest the presence of at least two str ucturally divergent EGase families in plants. Unlike ripening avocado fruit and bean abscission zones in which a single EGase mRNA predomina tes, EGase expression in tomato reflects the overlapping accumulation of both Cel1 and Cel2 transcripts in ripening fruit and in plant organ s undergoing cell separation. Cell mRNA contributes significantly to t otal EGase mRNA accumulation within plant organs undergoing cell separ ation (abscission zones and mature anthers), whereas Cel2 mRNA is most abundant in ripening fruit. The overlapping expression of divergent E Gase genes within a single species may suggest that multiple activitie s are required for the cooperative disassembly of cell wall components during fruit ripening, floral abscission, and anther dehiscence.