The hyp-1 gene is not a limiting factor for hypericin biosynthesis in the genus Hypericum

Biosynthesis of the hypericins that accumulate in the dark glands of some members of the genus Hypericum is poorly understood. The gene named hyp-1, isolated from Hypericum perforatum L. has been proposed as playing an important role in the final steps of hypericin biosynthesis. To study the role of this candidate gene in relation to the production of hypericins, the expression of this gene was studied in 15 Hypericum species with varying ability to synthesise hypericin. While the accumulation of hypericins and emodin, an intermediate in the respective pathway, was associated with the dark glands in the hypericin-producing species, the hyp-1 gene was expressed in all studied species regardless of whether hypericins and emodin were detected in the plants. The coding sequences of hyp-1 cDNA were isolated from all species and showed more than 86% similarity to each other. Although, in general, an increased level of the hyp-1 gene transcript was detected in hypericin-producing species, several of the hypericin-lacking species expressed comparable levels as well. Our results question the role of the hyp-1 gene product as a key enzyme responsible for biosynthesis of hypericins in the genus Hypericum. The function of the hyp-1 gene may not be restricted to hypericin biosynthesis only, or some additional factors are necessary for completion of hypericin biosynthesis.