Effects of hypergravity stimulus on global gene expression during reproductive growth in Arabidopsis

The life cycle of higher plants consists of successive vegetative and reproductive growth phases. Understanding effects of altered gravity conditions on the reproductive growth is essential, not only to elucidate how higher plants evolved under gravitational condition on Earth but also to approach toward realization of agriculture in space. In the present study, a comprehensive analysis of global gene expression of floral buds under hypergravity was carried out to understand effects of altered gravity on reproductive growth at molecular level. Arabidopsis plants grown for 20-26 days were exposed to hypergravity of 300 g for 24 h. Total RNA was extracted from flower buds and microarray (44 K) analysis performed. As a result, hypergravity up-regulated expression of a gene related to β-1,3-glucanase involved in pectin modification, and down-regulated β-galactosidase and amino acid transport, which supports a previous study reporting inhibition of pollen development and germination under hypergravity. With regard to genes related to seed storage accumulation, hypergravity up-regulated expression of genes of aspartate aminotransferase, and down-regulated those related to cell wall invertase and sugar transporter, supporting a previous study reporting promotion of protein body development and inhibition of starch accumulation under hypergravity, respectively. In addition, hypergravity up-regulated expression of G6PDH and GPGDH, which supports a previous study reporting promotion of lipid deposition under hypergravity. In addition, analysis of the metabolic pathway revealed that hypergravity substantially changed expression of genes involved in the biosynthesis of phytohormones such as abscisic acid and auxin.