TY - JOUR
T1 - Different sets of ER-resident J-proteins regulate distinct polar nuclear-membrane fusion events in Arabidopsis Thaliana
AU - Maruyama, Daisuke
AU - Yamamoto, Masaya
AU - Endo, Toshiya
AU - Nishikawa, Shuh Ichi
N1 - Publisher Copyright:
© The Author 2014. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved.
PY - 2014/6/27
Y1 - 2014/6/27
N2 - Angiosperm female gametophytes contain a central cell with two polar nuclei. In many species, including Arabidopsis thaliana, the polar nuclei fuse during female gametogenesis. We previously showed that BiP, an Hsp70 in the endoplasmic reticulum (ER), was essential for membrane fusion during female gametogenesis. Hsp70 function requires partner proteins for full activity. J-domain containing proteins (J-proteins) are the major Hsp70 functional partners. A. thaliana ER contains three soluble J-proteins, AtERdj3A, AtERdj3B, and AtP58IPK. Here, we analyzed mutants of these proteins and determined that double-mutant ovules lacking AtP58IPK and AtERdj3A or AtERdj3B were defective in polar nuclear fusion. Electron microscopy analysis identified that polar nuclei were in close contact, but no membrane fusion occurred in mutant ovules lacking AtP58IPK and AtERdj3A. The polar nuclear outer membrane appeared to be connected via the ER remaining at the inner unfused membrane in mutant ovules lacking AtP58IPK and AtERdj3B. These results indicate that ER-resident J-proteins, AtP58IPK/AtERdj3A and AtP58IPK/AtERdj3B, function at distinct steps of polar nuclear-membrane fusion. Similar to the bip1 bip2 double mutant female gametophytes, the aterdj3a atp58ipk double mutant female gametophytes defective in fusion of the outer polar nuclear membrane displayed aberrant endosperm proliferation after fertilization with wild-type pollen. However, endosperm proliferated normally after fertilization of the aterdj3b atp58ipk double mutant female gametophytes defective in fusion of the inner membrane. Our results indicate that the polar nuclear fusion defect itself does not cause an endosperm proliferation defect.
AB - Angiosperm female gametophytes contain a central cell with two polar nuclei. In many species, including Arabidopsis thaliana, the polar nuclei fuse during female gametogenesis. We previously showed that BiP, an Hsp70 in the endoplasmic reticulum (ER), was essential for membrane fusion during female gametogenesis. Hsp70 function requires partner proteins for full activity. J-domain containing proteins (J-proteins) are the major Hsp70 functional partners. A. thaliana ER contains three soluble J-proteins, AtERdj3A, AtERdj3B, and AtP58IPK. Here, we analyzed mutants of these proteins and determined that double-mutant ovules lacking AtP58IPK and AtERdj3A or AtERdj3B were defective in polar nuclear fusion. Electron microscopy analysis identified that polar nuclei were in close contact, but no membrane fusion occurred in mutant ovules lacking AtP58IPK and AtERdj3A. The polar nuclear outer membrane appeared to be connected via the ER remaining at the inner unfused membrane in mutant ovules lacking AtP58IPK and AtERdj3B. These results indicate that ER-resident J-proteins, AtP58IPK/AtERdj3A and AtP58IPK/AtERdj3B, function at distinct steps of polar nuclear-membrane fusion. Similar to the bip1 bip2 double mutant female gametophytes, the aterdj3a atp58ipk double mutant female gametophytes defective in fusion of the outer polar nuclear membrane displayed aberrant endosperm proliferation after fertilization with wild-type pollen. However, endosperm proliferated normally after fertilization of the aterdj3b atp58ipk double mutant female gametophytes defective in fusion of the inner membrane. Our results indicate that the polar nuclear fusion defect itself does not cause an endosperm proliferation defect.
KW - Arabidopsis thaliana
KW - Endoplasmic reticulum
KW - Female gametogenesis
KW - Molecular chaperone
KW - Nuclear fusion
UR - http://www.scopus.com/inward/record.url?scp=84944179107&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84944179107&partnerID=8YFLogxK
U2 - 10.1093/pcp/pcu120
DO - 10.1093/pcp/pcu120
M3 - Article
C2 - 25231968
AN - SCOPUS:84944179107
VL - 55
SP - 1937
EP - 1944
JO - Plant and Cell Physiology
JF - Plant and Cell Physiology
SN - 0032-0781
IS - 11
ER -