Endo-β-mannanase (EC 22.214.171.124) is involved in the hydrolysis of mannan-type polysaccharides that are present in plant cell walls, especially those of the seed endosperm. The genes encoding the endo-β-mannanases have been studied extensively in tomato (Solanum lycopersicum), and five genes (LeMAN1, LeMAN2, LeMAN3, LeMAN4 and LeMAN5) and/or their products have been isolated and characterized. LeMAN1, LeMAN2 and LeMAN3 are expressed in tomato seeds, LeMAN4 in the fruit and LeMAN5 in the flower. LeMAN5 and LeMAN2 are now considered to be the same gene, and the former is re-designated as LeMAN2*. Transcripts of LeMANs 1, 2 and 3 are detected only in the endosperm of tomato seeds, and their synthesis is promoted by gibberellic acid. LeMAN4, in the fruit, occurs as LeMAN4a and LeMAN4i genes that encode an active or inactive form of endo-β-mannanase, respectively. LeMAN1–4 enzymes encoded by these genes share 80% similarity in amino acid sequence. In tomato, the leucine amino acid present near to the C-terminus of the endo-β-mannanase is the most important for achieving full activity of the enzyme.