TY - JOUR
T1 - A guanine nucleotide exchange factor for Rab5 proteins is essential for intracellular transport of the proglutelin from the golgi apparatus to the protein storage vacuole in rice endosperm
AU - Fukuda, Masako
AU - Wen, Liuying
AU - Satoh-Cruz, Mio
AU - Kawagoe, Yasushi
AU - Nagamura, Yoshiaki
AU - Okita, Thomas W.
AU - Washida, Haruhiko
AU - Sugino, Aya
AU - Ishino, Sonoko
AU - Ishino, Yoshizumi
AU - Ogawa, Masahiro
AU - Sunada, Mariko
AU - Ueda, Takashi
AU - Kumamaru, Toshihiro
PY - 2013/6
Y1 - 2013/6
N2 - Rice (Oryza sativa) glutelins are synthesized on the endoplasmic reticulum as a precursor, which are then transported via the Golgi to protein storage vacuoles (PSVs), where they are proteolytically processed into acidic and basic subunits. The glutelin precursor mutant6 (glup6) accumulates abnormally large amounts of proglutelin. Map-base cloning studies showed that glup6 was a loss-of-function mutant of guanine nucleotide exchange factor (GEF), which activates Rab GTPase, a key regulator of membrane trafficking. Immunofluorescence studies showed that the transport of proglutelins and a-globulins to PSV was disrupted in glup6 endosperm. Secreted granules of glutelin and a-globulin were readily observed in young glup6 endosperm, followed by the formation of large dilated paramural bodies (PMBs) containing both proteins as the endosperm matures. The PMBs also contained membrane biomarkers for the Golgi and prevacuolar compartment as well as the cell wall component, b-glucan. Direct evidence was gathered showing that GLUP6/GEF activated in vitro GLUP4/Rab5 as well as several Arabidopsis (Arabidopsis thaliana) Rab5 isoforms to the GTP-bound form. Therefore, loss-of-function mutations in GEF or Rab5 disrupt the normal transport of proglutelin from the Golgi to PSVs, resulting in the initial extracellular secretion of these proteins followed, in turn, by the formation of PMBs. Overall, our results indicate that GLUP6/GEF is the activator of Rab5 GTPase and that the cycling of GTP- and GDP-bound forms of this regulatory protein is essential for the intracellular transport of proglutelin and a-globulin from the Golgi to PSVs and in the maintenance of the general structural organization of the endomembrane system in rice seeds.
AB - Rice (Oryza sativa) glutelins are synthesized on the endoplasmic reticulum as a precursor, which are then transported via the Golgi to protein storage vacuoles (PSVs), where they are proteolytically processed into acidic and basic subunits. The glutelin precursor mutant6 (glup6) accumulates abnormally large amounts of proglutelin. Map-base cloning studies showed that glup6 was a loss-of-function mutant of guanine nucleotide exchange factor (GEF), which activates Rab GTPase, a key regulator of membrane trafficking. Immunofluorescence studies showed that the transport of proglutelins and a-globulins to PSV was disrupted in glup6 endosperm. Secreted granules of glutelin and a-globulin were readily observed in young glup6 endosperm, followed by the formation of large dilated paramural bodies (PMBs) containing both proteins as the endosperm matures. The PMBs also contained membrane biomarkers for the Golgi and prevacuolar compartment as well as the cell wall component, b-glucan. Direct evidence was gathered showing that GLUP6/GEF activated in vitro GLUP4/Rab5 as well as several Arabidopsis (Arabidopsis thaliana) Rab5 isoforms to the GTP-bound form. Therefore, loss-of-function mutations in GEF or Rab5 disrupt the normal transport of proglutelin from the Golgi to PSVs, resulting in the initial extracellular secretion of these proteins followed, in turn, by the formation of PMBs. Overall, our results indicate that GLUP6/GEF is the activator of Rab5 GTPase and that the cycling of GTP- and GDP-bound forms of this regulatory protein is essential for the intracellular transport of proglutelin and a-globulin from the Golgi to PSVs and in the maintenance of the general structural organization of the endomembrane system in rice seeds.
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U2 - 10.1104/pp.113.217869
DO - 10.1104/pp.113.217869
M3 - Article
C2 - 23580596
AN - SCOPUS:84878448668
SN - 0032-0889
VL - 162
SP - 663
EP - 674
JO - Plant physiology
JF - Plant physiology
IS - 2
ER -