Expression of seed storage product genes (CRA1 and OLEO4) in embryogenic cultures of somatic tissues of Arabidopsis

Abstract

In Arabidopsis, immature zygotic embryos (IZEs) at the late cotyledon stage provide the only explants that can be used to induce in vitro somatic embryogenesis (SE) with high efficiency. The most conspicuous characteristic of SE-competent IZEs is the accumulation of seed storage reserves (SSR), as proteins and lipids. In order to elucidate an assumed role of these compounds in the mechanisms involved in tissue capacity for SE, the genes encoding the main seed storage protein, cruciferin (CRUCIFERIN1, CRA1) and the lipid body-related protein oleosin (OLEOSIN4, OLEO4), were studied. Significantly higher transcriptional activity of both genes, CRA1 and OLEO4, in embryogenic than in non-embryogenic cultures, were indicated. However, their activity under in vitro culture were found not to be induced by auxin treatment or LEC2 expression, and were unspecific for SE induction. In addition, the results on mutants severely impaired in SE response indicated that high activity of SSR genes in explant tissue is not sufficient for SE induction. On the other hand, the cra1 and oleo4 insertional mutants were found to be defective in their capacity for SE. In addition, it was found that the mutants displayed lower tolerance to high salinity and osmotic stress. Altogether, the results suggest an indirect influence of SSR genes on the embryogenic capacity of cultured tissues possibly via improvement of cell response to stress imposed in vitro.