Physiological and molecular analyses of chlorophyllase in sweet potatoes with different-colored leaves

Chlorophyllase (Chlase) is a hydrophobic enzyme that catalyzes the hydrolysis of chlorophyll (Chl) to chlorophyllide (Chlide) and phytol. The objectives of this research were to study Chlase characteristics of sweet potatoes (Ipomoea batatas, Ib) with various leaf colors: yellow (CN1927), green (TN57), and purple (CYY8467). Large variations in Chl and anthocyanin (Ant) and carotenoid (Car) existed in all plants, and CYY8467 contained significantly higher Chl, Ant, and Car levels compared to TN57 and CN1927. Various plants exhibited different Chlase activities, and Chl a degradation by Chlase of CYY8467 was higher than those of TN57 and CN1927. Nevertheless, Chlase activity in CN1927 exhibited a higher substrate preference toward Chl b than Chl a. Expression of the Chlase gene was detected in all leaves; however, IbChlase mRNA was most strongly active and regulated in TN57. The open reading frame sequences of IbChlase in TN57, CN1927, and CYY8467 shared 95% identity, and an eight-nucleotide sequence of Chlase in CYY8467 was missing due to a frame-shift mutation of the Chlase gene leading to early termination of gene translation. A phylogenetic analysis of Chlase indicated that 30 plants diverged into three clades, and sequences from TN57 and CN1927 were clustered together in a clade of the Chlase2.