In this study, to further clarify the mechanism of mulching treatment-induced β-cryptoxanthin accumulation, the effects of mulching on the expression of carotenoid metabolic genes were investigated in the flavedo of satsuma mandarin 'Aoshima unshiu' during fruit maturation from September to November. The results showed that the β-cryptoxanthin content in the flavedo was not significantly affected by the mulching treatment in September. However, the mulching treatment enhanced the

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... content in October and November, in which the β-cryptoxanthin content in the flavedo was 1.9-fold and 1.4-fold higher than that of the control, respectively. Gene expression results showed that expressions of CitPSY, CitPDS, CitZDS, CitLCYb2, CitHYb, and CitZEP, involved in carotene and xanthophyll syntheses, were higher than in the control in September and October. In particular, expression levels of CitLCYb2, CitHYb, and CitZEP in the mulching treatment were much higher than in the control. In November, expressions of CitLCYb1 and CitLCYb2 were significantly up-regulated by the mulching treatment. Both enzymes of CitLCYb1 and CitLCYb2 participated in the biosynthesis of β-carotene; especially the expression level of CitLCYb2 in the mulching treatment was particularly high from September to November. These results suggest that the upregulation of β, β-xanthophyll biosynthetic genes led to an increase of the β-cryptoxanthin content in the flavedo treated with mulching. In addition, it was suggested that the high expression of CitLCYb2 played an important role in the marked accumulation of β-cryptoxanthin in the mulching treatment.