Abstract
The Lentinula edodes fruiting body (Shiitake mushroom) senesces immediately after harvesting, becoming brown and soft. Fruiting body senescence causes significant quality loss of Shiitake mushrooms. To understand the mechanism of fruiting body senescence after harvesting, enzymes involved in fruiting body browning and softening are discussed in this paper. Phenol oxidases, such as laccase and tyrosinase, are involved in fruiting body coloration. A laccase (lcc4) and a tyrosinase (tyr) are involved in fruiting body browning after harvesting. Expressions of these two enzymes increase significantly after harvesting. Fruiting body softening occurs by cell wall degradation. Cell wall of L. edodes is constructed of several polysaccharides, such as β-1,3-glucan, β-1,6-glucan, chitin, and chitosan. It is revealed that cell wall degrading enzymes, β-1,3-glucanase (exg2, tlg1), β-1,6-glucanase (pus30A), chitinase (chi1, chi2), and chitosanase (cho1), are involved in cell wall degradation after harvesting. One of the cell wall components from L. edodes, lentinan (β-1,3-1,6-glucan), is used for antitumor therapy. Lentinan is degraded after harvesting caused by an increase in β-1,3-glucanase activity. It is revealed that the exg2 and tlg1 are involved in lentinan degradation after harvesting. One transcription factor gene, exp1, is considered to be involved in regulation of gene expressions for fruiting body senescence. It is believed that understanding the mechanism of fruiting body senescence after harvesting will be helpful for establishing the suppression method of fruiting body senescence after harvesting.
