Somaclonal variation in micropropagated oil palm. Characterization of two novel genes with enhanced expression in epigenetically abnormal cell lines and in response to auxin

Abstract

In vitro micropropagation based on somatic embryogenesis provides an efficient means to multiply selected genotypes of oil palm (Elaeis guineensis Jacq.). Despite its considerable potential, somatic embryogenesis can yield plants bearing a homeotic flowering abnormality known as mantled. Because the mantled abnormality is epigenetic, it cannot be detected with conventional structural molecular markers. Thus, to develop a means of discriminating among callus cultures carrying or lacking the mantled abnormality, we used a gene expression approach. We describe two novel oil palm genes, EgM39A and EgIAA1, both of which display increased transcript accumulation in epigenetically abnormal calli. EgIAA1 codes for an oil palm relative of the Arabidopsis thaliana (L.) Heynh. AXR3/IAA17 protein involved in early auxin response and EgM39A codes for a protein of unknown function sharing sequence similarities with asparagine synthetases. In addition to their enhanced expression in somaclonal variant callus lines, both genes displayed increased transcript accumulation in response to auxin treatment. Normal seed-derived zygotic embryos germinated in the presence of auxin accumulated increased amounts of EgIAA1 transcripts after a few hours of treatment, suggesting a role in auxin response similar to that demonstrated for IAA genes in other species. The EgM39A gene also displayed enhanced transcript accumulation in auxin-treated zygotic embryos. Although only a small increase was seen after 24 h, greater changes were observed after 15 days. Both genes show potential as early markers of clonal conformity and may help to elucidate the nature of the epigenetic changes causing the mantled abnormality.

Somaclonal variation associated with oil palm (Elaeis guineensis Jacq.) clonal propagation: A review

“…According to Evans et al (2003) and Morcillo et al (2006), there can be two major classes of somaclonal variation: genetic and epigenetic variations: Genetic (heritable) variability is caused by mutation or other changes in DNA such as changes in chromosome number and structure. Various molecular mechanisms are responsible for genetic variability associated with somaclonal variation.…”

“…Tissue culture media can change the level of DNA methylation and thus maybe one of the important causes of somaclonal variation (Evans et al, 2003;Morcillo et al, 2006). Source: Kushairi et al (2010).…”

“…The frequency of somaclonal variation in regenerated plants depends on the genotype of the material, type of explants used, age of culture, type of regenerative process (organogenesis or embryogenesis), stress inherent in cellular deprogramming induced by plant growth regulators such as the synthetic auxin 2,4-dichlorophenoxy-acetic acid (2,4-D) (Morcillo et al, 2006). Other stress conditions could be water deficiency, osmotic stress, heat, extreme procedure in tissue culture, nutrient media conditions etc.…”

“…1) Reversion of abnormal palms in the field over a period of years (Jaligot et al, 2000;Morcillo et al, 2006). 2) Non-Mendelian transmission of the trait by convention genetic crossing that is, inherited in non-Mendelian fashion (Morcillo et al, 2006).…”

“…2) Non-Mendelian transmission of the trait by convention genetic crossing that is, inherited in non-Mendelian fashion (Morcillo et al, 2006). 3) Absence of any detectable defect in DNA organization (Jaligot et al, 2000).…”