Cloning and characterization of Somatic Embryogenesis Receptor Kinase I (EgSERK I) and its association with callus initiation in oil palm

The somatic embryogenesis receptor kinase (SERK) gene has been extensively studied in many plant species due to its role in conferring embryogenic competence to somatic cells. The oil palm (Elaeis guineensis Jacq.) full-length SERK I (EgSERK I) cDNA was first isolated from cell suspension culture using RACE-PCR. Total length of EgSERK I cDNA was 2378 bp in length with a 5’UTR region (358 bp) longer than 3’UTR region (130 bp) and the ORF was 1890 bp (629aa). The deduced amino acid sequence of EgSERK I contained protein domains commonly present in reported SERK proteins, including the hallmark proline-rich region and C-terminal domains. EgSERK I was most highly expressed in leaf explants and also detected in all tested tissues, including vegetative tissues, reproductive tissues, embryogenic tissues, and non-embryogenic tissues, suggesting that it may have a broad role in plant growth and development. Expression of EgSERK I in leaf explant was upregulated by minimal auxin concentration at the initial 6 h of incubation in callus induction media. EgSERK I mRNA was detected in the adjacent cells of the vascular tissues in the midvein region of leaf explants which serves as the callus initiation point of callogenesis in oil palm. Collectively, our findings suggest that the EgSERK I gene is involved in the callus initiation stage of oil palm somatic embryogenesis by transducing the signal to switch on the dedifferentiation process, triggering cellular reprogramming to form callus.

     

Morpho-histological characterization of truncated leaf syndrome seedlings: an oil palm (E. guineensis Jacq.) somaclonal variant

A comparative phenotypic and morpho-histological study was carried out on tissue culture-derived truncated leaf syndrome (TLS) and wild-type oil palm seedlings to investigate their phenotypic and morpho-histological differences. On the basis of the percentage of TLS occurence in a clone, the TLS seedlings were categorized into three groups: severe (70–100%), moderate (40–69%) and mild (<40%). Wild and TLS seedlings differ in terms of growth, vigor, leaf size and shape, root number, volume, length as well as the size of shoot apical meristem (SAM). Differences were also found in fresh weight of leaf, root and SAM of TLS in comparison to wild-type seedlings. Depressed and wavy leaf surface, sunken and distorted stomata and coalesced epidermal cells were observed by scanning electron microscopy in TLS seedlings. The size, shape and number of stomata were also different in the TLS leaf compared to the wild type. Longer epidermal cells, depressed epidermal layer, larger sub-epidermal cells and loosely arranged less mesophyll cells were observed in TLS leaf than in wild type. Undifferentiated vascular bundle was found in TLS leaves where metaxylem and phloem were absent and root tips were impaired. The size and leaf primordial arrangement of SAM were remarkably different in TLS compared to wild-type seedlings suggesting that these alterations might be due to smaller SAM. Therefore, further detailed genetic analysis on TLS SAM is needed for clear understanding of TLS occurrence.     

Cytokinin Differences in In Vitro Cultures and Inflorescences from Normal and Mantled Oil Palm (Elaeis guineensis Jacq.)

The mantled abnormality phenotype of the oil palm affects fruit development and thus jeopardizes oil yield. Cytokinins have been implicated in the development of the mantled phenotype. Endogenous cytokinin levels in the normal and mantled phenotypes were compared to determine whether levels of specific cytokinins are associated with mantling. Endogenous cytokinins were identified and quantified in in vitro cultures and inflorescences from normal and mantled oil palms. Twenty-two isoprenoid cytokinins, comprising the zeatin, dihydrozeatin, and isopentenyladenine types, were quantified. Total cytokinin levels, particularly of trans-zeatin and isopentenyladenine types, increased during the in vitro culture process, with the highest levels detected at the proliferating polyembryoid stages. The cytokinins were present mainly in their inactive 9-glucoside forms during in vitro culture. On the other hand, the predominant trans-zeatin cytokinins in inflorescences were present mainly in their ribotide forms, suggesting a metabolic pool of cytokinins for conversion to biologically active free bases or ribosides. Levels of specific cytokinins were significantly different in tissues at different stages. Mantled developed inflorescences contained higher levels of isopentenyladenine 9-glucoside compared with normal inflorescences. Mantled-derived callus tissues had higher isopentenyladenine levels but significantly lower levels of trans-zeatin 9-glucoside, dihydrozeatin riboside, and dihydrozeatin riboside 5′-monophosphate cytokinins compared with normal-derived callus. It would be of considerable interest to verify these specific cytokinin differences in more callus cultures and clones.     

Vandachostylis ‘Sri-Siam’: an intergeneric hybrid with superior qualities as evidenced by its biochemical fragrance and transcriptome profiles

Journal of Plant Biochemistry and Biotechnology - Vandachostylis ‘Sri-Siam’ is a fragrant orchid, suitable as a potted plant for the floriculture and perfumery industries due to its...