FLA, which encodes a homolog of UBP, is required for chlorophyll accumulation and development of lemma and palea in rice.

KEY MESSAGE: FLA, the homolog of ubiquitin-specific protease does not have deubiquitination activity, but it is essential for flower and chloroplast development in rice. Ubiquitin-specific proteases (UBPs) are widely distributed and highly conserved proteins and are also members of the most important family of deubiquitination enzymes. Although the functions and phylogenies of UBPs from yeast, mammals and Arabidopsis have been widely reported, the functions and evolutionary relationships of UBPs in rice remain unclear. In this study, we characterized the rice flower and leaf color aberrant mutant (fla), which exhibited a variety of developmental defects, including abnormal floral organs and pollen development, and leaf bleaching. We isolated FLA by positional cloning and found that it encodes a homolog of ubiquitin-specific protease. FLA is a ubiquitously expressed gene with the highest expression in floral organs. Subcellular localization analysis indicated that FLA is a cell membrane protein. Through searches of the rice genome database ( http://rice.plantbiology.msu.edu ), we identified 35 UBP family members in the rice genome. These proteins were grouped into 16 subfamilies based on phylogenetic analysis, and FLA was found to belong to the G8 subfamily. In vitro activity assays revealed that FLA does not have deubiquitination activity. Our data suggest that FLA plays an important role in the development of floral organs and chloroplast in rice, but that this role probably does not involve deubiquitination activity, because FLA does not have an active site and deubiquitination activity.