Characterization and functional validation of ß-carotene hydroxylase AcBCH genes in Actinidia chinensis.

ABSTRACT

Carotenoids are the pigment substances of yellow-fleshed kiwifruit, and among them ß-cryptoxanthin has only been detected in the brighter yellow-fleshed variety 'Jinshi 1'. ß-Carotene hydroxylase (BCH) catalyzes the formation of ß-cryptoxanthin and zeaxanthin, but its molecular characteristics and functions have not been fully explained. Here we isolated two ß-carotene hydroxylase genes, AcBCH1 and AcBCH2 from kiwifruit (Actinidia chinensis), and their relative expression levels exhibited a close correlation with the content of ß-cryptoxanthin. AcBCH1 catalyzed the formation of ß-cryptoxanthin when transformed into ß-carotene-accumulating yeast cells. Moreover, silenced expression of AcBCH1 in kiwifruit caused decreases in the contents of zeaxanthin, lutein, and ß-cryptoxanthin, and an increase in ß-carotene content. The content of ß-carotene decreased significantly after the AcBCH1/2 genes were overexpressed in tomato. The content of zeaxanthin increased and ß-carotene decreased in transgenic kiwifruit seedlings. The results will enrich our knowledge of the molecular mechanisms of carotenoid biosynthesis in kiwifruit.