Vitamin E has been found to be associated with an important antioxidant property in mammals and plants. In photosynthetic organisms, the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD; E.C. 1.13.11.27) plays an important role in the vitamin E biosynthetic pathway. The full-length cDNA encoding HPPD was isolated from Lactuca sativa L. by rapid amplification of cDNA ends (RACE). The cDNA, designated as LsHPPD, was 1743 base pairs (bp) long containing an open reading frame (ORF) of 1338 bp encoding a protein of 446 amino acids. Sequence analysis indicated that LsHPPD shared high identity with HPPD from Medicago truncatula L. Real-time fluorescent quantitative PCR (qPCR) analysis revealed that LsHPPD was preferentially expressed in mature leaves compared with other tissues and that the LsHPPD expression was sensitive to high light and drought stress treatments. Transient expression of LsHPPD via agroinfiltration resulted in 12-fold increase in LsHPPD mRNA expression level and 4-fold enhancement in α-tocopherol content compared with the negative control. A decrease in chlorophyll content and inhibition of photosystem II were observed during stress treatments and agroinfiltration.
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