Abstract
Sandalwood (Santalum album L.) is highly valued for its fragrant heartwood and extracted oil. Santalols, which are the main components of that oil, are terpenoids, and these are biosynthesized via the mevalonic acid (MVA) pathway. Mevalonate kinase (MK) and phosphomevalonate kinase (PMK) are key enzymes in the MVA pathway. Little is known about the genes that encode MK and PMK in S. album or the mechanism that regulates their expression. To isolate and identify the functional genes involved in santalol biosynthesis in S. album, an MK gene designated as SaMK, and a PMK gene designated as SaPMK, were cloned from S. album. The sequences of these genes were analyzed. A bioinformatics analysis was conducted to assess the homology of SaMK and SaPMK with MK and PMK genes from other plants. The subcellular localization of SaMK and SaPMK proteins was also investigated, as was the functional complementation of SaMK and SaPMK in yeast. Our results show that the full-length cDNA sequences of SaMK and SaPMK were 1409 bp and 1679 bp long, respectively. SaMK contained a 1381 bp open reading frame (ORF) encoding a polypeptide of 460 amino acids and SaPMK contained a 1527 bp ORF encoding a polypeptide of 508 amino acids. SaMK and SaPMK showed high homology with MK and PMK genes of other plant species. Functional complementation of SaMK in a MK-deficient mutant yeast strain YMR208W and SaPMK in a PMK-deficient mutant yeast strain YMR220W confirmed that cloned SaMK and SaPMK cDNA encode a functional MK and PMK, respectively, mediating MVA biosynthesis in yeast. An analysis of tissue expression patterns revealed that SaMK and SaPMK were constitutively expressed in all the tested tissues. SaMK was highly expressed in young leaves but weakly expressed in sapwood. SaPMK was highly expressed in roots and mature leaves, but weakly expressed in young leaves. Induction experiments with several elicitors showed that SaMK and SaPMK expression was upregulated by methyl jasmonate. These results will help to further study the role of MK and PMK genes during santalol biosynthesis in S. album.
Highlights
Santalum album L., commonly known as Indian sandalwood, belongs to the Santalaceae and is a slow-growing, evergreen, root semi-parasitic tree widely distributed in tropical and temperate regions such as India, Sri Lanka, the Malay Archipelago, and southern C hina[1,2]
The full-length cDNA sequences of SaMK and SaPMK were obtained through RT-PCR and 5′/3′ rapid amplification of cDNA ends (RACE)
The results of BLASTN analysis on NCBI revealed that the SaMK and SaPMK sequences were highly homologous to Mevalonate kinase (MK) and phosphomevalonate kinase (PMK) genes from other plants (Table 1)
Summary
Santalum album L., commonly known as Indian sandalwood, belongs to the Santalaceae and is a slow-growing, evergreen, root semi-parasitic tree widely distributed in tropical and temperate regions such as India, Sri Lanka, the Malay Archipelago, and southern C hina[1,2]. We focused on the genes in the MVA metabolic pathway. An analysis of MK and PMK genes and their functions is important to be able to further study santalol biosynthesis in S. album. Two novel MK and PMK cDNAs, named as SaMK and SaPMK, respectively, were cloned and characterized from S. album by rapid amplification of cDNA ends (RACE) technology for the first time. Their structure and function were assessed by a bioinformatics analysis and yeast complementation assays. The expression patterns of SaMK and SaPMK following the induction by MeJA were investigated
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