Identification of two genes encoding microsomal oleate desaturases (FAD2) from the biodiesel plant Pongamia pinnata L.

The current study dissect microsomal oleate desaturase genes having differential expression pattern with respect to temperature from the seeds of Pongamia pinnata, and are grouped with other legumes and biofuel plants. Biofuel often is available as plant oil or products derived thereafter, such as biodiesel. In view of the anticipated fossil fuel shortage, the biochemical and genetic basis of vegetable oil biosynthesis is vital. We are focusing on the versatile oil-yielding legume tree Pongamia pinnata. Microsomal oleate desaturase (FAD2) is the key enzyme responsible for the production of linoleic acid in non-photosynthetic tissues. This work reports on the isolation of two full length cDNA clones, tissue expression and copy number detection of Pongamia FAD2 genes, and also on the transcriptional regulation at low and high temperatures. The deduced amino acid sequences of both PpFAD2 proteins share 83 % identity and display three typical histidine boxes that are characteristics of all membrane-bound microsomal oleate desaturases. Both sequences possess aromatic amino acid containing sequence motifs at the C-terminal end necessary for maintaining endoplasmic reticulum (ER) localization. Southern blot analysis is consistent with the presence of at least two copies of FAD2 in the pongamia genome. Quantitative real-time PCR analysis showed that PpFAD2-1 is expressed strongly in developing seeds and, showing very low levels of expression in vegetative tissues, whereas PpFAD2-2 is constitutively expressed in both vegetative tissues and the developing seeds, with higher transcript levels in roots, stems and leaves. In response to low temperature stress PpFAD2-1 and PpFAD2-2 were differentially expressed in various tissues. The PpFAD2-2 transcript dramatically decreased in roots, stems and leaves under low temperatures, whereas PpFAD2-1 showed a significant increase in these tissues.