Isolation of cold stress-responsive genes in the reproductive organs, and characterization of the OsLti6b gene from rice (Oryza sativa L.)

During their reproductive stage, rice crops often are exposed to cold stress, which leads to sterility and reduced yields. To understand the cold response mechanism at that stage, we used an mRNA differential display method to isolate cold-responsive genes from pre-anthesis flowers. Approximately 5,000 transcripts were identified here, of which 123 were found to be displayed differentially between the control (30 degrees C) and cold-treated (12 degrees C) flowers. Among them, 26 were analyzed by northern analysis; 8 of those clones were confirmed as cold-responsive. OsLti6b, encoding a hydrophobic protein homologous to Arabidopsis RCI2, was analyzed in detail. RNA blot analysis revealed that its transcript is increased by cold, salt, drought, or ABA treatments. In situ hybridization indicated that this transcript is highly accumulated in the ovaries and stamens of cold-treated flowers, particularly in the anther walls and vascular tissues of the filaments. Over-expression of OsLti6b increased cold tolerance as revealed by seedling wilting rates and ion leakages of mature leaves, demonstrating that the extent of the tolerance correlates well with its expression level.