RESUMO
KEY MESSAGE: FLO15encodes a plastidic glyoxalase I protein, OsGLYI7, which affects compound starch granule formation and starch synthesis in rice endosperm. Starch synthesis in rice (Oryza sativa) endosperm is a sophisticated process, and its underlying molecular machinery still remains to be elucidated. Here, we identified and characterized two allelic rice floury endosperm 15 (flo15) mutants, both with a white-core endosperm. The flo15 grains were characterized by defects in compound starch granule development, along with decreased starch content. Map-based cloning of the flo15 mutants identified mutations in OsGLYI7, which encodes a glyoxalase I (GLYI) involved in methylglyoxal (MG) detoxification. The mutations of FLO15/OsGLYI7 resulted in increased MG content in flo15 developing endosperms. FLO15/OsGLYI7 localizes to the plastids, and the in vitro GLYI activity derived from flo15 was significantly decreased relative to the wild type. Moreover, the expression of starch synthesis-related genes was obviously altered in the flo15 mutants. These findings suggest that FLO15 plays an important role in compound starch granule formation and starch synthesis in rice endosperm.
Assuntos
Endosperma/enzimologia , Regulação da Expressão Gênica de Plantas , Lactoilglutationa Liase/metabolismo , Oryza/enzimologia , Amido/metabolismo , Grânulos Citoplasmáticos/metabolismo , Endosperma/citologia , Endosperma/genética , Genes Reporter , Lactoilglutationa Liase/genética , Mutação , Oryza/citologia , Oryza/genética , Fenótipo , Filogenia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plastídeos/enzimologia , Sementes/citologia , Sementes/enzimologia , Sementes/genética , Técnicas do Sistema de Duplo-HíbridoRESUMO
Starch is the most widespread form of energy storage in the plant kingdom. Although many enzymes and related factors have been identified for starch biosynthesis, unknown players remain to be identified, given that it is a complicated and sophisticated process. The endosperm of rice (Oryza sativa) has been used for the study of starch synthesis. Here, we report the cloning and characterization of the FLOURY ENDOSPERM6 (FLO6) gene in rice. In the flo6 mutant, the starch content is decreased and the normal physicochemical features of starch are changed. Significantly, flo6 mutant endosperm cells show obvious defects in compound granule formation. Map-based cloning showed that FLO6 encodes a protein of unknown function. It harbors an N-terminal transit peptide that ensures its correct localization and functions in the plastid, and a C-terminal carbohydrate-binding module 48 (CBM48) domain that binds to starch. Furthermore, FLO6 can interact with isoamylase1 (ISA1) both in vitro and in vivo, whereas ISA1 does not bind to starch directly. We thus propose that FLO6 may act as a starch-binding protein involved in starch synthesis and compound granule formation through a direct interaction with ISA1 in developing rice seeds. Our data provide a novel insight into the role of proteins with the CBM48 domain in plant species.