초록
영어
Lentinula edodes (shiitake mushroom) is a very popular edible, cultivated mushroom in Japan. There are post-storage problems with shiitake mushrooms, such as gill browning and cell wall lysis of the fruiting body, which can result in loss of fresh food quality and consequent loss of value. Lentinan is a cell wall component of beta-1, 3-linked-D-glucan with beta-1, 6 branches, which was isolated as an anti-tumor active-substance from L. edodes. Lentinan content decreases following harvest as a result of increased glucanase activity. We isolated one exo-glucanase encoding genes, exg21) and two endo-glucanase encoding gene tlg12) and glu1 from L. edodes. Transcription level of the exg2, tlg1 and glu1 gene increased after harvesting. Enzymes encoded by the genes have lentinan degrading activity, therefore, these genes are involved in lentinan degradation after harvesting. We also identified several cell wall degradation- related enzyme-encoding genes3), such as mixed-linked glucanase (mlg1), chitinases (chi1, chi29), chitin deacetylase (chd1), and chitosanase (cho1). It is revealed that transcriptional levels of these genes increased after harvesting, by real-time PCR. Glucanase and chitinase activity increased following harvest as results of increased transcription of these cell wall degradation-related enzyme-encoding genes. Increase of these cell wall degradation- related enzyme activities would cause cell wall lysis and lentinan degradation during post-harvest preservation. We identified laccase and tyrosinase encoding genes (lcc4 and tyr, respectively) by PCR-subtraction. The lcc4 was a novel laccase-encoding gene in L. edodes. Transcription levels of lcc4 and tyr increased after harvesting, and these genes would be involved in browning of the fruiting body. 1) Sakamoto et al. (2005) Current Genetics, 48: 195-203 2) Sakamoto et al. (2006) Plant Physiology 141: 793-801 3) Sakamoto et al. (2009) Current Genetics 55: 409-423