The effect of hydra mutations on HD-START domain genes in Arabidopsis thaliana

Abstract

The study of sterol defective mutants of Arabidopsis thaliana has provided an invaluable opportunity to investigate the importance of sterols in plant development. The hydra mutants in particular - seedling lethal mutations - exhibit great phenotypic variation, leading to the supposition that sterols have a far more complex role in plant development than previously anticipated. It has been postulated that some sterol molecules are directly involved in the regulation of gene transcription during plant development. The binding of some sterols to START domains (sterol binding domains) found in some mammalian proteins has been noted, and it is possible that plant transcription factors containing START domains could be localised to the nucleus by the binding o f specific sterols. This hypothesis may be tested by creating HD-START::GFP fusion proteins to act as a reporter, permitting the subcellular localisation o f the produced protein to be viewed using confocal scanning laser microscopy. In order to determine if the expression of START domain transcription factors is itselfregulated by sterols, independent of possible roles for sterols in their localization to the nucleus, the comparative steady state transcription levels of five HD-START domain transcription factors were studied by real-time RT-PCR. A comparison of hydra mutant mRNA levels to their wild type counterparts was carried out to determine whether there is a requirement for sterols in the regulation o f the tested genes. Although the results do appear to suggest this to be the case, the data and the conclusions require further validation.