Part:BBa_K1959000

Modification of Phytoene synthase (PSY)

The BBa_K1959000 harbors a coding sequence of phytoene synthase (PSY) derived from maize (Zea mays). Codon-optimization has been made for rice (Oryza sativa). PSY catalyzes the conversion of geranylgenranyl diphosphate (GGDP) to phytoene, which is a key enzyme for carotenoid biosynthesis.

Usage and Biology

　Phytoene synthase (PSY, EC 2.5.1.32) is an enzyme involved and responded for the first synthetic reaction in β-carotene biosynthetic pathway. In this reaction, two GGDP are converted to one molecule phytoene and two diphosphates (Figure. 1). PSY genes had been applied to the nutrition-improved crops such as Golden Rice. PSY gene of maize (ZmPSY) was introduced into rice genome to achieve the synthesis of β-carotene. In our project, the ZmPSY was used to reconstruct the pathway of astaxanthin biosynthesis. For maize is a monocots similar to rice, thus the ZmPSY was not fused with transit peptide for plastid sorting.

Figure. 1 Enzymatic reaction catalyzed by PSY

Transcriptional activity of PSY

　Semi-quantitative RT-PCR was performed to detect the expression level of PSY involved in astaxanthin biosynthesis, total RNA of transgenic rice seeds were extracted and cDNA was synthesized from 1μg DNase-treated RNA. Expected bands of the PSY gene were observed on the gel, indicated that PSY gene was transcribed in endosperm.

Figure.2　　RT-PCR analyses of expression levels of PSY genes in several transgenic rice.
Rice OsActin1 was as an internal control. CK+, positive control (plasmid pYLTAC380MF-BBPC). WT, negative control (wild-type rice cultivar HG1).

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  INCOMPATIBLE WITH RFC[12]

  Illegal NheI site found at 1045
  Illegal NheI site found at 1164
  
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal NgoMIV site found at 105
  Illegal AgeI site found at 956
  
• 1000
  COMPATIBLE WITH RFC[1000]