Abstract
Thiamine, or vitamin B1 plays an indispensable role as a cofactor in crucial metabolic reactions including glycolysis, pentose phosphate pathway and the tricarboxylic acid cycle in all living organisms. Thiamine has been shown to play a role in plant adaptation toward biotic and abiotic stresses. The modulation of thiamine biosynthetic genes in oil palm seedlings was evaluated in response to root colonization by endophytic Hendersonia toruloidea. Seven-month-old oil palm seedlings were inoculated with H. toruloidea and microscopic analyses were performed to visualize the localization of endophytic H. toruloidea in oil palm roots. Transmission electron microscopy confirmed that H. toruloidea colonized cortical cells. The expression of thiamine biosynthetic genes and accumulation of total thiamine in oil palm seedlings were also evaluated. Quantitative real-time PCR was performed to measure transcript abundances of four key thiamine biosynthesis genes (THI4, THIC, TH1, and TPK) on days 1, 7, 15, and 30 in response to H. toruloidea colonization. The results showed an increase of up to 12-fold in the expression of all gene transcripts on day 1 post-inoculation. On days 7, 15, and 30 post-inoculation, the relative expression levels of these genes were shown to be downregulated. Thiamine accumulation was observed on day 7 post-colonization and subsequently decreased until day 30. This work provides the first evidence for the enhancement of thiamine biosynthesis by endophytic colonization in oil palm seedlings.
Highlights
Thiamine, known as vitamin B1, is required for key metabolic processes in cellular organisms
We examined the responses of oil palm seedlings to colonization by H. toruloidea, in terms of the expression of thiamine biosynthetic genes
On day 7, THI4, thiamine pyrophosphokinase (TPK), THIC, and TH1 were downregulated to levels that represented 2.85, 0.92, 0.44, and 1.07-fold changes, respectively, when compared to levels in control seedlings
Summary
Known as vitamin B1, is required for key metabolic processes in cellular organisms. The active form, thiamine pyrophosphate (TPP), is a cofactor in important metabolic reactions, notably glycolysis, tricarboxylic acid cycle, pentose phosphate pathway, and synthesis of branched amino acids (Goyer, 2010). The thiamine biosynthesis pathway in plants is similar to that in bacteria and yeast (Begley et al, 1999; Li et al, 2010). This pathway consists of two separate branches: the thiazole branch and pyrimidine branch. The pyrimidine moiety of thiamine, hydroxymethylpyrimidine phosphate (HMP), is produced from the precursor 5-aminoimidazole ribonucleotide (AIR) by the enzyme HMP synthase, encoded by the THIC gene.
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