Comparative analysis of tocopherol biosynthesis genes during seed development in the Asian spiderflower, Cleome viscosa (Cleomaceae)
Cleome viscosa (common names, wild mustard, Asian spiderflower, and tick weed) is an annual oilseed crop plant that has a high vitamin E content, with the most active forms being the tocopherols (α, β, γ and δ). These act as antioxidants in plants and are also useful for human health. The gene expression profiles and partial-length cDNA encoding tocopherol cyclase (CvVTE1), homogentisic acid prenyltransferase (CvVTE2), MPBQ methyltransferase (CvVTE3), gamma-tocopherol methyltransferase (CvVTE4), hydroxyphenyl-pyruvate dioxygenase (CvHPPD) and homogentisate solanesyltransferase (CvHST) genes involved with tocopherol biosynthetic enzymes were determined. Partial cDNA sequences of six genes as 694 bp CvVTE1, 375 bp CvVTE2, 387 bp CvVTE3, 402 bp CvVTE4, 334 bp CvHPPD and 461 bp CvHST showed high identity to their homologs in other higher plants. Expression levels of CvVTE1, CvVTE2, CvVTE3, CvVTE4, CvHPPD and CvHST genes were analyzed by real-time quantitative PCR (qPCR) at plant nodes L1-L3 in leaves and 1-4 weeks after fruit set (WAF) of seeds. CvVTE3 and CvHPPD were predominantly expressed in the leaves, while in seeds CvVTE2 was expressed at both 2 and 3 WAF at rates of 231-fold and 224-fold, which coordinated with CvVTE1 and CvVTE3 expression. Co-expression of CvVTE4 and CvHPPD supports high levels of flux toward the synthesis of tocopherols at 4 WAF without any down regulation. We conclude that CvVTE2 plays a key role in tocopherol biosynthesis in C. viscosa seeds.