Abstract
Rice glutelin is synthesized on the ER membrane as a precursor, which is then transported via the Golgi to the protein storage vacuole (PSV) where it is proteolytically cleaved into two subunits. To elucidate the genetic mechanism for intracellular transport and accumulation of seed storage proteins, rice mutants accumulating glutelin precursor, generated by N-methyl-N-nitrosourea mutagenesis, were analyzed.
Among them, esp2, glup4 and glup3 mutants were deficient in protein disulfide isomerase (PDI), Rab5a, a GTPase involved in vesicular transport, and vacuolar processing enzyme (VPE), respectively. Genetic analysis demonstrated that esp2 gene was epistatic to two other genes and glup4 gene was epistatic to glup3 gene. Immunocytochemical and biochemical studies of the mutants suggest that PDI, Rab5a and VPE participate in protein sorting within ER, vesicular transport of the precursor from ER and the proteolytic cleavage of it within PSV, respectively, on transport and accumulation pathway of it from ER to PSV.
