Using subtractive hybridization a submergence-induced gene was identified from deepwater rice, OsUsp1, that encodes a homologue of the bacterial universal stress protein family. Sequence analysis revealed that OsUSP1 is most closely related to the bacterial MJ0577-type of ATP-binding USP proteins which have been suggested to act as a molecular switch. USP protein homologues appear to be ubiquitous in plants and are encoded by gene families, but are absent in animal species. In the youngest internode of deepwater rice plants, OsUsp1 expression was very strongly induced within 1 h of submergence. Elevated transcript levels were observed in dividing cells, in expanding cells and in differentiated tissue indicating that USP1 mediates a general process. Gene induction was shown to be regulated by ethylene with a highly similar expression pattern to that observed with submergence treatment. Based on sequence information and on expression data it is hypothesized that OsUSP1 plays a role in ethylene-mediated stress adaptation in rice.

DNA replication is a process that is highly conserved among eukaryotes. Nonetheless, little is known about the proteins involved in it in plants. Replication protein A (RPA) is a heterotrimeric, single-stranded DNA-binding protein with several functions in DNA metabolism in humans and yeast and supposedly also in plants. Here we report on the regulation of OsRPA2, the 32-kDa subunit of RPA from rice ( Oryza sativa L.). We found conserved regulation mechanisms at the level of gene expression between animal and plant RPA2 genes and distinct features of OsRPA2 regulation at the level of protein expression. Unlike in animals or in yeast, protein abundance in rice was regulated in a cell cycle phase-specific manner and was altered after UV-C light exposure. On the other hand, posttranslational modification through phosphorylation did not appear to play a pivotal role in rice as it does in animal cells. Our results indicate that plant-specific mechanisms of regulation have evolved for RPA2 within the generally well-conserved process of DNA replication, suggesting specific requirements for regulation of DNA metabolism in plants as compared to other eukaryotes.