Minisymposium 22: Salinity

Abs # 43005: During stress-induced ovule abortion, the gene expression profile changes in Arabidopsis pistils

Presenter:	Sun, Kelian , kelian@ufl.edu
Authors	Sun, Kelian  (A)   Hauser, Bernard A. (A)
Affiliations:	(A): Dept. of Botany, Univ. of Florida

In Arabidopsis thaliana, environmental stress dramatically reduces plant reproduction. The effects of salt stress were investigated using plants grown in a hydroponic medium. To elicit stress responses, this medium was supplemented with 200 mM NaCl. Twelve hours of salt stress caused 95% of the developing ovules to abort. During ovule abortion, developing gametophyte cells became vacuolated and senesced. In contrast, maternal cells in the chalaza and the integuments underwent programmed cell death, which was characterized by DNA fragmentation. Using Affymetrix 24k microarrays, gene expression was monitored as these physiological changes occurred. Transcript levels were measured in healthy plants and plants that were stressed for 6, 12, 18, and 24 hours. Over the course of this experiment, a total of 535 salt responsive genes were identified (P < 0.05). Of these genes, 404 were induced, while 131 were repressed more than 2.5 fold. The genes encoding proteins for sugar metabolism (two fructokinases), protein synthesis (L5 ribosomal protein) and cell division (PROLIFERA) were repressed. These changes in gene expression are consistent with ovules decreasing their rate of cellular growth and altering sugar metabolism. Adjustments in sugar metabolism might result from a reduction in biosynthesis in the gametophyte or embryo, as well as, sugar export from aborting ovules. Enzymes that salvage amino acids following protein degradation were up-regulated. In addition, genes involved in osmolyte biosynthesis were induced. The expression of several cation exchangers and ion transporters was induced. Presumably the expression of these genes either reestablishes ion concentrations similar to those levels found in healthy plants or allows reproductive organs to acclimate to changes in ion levels following stress. ROS (reactive oxygen species) detoxification genes, including ascorbate peroxidase, peroxidase, and superoxide dismutase, were down-regulated 18 hours after plants were stressed, perhaps, indicating ROS plays a role in ovule abortion. Following salt stress, the expression levels of about 22 signal transduction components and 59 transcriptional factors changed significantly. Binary hierarchical cluster analysis of the transcriptional factors showed waves of gene expression. Evaluation of changes in genes expression provides an avenue to further explore physiological and molecular changes that occur during ovule abortion.