A novel FLOURY ENDOSPERM2 (FLO2)-interacting protein, is involved in maintaining fertility and seed quality in rice

Crop plants accumulate a large amount of storage starch and storage proteins in the endosperm. Genes involved in the biosynthesis of these substances work in concert during development of the rice endosperm. The rice <i>flo2</i> mutant produces aberrant seeds with reduced grain quality. <i>FLOURRY ENDOSPERM 2 (FLO2)</i>, the causative gene of the <i>flo2</i> mutant, is considered to be a regulatory protein that controls the biosynthesis of seed storage substances. FLO2 contains tetratricopeptide repeat (TPR) motifs that may mediate protein-protein interactions. In this study, we identified the protein that interacts with the TPR motif of FLO2. We generated a transformant that produced the FLAG-tagged fusion FLO2 protein in the <i>flo2</i> mutant and used this in the shotgun proteomic analysis. A protein, which we named FLOC1, interacted with FLO2. In vitro pull-down assays indicated that the TPR motif was involved in this interaction. A knock-down transformant of FLOC1 showed significantly reducted fertility and generation of seeds with abnormal features. These findings suggest that FLOC1 is involved not only in seed fertility but also in seed quality. These phenotypes were also observed on the RNAi transformants of the <i>flo2</i> mutant although the effect of the <i>flo2</i> mutation remained. these findings imply that there is a difference in the functions of FLO2 and FLOC1 although both of appear to be involved in the control of seed quality during seed formation.