Using watermelon inbred line‘ 97103’ as test material，this study measured the contents of
free IAA in fresh and rind at different fruit development stages. Results showed that the free IAA content in fresh
was significantly increased at late fruit development stage，while that in rind was maintaining at a low level，
speculating that free IAA in flesh might play an important role in fruit ripening and sugar accumulation. By bioinformatics，
the paper also identified the rate-limiting enzyme gene family YUCCA of tryptophan dependent
pathway for auxin synthesis，and carried out qRT-PCR detection about its expression level in fruit flesh and rind.
The results indicated that there were 10 members in watermelon YUCCA family，and all had the conserved FMOs
domain，watermelon YUCCA genes was divided into 2 classes by cluster analysis. Gene structure analysis showed
all these genes included 2-5 exons. In addition，qRT-PCR analysis revealed that ClYUCCA4，ClYUCCA6，
ClYUCCA10b and ClYUCCA10c，etc. 4 YUCCA genes were expressed in watermelon fresh and the expression
was significantly up-regulated at the late fruit development stage. The expression quantity alteration of ClYUCCA4
and ClYUCCA10c were consistent with IAA content variation in fruit fresh and rind，while their expressions
were barely detected in the other tissues，indicating that they might involve in the regulation of watermelon fruit
ripening.