Overexpression of the OsChI1 gene, encoding a putative laccase precursor, increases tolerance to drought and salinity stress in transgenic Arabidopsis.

In a previous study, we identified a number of genes induced by chilling using a microarray approach. In order to investigate the molecular mechanism underlying chilling tolerance and possible crosstalk with other abiotic stresses, we selected a rice gene, OsChI1 (Os01g61160), for further analysis. The OsChI1 gene encodes a putative laccase precursor protein. In accordance with our previous results, its transcript is highly accumulated during a 12-day period of chilling treatment. Higher expression of the OsChI1 gene was also detected in roots and tissues at the vegetative and productive stages. In addition, we also observed increased transcript levels of the OsChI1 gene during dehydration and high salinity conditions. Transient expression of OsChI1 proteins tagged with fluorescence protein in rice protoplasts revealed that OsChI1 is localized in the plasma membrane. The Arabidopsis transgenic plants overexpressing OsChI1-EGFP resulted in an increased tolerance to drought and salinity stress. In silico analysis of OsChI1 suggests that several genes coexpressed with OsChI1 in the root during various abiotic stresses, such as chilling, drought and salt stress, may play an important role in the ROS signaling pathway. Potential roles of OsChI1 in response to abiotic stresses are discussed.

The rice RING finger E3 ligase, OsHCI1, drives nuclear export of multiple substrate proteins and its heterogeneous overexpression enhances acquired thermotolerance.

Thermotolerance is very important for plant survival when plants are subjected to lethally high temperature. However, thus far little is known about the functions of RING E3 ligase in response to heat shock in plants. This study found that one rice gene encoding the RING finger protein was specifically induced by heat and cold stress treatments but not by salinity or dehydration and named it OsHCI1 (Oryza sativa heat and cold induced 1). Subcellular localization results showed that OsHCI1 was mainly associated with the Golgi apparatus and moved rapidly and extensively along the cytoskeleton. In contrast, OsHCI1 may have accumulated in the nucleus under high temperatures. OsHCI1 physically interacted with nuclear substrate proteins including a basic helix-loop-helix transcription factor. Transient co-overexpression of OsHCI1 and each of three nuclear proteins showed that their fluorescent signals moved into the cytoplasm as punctuate formations. Heterogeneous overexpression of OsHCI1 in Arabidopsis highly increased survival rate through acquired thermotolerance. It is proposed that OsHCI1 mediates nuclear-cytoplasmic trafficking of nuclear substrate proteins via monoubiquitination and drives an inactivation device for the nuclear proteins under heat shock.