Transient expression of the homogentisate phytyltransferase gene from Clitoria ternatea causes metabolic enhancement of α-tocopherol biosynthesis and chlorophyll degradation in tomato leaves

Homogentisate prenyltransferase (HPT) is an important enzyme involved in the α-tocopherol (vitamin E) biosynthetic pathway of all plant taxa. Tocopherol biosynthesis and chlorophyll degradation are related, but more information is needed to explain their relationship. In this study, a candidate gene for HPT from Clitoria ternatea (CtHPT) was isolated and identified via a phylogeny-based approach, and its hypothetical protein sequence was analyzed. Transient expression of CtHPT with Agrobacterium-mediated infiltration into tomato leaves was then performed and observed for the metabolic relationship between the α-tocopherol biosynthesis and chlorophyll degradation by gas chromatography–mass spectrometry. In silico analysis showed that CtHPT contained a chloroplast signal peptide and nine-transmembrane α-helixes. The results showed that, the content of α-tocopherol increased in transient expression of CtHPT, with the increased pool sizes of its biosynthetic intermediates: 2-methyl-6-phythylbenzoquinol and 2,3-dimethyl-5-phythylbenzoquinol, and the increased levels of phytol and various fatty acids. Moreover, the CtHPT transient expression was observed to cause chlorophyll deficiency in the tomato leaves with simultaneous increase of phytol and fatty acids, presumably the degradative products of chlorophyll and chloroplast membranes, respectively. It was concluded that the overexpression of CtHPT may enhance the metabolic flow of the α-tocopherol biosynthetic pathway, causing the degradation of chlorophylls, thereby increasing the supply of the precursor phytol for the α-tocopherol biosynthetic pathway.