Comparative Characteristics of Genes 9-Cis-Epoxycarotinoid-Dioxygenase SlNCED1 and SlNCED2 during the Development

Tomato Solanum lycopersicum L. is an important agricultural crop and, at the same time, a model for studying the ontogeny of the succulent fruit. The decisive role in the ripening of the fruit is played by abscisic acid, which is formed as a result of the oxidative cleavage of epoxycarotenoids 9-cis-epoxycarotenoid dioxygenases NCED. Gene-expression profiles of SlNCED1 and SlNCED2 and the content of carotenoids in fruits at different stages of development were determined in three varieties of tomato with different color of ripe fruit. It was shown that transcripts of both genes are present in all organs. Transcript level of SlNCED1 was approximately four to six times higher than the level of SlNCED2 transcripts; peak activity of SlNCED1 occurs in the late stages of ripening, while that of SlNCED2 is at the initial stage. Ripe fruits are characterized by the highest amount of carotenoids; lycopene was found only in the fruits of late stages in red-fruited varieties, the highest content of β-carotene was found in ripe fruits of the yellow-fruited variety. The precursor of abscisic acid, violaxanthin, is present only in the immature fruit; the other precursor, neoxanthin, decreases with ripening and is absent at the ripeness stage. In red-fruited varieties, a correlation was found between the level of SlNCED1 and SlNCED2 transcripts with the content of β-carotene. Findings suggest the coparticipation of SlNCED1 and SlNCED2 in the biosynthesis of abscisic acid during the development and ripening of tomato fruit. In this case, the key role belongs to the gene SlNCED1, the peak of activity of which falls on the stage of changing the color of the fruit. Lower levels of SINCED2 transcripts and its peak activity in the early stages of fruit development suggests a division of NCED functions between the two enzymes.