A family of at least seven beta-galactosidase genes is expressed during tomato fruit development

During our search for a cDNA encoding beta-galactosidase II, a beta-galacto sidase/exogalactanase (EC 3.2.1.23) present during tomato (Lycopersicon esc ulentum Mill.) fruit ripening, a family of seven tomato beta-galactosidase (TBG) cDNAs was identified. The shared amino acid sequence identity among t he seven TBG clones ranged from 33% to 79%. All contained the putative acti ve site-containing consensus sequence pattern G-G-P-[LIVM]-x-Q-x-E-N-E-[FY] belonging to glycosyl hydrolase family 35. Six of the seven single-copy ge nes were mapped using restriction fragment length polymorphisms of recombin ant inbred lines. RNA gel-blot analysis was used to evaluate TBG mRNA level s throughout fruit development, in different fruit tissues, and in various plant tissues. RNA gel-blot analysis was also used to reveal TBG mRNA level s in fruit of the rin, Mor, and Nr tomato mutants. The TBG4-encoded protein , known to correspond to beta-galactosidase LT, was expressed in yeast and exo-galactanase activity was confirmed via a quantified release of galactos yl residues from cell wall fractions containing beta(1-->)-D-galactan purif ied from tomato fruit.